# MagCharger Circuit: Can You ID the Components?



## Ginseng (Apr 7, 2004)

Hi,
Here are three pics of the guts inside the MC cradle. Can anyone tell me what the parts are and what needs to be replaced to modify the voltage or current output?









The colors on the blue one are from top to bottom:
brown
red
black
orange
brown

On the other bigger one:
white
brown
gold
gold




I hope you can make out where the traces go. I could not bend it back any further to get a "flat" shot.

Thanks,
Wilkey


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## php_44 (Apr 7, 2004)

This is a constant current regulator using a standard LM317 regulator IC. There appears to be an LED to indicate charging current is flowing. The LED appears to be shunted by a resistor.

The charge voltage will vary with this circuit design, but the charge current will remain constant. The smaller bluish resistor sets the current level. It is hard to tell from the picture the color of the bands on that resistor. Regardless, you you can try connecting one or more 1K ohm resistors in parallel with that part to increase the current. If you're careful, you can try a 1/4 watt 1K ohm trimpot in parallel - giving you a nice adjustment range. To decrease the charge current - you'd need to connect some resistance in series with that bluish body resistor - again a 1K trimpot would be fine.

If you increase the current - keep in mind you may have to reduce the value of the LED shunt resistor, or risk burning out the resistor and/or the LED. Also, the LM317 can output at most about 1A. If you increase the current more than 20% or so - the LM317 might get noticeably hot - insure you heat sink it properly. Make sure that the transformer powering this circuit can handle any extra current you want to deliver without overheating - that could be very hazardous. It might be better to find another power source if you increase the charge current by more than 10-20%.

If your goal is to reduce charge current - the existing transformer, LED, and shunt resistor will be fine.


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## koala (Apr 7, 2004)

The LM317T can be a configured in either voltage or current regulator. The main component to mod is probably the 1watt(maybe 1/2watt) 9.1ohm resistor on the left or the blue 1% resistor on the right. Sorry I can't guess the resistance of the right blue, the color of the strips are not very clear.

It would be helpful if you can show us the circuit traces on the other side of the board. I am pretty sure it's single layered as this is not very complex circuit with a few components.

I love to guess...

EDIT: ARGHHHHHH php_44 beat me to it...

Vince.


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## Ginseng (Apr 7, 2004)

I will try to take a picture in daylight today (sorta cloudy) and include a picture of the underside as well. Thanks guys!

Wilkey


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## RussH (Apr 7, 2004)

First, I agree with php44, this is a constant current regulator. The small resistor with the 5 bands is a 1% resistor that is setting your current level. So while you are at it Wilkey, tell us what color those bands are. Your eyes are going to be a lot more reliable than camara/computer/computer/etc. Without seeing the rest of the components it's difficult to tell how much you can MOD this. But as php44 said, it can easily be modded to increase the current - probably enough to really help with your custom hi capacity battery packs. Note, also, that since this is current regulated, making it work with higher voltages for those battery packs with an extra cell or 5 is also easy. It probably will mean you need to increase the transformer voltage - easy with a wallwart. My solution for transformers that are too small is a) get a bigger wallwart, bypassing internal transformers when required, or b) add a fan for about 5 times cooling which might allow up to double original output... -RussH


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## php_44 (Apr 7, 2004)

If your intention is to use the modified circuit to charge a different number of cells than it was designed for then you can do the following:
<ul type="square">[*] Less cells than designed for - the input voltage level can be left alone, but the regulator will generate more heat.
[*] More cells than designed for - you need to provide the charger with 3-5V more than you expect the charged pack to reach. If you go with more input voltage, keep in mind that you can use the charger to charge fewer cells, but at the cost of the regulator outputting significantly more heat.
[/list]

It's like this. In current regulation mode the regulator will need to safely dissipate an amount of heat given by:
<font class="small">Code:</font><hr /><pre>
[(input voltage) - (battery pack voltage)] * (charge current in amps)
</pre><hr />
So if you reconfigure the charger to 0.5A output, and your input voltage is 15V, here's some interesting info:
<ul type="square">[*] charging 2 NiMH cells in series at 1.25V each the regulator will need to dissipate (15V-2.5v)*0.5 = 6.25w (!!!!!!) A fan and or big heat sink would be a good idea.
[*] Charging 8 nimh cells in series at 1.25V each the regulator will need to dissipate (15V-(8*1.25))*0.5 = 2.5w A reasonable heat sink will handle this.
[/list]
For this example - you'd have to recalculate the LED's shunt resistor or it would burn up along with the LED.

PS - you can pretty much see the PCB traces in the pictures posted.


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## turbodog (Apr 7, 2004)

I don't agree with the above calculations. 1) My magcharger does not get hot enough for the circuit to be outputting that much heat. 2)The calculation, inaccurate as it is, more accurately describes the amount of power the batteries are taking in.

I am sure I am not totally right here, but it seems that the whole idea behind solid state charge circuits was to keep from having all excess power bled off as heat.


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## php_44 (Apr 7, 2004)

Keep in mind - I don't have a magcharger or know the specs of an unmodified unit. Sooooo, my hypothetical example was for someone to take the circuit shown and re-use it for the purpose in my example.

The calculations are correct for the voltages and currents given. For the two cell example - the cells get 1.25watts and the regulator gets 6.25w for a total of 7.5w (which is 15v @ 0.5A - it all adds up). Likewise, for the 8 cell example, the cells get 5w and the regulator gets 2.5w for a total of (you guessed it) 7.5w (again 15v @ 0.5A).

If the charger out of the box does two cells in series from a 6V transformer at 100mA, then the regulator is dissipating (6V-2.5)*0.1A = 0.35watts. This wouldn't even feel warm.

Big difference, huh?

Regardless - my example is meant to illuminate what you might face if you want to push that circuit hard. You can't change physics - _*even if you don't like the answer!!*_ /ubbthreads/images/graemlins/smile.gif /ubbthreads/images/graemlins/wink.gif


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## Ginseng (Apr 7, 2004)

The first post has been edited with new pictures and a description of the color bands on the resistors. The specs say 235 mA delivered. Without a load, the voltage is between 19-20V. The wall wart puts out 14V at 220 mA.

So is the determination that I would not need to make any modifications to charge a 6-cell pack at the same voltage? Would it also deliver 235 mA? What if I wanted to charge a 10.8V nominal/12.15V max pack of 9 cells? 

Wilkey


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## turbodog (Apr 7, 2004)

Yeah I know you can't change physics. Got a degree in that BTW. I'm a little rusty at times, so I'm sitting here trying to make sure I'm not making a reasoning flaw.

Guess what't I'm talking about is regulator efficiency. My magcharger power supply outputs 220ma @ 14vdc. The pack is 2.2Ah, 5 cells. It charges in about 14 hours. That's .157a of charge current @ 100% efficiency. Now nicd cells are about 80% charge efficient I think, so we really need to charge @ .196 amps. So, .196a * 6.25v = 1.23 watts of power.

The transformer puts out 3.08 watts (14*.220). That leaves extra capacity of 1.85 watts. If we used a resistor to limit charge current, yes I would expect the 'regulator' to dissipate the full 1.85 watts. Since this is electronic, I would hope that it is slightly more efficient with power.

I know it has some losses, but to assume ALL extra capacity from the source supply is lost as heat is taking things a little too far.


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## turbodog (Apr 7, 2004)

Ginseng:

Trying a 6 cell pack should not hurt. If possible, try to measure the actual voltage and current going to the battery pack (stock) first. 6 cell is higher voltage and higher resistance... which should tax the charger less, hence it's prob ok to try (since the diff in voltage between supply and load is less, the regulator works less hard).

Heck, wait a min...

I just checked mine with 2 different brand packs at different states of charge and they both hit EXACTLY .215 amps to the battery pack.

Ok wait again...

I just put a 6 cell pack in it... dead on .215 amps again.

I measure .116a with a 9 cell pack.

There's some point that pack voltage is too high to maintain the regulated .215a current. Wonder if this could be overcome with a slightly higher voltage wall-wart supply?


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## evan9162 (Apr 7, 2004)

[ QUOTE ]

I know it has some losses, but to assume ALL extra capacity from the source supply is lost as heat is taking things a little too far.


[/ QUOTE ]

It is lost as heat. A linear regulator simply burns the extra power off as heat. The regulators that don't simply burn the extra power as heat are switching regulators. Those are more costly and complicated to implement.

As for your surprise at the current level, what you are seeing is EXACTLY what an LM317 in current mode does. It supplies the same amount of current to the load, regardless of the resistance/voltage drop the load presents. If you were to drop a single cell across the MC charger terminals, you would still see 215mA.

I don't know about the On Semiconductor LM317 (the one in the charger), but National's LM317s are power dissipation and temperature protected. If you disspiate too much power in the regulator, or the regulator gets too hot, they will simply shut down (in the case of overheating), or limit current (in the case of dissipating too much power). They are also internally limited to 1A or so, so they are also short circuit safe.


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## Ginseng (Apr 7, 2004)

Ahh, thanks T-Dog. That is most helpful. What would you suggest as a suitable wallwart? Perhaps 18V 300mA? On the other hand, 0.116 turns out to be a pretty gentle 0.05C trickle rate for 2.1Ah AA nimh. If we're not worried about fast charging, the light could be left on charger perpetually at that rate. Excellent...

Thanks for sharing the analysis php. I'm a chemical engineer and despise all things electrical. Although, it looks like I;m going to have to come up to speed fast.

Wilkey


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## turbodog (Apr 7, 2004)

evan.... ok I am remembering all this in more detail now. The linear/switching was the part where I messed up. Apologies to all... have worked around switching equipment too much.

As far as guessing which supply to put with the MC... you're on your own.

Also, I'm sure there's some implications of the transformer putting out 14volts and being able to measure 19 at the charging terminals.


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## MoonRise (Apr 7, 2004)

The blue resistor is a 120kOhm 1% tolerance resistor and the other one is a 9.1 Ohm 5% tolerance resistor. Like the other folks said, it's using a standard LM317T IC.

Circuit details as the other folks said. Tweak the resistance across the blue resistor DOWN for more current output. The trick about the adjustable pot in parallel is a good one, but I think you would be better off with a 1M Ohm pot. That would allow you to adjust the the effective resistance over a range of 107K to 1 Ohm. Resistance in parallel is always less than the smallest resistor. Tweak the resistance UP for less current by adding a 120kOhm pot in series for a nice range there. That would give you an effective resistance range of 120K up to 240K. Or just remove the blue resistor and put a 0 - 250k Ohm pot in its place, that way you can go from more to less no fuss. /ubbthreads/images/graemlins/grin.gif

A data sheet for the IC is here at Digi-Key LM317T data sheet PDF 
. Pin (ONE) is the adjust pin, pin TWO is Vout, and pin THREE is Vin. Max output current is over 1.5A, and the IC includes internal thermal overload protection. Max (Vin - Vout) = 40V.

Side note, the PDF data sheet includes a schematic to make a "lab" power supply. /ubbthreads/images/graemlins/smile.gif


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## turbodog (Apr 7, 2004)

Well, there you go... drop in a 20 volt or so power supply and you should be good for those 9 cell packs.


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## RussH (Apr 8, 2004)

It looks like the OEM setup would provide constant current up to 7 cells with the existing wallwart (ww). It's not unusual these days for the open circuit voltage to be 20v with a nominal 12v wallwart. It's also not unusual to label the same ww with 12, 13.8, 14-15v, etc. I would expect different currents at each voltage. 

This particular ww might be 300-350ma @12v, its rated 220ma (or 235ma?) @14v, and your 116ma indicates its operating roughly half way between 14v and the open circuit voltage (20v?) or at around 17v to charge 9 cells. It should be able to handle 8 cells @ 1.42v charge x 8 = 11.2v, allowing for 3 volts drop for the regulator would mean you need 14.2v to charge 8 cells @ 220ma. It looks like this wallwart is not quite reaching its rated output. 

My approach would be to use a more robust ww, say 500ma with a 20-21v open circuit (oc) voltage. Most 500ma 12v ww that I have seen lately were in the 20voc range. But it won't hurt anything if you use a 750ma or 1000ma transformer, the voltage difference is what determines the losses in the regulator. You might find that a 1200ma ww with an oc voltage of 19v would work great. The bigger transformers will not have their voltage pulled down as much as your wimpy 220ma ww. Try what you have on hand and take measurements to see what they actually deliver. I do that with just about every ww I use, especially when I'm trying to use one that didn't come with the equipment...HTH, -RussH
Hey php44, I liked your example even if no one else did....


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## Ginseng (Apr 8, 2004)

Thanks Russ,

I understand the situation much better with your explanation.

Wilkey


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## js (Apr 8, 2004)

Ginseng! I have the WallWart that you need! It is a 15VDC wallwart with an o.c. voltage of 18V, 900 mA current rate maximum, and it works fine to trickle charge my 9 cell KAN 1050 pack. They are like $4 each from www.powersupplydepot.com, but they have a $15 min. order. I got four for the TL85. Want me to send you one?


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## Phaserburn (Apr 8, 2004)

Very nice, js. Are you going to join the SuperMagCharger club?


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## Ginseng (Apr 8, 2004)

*Modding Musings*

Jim,
Thanks a bunch! Would you mind holding onto it for right now? You can include it with the SL-35X LA, etc. on return ship to me. 

Phaser, 
I think we're starting to see a convergence of the TL and MC as hosts. It's really a fascinating phenomenon. I think it speaks more to the basic, ultimate limitations of the handheld, tubular format. Still, there's a significant gap between even the MC85 and TL85 and the Aurora. This means that there are still one or two significant incremental evolutions which remain to be realized. One of these would be a tube-torch that accepts the H3 automotive bulb base. This was suggested to me by Illuminated many months ago and I think that we had to work through the intervening evolutions before we had the experience to tackle it. Not only will the 12V H3 auto bulbs be accessible but also the axial filament 6V Vector spotlight bulbs. This is a very exciting time in hot wire modding, no? /ubbthreads/images/graemlins/wink.gif

Ok, enough jawing, back to the modding!

Wilkey


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## js (Apr 8, 2004)

[ QUOTE ]
*Phaserburn said:*
Very nice, js. Are you going to join the SuperMagCharger club? 

[/ QUOTE ]

Well, it depends on what you mean by "join". If you are asking if I am going to buy one, the answer is "no" with a "no offense intended". But if you are asking whether or not I want to help in any way I can with Wilkey's MC modding and upgrading, the answer is a definite "yes."


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## Illuminated (Apr 9, 2004)

Wilkey,

I can't quite make out the MC charger circuit details from your pics, but those resistor values don't quite add up for the LM317T configured in constant current mode. If that is in fact a 9.1 ohm resistor setting the current level, 1.25V/9.1 ohms = 138.8 mA, NOT 235 mA. There seems to be something odd about those resistor values.

The other points about the wallwart not putting out enough voltage under load using the 9-cell pack are likely correct. The supply voltage to the LM317T CC circuit needs a good 3V above Vbatt while under load to maintain regulation.

I'll try to decipher the pics again to diagram the circuit when I get time.

Later - John


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## turbodog (Apr 9, 2004)

where did 235 come from?
I keep measuring .215 a


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## Illuminated (Apr 9, 2004)

My bad - it was posted as 215 mA - NOT 235 mA.

I think I have the circuit diagrammed now and I'm investigating - I'll report back here later...

John


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## js (Apr 9, 2004)

John,

Yeah, I wondered about that too! The current regulating resistor can't be 9 ohms for .215 amps. Do you think there are two resistors in parallel to get the custom resistance they needed from stock values available? That'd be my guess, but we'd need to get a closer look at the circuit.


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## Illuminated (Apr 9, 2004)

Working on it. Lemme finish analyzing the curcuit - I'll be back later.

John


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## Ginseng (Apr 9, 2004)

Thanks! I was hoping John would show up /ubbthreads/images/graemlins/smile.gif

Turbo, the manual lists the operating current as 230mA. That's on page 13 I think.

Wilkey


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## Illuminated (Apr 9, 2004)

[ QUOTE ]
*turbodog said:*
where did 235 come from?
I keep measuring .215 a 

[/ QUOTE ]

[ QUOTE ]
*Ginseng said:*
...The specs say 235 mA delivered... 

[/ QUOTE ]

OK - I'm NOT losing my mind!!! /ubbthreads/images/graemlins/twakfl.gif


OK, now - here's the circuit:







In the _normal_ LM317 constant-current circuit, Iout=Vref/R where Vref=1.25V and R is the resistance connected between the Vout pin and the ADJ pin. Output is also connected directly to Vout pin. For Iout = 235 mA, R should be about 5.3 ohms.

In this _non-conventional_ MC circuit, I'll make the following assumptions:

1) R1 = 9.1 ohms
2) R2 = 12 ohms 
3) Iout = (Vref+VR1)/R2 = 235 mA

Now, based on those assumptions I calculated the following:

1) VR1 = 1.57 Volts
2) Iled = 62.5 mA
3) IR1 = 172.5MA

In making these calculations, I worked backwards from the assumed total output current of 235 mA. We know that Vref = 1.25 volts. Rearranging my approximate formula for Iout, Iout (235 mA) * R2 (12 ohms) = 2.82 Volts (Vref+VR1), and 2.82V-1.25V = VR1 = 1.57 Volts. Next, I divide the 1.57 Volts (VR1) by R1 (9.1 ohms) to get IR1 = 172.5 mA. Finally, subtracting IR1 from Iout, we get Iled = 62.5 mA.

I didn't re-calculate using the 215 mA measured output, but I probably should just to see if the LED current looks more reasonable. Could also be that the series resistance of the R1/LED combo causes regulation to vary with load, and maybe even the LED brightness level would vary. Admittedly, I'm a bit intrigued with this whole circuit config...

I still believe that you could charge a 9-cell pack with a higher input voltage with no problems. If you want to change the charging current, however, I reckon you'd have to re-calculate for both R1 and R2 working backwards from the target Iout value. Too much current through that poor little red LED and it'll die.

OK - Anybody wanna throw some rocks at this and see if I'm even close to having it right? Any/all comments welcome...

Later - John


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## Ginseng (Apr 9, 2004)

John,
Would it help if I sent you the circuit board?
Wilkey


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## js (Apr 9, 2004)

Well, that's &*%^&** screwed up! Why is this done this way?

Good grief. I hope there's a good reason.


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## js (Apr 9, 2004)

One of the other operators here at work (who is more or less an electronics genius) and I went through Wilkey's pictures to come up with a circuit. Mostly because when I showed him John's circuit diagram, he said "That's wrong. That can't be that way."

So we puzzled through the pictures, and . . . came up with exactly the same circuit diagram. I never doubted you, John.

Anyway, yup, it's messed up. My advice to you, Wilkey, is don't try to change anything, just try one of the 15VDC wallwarts I have.

It is curious, though, because a 12 ohm resistance in parallel with a 9 ohm resistance yields just about the right value to give a .235 amp current from the 1.25V = I * R formula. Is it possible that the circuit board is visually misleading or tricky somehow, but that the actual circuit is the straight forward LM317T circuit setup? Wilkey, could you try to electrically verify John's diagram with your DMM?


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## evan9162 (Apr 9, 2004)

A third confirmation on that circuit. A large chunk of the charging current is being handled by that LED. If you black-box the LED in parallel with the resistor, I bet that would approximate a ~5 ohm resistor. It's quite sadistic to pump 60mA or more through a resistor, but we are talking about Mag here /ubbthreads/images/graemlins/tongue.gif


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## IsaacHayes (Apr 9, 2004)

What is the difference between having the resistor on the adjus pin before it's connected to ouput pin, vs having a resistor connected to the output pin and the adjus pin connects after that? I've seen the circuit both ways, but this one does them both?!

Would switching between the 2 setups cause any problems? Would it make sense to do it the first way I said as wouldn't that reduce the wattage needed for the sense resistor as no load is being pulled through it?

Also, if one were to build one of these, and set it at say 180ma to charge 1800mah NiMH AA's, and power it with a suffeicent WW, you could charge any number of AA's in series and they all would get 180ma charge? What suitable WW would one use to charge 1-6 AA's in series?

Also, the LED goes out I assume when the AA's are full right?


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## evan9162 (Apr 9, 2004)

Erhm...edited because that's a 12K ohm resistor


I think I've got it!

Like someone said, that 12K ohm resistor will control the current

Here's how:

There's about 50uA flowing OUT the Adj pin. through the 12K resistor which, causes a voltage drop of 0.6V (+ at the ADJ pin, - where R2 connects to out)

Now, the 317 tries to maintian 1.25V between Adj and out, but out is the + of that 1.25V difference. Using voltage loops:

1.25 (Vout -> Adj) = V(R1) + V(R2) (looking clockwise)

V(R2) (output -> Adj direction) = -0.6V

V(R1) = 1.25 - V(R2) = 1.25 - (-0.6) = 1.85V

V(R1) = 1.85V

I(R1) = 201mA

Thus, I(LED) ~ 15-30mA. 

I(total) = 215-230mA.


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## CNC Dan (Apr 9, 2004)

It looks like the LED would light only when there is enough current flowing through the 9.1 ohm resistor, making it a 'charge in progress' indicator. When the battery pack comes up to voltage, the diferance between Vin and Vbat is smaller and less current will flow. Less current through the 9.1 ohm resistor means less voltage across that resistor, and the LED won't light. If this is so, then the Vin from the wall wart, under load, may be important for the LED to indicate the charging status, and to reduce charge current to a full battery pack.


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## evan9162 (Apr 9, 2004)

CNC Dan,

I think I remember that NiCDs are safe to continuously trickle at C/10. Given that the magCharger is a 2.4Ah NiCD pack, they may choose a C/10 charging rate (230mA), given that it's relatively "safe" to leave it charging at that rate indefinitely. Thus, they don't have to design any charge termination circuitry.

I guess the question is: does the charge LED turn off when the battery is charged, or does it remain on all the time?


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## turbodog (Apr 9, 2004)

stays on


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## evan9162 (Apr 9, 2004)

Sounds like they've made it a constant current, always trickling, C/10 NiCD charger.

What's neat about this thread is that it shows a way to make an adjustable constant current regulator without having to use a huge rheostat. Replace the 12K resistor with a potentiometer. The value R1 sets the minimum current, while R2 increasing from 0 will increase the current. I'm sure there's a maximum limit to how high current can be adjusted to.

I'll try building this to see if it actually works that way.


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## Illuminated (Apr 10, 2004)

Wilkey,

Could you possibly measure the IOut of your charger connected to the 5-cell battery, and also measure the voltage across R1?

Solving for Turbodog’s measured Iout of 215 mA, and assuming 0% tolerance on the 9.1 (R1) and 12 (R2) resistors, I calculate the following values:

1) VR1 = 1.33 Volts
2) VRef + VR1 = 2.58 Volts
3) IR1 = 146 mA
4)ILed = 68.8 mA

So, without further measured values or having tested the circuit myself, I’ll potentially expose my self-taught knowledge of electronics to ridicule and make the following theoretical statements about this circuit:

The difference between the measured IOut of different charger units and Mag’s specified 230 mA is due to the fact that IOut is split between R1 and the LED. Since different LED’s have different Vf’s, ILed will also vary and so will VR1 and IR1. Summarily, R1 and the LED together appear to the LM317T as a simple resistor, and thus programmed IOut will vary since they are included with R2 in determining IOut as used in this configuration. I seriously doubt that Mag would be using “binned” LED’s for this circuit.

If one wants to change the programmed IOut significantly, the values of both R1 and R2 will have to be adjusted accordingly or the LED will either get way too much current, or not enough current to be turned on.

I won’t go as far as to say that the circuit is bogus, but I will say that I think it was chosen as a less expensive (read:cheaper) way of providing a “charger connected” indication. In contrast, the TigerLight charger uses a separate transistor circuit that senses current flowing through the output and turns on the LED with a fixed current that is not directly dependent on the LM317’s output. In other words, the LED circuit does not influence the LM317’s programmed output current. This makes it much simpler to change IOut using the formula straight from the LM317T datasheet.

To plagiarize Dennis Miller:

“Of course - that’s just MY opinion; I could be wrong...”

Later - John


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## evan9162 (Apr 10, 2004)

Illumated,

R2 is 12K ohms, not 12 ohms. If it were 12 ohms, there would be no point of it being in the circuit. You have to re-do your calculations to take account the voltage drop that Iadj causes across R2.


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## Illuminated (Apr 10, 2004)

evan9162,

The third band is black (multiplier of 1) - counting from either end. How do we get 12K rather than 12 or 13 ohms?

John


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## evan9162 (Apr 10, 2004)

It's a 5 band resistor - probably really 13K ohms (brown orange black red)


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## Illuminated (Apr 10, 2004)

OK-

First, let me say that I mean no offense to anyone here (I can be a little thick sometimes...). I mean that I respect all evaluations of this circuit posted here.

My comments so far have been entirely based on my best guesses about how this circuit might behave, and without having tried to duplicate and test it.

evan9162,

I didn't quite understand your evaluation at first, and I was further confused by the color bands of R2. So, I took another look at your posts, and what you said now seems to make more sense to me...

evan9162 said:

"The value R1 sets the minimum current, while R2 increasing from 0 will increase the current."

I had not considered that VR2 might be *negative* with respect to VR1.

php_44 said:

"To decrease the charge current - you'd need to connect some resistance in series with that bluish body resistor - again a 1K trimpot would be fine."

This appears to be exactly the opposite of evan9162's evaluation.

If evan9162 is correct in that R1 sets the minimum Iout and increasing R2 from zero ohms increases Iout, then the value R1 must be increased if Wilkey wants to reduce the current, and R2 could be set to zero for minimum Iout.

If php_44 is correct in that increasing value of R2 will decrease the current, then Wilkey will need only increase the the value of R2.

I'm anxious to play with the circuit and see how it actually behaves...

Thanks to all of you for your evaluations of this circuit. I love learning new things, even if it means I have to admit to being wrong /ubbthreads/images/graemlins/blush.gif

John


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## evan9162 (Apr 10, 2004)

I just built this circuit and my theory is correct.

Well, I didn't build the exact circuit, but here's what I did build:

R1=7.2 ohms
R2=100K pot
No LED

At R2=0 ohms, the circuit outputs 0.17 Amps
At R2=80K ohms (highest the little pot goes to), the circuit outputs 0.87 Amps 

If I unplug the wire from the load to the Adj pot (simulating an R2=infinite), then the current jumps to 1.25A, the maximum that the 317 will output (it is internally current limited).

This looks like a slick way to make an adjustable current source without having to switch out large resistors, nor having to use a giant rheostat to adjust current. A tiny potentiometer will adjust the current if it is put in place of R2. 

Remember, R1 sets the MINIMUM current - so increasing R1 will DECREASE the minimum current. R2 sets the current. INCREASING R2 will INCREASE the current. Setting R2=infinity will essentially open the regulator wide-open, having it attempt to pour the maximum amount of current into the load. 
In that case, an LM317 will pour in 1.25A, an LM350, 3.5A, and an LM338, 5A (of course, if Vin isn't great enough to put that much current into the load, then Vin will be the limiting factor). R1 needs to be able to meet power requirements for the maximum current that will flow through it In my case, 0.87A, it would need to dissipate 5.4W - for this case, my R1 was made from two 3.6 ohm, 1W resistors in series - so they weren't sufficient for this circuit - I would need two 3W or 4W resistors to be safe.

To get the most range of current, you would need a 1Mohm pot (does such a thing exist?) or several smaller pots in series.


----------



## Illuminated (Apr 10, 2004)

evan9162... /ubbthreads/images/graemlins/bowdown.gif /ubbthreads/images/graemlins/bowdown.gif /ubbthreads/images/graemlins/bowdown.gif

Thanks for "schooling" me on this one /ubbthreads/images/graemlins/smile.gif

John


----------



## evan9162 (Apr 10, 2004)

It was fun to figure this one out. This particular circuit configuration isn't mentioned in the National LM317 datasheet (there are like 20 different sample circuits in that datasheet).


----------



## Illuminated (Apr 10, 2004)

Exactly!

BTW - waddya suppose the diode is there for?

John


----------



## evan9162 (Apr 10, 2004)

Probably to prevent the battery from draining back into the charger if the charger is unplugged with the battery still connected. I have a 317-based current supply that I built, with a fan to cool the regulator. If I've used it to charge a 6+ volt pack, then unplug the power brick from the current supply (while leaving the battery plugged in), then the fan will still run slowly, powered by the battery.


----------



## Ginseng (Apr 10, 2004)

Ah,

Ok, so now that I understand none of the above posts, let me ask a question. I typically use my standalone RC charger to cycle my packs. Sometimes when I put a freshly charged pack (or even one with 10-15 minutes or more of runtime) on the cradle, the LED does not go on. If I then run the light for a few minutes and slap it back on the charger, the LED lights. What in the heck is going on?

Wilkey


----------



## Ginseng (Apr 10, 2004)

One more thing. If there is a diode in the charger, why would you need one in the torch itself?

Wilkey


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## evan9162 (Apr 10, 2004)

To prevent a short across the charger contacts on the flashlight body from discharging the batteries. If I understand right, the TigerLight charger contacts are hot, and there is a risk of shorting the battery on them.


----------



## Nitro (Apr 10, 2004)

[ QUOTE ]
*Ginseng said:*
Ok, so now that I understand none of the above posts, let me ask a question. I typically use my standalone RC charger to cycle my packs. Sometimes when I put a freshly charged pack (or even one with 10-15 minutes or more of runtime) on the cradle, the LED does not go on. If I then run the light for a few minutes and slap it back on the charger, the LED lights. What in the heck is going on?


[/ QUOTE ]

My quess is the charger knows (checks voltage) it's not at full capacity and starts charging, so the led turns on. When it's charged (checks voltage) the led turns off. I could be wrong though. What if you check the voltage to see when the led is on and off?


----------



## Illuminated (Apr 10, 2004)

Ok Wilkey,

So...if I understand evan9162's explanation of the MC circuit, all you would need to do to reduce the charging current is replace R1.

Replace R1 with a single 18 or 20 ohm 1/2 watt resistor to get between 100-130 mA. I can't be more exacting because I don't know how much current is flowing through the LED.

I checked, and both 18 and 20 ohm 1/2 watt resistors are listed in the Newark catalog, so I know they're available somewhere.

Two possible "Radio Shack" options would be to either use two 10-ohm 1/2 Watt resistors in series, or use two 39-ohm 1/2 watt resistors in parallel. Either option should get you close to what you're after, and should fit in the existing space of the 9.1 ohm 1-watt.

Again, If I understand the circuit correctly, I wouldn't suggest changing the blue resistor (R2) because that would change VR1 and the LED current. By only changing R1 to reduce the output current, VR1 and the LED current would remain the same.

Hopefully, evan9162 will correct me if I'm wrong about this.

Later - John


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## Nitro (Apr 10, 2004)

[ QUOTE ]
*evan9162:*
Remember, R1 sets the MINIMUM current - so increasing R1 will DECREASE the minimum current. R2 sets the current. INCREASING R2 will INCREASE the current. Setting R2=infinity will essentially open the regulator wide-open, having it attempt to pour the maximum amount of current into the load. 
In that case, an LM317 will pour in 1.25A, an LM350, 3.5A, and an LM338, 5A (of course, if Vin isn't great enough to put that much current into the load, then Vin will be the limiting factor). R1 needs to be able to meet power requirements for the maximum current that will flow through it In my case, 0.87A, it would need to dissipate 5.4W - for this case, my R1 was made from two 3.6 ohm, 1W resistors in series - so they weren't sufficient for this circuit - I would need two 3W or 4W resistors to be safe.

[/ QUOTE ]

I have dumb a question. What is the point of having a MINIMUM current setting?

I have another dumb question. What exactly are we trying to accomplish here? Is it reducing the current so it won't damage the battery pack?


----------



## Illuminated (Apr 10, 2004)

Nitro,

Evan9162 is just describing how the MC charger circuit would work if on wanted to make the current adjustable.

Wilkey has indicated that he would like to reduce the charge current to a safe "standby" level for the custom battery packs. This would be a level that would have little or no detremental effects if they were left on the charger for long periods of time.

I don't think the objective here was to turn it into a rapid charger because it is not a "smart" charger and there would be a significant risk of causing permanent damage to the batteries. I personally wouldn't want to risk that after investing the time/money into these custom battery packs.

Later - John


----------



## Nitro (Apr 10, 2004)

That's what I thought. Just wanted to make sure. What is the maximum constant current (trickle current) the battery can take at full charge for long periods? Also, what's the maximum current (rapid charge) these batteries can take while charging? The issue is, if you reduce the current to a trickle, it will take longer to charge. Which is already pretty long. Why not put a switch in for rapid and trickle charge? It would require manual switching when the battery is charged.

Or better yet, why don't we turn this baby into a smart charger? When the batteries get to a particular voltage, it switches automatically to trickle. /ubbthreads/images/graemlins/thumbsup.gif

Probably easier to just buy another charger though. /ubbthreads/images/graemlins/banghead.gif


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## Doug Owen (Apr 10, 2004)

I think folks are missing the 'trick' here. The resistor in the adj lead is not to increase current, or allow the maker to trim it in production or test. While Iadj is indeed stable to a few percent over temperature (good enough for the use) it is only typical at 50 uA, it can be up to 100 uA per the specs. This is a big range, and would mandate careful selection of the value, something that costs money. It also increases headroom load (minimum voltage requirement) and power rating on the sense resistor. All destinct disadvantages on the product.

It does, however, add .6 Volts or so to the necessary drop across the sense resistor (9.1 ohms in our case) up to the point where it will *light the (red) LED*.

Doug Owen


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## Ginseng (Apr 10, 2004)

John hit it right on the head. This is only a concern for the 1.2.x class MC mods where I am shooting for a variety of high outputs while retaining the stock form factor. The 2.x class MC mods will have no such concern since they will be free to use the 3.5Ah nimh or 2.5Ah nicad cells and the stock value of 215-230mA will be fine. I am shooting for something in the range of 115mA for 1.7Ah to 2Ah cells.

If the intended usage pattern is to use the torch/battery to pack exhaustion each night, then this slow trickle would not be appropriate. I just want a very bright, always ready light for brief squirts every few nights. 

In any case, I have the Triton charger in case I need to fast charge a pack. 

Doug, I have no idea what you just said but it sounds intelligent /ubbthreads/images/graemlins/grin.gif

Wilkey


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## turbodog (Apr 10, 2004)

I'd love it if someone would dissect the regular stinger charger. Would be nice to know about it as well.


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## Doug Owen (Apr 10, 2004)

[ QUOTE ]
*Ginseng said:*
....I am shooting for something in the range of 115mA for 1.7Ah to 2Ah cells.



[/ QUOTE ]

Ah, so!

That's where this is going? Easy, you want half the current, double the sense resistor. Make the 9.1 ohms 18.2. Better still, lift one end, add a second 9.1 in series (total 18.2) and then add a switch to short out one or the other. The switch now does the 115/230 mA change for you. The value doesn't need to be spot on, using a ten ohm instead will only have you off by about 5% (you end up at 110 or 120 mA instead).

You might get cute with a magnet in the flashlight cap and a reed switch in the charger to automatically select rates?

Doug Owen


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## Illuminated (Apr 11, 2004)

Just for the sake of comparison, here's the TL charging circuit -






Conventional use of the LM317 CC mode, with separate transistor for driving LED indicator when output current flows.


Happy Holiday!

John


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## Doug Owen (Apr 11, 2004)

180 mA for charging current? Interesting.

You confused me for a bit with your non standard use of the symbols. The bottom '317 pin' is typically the adj lead (but out in yours?), while the right is out (not adj?)? I suggest labels or using the conventional symbol.

Otherwise, clever use of the PNP as an emitter follower. Drives the LED with a *fixed* 20 mA with no increase in costs. Cool.

Doug Owen


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## Nitro (Apr 11, 2004)

[ QUOTE ]
*evan9162 said:*
Erhm...edited because that's a 12K ohm resistor


I think I've got it!

Like someone said, that 12K ohm resistor will control the current

Here's how:

There's about 50uA flowing OUT the Adj pin. through the 12K resistor which, causes a voltage drop of 0.6V (+ at the ADJ pin, - where R2 connects to out)

Now, the 317 tries to maintian 1.25V between Adj and out, but out is the + of that 1.25V difference. Using voltage loops:

1.25 (Vout -> Adj) = V(R1) + V(R2) (looking clockwise)

V(R2) (output -> Adj direction) = -0.6V

V(R1) = 1.25 - V(R2) = 1.25 - (-0.6) = 1.85V

V(R1) = 1.85V

I(R1) = 201mA

Thus, I(LED) ~ 15-30mA. 

I(total) = 215-230mA.


[/ QUOTE ]

Where did you get 50uA flowing OUT the Adj pin? Is that constant?

So what is the formula for I(Out) based on R1 and R2 values?


----------



## evan9162 (Apr 11, 2004)

The datasheet for the LM317 states that Iadj is about 50uA (but may be a maximum of 100uA). 

In this circuit, assuming Iadj remains at 50uA, then 

Iout = (1.25 + (50uA * R2) ) / R1

or

Iout = (1.25 + (Iadj * R2) ) / R1


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## Nitro (Apr 11, 2004)

That's what I thought.

However, if R2=80K and R1=7.2 then
Iout = (1.25 + (50uA * 80K)) / 7.2
Iout = 729mA

But didn't you measure Iout = 870mA?

Edit: R1 = 7.2 instead of 9.1


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## Illuminated (Apr 11, 2004)

Sorry Doug,

I sketched this in a real hurry over a year ago for my own use. I never before thought of posting it, or I might have drawn it to be more concise. I too liked the PNP emitter follower driving the LED.

I figured the 180 mA rate was roughly 0.1C for the TL battery pack. A relatively safe rate for the intended application I think.

John


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## evan9162 (Apr 11, 2004)

[ QUOTE ]
*Nitro said:*
That's what I thought.

However, if R2=80K and R1=7.2 then
Iout = (1.25 + (50uA * 80K)) / 7.2
Iout = 729mA

But didn't you measure Iout = 870mA?

Edit: R1 = 7.2 instead of 9.1 

[/ QUOTE ]

I guess my reported numbers were a bit off

output current was 0.82A
R2 was 84.8K
Iadj was 56uA


putting all this together gives us:

(1.25 + (56uA * 84.8K)) / 7.2 = 0.83


R1 was really 7.3 ohms, which gives 0.82A


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## Nitro (Apr 11, 2004)

Ok, makes sense. But if we are going calculate Iout before implementing, how do we get Iadj without actually trying it?


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## evan9162 (Apr 11, 2004)

I think you'll have to expect some variation with this method. That might explain why one person measured 235mA, and the other 215mA with their MC charger.


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## turbodog (Apr 11, 2004)

for the record... 235 was from the book and the only measured value around here was 215


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## Ginseng (Apr 11, 2004)

That was me misquoting "235mA." The book actually says 230mA. I have not done a measurement.

Wilkey


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## Doug Owen (Apr 11, 2004)

[ QUOTE ]
*Illuminated said:*
I figured the 180 mA rate was roughly 0.1C for the TL battery pack. A relatively safe rate for the intended application I think.



[/ QUOTE ]

I agree. This seems like a solution for NiCd cells, it would of course be very bad for NiMH.

Doug Owen


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## Doug Owen (Apr 11, 2004)

[ QUOTE ]
*evan9162 said:*
I think you'll have to expect some variation with this method. That might explain why one person measured 235mA, and the other 215mA with their MC charger. 

[/ QUOTE ]

Even though the 235 number was later changed, this is absolutely true. Given the parts involved, the exact value is going to vary from unit to unit.

"Only Engineers sweat the last few percent"

Doug Owen


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## Illuminated (Apr 11, 2004)

[ QUOTE ]
*Doug Owen said:*
[ QUOTE ]
*Illuminated said:*
I figured the 180 mA rate was roughly 0.1C for the TL battery pack. A relatively safe rate for the intended application I think.



[/ QUOTE ]

I agree. This seems like a solution for NiCd cells, it would of course be very bad for NiMH.

Doug Owen 

[/ QUOTE ]

Just to be cautious, I only "top off" my TL for a short period once a week. Longer if I've used it - never 24/7...

John


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## turbodog (Apr 11, 2004)

[ QUOTE ]
*Doug Owen said:*
[ QUOTE ]
*evan9162 said:*
I think you'll have to expect some variation with this method. That might explain why one person measured 235mA, and the other 215mA with their MC charger. 

[/ QUOTE ]

Even though the 235 number was later changed, this is absolutely true. Given the parts involved, the exact value is going to vary from unit to unit.

"Only Engineers sweat the last few percent"

Doug Owen 

[/ QUOTE ]

Well guess what I am then. /ubbthreads/images/graemlins/grin.gif


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## Doug Owen (Apr 12, 2004)

[ QUOTE ]
*turbodog said:*
[ QUOTE ]
*Doug Owen said:*
[ QUOTE ]
*evan9162 said:*
I think you'll have to expect some variation with this method. That might explain why one person measured 235mA, and the other 215mA with their MC charger. 

[/ QUOTE ]

Even though the 235 number was later changed, this is absolutely true. Given the parts involved, the exact value is going to vary from unit to unit.

"Only Engineers sweat the last few percent"

Doug Owen 

[/ QUOTE ]

Well guess what I am then. /ubbthreads/images/graemlins/grin.gif 

[/ QUOTE ]

Not to worry, we're all running from something in the past.

Just how many of us cowboys you think use our real names when we come to town?

Doug Owen


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## Nitro (Apr 12, 2004)

[ QUOTE ]
*Ginseng said:*
John hit it right on the head. This is only a concern for the 1.2.x class MC mods where I am shooting for a variety of high outputs while retaining the stock form factor. The 2.x class MC mods will have no such concern since they will be free to use the 3.5Ah nimh or 2.5Ah nicad cells and the stock value of 215-230mA will be fine. I am shooting for something in the range of 115mA for 1.7Ah to 2Ah cells.


[/ QUOTE ]

What if you SHORT R2? That will give you ~137mA. If that current is low enough, it would make the mod real simple. Just a thought.


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## js (Apr 13, 2004)

Doug Owen,

The owner of TigerLight has left his NiMH battery pack on the .1C charger for months and months and he SAID that it still worked fine. Granted, I agree it's certainly not good, but it would seem that the stock battery pack CAN take it, although it is specifically not recommended in the TL manual. Any hard info on continuous .1C charging of NiMH batteries and its deleterious effects?


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## Doug Owen (Apr 13, 2004)

[ QUOTE ]
*js said:*
Any hard info on continuous .1C charging of NiMH batteries and its deleterious effects? 

[/ QUOTE ]

Yup. All the makers say don't do it. Good enough for me.

NiCd cells are OK at low enough rates, for NiMH that 'safe rate' is c/300 as I recall. Yup, just checked:

Duracell NiMH charging 

They say 'minus delta V', then *a half hour* at .1C (optional) then C/300 if you want.

That's why NiCds are still the call in some cases.

Doug Owen


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## Ginseng (Apr 13, 2004)

Doug, 
I do beg to differ on the statement that "All the makers say don't do it." Gold Peak states the following in their NIMH Technical Manual:

[ QUOTE ]

3.2.5 Trickle charging
In most applications - where cells and batteries
need to be in a fully charged condition - maintaining
a trickle charge current to compensate for the loss
of capacity (due to self-discharge) is recommended.
The suggested trickle charge current to be used
is 0.05C to 0.1C.

[/ QUOTE ]

And in the technical data sheet for the GP3300, 3.3Ah high current nimh:

[ QUOTE ]

330mA maximum current
No conspicuous deformation and/or
leakage

[/ QUOTE ]

That's 0.1C.

Wilkey


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## Doug Owen (Apr 13, 2004)

[ QUOTE ]
*Ginseng said:*
Doug, 
I do beg to differ on the statement that "All the makers say don't do it." Gold Peak states the following in their NIMH Technical Manual:


[/ QUOTE ]

I sit corrected. At the risk of saying something unkind about our friends at GP, one has to decide if they really know how to make a better cell....or just have a different idea on how to market them. In other makers cells, this leads to short life span.

Again, this is why we see NiCd cells in 'standby' use.

But, yes, GP does allow it.

Doug Owen


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## js (Apr 14, 2004)

[ QUOTE ]
*Doug Owen said:*
Yup. All the makers say don't do it. Good enough for me.

[/ QUOTE ]

It's good enough for me too, Doug, but this is hardly what I'd call "hard info"! I mean, does anyone have access to actual laboratory type test results comparing continuous .1C trickle charged batteries to peak charged batteries, looking at life cycle differences, capacity decreases, changes in internal resistance, current carrying capability, and so on. I have no idea what would be the relevant variables other than number of useable cycles, but someone somewhere must have done some tests on this, right? As soon as I get my hands on "Batteries in a portable world" I'll look for some hard info in there.

As for GP intentionally recommending a charging method that they know to be detrimental in an effort to garner more sales . . . well, let's just say I think this interpretation is a little bit cynical. GP seems to me to make some kick butt batteries. Do you think they are a disreputable company?


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## Doug Owen (Apr 14, 2004)

Aside from the maker's own testing the DOE runs a killer Lab at either Sandia or Los Alamos (I can't recall which) for just this use (rechargable life times). I've long ago forgotten the chemestry behind it, but as I recall it has to do with recombining gasses.

If you're asking if maximum number of user charging cycles is what drives GP (or anyone else's for that matter) Marketing decisions, yes I think that's entirely possible they could knowingly recommend a use that didn't yield maximum life span. And I think it's cynical, not paranoid.

Let me ask it as a Capitolist: 'Since we know the chemestry is basically the same, as are construction details, if this form of trickle charging was OK why would Mallory, Eveready and the rest not join in? Why do our friends at Sure Fire and all the rest still use NiCd for their 'always on the charger' products when they could go to NiMH and get longer run times and avoid the cadmium? Why don't they just buy their cells from GP?'.

Doug Owen


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## js (Apr 14, 2004)

Doug, you are absolutely right, I should have said "a little bit cynical" and not "a little bit paranoid." I edited my post to correct my diction.

I think if a company is smart it recommends mehods of care that yield the best results and longest life because that puts their product in the best light and gives it a better reputation. A person whose batteries die prematurely is likely to choose another brand when he next buys batteries, rather than just buy an increased number of the same batteries.

As for why SureFire and all the rest use NiCds, I would think that it has more to do with how well NiCds stand abuse, especially being drained down to near zero voltage. Standing up to trickle charging could also have something to do with it, and they are easier to peak detect when designing circuitry for a fast charger. Plus they have, all other things being equal, a longer life. And they are a proven and time tested technology.

It could be that the other companies are being more conservative than necessary in their charging recommendations for NiMH. Or it could be that GP batteries are better built and can stand up to a continuous .1C trickle charge. Or it could be that high rate NiMH batteries in general can disipate the excess charge as heat better and faster than general use or high capacity NiMH batteries.

It *could be* but I don't know and won't feel that I know for sure until I see some *hard, quantitative* information on the subject. I do not accept a cynical interpretation as correct simply because mercenary motives do seem to rule the commercial world.

And, of course, you could be right on in what you say. All I'm saying is that at the moment, I'm not convinced one way or the other.

Fair?


----------



## Doug Owen (Apr 14, 2004)

Jim,

Absolutely. Don't take my (or anyone else's) word for it when you can research it yourself.

You might want to check some of your assumptions first. For instance, NiCds have *short* lives (few hundred cycles) relative to NiMH (maybe a thousand or more). True, they take deep discharge better, but have memory (which is really real), shorter lifetime, lower capacity and toxics issues. You don't use them unless you need to (like from full time charging).

By all means research it. And yes, I do think GP could do this, do they even offer NiCd? Their base market is entirely different that what we're used to.

Doug Owen


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## RussH (Apr 14, 2004)

I personally don't like to leave NiMH batteries on charge for extended periods. Note their relatively short life in phones that do that. I'd like to see some hard data, or at least an estimate by the manufacturer on how much continuous trickle charging at, say, .05C would reduce life. Then I could determine for myself if the tradeoff was justified. As it is, I have left NiMHs on trickle chargers for several days when that was convenient. I'm not too worried about it, but I still prefer to keep the trickle charge period down to less than a day. -RussH


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## js (Apr 14, 2004)

Doug,

I remember reading the opposite at battery university (do a search and you will find it--can't remember the link at the moment). He said that NiMH had fewer cycles in their lifespan than NiCd's. But I'm sure I could be mis-remembering. In any case, that would suit me just fine. I like NiMH's. I'll check my assumptions at any rate. Thanks.


----------



## RussH (Apr 14, 2004)

Jim (and Doug) I'm not sure I believe everything that I see at battery university. It's good info overall, but new data comes up from time to time, and not everything there is as thouroughly researched as I'd like. Anyway, memory in Nicads hasn't been a problem since sometime in the '70s. The manufacturers, due to complaints, made changes to eliminate or get rid of memory. It can occur, but you have to work at it. It doesn't keep me from taking steps to avoid it, but I haven't had any reason whatsoever to worry about it since 1975 or thereabouts. 

Usually Nicads are advertised as having 1000 cycle life or longer. This has only recently been true of NiMH. Previously, maybe 2 years ago, 500 cycles used to be claimed for NiMH. They have made some improvements, primarily in the chargers, so 1000 cycles may now be possible with NiMH. I still think NiCads will last more cycles, but twice as many cycles with half as much capacity doesn't get you ahead. NiCads are still more robust and last longer in adverse conditions than NiMH. There is a reason that they have held on in portable tools for years after NiMH could double the capacity.


----------



## SilverFox (Apr 14, 2004)

Hello Jim,

I just want to clear up what you said about Randy Teig leaving his TigerLight on the charger for extended periods of time. He uses his light every night and leaves it on the charger between uses (and weekends). I believe this is a little bit different than "storing" in on the charger.

Refer to this link. 

He does go on to mention that he has little concern about non law enforcement people leaving their lights on the chargers for an extended time. At the time of the post, TigerLight had not had any issues with dead battery packs.

Tom


----------



## js (Apr 14, 2004)

Tom,

Thank you so much for the clarification! Yes, there is a big difference between that and what I had remembered the situation to be.


----------



## gwbaltzell (Apr 14, 2004)

I don't recall ever seeing a manufacturer recommend against true trickle charging. I think the reason NiCds are still used in power tools is they stand up better to the abuse the standard dumb charger puts them through. I've glanced at the NASA tech. paper that shows a charging method that extends the life of both nickel chemistries beyond the 1000 cycles and also appears to be better for lead-sulfur. A few commercial chargers are using it. Already goes by three different names: reverse pulse charging, negative pulse charging, "burp" charging.

I wish I could find the NASA paper on "memory" because it corrected the notion that problem was likely ever to occur anywhere on earth and that even then it is fully reversible by modifying (varying) the charge/discharge cycle.


----------



## turbodog (Apr 14, 2004)

oh please... please don't ruin this nice informative thread by going off into the voodoo of cell technology


----------



## gwbaltzell (Apr 14, 2004)

Sorry, thought it had already wandered there! The "memory" nonsense is too often used as an excuse for bad cells and bad charging methods. And most tool rechargers fall into that last category. Its all voodo. One of the secrets I didn't know until recently is NiCds (but not NiMhs) get colder as they're being properly charged, a least till near the end. I won't post anymore on your nice thread.


----------



## Ginseng (Apr 14, 2004)

Hey,
This is my thread...and feel free to keep posting. I'm always looking to learn.
Wilkey


----------



## gwbaltzell (Apr 14, 2004)

Thanks, Wilkey. It was probably an idle threat anyway. /ubbthreads/images/graemlins/grinser2.gif I mostly was trying to get you to look at the "burp" method. Though NASA disproved the inventor's theory of how and why it worked, the research seems to indicated it does work. And the patent has expired. They think that the short controlled pulse of reverse current causes the hydrogen bubbles to be re-absorbed and reduce the formation of crystals (whiskers) that cause many of the problems and limited life in both nickel chemistries. Note: at least one R/C site refutes any advantage to "burp" charging. Before I came across this I had used a crudder method to partially restore the capacity of some cells with mixed results. Of course, some I just blew the "whishers" off of with a heavy current. Thinking of building a "burp" charger to try.

George


----------



## Ginseng (Apr 14, 2004)

George,

I had read a bit on pulse charging and it does sound promising. Even something as archaic and as commonplace as batteries is open to advancements. Sometimes all it takes is an inquisitive mind to see new possibilities.

Wilkey


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## Doug Owen (Apr 14, 2004)

It used to be called 'reflex charging' as I recall. Bottom line I remember (never a solid asset, trust me.....) is it's 'not enough better to justify the cost....at best'.

Line then was 'it's what electroplaters use to get a really perfect finish'. Hey, works for me....

Still, if our tax $$ at work though NASA say it's cool....

Gotta wonder why in all those years someone didn't clone the charger that doesn't exist.

Doug Owen


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## evan9162 (Apr 14, 2004)

The burp charger wouldn't be hard to build.

All it would take would an LM555 timer-based circuit with a counter. You would just match one of the counts to be a discharge state, then go back to charging for the rest of the cycles. There must not be a compelling advantage to the method - the circuit would be relatively straightforward.


----------



## gwbaltzell (Apr 14, 2004)

Evan9162: I'm thinking a large capacitor too for the large current, and short burst and to limit current if the switching MOSFET fails. Of course I could buy one of the ready made chargers, but were's the fun in that.

There is a compelling reason to make a constant current charger and it only takes a LM317T and one resistor but that's too much for most. And only two more resistors and the circuit reduces the charging rate at full charge. We're probably lucky they put the resistor in between the wall wart and the battery in the bulk of the charges. I'm surprised M*g sprang for the LM317T.

The main advantage to "burp", if NASA's right, is better maintenance of capacity and useful life well beyond 1000 full cycles. It looks like they have used this method in at least one Earth orbiting satellite.

George

BTW - I thought the main trick in gold plating to get a smooth finish (for jewlery not electrical) was to add sugar!


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## js (Apr 15, 2004)

[ QUOTE ]
*gwbaltzell said:*

There is a compelling reason to make a constant current charger and it only takes a LM317T and one resistor but that's too much for most. And only two more resistors and the circuit reduces the charging rate at full charge. . . . 

[/ QUOTE ]

Details, please! How do you place the additional resistors to get a lower current once the battery pack is fully charged?


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## Doug Owen (Apr 15, 2004)

[ QUOTE ]
*evan9162 said:*
The burp charger wouldn't be hard to build.

All it would take would an LM555 timer-based circuit with a counter. You would just match one of the counts to be a discharge state, then go back to charging for the rest of the cycles. There must not be a compelling advantage to the method - the circuit would be relatively straightforward. 

[/ QUOTE ]

Actually, the implementations I recall were even simpler, you leave the charge current on all the time and gate the load on and off. You put like a few C load on a percent or two of the time.

Use your 555 to drive a big NPN (like 2N3055) on at low duty cycle. Hook a suitable load resistor between collector and plus on the battery, minus to emitter and you're jake. You can convert a normal charger and try. I suspect it'd fool a 'smart charger', but maybe not if it was done fast enough?

Yup, not only is it easy to do (several ways), but the idea has been around a long time (with the claims). And I recall it being cited as 'electroplater prior art', meaning a patient wouldn't work anyway.

Of course, if you have a base made of the true cross, like this one here......

Doug Owen


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## gwbaltzell (Apr 15, 2004)

If I told you then everyone would know!

Seriously, its in National's datasheet. The example is for a 12V lead-acid. But its just putting the current sense before the voltage set resistors. Final voltage is still calculated with the same formula 1.25 * (1+R2/R1) but the impedance is calculated with the formula Rs (the sense resistor) * (1+R2/R1)
<font class="small">Code:</font><hr /><pre>
Vin ______ Vout Rs
__________| |_____________/\/\/\________
| | |
|______| |
Adj | R1 |
|________________/\/\/\____| 
|
| R2
|_____/\/\/\__
__|__
___
-</pre><hr />
Rs still has to handle the power drop across it so remember the other form of Ohm's law P = I^2 * R or if you just want to play it safe the worst I^2 is 2.25 (LM317T limits to 1.5 A and any value > 0 for Rs is going to put you below that).
For NiMh looks like the voltage needs to be 1.5 V per cell to get a full charge. But after that the voltage is going to fall again. So even then you may want to limit time on the charger. NiCd fast charge looks about the same but at the normal 0.1C, dropping the voltage to 1.45 looks like it might maintain a proper trickle. You'd likely want to put a small adjustable in series with R2


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## gwbaltzell (Apr 22, 2004)

I've been re-reading Nickel charging info. forget 1.5 V above. And note the voltage would have to be set for a specific pack size. I've found one maker, Panasonic, that specifically says unlimited trickle at any rate shortens NiMh life. They do recommend the charge switch to a normal trickle rate (1/20 - 1/30 C) after a rapid charge, but the total charge cycle be limited to 10 - 20 hr. Their method of topping off NiMh? When the voltage reaches 1.3 V a 16 hr. timed cycle at 1/10 C! This surprised me because their only recommend recharging method for cyclical use is a negative delta V terminated rapid charge (with at lot of other conditions checked for). Best long term trickle rate for NiCd is 1/30 - 1/50 C.


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## Ginseng (Apr 22, 2004)

Thanks George, that's valuable information.

Wilkey


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## srue (Apr 30, 2004)

[ QUOTE ]
*Nitro said:*
[ QUOTE ]
*Ginseng said:*
John hit it right on the head. This is only a concern for the 1.2.x class MC mods where I am shooting for a variety of high outputs while retaining the stock form factor. The 2.x class MC mods will have no such concern since they will be free to use the 3.5Ah nimh or 2.5Ah nicad cells and the stock value of 215-230mA will be fine. I am shooting for something in the range of 115mA for 1.7Ah to 2Ah cells.


[/ QUOTE ]

What if you SHORT R2? That will give you ~137mA. If that current is low enough, it would make the mod real simple. Just a thought. 

[/ QUOTE ]

I shorted R2 (the blue resistor) on my charger and now the current is 137.3mA, which is just about perfect for my purposes. The voltage is 7.34V. Now I should be able to leave the light on the charger all the time with NiMH cells in it. (The spec sheet for Wilkey's UMP cells say the maximum overcharge current is 175mA. 137.3mA is very comfortably below that.)

Thanks for the great info everyone.

-Stuart

Edit: One important note - the LED does not light up. Everything else seems to work perfectly though.


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## Ginseng (Apr 30, 2004)

Excellent. Can you do it just by soldering a wire across the resistor leads?

Wilkey


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## srue (Apr 30, 2004)

Yes you can. Though there's not much room on the board, so I just folded a piece of copper wire and jammed it under the resistor so that it was touching both the leads. The slight tension of the folded wire kept it firmly in place, so I don't think there's any danger of it falling out. 

Believe me, if someone like me can do this mod, anybody can do it.

-Stuart

P.S. I'll stay in this thread so as not to hijack your group buy.


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## Ginseng (Apr 30, 2004)

I love a mod that's just this easy. Thanks srue!

Wilkey


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## Illuminated (May 1, 2004)

Hey Wilkey,

I hope to work on your MC circuit yet this weekend before I have to go back out of town on business. If I get the results we're looking for, I may have to send it to you from the road. Sorry I haven't done it yet...

John


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## Ginseng (May 1, 2004)

No prob John. I appreciate it.

Wilkey


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## Nitro (May 1, 2004)

[ QUOTE ]
*srue said:*
[ QUOTE ]
*Nitro said:*
[ QUOTE ]
*Ginseng said:*
John hit it right on the head. This is only a concern for the 1.2.x class MC mods where I am shooting for a variety of high outputs while retaining the stock form factor. The 2.x class MC mods will have no such concern since they will be free to use the 3.5Ah nimh or 2.5Ah nicad cells and the stock value of 215-230mA will be fine. I am shooting for something in the range of 115mA for 1.7Ah to 2Ah cells.


[/ QUOTE ]

What if you SHORT R2? That will give you ~137mA. If that current is low enough, it would make the mod real simple. Just a thought. 

[/ QUOTE ]

I shorted R2 (the blue resistor) on my charger and now the current is 137.3mA, which is just about perfect for my purposes. The voltage is 7.34V. Now I should be able to leave the light on the charger all the time with NiMH cells in it. (The spec sheet for Wilkey's UMP cells say the maximum overcharge current is 175mA. 137.3mA is very comfortably below that.)

Thanks for the great info everyone.

-Stuart

Edit: One important note - the LED does not light up. Everything else seems to work perfectly though. 

[/ QUOTE ]

Wow! Only 0.3mA off. I didn't think it would be that close.

I'm going to do it too, because I like the idea of leaving the torch in the charger.

Thanks for the imperical data Srue.


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## srue (May 1, 2004)

No prob, Nitro. Thanks for the idea.

Actually, the current now seems to stabilize at 137.0mA. Talk about exact calculations. Nice work.

I now feel like I have a complete MagCharger solution. I'm running a WA01160, Wilkey UMP, UCL-LDF lens, and soon Otokoyama's orange-peel PMR. I've got a good balance between brightness and runtime, I like the beam quality, and now I can leave the light on the charger indefinitely. I can't think of any more changes I'd want to make.


----------



## Nitro (May 2, 2004)

[ QUOTE ]
*srue said:*
No prob, Nitro. Thanks for the idea.

Actually, the current now seems to stabilize at 137.0mA. Talk about exact calculations. Nice work.

I now feel like I have a complete MagCharger solution. I'm running a WA01160, Wilkey UMP, UCL-LDF lens, and soon Otokoyama's orange-peel PMR. I've got a good balance between brightness and runtime, I like the beam quality, and now I can leave the light on the charger indefinitely. I can't think of any more changes I'd want to make. 

[/ QUOTE ]

Me too!

Now all I need is the Aurora. /ubbthreads/images/graemlins/cool.gif


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## Illuminated (May 2, 2004)

Wilkey, 

I modified your MC circuit following Doug Owen's suggestion of changing the 9.1-ohm to 18 ohms. Actually, I had to use a 100-ohm in parallel with a 22-ohm. Owing to resistor tolerances I measured about 17-ohms for the combination.

Hooked up to a regulated 13.8V supply and a 6-cell NiCad pack, initial current at room temperature measured at 116.7 mA, and the LED indicator works fine.

Current started climbing slowly until stabilizing at about 120 mA. The circuit is temperature sensitive, as I could lightly blow on it and the current would immediately start to creep downward until I stopped, then it would start climbing again.

I suspect that once installed in it's enclosure it might climb a few milliamps more due to the temperature effect.

At no time did the circuit feel more than only slightly warm to touch.

Later - John


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## Ginseng (May 2, 2004)

Thanks John,
I appreciate the assist!
Wilkey


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## Ginseng (May 10, 2004)

John,

I put your mod to the test today and it performs very well. With the uprated wallwart from Jim (15VDC/900mA), it even lights up when charging the 9-cell pack for the MC85. I'll measure the current tomorrow as I blew the 200mA fuse in my cheapo DMM.

Wilkey


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## mckevin (Mar 18, 2005)

I shorted the blue resistor today in my MC charger. I get 138mA and 19.6 volts at the charging terminals (el cheapo DMM). Any guesses as to why the voltage is so much higher than the 7.4 that srue got? Should I be concerned about using it this way with a 9 cell CBP1650 pack?


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## Ginseng (Mar 19, 2005)

Your voltage will drop once there is an actual load on the circuit. I would place the light on cradle and then touch the two DMM probes on the two rings. This should give you tha actual loaded voltage.

Wilkey


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## srue (Mar 19, 2005)

Yep, what Wilkey said. And as the cells charge, the voltage will slowly rise until the cells top off. The beauty of this setup is that you can change battery configurations (such as going from 5-cell NiCad to 9-cell NiMH and vice versa) without having to change the charger.


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## mckevin (Mar 19, 2005)

Cool, I put it on at noon & got ~9.1 volts, this evening it's at 10.2.
'preciate the help!!

(I fired the MC85 up tonight for the first time. It makes me VERY happy!)


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## Wetterman (Dec 9, 2006)

Has anyone drawed a schematic of the charger?


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## EvilLithiumMan (Dec 10, 2006)

Here is a schematic of my Magcharger cradle. Please excuse my drawing skills, I have only Microsft Paint to work with, no fancy AutoCad or PSpice tools. I have checked it numerous times and believe it to be 100% accurate. There are only six nodes in the circuit. (A node meaning a unique electrial point). I have listed the nodes on both the schematic and on the PCB assembly pics, so you can verify my results.

Node list:
1 - Vin, positive (the wall wart) and "Input" pin of the LM317T
2 - Vin, negative (wall wart)
3 - Vout, negative output of the cradle
4 - "ADJ" - the adjustment pin of the LM317T
5 - "Out" - the output pin of the LM317T
6 - Vout, positive output of the cradle
















ELM


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## Lips (Dec 10, 2006)

.












This one is connected to a 9.6v to 18v pack charger for the "Big Mac"  


Pack Charger can be disconnected and used as normal if need be...










.


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## Wetterman (Dec 10, 2006)

EvilLithiumMan that blue resistor must be 13k. Brown-orange-black-red-brown.


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## EvilLithiumMan (Dec 10, 2006)

Wetterman said:


> EvilLithiumMan that blue resistor must be 13k. Brown-orange-black-red-brown.



OK - I thought it measured 13 ohms, but the units indicator on my DMM is tiny and well could have said "k" and I missed it. What kind of stymies me on this circuit is that I have used 317's in many projects, but this follows neither the conventional "voltage" mode, where Radj (13K) goes to a voltage divider across the output, or the "current" mode where Radj goes directly to the 317's output pin, so I never could figure out the exact equation for calculating the charge current. 

(The red "charge indicator" LED has a typical Vf of 1.7V, so that would mean about 180mA through the 9.1 ohm shunt resistor and I assume the balance of the MC's nominal 220mA charge current, 40mA, is going through the LED)

I built a 317 constant current supply years ago with steps of 50, 100, 150, 300, 600 and 1200mA and handles from 1 to 24 cells. No temperature or deltaV shutoff, just a plain "you got to watch it" charger. I still use it on a regular basis.


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## Wetterman (Dec 10, 2006)

After reading this whole thread through a few times I still can't understand how the 13k resistor makes the 220mA(or 230) to output if the Vref is 1.25V.


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## evan9162 (Dec 10, 2006)

Please read my explanation here:

http://candlepowerforums.com/vb/showpost.php?p=529667&postcount=35


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## EvilLithiumMan (Dec 10, 2006)

I remeasured the resistor and it is indeed 13K.

evan9162 - Thanks for the explanation! I never would have figured it out.


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## Wetterman (Dec 11, 2006)

Yes Of course if you subract -0.6V from +1.25V you actually add .6V to 1.25V. 
That's where I lost the track. Should do some math more often


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## Wetterman (Dec 12, 2006)

Couple of questions, does the Iadj have anything to do with the Vref? and is the Vref + really in the Out pin and - on the adjust pin?
These questions might be stupid but I'm really a rookie when it comes to electronics.

EDIT: OK I got it.


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## Wetterman (Dec 15, 2006)

I connected a 12V DC converter to the cradle that gives exactly 12.12V. The led lights up for a few minutes and goes off. It seems that 12V is not quite enough to charge 5-cell pack. My MC's original wallwart gives 14.1V and the led stays on indefinately.


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## EvilLithiumMan (Dec 15, 2006)

Wetterman said:


> I connected a 12V DC converter to the cradle that gives exactly 12.12V. The led lights up for a few minutes and goes off. It seems that 12V is not quite enough to charge 5-cell pack. My MC's original wallwart gives 14.1V and the led stays on indefinately.



If I add up the voltages used by the circuit, I come up with:

7.25V - This is 5 x 1.45V for fully charged ni-cads
1.85V - The calculated drop across the 9.1 ohm resistor
1.25V - The minimum Input-Output differential needed by the LM317
0.7V - Drop across the input protection diode on the MC PCB
0.7V - Drop across the built in protection diode in the MC body
----------
11.75V Total, pretty close to your 12.12

If you assume the charging current through the 9.1 ohm resistor has dropped to 150ma, that gives .15 x 9.1 = 1.35V

1.35V is probably not enough drop to power the charge indicator LED, which needs 1.6-1.7V. So it would be unlit, while there is still some nominal current flowing into the cells. I suspect the 12.12V is charging the cells, just at some level below the rated 220ma.
Can you measure the current while the MC is in the cradle?


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## Wetterman (Dec 15, 2006)

Yes I measured the currents, but I don't know if I can trust that cheap *** Extech multimeter. I got about 90mA with the 12VDC converter but then the led didn't light up.. whatever that means.. Though I got the 215mA with the ww connected. It just made me think why the led would not light up with the 12.12V connected...??


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## EvilLithiumMan (Dec 15, 2006)

Wetterman said:


> Yes I measured the currents, but I don't know if I can trust that cheap *** Extech multimeter. I got about 90mA with the 12VDC converter but then the led didn't light up.. whatever that means.. Though I got the 215mA with the ww connected. It just made me think why the led would not light up with the 12.12V connected...??



Here is why: 90ma through the 9.1 ohm means there is .82 volts across the resistor (.090 x 9.1 = .819). The red LED charge indicator is also seeing the same .82 volts, but .82 volts is way below the approx. 1.6 volts the LED needs to conduct current, so it won't be on at that level.


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## Wetterman (Dec 16, 2006)

I meant that the led lights up for a few minutes(if the battery is empty then ofcourse for longer)normally but when I connect the multimeter it won't light up at all. So I don't know if I can trust the current measurement in that case.


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## evan9162 (Dec 16, 2006)

What scale on your multimeter are you using? You want to use the highest scale possible. If you have a 10A scale, use it.

If you're using a 1A scale, then that's your problem. Typically, the 1A or 2A scale of a multimeter uses a 1 ohm shunt resistor that it puts inline with the circuit. Thus, when you use the meter to measure current, you're likely significantly modifying the behavior of the circuit by adding that (rather large) resistance.

Using the 10A scale will affect the circuit much less - the current shunt for a 10A scale is typically 0.05-0.1 ohms. Thus, when using the 10A scale, the cirucit will behave much more like when the meter is not measuring it.

If you happen to be using the 200mA scale, then that is definitely the source of your problems - it is probably using a 10 ohm resistor, which is really changing things.


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## Wetterman (Dec 16, 2006)

I have this multimeter that has automatic range selection
http://www.globaltestsupply.com/test_equipment/Extech_DM220_Mini_Pocket_MultiMeter.cfm


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## evan9162 (Dec 16, 2006)

You need to see if you can force it to use a specific range in current mode - if it's autoranging, it might see that it can measure properly on the 200mA scale or 1A scale and not bother trying the 10A scale.


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## EvilLithiumMan (Dec 16, 2006)

Wetterman said:


> I have this multimeter that has automatic range selection
> http://www.globaltestsupply.com/test_equipment/Extech_DM220_Mini_Pocket_MultiMeter.cfm



I just viewed the data sheet for this meter. Maximim DC current is only 200ma, way too low to achieve an accurate reading. As already stated, you would want a meter with a 10 or 20 amp capacity. As a general rule, you would want your meter to be able to handle 10x the current you are measuring, in order to minimize the effect of inserting the meter into the circuit.


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## Wetterman (Dec 17, 2006)

I'll try it next week, at work I have a 10A multimeter. My guess is the current might be a little over 100mA with the 12.12V with fully charged battery.


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## EvilLithiumMan (Dec 17, 2006)

Here are some "real world" voltage and current readings of the Magcharger circuit. The setup was as follows:

A variable AC Input source was used. (An autoformer, some commercial names are Variac and Powerstat).

A digital line analyzer which contains an accurate line voltage meter.

Copper braid (Solder Wick) was attached to the Maglite so I could connect a DMM between the cradle and the MC to measure the current.

A Fluke 177 DMM was used to measure voltages on the MC PCB. Refer to my post #123 in this thread to see the schematic, node list and PCB layout.











I took readings at AC input voltages of 97, 105, 110, 117, 124 and 140 volts. Why those voltages?. The last time I spoke the local power company, they stated the nominal line voltage is 117, plus or minus 7 volts. I tested at 105 because I noticed as soon as I went below 110, the charging current began to drop, and wondered what effect another 5 volt drop would have. I tested at 97 volts because at this level, there was no discernable illumination of the LED charge indicator. And I tested at 140VAC because, ah, well, um, I'm Evil!

Here are the results:





Some notes/observations - 

The test setup was left on for 24 hours prior to taking measurements, to ensure the Nicad pack was fully charged.

The difference between the VDC Input (wall wart) and the LM317 Input is due to the reverse polarity protection diode on the PCB, approximately a .87V drop.

The VDC Ouput is a little high for 5 Nicad cells, but that's because of the diode built into the MC itself. Assuming it also drops .8 volts, the voltage makes sense. (Wish there was some way to get at the diode itself. I hate guessing and feel much better having an actual reading).

Another guess - the charge indicator LED (along with the 9.1 ohm resistor) has 2 volts across it. (Node 5 - Node 6) Standard red LED's usually have a drop of 1.6 volts, so I am guessing the LED Mag uses has a built in current limiting resistor. They are available, so it's not impossible to imagine.

The current out of the LM317 Adj. pin is spec'd at a nominal 50uA, but may be as high as 100uA. Given the voltage drop between nodes 4 and 6 on my unit, there is 65uA flowing through the 13K resistor.

Given it's relative unsophistication, the MC circuit is pretty stable through a wide operating range.

ELM

OK - I just couldn't take it any longer. I just know there has to be a resistor in the red LED. Why? Because once any diode junction (LED or not) starts conducting it essenially becomes a very low impendence path. And any increase in current has to be through that junction, the resistor becomes meaningless. So I removed the red charge indicator LED and hooked it up directly (no limiting resistor) to a variable power supply. If I was wrong, the LED would start drawing excessive current once it came on and would probably burn up if I didn't quickly throttle back the supply. Here are the readings:






Clearly, the LED has a built-in resistor. 3.0V across an LED with a Vf of 1.6V and no resistor would have drawn 100's of mA and burned up in short order.


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## Wetterman (Dec 18, 2006)

Great post ELM.
The lack of resistor made me also think if it's true or not. I knew there are leds with built-in resistors but didn't know the resistors were so invisible.


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## Wetterman (Dec 22, 2006)

I modified a little one of my MC charging cradles. Seems that the smart charger can be connected to a circuit that is protected by a diode like the MagCharger is. So it doesn't measure the battery pack voltage.


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## Wetterman (Dec 22, 2006)

Double


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## EvilLithiumMan (Dec 23, 2006)

Wetterman - Have you actually verified that the Universal Smart Charger will properly charge the MC Nicad pack without overheating? From the Universal Smart Charger sales thread:

"Uses pulse negative and positive pulses to avoid overheating during fast charging"

The protection diode built into the MC body will prevent any "pulse negative" charge from occuring. To be safe, I'd charge the MC pack removed from the light and just use a pair of Alin10123's 'magnets with leads' with his Smart Charger. Just my opinion.


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## Wetterman (Dec 27, 2006)

No I havent. What actually the pulse negative means? Do you mean it puts negative on the battery positive? How could that work even without the diode?


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## Lips (Dec 28, 2006)

Wetterman said:


> I modified a little one of my MC charging cradles. Seems that the smart charger can be connected to a circuit that is protected by a diode like the MagCharger is. So it doesn't measure the battery pack voltage.





Hello Wetterman

Is there a benefit of doing it this way over just connecting the smart charger to the post as I did in post 124...


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## Lips (Dec 28, 2006)

EvilLithiumMan said:


> Wetterman - Have you actually verified that the Universal Smart Charger will properly charge the MC Nicad pack without overheating? From the Universal Smart Charger sales thread:
> 
> "Uses pulse negative and positive pulses to avoid overheating during fast charging"
> 
> The protection diode built into the MC body will prevent any "pulse negative" charge from occuring. To be safe, I'd charge the MC pack removed from the light and just use a pair of Alin10123's 'magnets with leads' with his Smart Charger. Just my opinion.





Hello ELM


Where in the MC body is the built-in diode. Can it be disabled to allow the pack chargers to work properly with "pulse negative" (they may work anyway...)

The sweet feature of the MC is you don't have to or want to remove the battery to charge.

Thanks and nice work guys! Very imformative stuff!


.


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## Luna (Dec 28, 2006)

I popped the diode in my MC months ago when charging using the cradle wired for a Triton. I've been too lazy to open it up (something to do with a 6week old I think)

I need to figure out what the specs on it, anyone have a clue?


----------



## EvilLithiumMan (Dec 28, 2006)

Luna said:


> I popped the diode in my MC months ago when charging using the cradle wired for a Triton. I've been too lazy to open it up (something to do with a 6week old I think)
> 
> I need to figure out what the specs on it, anyone have a clue?



Just an educated guess. The MC cradle is designed to operate at a nominal 220-240ma trickle charge rate, so there really wouldn't be much economic justification for the engineers to use a diode greater than one amp. If you were running a charger sending 3-5A pulses through it, it's not hard to imagine it failing.

(I've kind of been meaning to open up my MC and look at the diode, but from what I've read, it's pretty tricky to remove without destroying it. With my ham-fisted technique, it wouldn't stand a chance)


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## Luna (Dec 28, 2006)

I've love to just bypass it so I could condition the light but the obvious short possibility is something that isn't worth it.


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## Wetterman (Dec 29, 2006)

Lips said:


> Hello Wetterman
> 
> Is there a benefit of doing it this way over just connecting the smart charger to the post as I did in post 124...



No other benefits than it was easier to do. I just removed the diode and the other resistor and soldered it straight to the circuit board.


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## Wetterman (Dec 29, 2006)

Luna said:


> I've love to just bypass it so I could condition the light but the obvious short possibility is something that isn't worth it.



the obvious short possibility is a short circuit.


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## jayrob (Oct 15, 2012)

Hi, I know this is an old thread, but was wondering if anybody can answer the following... (about the Mag Charger)

Does anybody know if it is possible to modify the stock charging cradle to work with 3X NiMH cells installed into the Mag Charger light instead of the 5 cell pack?

I mean the charge indicator LED is red while charging, and changes to green when fully charged. So can it still monitor full charge with a 3 NiMH configuration?

And if possible, can it also be made to still work with the wall charger and cig lighter car supply as well??

I figure that I could just disable all the components in the charge cradle, and use a stand alone NiMH charger and splice wires to the cradle plug, etc... 

But was wondering if getting a new charger was needed. Possibly it would not be difficult to modify the charge cradle??

Thanks for your input!


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## Bad Karma (Oct 24, 2012)

Jay, the led lights up red when current is flowing and stays the same when the battery is full. It is a 'trickle charger' meaning that the current flow isn't enough to cause battery damage in modern cells, so you can just leave it in the cradle and it will always be ready (and also 'always charging'). This means it must flow at about 1/10C or less. 

I just finished modifying (your) charge cradle, and I'm testing it to make sure it doesn't overheat or anything. 

All I did was clip the center pin from the LM317 (the adjustment pin) so it no longer reduces it's current flow (the led no longer lights up either, but I could put in a big resistor instead to fix that). The LM317 will now flow the maximum, or about 1.25ah. I also replaced the wallwart with one that will work with 3.6v batteries: in this case, an unregulated 9v 1a supply. I would be happier with 1.5a since the LM317 is asking for 1.25a, but the wallwart supplies 1a at 9v, so (hopefully) at 7v it will provide somewhat more (fingers crossed).

It is important to use an UNREGULATED supply in this case, as the voltage will vary depending on current flow. A regulated supply will always give the specified voltage, but with these UNregulated wallwarts the voltage will float up to 12v or so with no load, and as low as 6v or so with a heavy load. I chose 9v because the stock MC supply is 12-14v to charge a 6v battery. I know that the LM317 current regulator needs aout 3v overhead, so I needed at least 7v to charge a 3.6v pack. I also wanted it high enough voltage to charge 6v packs (like the stock MC battery or a 5D Mag Charger build). It is important to note, though, that it is unsafe to charge the stock battery packs (2500-3500 mah) at these higher rates (1.25ah). If one were to reconnect the center (adjustment) pin on the LM317 it would again reduce the current flow to about 235mah, perfect for the lower amperage packs. I will be doing this by way of a switch in the housing for my build, so I can charge either battery type. If I get really crazy I might use a reed switch and a magnet in the light (as mentioned earlier in the thread by others) so it automatically selects the appropriate charge current based on which light is placed in the cradle. 

Hopefully this knowledge is of some use to those who run Mag Chargers at lower voltages, i.e. in LED conversions made by Jayrob!


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## jayrob (Oct 24, 2012)

Bad Karma said:


> Jay, the led lights up red when current is flowing and stays the same when the battery is full. It is a 'trickle charger' meaning that the current flow isn't enough to cause battery damage in modern cells, so you can just leave it in the cradle and it will always be ready (and also 'always charging'). This means it must flow at about 1/10C or less.
> 
> I just finished modifying (your) charge cradle, and I'm testing it to make sure it doesn't overheat or anything.
> 
> ...



Wow that sounds awesome thanks for that explanation!

I just don't know enough about the charging specs to try to modify it myself...

I mean, I know with Li-Ion's, it can be dangerous. (fire hazard)

But I guess with NiMH's, it's not near as critical huh?

So with 1.5 Amps going to the 3 NiMH cells, what cuts off the current input to the cells if the Mag Charger light is left in the charging cradle?


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## Bad Karma (Oct 24, 2012)

jayrob said:


> So with 1.5 Amps going to the 3 NiMH cells, what cuts off the current input to the cells if the Mag Charger light is left in the charging cradle?



Nothing. Current continues flowing and gets turned into heat that the battery dissapates.




http://www.greenbatteries.com/bachfa.html said:


> *What is trickle charge?*Theoretically a trickle charge is a charge rate that is high enough to keep a battery fully charged, but low enough to avoid overcharging. Maintenance charge is another way to describe trickle charge. Determining the optimum trickle charge rate for a particular battery is a bit tricky to describe but is generally accepted to be around ten percent of the battery capacity - i. e. Sanyo 2500 mAh AA NiMH optimum trickle charge rate is at or below 250mA. One of the reasons it is important for you to understand the optimum trickle charge rate for your charger and batteries is to compensate for the self discharge of NiCD and NiMH batteries. Another reason is because overcharging a battery will definitely reduce its useful life. Although most manufacturers do not recommend that you leave a battery in the charger for long periods of time, many people leave their batteries in the charger on trickle charge for days or weeks to keep their batteries "ready to use". If you know the rate of trickle charge that your charger puts out and it is around one tenth of the battery capacity or less, then you should be alright if you are just going to do this occasionally. Generally speaking, though you do not want to leave a battery charger plugged in unattended for long periods of time.​


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## jayrob (Oct 24, 2012)

Bad Karma said:


> Nothing. Current continues flowing and gets turned into heat that the battery dissapates.



I see said the blind man...

Hey just a thought, but if it's possible to have it about half that current, it might be a little better for someone who may not be using the light every night...

But if your using it constantly (law enforcement or something), then I can see why you might want it charging at a higher rate...

Hey is it just a resistor at the center leg??

Because if a 1 Watt, 1.7 Ohm resistor is used, it will be 750mA's output per this LM317 calculator:
http://www.reuk.co.uk/LM317-Current-Calculator.htm


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## Bad Karma (Oct 24, 2012)

jayrob said:


> I see said the blind man...
> 
> Hey just a thought, but if it's possible to have it about half that current, it might be a little better for someone who may not be using the light every night...
> 
> ...



Not a bad idea, especially if you use the 10ah or 8.5ah LSD nimh cells. I can do this for you if you like. The status led should light up then, too.

The circuit you link to is slightly different than the way the LM317 is used in the MC circuit, but similar enough.


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## jayrob (Oct 24, 2012)

Bad Karma said:


> Not a bad idea, especially if you use the 10ah or 8.5ah LSD nimh cells. I can do this for you if you like. The status led should light up then, too.
> 
> The circuit you link to is slightly different than the way the LM317 is used in the MC circuit, but similar enough.



That would be the preferred set up I think! 

And the LED charging light would also be enabled again too... 

I owe you man!

Not sure if you can find a 1 Watt 1.7 Ohm resistor, but maybe get close...

Edit: Here's a 1 Watt 1.6 Ohm resistor: (that would be about 780mA's current)
http://www.mouser.com/ProductDetail/Xicon/294-16-RC/?qs=w181GGkxDgHwpiSu0nxojQ==

Or a 1 Watt 1.8 Ohm would give about 695mA's: (good enough I think - little less heat too)
http://www.mouser.com/Passive-Compo...on-Film-Resistors/_/N-7h7z9?P=1z0x6wdZ1z0vocv

I think I like the idea of the 1.8 Ohm vs the 1.6...


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## Bad Karma (Oct 24, 2012)

I'll have to experiment a little (see earlier in this thread) as the MC circuit is somewhat different. I'll post the results here in case anyone else wants to do this mod.


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## jayrob (Oct 24, 2012)

Bad Karma said:


> I'll have to experiment a little (see earlier in this thread) as the MC circuit is somewhat different. I'll post the results here in case anyone else wants to do this mod.



Ah...

Probably should heatsink the LM317 as well. I can make up some copper heatsinks that would probably be easy to just thermal glue to the metal part of the LM317 as long as there is room in there... 

Let me know if you need that! I've got 1/2" X 1/4" copper bar. If that will work, let me know how long a piece will fit, and I'll send you a couple. (or how ever many you need)


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