# MCP73861 IC charger prototype - some observations and questions



## wapkil (Jun 13, 2009)

Hi all,

After testing a few inexpensive Li-Ion chargers that turned out to be using some strange and incorrect ways to charge the batteries, I decided to try to build a charger for myself that would use a dedicated IC. I chose to go with the Microchip's MCP73861. I think no one described it previously on CPF so I thought I would share the experience and use it as an opportunity to ask some questions.

The MCP73861 is an integrated charge management controller. It is relatively inexpensive (~$3), capable of charging with any current between 100mA and 1.2A (programmable), has programmable safety timers and thermistor input. It is specified as a true CC/CV charger with the voltage regulation at 4.1V or 4.2V (selectable) and ability to precondition (i.e. start with a trickle charge) deeply discharged cells. The MCP73861 offers acceptable voltage regulation accuracy of 0.5% (so ~0.021V) and has two LED outputs to inform about the status of the charge. As it is usually the case with the charge management ICs, the voltage regulation accuracy doesn't depend on the accuracy of the external components so cheap, low accuracy resistors and capacitors can be safely used. Finally, the IC accepts input voltage from 4.5V to 12V (13.5V absolute max.) so it can be used with a wide variety of power sources like USB ports (with appropriately low charge current), car adapters and different power supplies.

The circuit has everything that's needed to charge a single Li-Ion battery already built in. One has only to add two filter capacitors, one timer capacitor, temperature output resistors, current programing resistor (or a few of them, if user selectable current is required), a status LED and two resistors for voltage regulation selection and logic enable pins to have a fully functional Li-Ion charger. The MCP73861 is available in a SOIC16 package so it's relatively easy to solder.

As you can see from the description above I was quite satisfied with the IC specification so I bought it and built a prototype to test how it really behaves. I started from checking the safety timers and thermistor functionality, which behaved as expected. Then I proceeded to looking at the voltage and the current during the charge:





I made other tests with different batteries at different states of charge and the charger behavior is consistent. It starts at the preconditioning current level of 10% of the selected CC current (63mA at the plot above) immediately after this it goes to the CC current level (630mA). So far so good, but then it drops down fast to ~75% of the selected current and then slowly raises the current until the end on the CC phase. The CC phase ends at around 3.14V and then the charger proceeds to charging with the lowering current and the voltage raising up to 4.18V-4.19V.

This charging algorithm looks quite good to me but it is not exactly the CC/CV as described in the IC datasheet. I made this prototype on a breadboard but the behavior seems too consistent and thought out to be just a result of using too long cables. Do you have an idea why the charger behaves this way?

I couldn't find precise measurements of other CC/CV chargers - does anyone have them or know where to find them for the Pila IBC, Schulze or other respected chargers?

The last question I have is about the 4.1V level - is there a point in selecting it instead of the usual 4.2V level for LiCoO2 cells? Would I gain cell longevity at the expense of slightly undercharging the cells?


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## Mr Happy (Jun 13, 2009)

That looks quite nice to me.

Note that the CC/CV algorithm is not in any way a requirement for correct charging, it is just an idealized charging profile for reference purposes. As long as the charger keeps the voltage below Vmax and the charging current below Imax then you can say it is working fine. The circuitry is probably set up to be a little on the conservative side for safety.

My only problem with that chip would be the lack of adjustment to different voltages for other kinds of cell like LiFePO4.


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## wapkil (Jun 13, 2009)

Mr Happy said:


> That looks quite nice to me.
> 
> Note that the CC/CV algorithm is not in any way a requirement for correct charging, it is just an idealized charging profile for reference purposes. As long as the charger keeps the voltage below Vmax and the charging current below Imax then you can say it is working fine. The circuitry is probably set up to be a little on the conservative side for safety.



I know that this charging profile won't harm the cells but it doesn't look right to me - it's not how it should be according to the specification. 

I think that in the meantime I found out what may be going on. I'm not heat sinking the IC and it has the thermal regulation built in. Will have to test it but probably 630mA makes the IC overheat so it reduces the current. They even described this charging profile in the datasheet. I should have paid more attention while I was reading it for the first time


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## txg (Jun 13, 2009)

This is an interesting project, especially because of the size of the ic. I've ordered some li-ion charger samples from maxim some years ago, and it is absolutely impossible to solder them on a board...they're extremely small.

can you show some pictures of your prototype? I'm thinking about building a small, usb-powered charger with this chip for holidays.

did you get your ic as a free sample?


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## wapkil (Jun 13, 2009)

txg said:


> This is an interesting project, especially because of the size of the ic. I've ordered some li-ion charger samples from maxim some years ago, and it is absolutely impossible to solder them on a board...they're extremely small.
> 
> can you show some pictures of your prototype? I'm thinking about building a small, usb-powered charger with this chip for holidays.
> 
> did you get your ic as a free sample?



There's currently not much to see. It's only a prototype on a breadboard. Here's how it looks like now, actively cooled to check my hypothesis about it overheating (seems to be true) and charging a TrustFire battery:





(you can click for a larger version, if you want).

Please note that this is still an SMD IC - larger and much easier to solder than e.g. an MSOP package but may not be larger that the ICs that you received from Maxim.

The price of this IC is so low that I haven't thought about ordering samples and simply bought it.


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## Mr Happy (Jun 13, 2009)

Nice. You soldered it onto a ready-made break-out board for easy breadboarding?


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## wapkil (Jun 13, 2009)

Mr Happy said:


> Nice. You soldered it onto a ready-made break-out board for easy breadboarding?



Yes, that's exactly what I did  I used an adapter that I bought in a local electronic parts store, similar to the RE932-04 from Roth.


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## wapkil (Jun 13, 2009)

wapkil said:


> I think that in the meantime I found out what may be going on. I'm not heat sinking the IC and it has the thermal regulation built in. Will have to test it but probably 630mA makes the IC overheat so it reduces the current.



It seems that I was right. I made a test with the IC cooled with a fan. The charging profile looked as follows:





The current drops down a little at the start but I still don't have a proper heat sink on the IC. This time I charged a TrustFire battery, not an AW's one as in the previous plot. Compared with my previous test with the same TrustFire battery but without cooling, the CC phase became ~30% shorter and the CV phase longer. The full charge took approximately the same time (less than 1% difference). It would be interesting to know if this affects the charge results in any way.


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## mdocod (Jun 13, 2009)

Great project. Both your before and after heat-sinking charge plots are ideal IMO. The second one looks nicer but is not any "better" as far as the charging method is concerned. 

Slap 4 of these things in a cradle unit that can support everything from a 10440 up to a 26700 size cells in each slot. 

Put a POT on the current select for each channel. 

Configure a switch and some resistors on each channel to user-select between 4.10V and 4.20V termination. 

~30W 12V AC>DC power supply. 

You could sell something like that for good money. Probably hundreds of em if I had to take a guess.... If you don't want to I just might look into it 

--------------

To answer the question about the advantage of 4.10V vs 4.20V..

4.10V shouldn't really be thought of as less than a full charge. For many years, 4.10V was the termination point for LiCo chemistry cells. Advancements were made that allowed the cells to "survive" a charge to 4.20V with reasonable cycle life. Those same advancements also meant, that when charged to 4.10V, the cells cycle life is actually WAY better. (like more than double in most cases). Many CPF members have expressed a desire for a charger that would terminate at 4.10V, to extend the useful life of their cells. Trading that 10% of extra capacity per cycle is well worth it in most peoples eyes to gain huge cycle life... Especially for anyone who is trying to keep operation costs down, and is running a light every day and charging every day. 

-Eric


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## wapkil (Jun 14, 2009)

mdocod said:


> Great project. Both your before and after heat-sinking charge plots are ideal IMO. The second one looks nicer but is not any "better" as far as the charging method is concerned.
> 
> Slap 4 of these things in a cradle unit that can support everything from a 10440 up to a 26700 size cells in each slot.
> 
> ...



Thank you for the kind words. I planned to build a charger for myself, similar to the one that you described. Unfortunately I don't have time to make more of them. I would be more than happy if you could transform this little project into something available and useful for other CPF members 

In my charger the current will probably be selected by a 6 position switch. I think that the relation between the resistance and the current is too complicated to be conveniently set by a pot (it's neither linear nor logarithmic).

One thing to be aware of is that this IC doesn't have a protection for reverse battery insertion. I'm afraid that if the user does it, the IC would be fried. Something should probably be done with it, if the charger were to be sold to "ordinary users".

The selection between 4.1V and 4.2V voltage regulation is done by connecting a selection pin to the ground or the input supply (via a resistor, to be safe) so nothing complicated here - just a single switch.

Thank you for the information about the 4.1V level. I thought that it may be good for batteries. With double the lifetime, I will probably completely switch to it.


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## TexLite (Jun 14, 2009)

Nice work.

VanIsleDSM has some charger projects based on this chip. 

Here on CPF proper: 1200mA HIGH QUALITY Li-Ion Charger

And here in the Marketplace: 1200mA High Quality Li-Ion Charger

He's awaiting parts to finish the chargers he built and has for sale.

-Michael


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## wapkil (Jun 14, 2009)

TexLite said:


> Nice work.
> 
> VanIsleDSM has some charger projects based on this chip.
> 
> ...



Thank you for the information. I couldn't find those threads as the IC name doesn't appear anywhere in them  Fortunately there also seems to be no experimental analysis of this IC behavior, similar to what I'm doing here, so at least I'm not repeating anything.

There are really valuable information from the CPF members there, especially in the first thread. I haven't finished reading it yet but I saw that for example the thermal behavior, effects of which I observed, is discussed.

Have you bought one of those chargers? If I understood correctly, some were built and sold in the first batch.


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## TexLite (Jun 14, 2009)

wapkil said:


> Thank you for the information. I couldn't find those threads as the IC name doesn't appear anywhere in them



Your welcome. VanIsleDSM linked to the chip datasheet instead of posting the part number. I just recognized the part number.



wapkil said:


> Have you bought one of those chargers? If I understood correctly, some were built and sold in the first batch.



You'd have to ask VanIsleDSM how many were sold, I'm not sure.

I've got a build in progress exactly like mdocod described, the problem with the 4 cell version is finding a suitable universal charge cradle. It is difficult to locate a truly universal cradle to do 16340 thru 32650, and with additional length capacity for 67mm long cells without spending ~$40.00 on a Voltcraft.

I'm think I'm going to settle on a two cell variant.

Good luck with your project, looks like its going great.

-Michael


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## wapkil (Jun 15, 2009)

wapkil said:


> Thank you for the information about the 4.1V level. I thought that it may be good for batteries. With double the lifetime, I will probably completely switch to it.



I made charge and discharge tests for the 4.10V voltage regulation. The charge went as expected:





What was more interesting for me is the results of the discharge test. I compared the same battery charged to 4.10V and 4.20V levels. It was discharged with a 10 ohm resistor:





As you can see, the difference in the energy available is quite significant - approximately 20%-25%. At least for me this makes the decision at what level should I end the charge more complicated. 

Has anyone performed some tests with contemporary batteries to see how the level at which the charge is finished affects the cells life?


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## Mr Happy (Jun 15, 2009)

wapkil said:


> As you can see, the difference in the energy available is quite significant - approximately 20%-25%.


Really? From my analysis of the chart, looking at a 3 V cut-off level, I see a difference of about 15 minutes in 135 minutes, which would make the 4.1 V capacity approximately 11% less than the 4.2 V capacity, or 4.2 V being 12.5% more than 4.1 V. Not insignificant of course, but maybe more bearable.


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## wapkil (Jun 15, 2009)

Mr Happy said:


> Really? From my analysis of the chart, looking at a 3 V cut-off level, I see a difference of about 15 minutes in 135 minutes, which would make the 4.1 V capacity approximately 11% less than the 4.2 V capacity, or 4.2 V being 12.5% more than 4.1 V. Not insignificant of course, but maybe more bearable.



You're right. This is not a constant-power chart so I couldn't look only at the time - I tried to take into consideration also at the differences in the voltage and the current. Nevertheless by looking at the plot I thought that the difference is larger than it really is. When calculated, it turns out to be 11.57% for 4.1V vs. 4.2V (and 13.08% for 4.2V vs. 4.1V).


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## spencer (Jun 15, 2009)

Thanks for posting. Another thing to put on the to do list, make a decent 10440 charger.


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## NetKidz (Jun 15, 2009)

wapkil,

Nice work! :thumbsup: 

Is it possible to charge LiFePO4 battery if set the IC to terminate at 4.1v and add a diode in series with the battery?

Thanks.


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## NetKidz (Jun 16, 2009)

spencer said:


> Thanks for posting. Another thing to put on the to do list, make a decent 10440 charger.



If you only want to charge 10440, maybe MCP73831 is simpler?  It's like LTC4054 but max charge current is 500mA.


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## wapkil (Jun 16, 2009)

NetKidz said:


> Is it possible to charge LiFePO4 battery if set the IC to terminate at 4.1v and add a diode in series with the battery?



Has anyone tried it with a CC/CV charger? I'm not sure how it would work but I think that the IC would still want to achieve 4.1V on the battery. If it succeeds, the battery is overcharged. If the IC fails because the diode requires the IC to go above 4.1V and it refuses, I doubt it would want to go to the CV phase. The voltage drop on the diode depends on the current so it also would be a problem.

That's how I see it, without thinking too much about it  Maybe someone else has other ideas?


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## Benson (Jun 16, 2009)

wapkil said:


> Has anyone tried it with a CC/CV charger? I'm not sure how it would work but I think that the IC would still want to achieve 4.1V on the battery. If it succeeds, the battery is overcharged. If the IC fails because the diode requires the IC to go above 4.1V and it refuses, I doubt it would want to go to the CV phase. The voltage drop on the diode depends on the current so it also would be a problem.


The IC has no connection to the battery in this scheme; it tries to put a voltage of 4.1V across the entire battery and diode combination. The knee between CC and CV will occur (for a typical silicon diode) at about Vbat = 4.1V-0.7V = 3.4V, but the CV phase terminates at ~10% of the full charge current, so it'll end up at 3.5V or so, then stop charging.

The only issue here (which is specific to the IC, rather than the CC/CV+diode plan in general), is the behavior after charge termination -- since the current drops to (near?) zero, the diode's voltage drop vanishes or at least shrinks dramatically. It's likely that this throws the charger back into charging mode -- I haven't looked at the datasheet enough to know the amount (or even sign) of the leakage current in that phase, but I doubt it's enough to keep the charge from restarting; offhand, you'd need >> 1 mA to make it work. I suppose you could add a bias circuit (e.g. voltage divider) to keep the diode's Vf high enough, but it's probably simpler to just find a charging IC more suited to this application.


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## wapkil (Jun 16, 2009)

Benson said:


> The IC has no connection to the battery in this scheme; it tries to put a voltage of 4.1V across the entire battery and diode combination.



Thank you for the explanation. The IC has a separate voltage sensing pin and for some strange reason I thought that it would still be connected directly to the battery. Probably some time later I could check what would happen if a diode was added. I would have to use a LiCoO2 since I don't have LiFePO4 batteries but if I had them, I would also prefer to use a dedicated IC.


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## NetKidz (Jun 16, 2009)

Hi wapkil and Benson,

Thanks for your information. I remembered there's test about the diode but I couldn't find it now. It'll charge the LiFePO4 to a higher voltage (3.7 or 3.8?). Thus I think maybe 4.1v termination will work. 

I just found a local dealer for the IC. I'll order some and test it in July.

Thanks again.


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## LED Boatguy (Jun 16, 2009)

Hey: I've made several of these using the QFN16 package. Small little suckers, but their thermal pad (Via'd to the back of the board) allows you to run them at 1.2 charging amps without it going into thermal regulation like the SOIC version did. 2oz boards help too. These QFNs must be reflow soldered, as the pads are on the bottom.

One way to keep it cool is to only give it ~5 volts, so I use a 5A Simple Switcher (~95% efficient), and can run several of these chargers at once using car power. If power is no issue, you can feed it with a 7805-type device.

Good luck, and be safe with those damn lithiums! So far, these chargers have worked fine on 18650s, Cs and Ds, though you need to add time to the timer for the larger batteries.

PS Putting the battery in backwards will release the chip's Magic Smoke :green:


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## DM51 (Jun 17, 2009)

LED Boatguy, please could you resize that picture to comply with Rule 3. It is too large.


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## wapkil (Jun 17, 2009)

LED Boatguy said:


> Hey: I've made several of these using the QFN16 package. Small little suckers, but their thermal pad (Via'd to the back of the board) allows you to run them at 1.2 charging amps without it going into thermal regulation. 2oz boards help too. These QFNs must be reflow soldered, as the pads are on the bottom.
> 
> [...]



It's nice to hear that others are also using this IC  It was quite nice for me. I haven't released the magic smoke yet but seeing nothing about protection against it, I suspected it may be there. 

One of the main reasons for me to use this IC was the SOIC package it could be bough in. If I knew how to use QFN (or BGA or something else inconvenient to solder) I would probably go with a switching charger. 

If someone knows a decent switching charger IC that can be easily soldered, please let me know.


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## NetKidz (Jun 17, 2009)

wapkil said:


> If someone knows a decent switching charger IC that can be easily soldered, please let me know.



Maybe you could look at LTC4002. 4.7~22v input for 4.2v version. It has two package, DFN10 and SOIC8. The pin on DFN package is exposed a little and it should be able to hand solder.

It also have 10% trickle charging for low voltage battery, and NTC pin for battery temperature detection. But the charging termination is a little different. The charging time is hard coded as 3 hours, thus you must select proper charging current for your battery. For LED indication, when the charging current drop to 25% (4.2v version), there's a near end-of-charging status. I think it could also be considered as a fast-charging end.


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## LED Boatguy (Jun 17, 2009)

wapkil said:


> One of the main reasons for me to use this IC was the SOIC package it could be bough in. If I knew how to use QFN (or BGA or something else inconvenient to solder) I would probably go with a switching charger.
> 
> If someone knows a decent switching charger IC that can be easily soldered, please let me know.


 
The reason I went with a linear charger is I usually charge 5 batteries at once (1P), and that's a lot of inductors, diodes, etc, so I went with a 5+ amp Switcher to feed ~5 volts to 5 linear chargers. Works like a champ.

...now if I can just get this 25mm round LM3401 MC-E driver board to work.


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## wapkil (Jun 18, 2009)

NetKidz said:


> Maybe you could look at LTC4002. 4.7~22v input for 4.2v version. It has two package, DFN10 and SOIC8. The pin on DFN package is exposed a little and it should be able to hand solder.
> 
> It also have 10% trickle charging for low voltage battery, and NTC pin for battery temperature detection. But the charging termination is a little different. The charging time is hard coded as 3 hours, thus you must select proper charging current for your battery. For LED indication, when the charging current drop to 25% (4.2v version), there's a near end-of-charging status. I think it could also be considered as a fast-charging end.



Thank you for the info on it. I think I will restrict my search to the true CC/CV chargers. I have no idea how to judge the impact that different charging methods may have on the battery life but the CC/CV is most frequently recommended and seems to be the simplest and most reliable.


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## NetKidz (Jun 18, 2009)

wapkil said:


> Thank you for the info on it. I think I will restrict my search to the true CC/CV chargers. I have no idea how to judge the impact that different charging methods may have on the battery life but the CC/CV is most frequently recommended and seems to be the simplest and most reliable.



LTC4002 is also CC/CV charger. 

It's just different for the end-of-charge. Most chargers consider the current below 10% of programmed rate as end-of-charge. LTC4002 doesn't do so, it just let the current go lower and lower in CV phase and terminate when the 3 hours charge timeout.


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## LED Boatguy (Jun 19, 2009)

Now that I'm using larger batteries (C and D), the voltage loss to the battery's cradle--that was acceptable for smaller batteries--is making for too long of a charge time. Along side with working on lowering the resistance to the cradles, I'm going to use a third wire in the charge harness. The third wire will go from the positive connection on the cradle to the voltage sense pin on the chip--VBat3. This will keep the chip going at full throttle longer rather than by being fooled into thinking the battery is more charged than it really is because of voltage loss in the harness/connectors.

If anyone wants, I'll post the new board layout.

PS The solder wick in the spring trick was good for 30mv, and I now only show a .01V loss from the solder point on the cradle and the battery negative.


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## wapkil (Jun 19, 2009)

NetKidz said:


> LTC4002 is also CC/CV charger.
> 
> It's just different for the end-of-charge. Most chargers consider the current below 10% of programmed rate as end-of-charge. LTC4002 doesn't do so, it just let the current go lower and lower in CV phase and terminate when the 3 hours charge timeout.



Yeah, I meant the version of the CC/CV algorithm that we usually see. I think it's nice because it's flexible and forgetful. If I don't go completely overboard, no matter what current I set it will "self-balance". With a higher current the CC phase will be shorter but the CV longer, with a lower current the other way round. I think every time the end result should be similar.

I skimmed through the LTC4002 datasheet but I'm still not sure what it exactly does. If my battery charges with 1A (=1C) current and an "usual" CC/CV algorithm in 2 hours, what would happen if I set the same current for this IC? After 2 hours the current should lower to, say, 80mA. Then the LTC4002 would continue the charge putting additional 30mAh-40mAh into the battery. That's additional 3%-4% so it shouldn't matter much if I carefully select the current to end up with my 80mA at 3 hours or just leave the IC to charge slightly longer. 

On the other hand I don't feel comfortable with this IC because I simply don't understand why it does what it does. It has the detection of 25% current to signal "near end-of-charge" for 4.2V. It even has 10% current detection for 8.2V. Why different percentage for different voltages? If there already is the detection, why not terminate the charge normally at 10% or 8%? Why additional hour of "almost-no-additional-charge"? It's weird to me...


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## wapkil (Jun 19, 2009)

LED Boatguy said:


> Now that I'm using larger batteries (C and D), the voltage loss to the battery's cradle--that was acceptable for smaller batteries--is making for too long of a charge time. Along side with working on lowering the resistance to the cradles, I'm going to use a third wire in the charge harness. The third wire will go from the positive connection on the cradle to the voltage sense pin on the chip--VBat3. This will keep the chip going at full throttle longer rather than by being fooled into thinking the battery is more charged than it really is because of voltage loss in the harness/connectors.
> 
> If anyone wants, I'll post the new board layout.
> 
> PS The solder wick in the spring trick was good for 30mv, and I now only show a .01V loss from the solder point on the cradle and the battery negative.



Thanks for all the information. I actually saved the last layout you posted, before you had to remove it because of a too large size. I'm not sure how many people will use it but this IC seems nice and turned out to be already used by a few CPF-ers. I believe if you can post the layout, sooner or later someone will be really grateful for it


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## LED Boatguy (Jun 19, 2009)

wapkil said:


> Thanks for all the information. I actually saved the last layout you posted, before you had to remove it because of a too large size. I'm not sure how many people will use it but this IC seems nice and turned out to be already used by a few CPF-ers. I believe if you can post the layout, sooner or later someone will be really grateful for it


 
Thanks. I'm etching the new design right now. Almost forgot to drill the hole beneath the QFN heat pad. After I reflow solder on the parts, I flip over the board. Looking through the hole now, I can see most of the chip's heat transfer pad. While making sure the chip is what's being pushed against, I STUFF the hole with finely-stranded copper wire till it just won't hold anymore, then solder the whole mess. This gives me the via from hell, and can it transfer several watts to the back of the board and/or a heat sink while the chip on the top stays warm to the touch.

I'll solder it up tonight, then have a "charge off" between the old and new (sense wire) chargers and let you know what happens.


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## mdocod (Jun 20, 2009)

NetKidz said:


> wapkil,
> 
> Nice work! :thumbsup:
> 
> ...



LiFeP04 can actually handle a charge to 4.20V repeatedly without much conflict. It would be best if this charge rate were reasonably fast though (in comparison to the capacity of the cell, like ~0.5-1C I'm thinking))... At 4.10V the loss in cycle life would be even less than at 4.20V and may be acceptable depending on the application. K2 energy recommends charge termination anywhere from 3.65 - 4.20V for their LiFeP04 RCR123s. IMO 3.8V is probably the best compromise on them but they are far more flexible than ordinary lithium cobalt or lithium manganese. It would be interesting if someone had the ability and free time to do some cycle life testing on LiFeP04 on different charge terminations. 

-Eric


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## LED Boatguy (Jun 21, 2009)

OK, here's the charger board with the sense pad (under the B in Bat+).

http://i474.photobucket.com/albums/rr105/Fishnut609/chargersense.jpg

If you read the test results I had typed in here before, forget it. I had forgotten to change the safety timer capacitors to accommodate the larger cells. They maxed out the CC mode at 1.5 hours. DOH!


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## wapkil (Jun 22, 2009)

LED Boatguy said:


> OK, here's the charger board with the sense pad (under the B in Bat+).
> 
> http://i474.photobucket.com/albums/rr105/Fishnut609/chargersense.jpg
> 
> If you read the test results I had typed in here before, forget it. I had forgotten to change the safety timer capacitors to accommodate the larger cells. They maxed out the CC mode at 1.5 hours. DOH!



Thank you for the board layout. I actually read these results and forgot the details, really  I looked at them and planned to go back to them later but if they were invalid there's no need to anymore.


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## LED Boatguy (Jun 23, 2009)

Well, I did the test, charging D cells at LVC--3.2v. One setup was a foot long ~24 ga with a JST connector while the other was 4" long with 18 gauge wire plus a voltage sense wire. The difference? Hardly any. The one with the voltage sense wire did charge to a higher resting voltage--4.195V vs 4.155V. My guess is that a crummy ol 3-wire JST-size setup (with voltage sense) will do just fine.

Now the other thing: Linear's got a new 2 amp 1 and 2 cell charger. It's a switcher, but there are hardly any components. I ordered some samples. Hand solderers--don't even think about this one. It's a DFN12. Yuck.

http://cds.linear.com/docs/Datasheet/36504142f.pdf


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## wapkil (Jun 23, 2009)

LED Boatguy said:


> Well, I did the test, charging D cells at LVC--3.2v. One setup was a foot long ~24 ga with a JST connector while the other was 4" long with 18 gauge wire plus a voltage sense wire. The difference? Hardly any. The one with the voltage sense wire did charge to a higher resting voltage--4.195V vs 4.155V. My guess is that a crummy ol 3-wire JST-size setup (with voltage sense) will do just fine.
> 
> Now the other thing: Linear's got a new 2 amp 1 and 2 cell charger. It's a switcher, but there are hardly any components. I ordered some samples. Hand solderers--don't even think about this one. It's a DFN12. Yuck.
> 
> http://cds.linear.com/docs/Datasheet/36504142f.pdf



Ha, I remember now what I wanted to write in response to your last post. The resting voltages were similar in it. I think that 0.04V is not that important but it's not completely negligible either - 5%-7% I guess [edit: I think it's not clear - I meant 5%-7% total capacity less]. I was also getting ~4.15V resting voltages in my tests - good to know the reason.

DFN12, well it's surprising that without a scanning microscope you can still see what you bought... What happened to all the good old DIP dinosaurs? :mecry:


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## LED Boatguy (Jun 23, 2009)

wapkil said:


> DFN12, well it's surprising that without a scanning microscope you can still see what you bought... What happened to all the good old DIP dinosaurs? :mecry:


 
I don't know what powers my stereo microscope has, but I wouldn't be attempting this crap without it. I notice Eagle has no footprint for the DFN12. It has 10s and 14s, but they are a little different between centers. The 14 looks close enough. I'll print it out and put it under the microscope to see if the pins are aligned. Thank God for solder paste and small needles! Drilling out the board for the via from Hell ought to be a hoot. The 4 X 4 QFNs were tough enough--these are 3 X 4s.

Oh, I bought the 3/3 boards. Should ship tomorrow from Florida.

PS Can someone point me to a cheap 3-pin JST type plug?

PPS Here's Linear's new 2A switching charger. Looks pretty straightforward.

http://i474.photobucket.com/albums/rr105/Fishnut609/LT3650.jpg

Time to go hold my daughter---got her wisdom teeth pulled today .


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## ToTo (Jul 7, 2009)

do you consider selling some chargers?
would be very interested


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