# Super Simple DIY Li-Ion Rechargeable Charger



## djpark

There is a new post with slightly improved design here . However, all information in this thread is still all valid.


*DIY Li-Ion Rechargeable Battery Charger HOWTO*
by D. J. Park
First created on 21 Aug 2004
Last updated on 13 Sep 2004
[Edit] _Output capacitor added as per MrAl's reccomendation and led status explain respectively._ 

This document describes my experience on making a home made DIY (Do-It-Yourself) charger for Li-Ion rechargeable batteries.


*Table of Contents*

1. About this document
2. Basic design using LTC4054
3. Advanced design ideas using LTC4054
4. Basic design with MCP73843
5. Other designs



*1. About this document*

This is the first version of HOWTO document to describe my experience of making a home made li-ion rechargeable battery charger. Though there are many commercial chargers already available, the only chargers for li-ion battery are one PILA charger and another one for Nikon camera. When I acquired some 16750, 14430 and 14500 battries, I thought it is about time to make a charger for myself. Candle Power Forums ( CPF ) has been my main source of information, idea and knowledge and so this document is presented on CPF with hope to benefit those who need a li-ion charger but didn't know where to start to make one. (I don't put buying a ready made one as an option since I am a DIY guy.)

There are just too many great members on CPF who inspired me to do this diorectly and indirectly and I find it impossible to mention the names. Ok, just blame me for simply being lazy to write down all the names, some day I might do. Or I may be a chiken not to do so in case I miss someone accidently.

I try not to get into the technical detail of the operation and theory or rule of charging a li-ion rechargeable cell. There are many CPF thread discussing these subjects and I will not try to act as an expert in the area. But I will describe how I made a charger and how it performs. I believe it is more beneficial and practical to most members and that is the main purpose of this HOWTO.

I am focusing on a single cell charger particularly AA (14500) size. But it can be easily adapted to charge different size batteries such as AAA or 17650. This document is not completed and will be updated as necessary -- correction and/or additional chapters, etc..

I do not guarantee the unit I produce will meet your requirement. I disavow any potential liability for the contents of this document. No responsibility is accepted by me for any loss or damage caused in any way to any person or equipment, as a direct or indirect consequence of following these examples. Use of the concepts, examples, and/or other content of this document is entirely at your own risk.

All copyrights are owned by their owners, unless specifically noted otherwise. Use of a term in this document should not be regarded as affecting the validity of any trademark or service mark. Naming of particular products or brands should not be seen as endorsements.

The text contents of this HOWTO is NOT copyrighted except the pictures and the data analysis charts. Whatever I write here is purely reproduction of what is described in the datasheet of the charger control IC I used and I just added my observation only. You are free to quote in any way. But you need my written consent to use the pictures and charts if you want to include in your publishing. Also I always appreciate any correction or suggestion to be made to this document (when I can find the time to do so).


*2. Basic design using LTC4054 (Super Simple Li-Ion Charger)*

_2.1_ This design uses a charger controler LTC4054-4.2 (datasheet is found here ). To get a working li-ion charger, only 1 capacitor and 1 resistor is used with optional led and 1 resistor for status indicator.

Here is the circuit I used.
[Edit] _This is the 2nd circuit to be used. The 1st one is here._ 







_2.2_ The power is supplied from a computer USB connector (type A) and the pcb is made to fit in the half of 2AA battery holder. I used Type A male both end and cut to half to get 2 cables. There are 4 wires plus 1 shield. Usually there are red and black wires which can be used to provide the power. Join black and the shield to connect to the ground and the red wire to Vcc.






_2.3_ I don't have any means to produce a nice pcb, so I use a perforrated board. This is the bottom view, the small pieces are to hold the sot23-5 chip and convert it to PDIP size.






_2.4_ Cut the small pcb following the patten and solder the chip. This will effectively convert the SMT chip to a PDIP size. 3 leg is left hand side, a short wires are added to the top 2 legs.






_2.5_ This is the finished parts arrangement. The bottom view is flipped upside down.






I wanted to provide a parts arrangement with bottom wiring, but I don't know how to do. Perhaps someone can help me. Meantime, a text version here, I hope ypu can figure out. From left,

LTC4054 module (X,Y) = 3,2 to 6,4
3.9K ohm resistor (X,Y) = 8,2 to 8,3
LED (X,Y) = 10,1 (cathode) to 10,2 (anode)
330 ohm (or 1K) resistor (X,Y) = 12,2 to 12,4
10uF capacitor (X,Y) = 15,3 (-) to 15,4 (+)

[Edit] _Resistor values are slightly changed to be more reasonable operation -- 3.9K=>3.3K 330=>470 ohm. Refer to the advanced section for controlling the charging current. _ 

[Edit] _ The output 10uF capacitor is not shown in the photograph as it is added in later. But there is enough space to add it, you may need to move all the components 1 or 2 position to the right to make space for it. _ 

_2.6_ This the complete unit. I thought having the pcb and the battery on the same side will be easier to handle, but the reality is that it is actually harder to put in the battery and take out. So I suggest to use the battery holder where the pcb and the battery go to the opposite sides.






_2.7_ I recorded the charging performance of this charger.






The battery was drained to 2.5V on load, rested some time and the open voltage recovered to 3V, then repeat again a few times. With LED as a load, I was not able to discharge below 2.5V. That means, we don't need a low voltage protection circuit to direct drive an LED.

As soon as the charging starts, the battery voltage jump up above 3.5V within a few seconds and I hardly managed to catch a few seconds of trickle charging before the constant current charging starts. It is interesting to know that the charging current starts dropping linearly at 2.4 hours even though the battery voltage is only 4.08V, and the current starts free falling when the battery voltage reaches 4.2V.

The initial trickle charge was done at 10% of the programmed charge current and the charge cut-off at completion was also when the charging current dropped to 10% of the programmed current. This is exactly the way how it is supposed to be done.

For those who wish to measure and log themselves, please note that the charging current can be calculated by Ibat = Vprog / Rprog using Vprog measured between Rprog and ground. The low impeadance measuring equipment can cause erratic behavior of the charger and I suggest to use a 10K resistor in series to measure any voltage especially the battery voltage.

_2.8_ It is important to know the behavior of the status led. According to the datasheet, this /CHARG pin acts as an open drain with strong pulling to sinks max 10mA during the charging cycle, so it turns on the led. When the charge is complete, it is in 20uA weak pulldown condition and the led is turned off, but the led may show very (really) tiny bit of light if a bright led with clear acryl is used.

[Edit] _ The led status behavior is corrected with the addition of the output capacitor. _ 

When there is no battery connected, the 1st version without output capacitor will light up the led thinking it is charging possibly due to unstability. With output capacitor added as the current design, the led will produce dim blinking as trickle recharge cycle. This is achieved with MrAl's suggestion of adding the output capacitor.

The datasheet suggests to use a Micro-P to read the pin and determine the status, but I think it is an overkill for this basic design. But I think it can be an idea to have dual color led to indicate the status -- red=charging, green=cmplete.


*3. Advanced design ideas using LTC4054*

As you see in the picture above, I made one set with 7805 regulator to accept power from a DC supply instead of the computer USB cable. You need to supply at least 6.5-7V to get the 5V output at the regulator. The regulator becomes very hot during the charging without a heat sink. But so far it seems it can take the heat from 10V supply and max charging current of 425mA on that unit.

The datasheet provides many examples of configuration such as input reverse polarity protection, combining wall adaptor and USB power and more.

Since the charging current can be programmed using a common resistor value, it can be a good idea to put a toggle or slide switch to change the charging current for fast/slow charger, or AA or AAA or even 17650 cells.

[Edit] _ Charging current calculation added. I thought I included in the original post, but can't find now. So I added now. _ 

The max constant charging current can be set by changing the resistor between PROG pin and GND. The value can be calculated using this formula Rprog = 1000 / Ichrg.

Initially I used 3.9K to program, so the max charge current of 1000/3900 = 256mA. Using 3.3K will set the max charge current to 1000/3300 = 303mA and it seems more reasonable for 650-700mAh li-ion cell at 0.5C charging.

Some recommended values of Rprog:

1.3K => 769mA suitable for 16750
3.3K => 303mA suitable for AA
6.6K => 151mA suitable for AAA

I am planning to make a box containing a 7805 with heat sink which will provide power to 2 battery slots, each slot independantly having separate battery holder for AA/AAA and 16750 cells. A 3 points slide switch for each slot to select which battery holder the charging current go and also select appropriate charge programming resistor, one of the point is no resistor which will set the charger to shutdown mode. If a small PIC is used, it may bring moer meaningful status indicator and also software control of the charging current... No time to prepare the circuit diagram, but it is a simple one. Can someone draw?


*4. Basic design with MCP73843*

I made this charger using MCP73843-4.2 from Microchip before I made LTC4054 version. This IC requires a P-channel FET, and also the current sense resistor needs to be a small value such as 0.15 ohm.

The information of the chip is here and you can request for the sample from the same web page.

Beside I could get the free sample of the chip, the controller also handles the status led the way we expect - on for charging, off for none or complete, blink for error.

Here is the photo of the charger and the charging cycle data chart.










*5. Other designs*

I have seen a design on the web using LM317 regulator. It is out of my scope for this document to mention if this is suitable for li-ion charging or not. But I expect quite a number of people are actually using this design or something similar. I even used to charge li-ion cells using a constant voltage / constant current bench power supply to charge te li-ion cells without trickle charge stage.

I have no idea how many or what other designs are available on the net. But I will not list or describe those designs since it is not the purpose of this document to list them, but to provide some ideas for others from what I experienced. Also I don't intent to try all other types to be expert in this area, either.


-- end of HOWTO


I hope you find it helpful to you.

-- dj


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## 4sevens

dj, 

Absolutely beautiful! And you always make such nice graphs!

I particularly like the fact that when discharging a Li-ion with
an led, you really can't over discharge the cell because of the V
need to drive an LED. /ubbthreads/images/graemlins/smile.gif

great! /ubbthreads/images/graemlins/smile.gif


----------



## shiftd

i like them
totally awesome

so Dj, in your post, you did not mention which one you like the most, the LTC or the MCP. 


a bit correction here
on the fourth paragraph of number 1, you said
"I am focusing on a single cell charger particularly AAA (14500) size. "
don't you mean AA?


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## vacuum3d

dj, thank you so very much!!!

ernest


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## djpark

[ QUOTE ]
*shiftd said:*
i like them
totally awesome

so Dj, in your post, you did not mention which one you like the most, the LTC or the MCP. 


a bit correction here
on the fourth paragraph of number 1, you said
"I am focusing on a single cell charger particularly AAA (14500) size. "
don't you mean AA? 

[/ QUOTE ]

Thank you, it is corrected now.

I like MCP because I could get the IC free (sample) and the LED status is more meaningful.

But I still prefer LTC because it uses common value resistor for current programming, does not need FET, and I can measure the current flow by measuring the program voltage.

With MCP, I had to measure the voltage drop at DMM in series to the battery.

Now, someone may want to organize a group buy of LTC4054?

-- dj


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## djpark

[ QUOTE ]
*4sevens said:*
dj, 

Absolutely beautiful! And you always make such nice graphs!

I particularly like the fact that when discharging a Li-ion with
an led, you really can't over discharge the cell because of the V
need to drive an LED. /ubbthreads/images/graemlins/smile.gif

great! /ubbthreads/images/graemlins/smile.gif 

[/ QUOTE ]

David, I made a simple data logger using PIC12F675. It collects data every second and I feed them to Excel. When I find time, I will post a HOWTO make the logger.

It is indeed a pleasant surprise to find the white LED not being able to overdischarge a li-ion. But you will want to check red or yellow with Vf below 2V.

-- dj


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## MrAl

Hello there,

Very nice work dj! Thanks for posting your results too.
I might want to try this type of charger myself.
It would be nice if you looked into the max charging
current too for such cells as the 18650, which can
take 1 amp charging current for quick charge.

Take care,
Al


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## vacuum3d

dj,
Thanks to your excellent instructions, I just placed an order for 10 LTC4050. I'm gonna locate the rest of the parts and possibly put a few kits together to share.

ernest


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## djpark

[ QUOTE ]
*MrAl said:*
Hello there,

Very nice work dj! Thanks for posting your results too.
I might want to try this type of charger myself.
It would be nice if you looked into the max charging
current too for such cells as the 18650, which can
take 1 amp charging current for quick charge.

Take care,
Al 

[/ QUOTE ]

The max charging current of LTC4054 is 800mA and the current programming resistor shall be 1000 / 0.8 = 1250 ohm.

When the temperature of the chip goes up, the current will be automatically reduced.

-- dj


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## MrAl

Hello again,

Thanks dj...this sounds like a part i would be interested
in trying too.

Take care,
Al


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## moraino

Hi DJ,

It is excellent post. Thanks you so much for sharing.

Now I need a magnifying glass to get busy.

Henry


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## cgpeanut

DJ,

Simply awesome Thank you DJ. This would be my next prject /ubbthreads/images/graemlins/smile.gif


----------



## Mgz

Hi djpark, do you know that Maxim also offer free sample of Battery Chargers ICs, plz take a look at there http://para.maxim-ic.com/compare.asp?Fam=Batt_Chrg&Tree=PowerSupplies&HP=PowerSupplies.cfm&ln= 

Order sample at here http://dbserv.maxim-ic.com/samplescart.cfm?Action=Step1&ln=en

I have no idea about EE, but I think a free sample Maxim IC might further improve the charger, and save us poor flashaholcis couple bucks /ubbthreads/images/graemlins/frown.gif /ubbthreads/images/graemlins/broke.gif


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## djpark

[ QUOTE ]
*Mgz said:*
Hi djpark, do you know that Maxim also offer free sample of Battery Chargers ICs, plz take a look at there http://para.maxim-ic.com/compare.asp?Fam=Batt_Chrg&Tree=PowerSupplies&HP=PowerSupplies.cfm&ln= 

Order sample at here http://dbserv.maxim-ic.com/samplescart.cfm?Action=Step1&ln=en

I have no idea about EE, but I think a free sample Maxim IC might further improve the charger, and save us poor flashaholcis couple bucks /ubbthreads/images/graemlins/frown.gif /ubbthreads/images/graemlins/broke.gif 

[/ QUOTE ]

Thanks for the info. You are actually the second person mentioned that IC. Now I look at it again carefully, I find that MAX1555 seems much interesting -- 100mA fixed charging current with USB power and 280mA from DC power -- good for AA/AAA or even bigger cells at slow charging. The price is also cheaper, half of LTC4054.

When I pump up the charging current with LTC4054 and 7805, the heat made the charging current drop and the constant current charging phase was a few minutes only. So slow charging with a low charging current may be better for the battery and charger.

I did get some others samples from Maxim before. They came by the regular air mail and during the last Christmas season, it took a month to reach me sitting in the local post office warehouse. Micochip always send by FedEx and TI send by UPS.

Talking about the sample request, I find that TI is the most generous of all. /ubbthreads/images/graemlins/thumbsup.gif Linear Technology raised many questions through the email and in the end my request for just 2 items was turned down. /ubbthreads/images/graemlins/thumbsdown.gif

-- dj


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## 4sevens

dj,

I'm trying to lift a SMT part from a circuit and was wonder
what was the exact marking on the LTC4054 package.

thanks
david


----------



## djpark

[ QUOTE ]
*4sevens said:*
dj,

I'm trying to lift a SMT part from a circuit and was wonder
what was the exact marking on the LTC4054 package.

thanks
david 

[/ QUOTE ]

Mine says "LTH7".

Fro the datasheet,

"LTH7" for LTC4054ES5-4.2 (800mA)
"LTADY" for LTC4054XES5-4.2 (800mA, no trickle charge)
"LTAFA" for LTC4054LES5-4.2 (10-150mA)

Regards,

-- dj


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## Klaus

Nice one dj - I have a similar one setup for the smaller R123s - CPF-er CM was introducing the LTC4054 a while ago and I named this USB-charger the CM-4054 DIY Kit then - at 1.x USD a pop for the chip the total cost is quite reasonable I think - I think the toughest part for most will be to solder down the pretty tiny LTC chip itself - if a kit would be done this part could be pre-soldered to a small board already like yours - to add the other parts is cake I think - thanks for sharing.






Klaus


----------



## djpark

[ QUOTE ]
*Klaus said:*
Nice one dj - I have a similar one setup for the smaller R123s - CPF-er CM was introducing the LTC4054 a while ago and I named this USB-charger the CM-4054 DIY Kit then - at 1.x USD a pop for the chip the total cost is quite reasonable I think - I think the toughest part for most will be to solder down the pretty tiny LTC chip itself - if a kit would be done this part could be pre-soldered to a small board already like yours - to add the other parts is cake I think - thanks for sharing.

Klaus 

[/ QUOTE ]

Klaus,

Truly I want to say that I was inspired by your charger to make it in the battery holder, and also it is your post which let me know about LTC4054. /ubbthreads/images/graemlins/thumbsup.gif Thank you!

Putting SOT23 chip on a perforated board wasn't that bad, but if a pcb with more area for gound was made, the heat dissipation would be better.

-- dj


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## moraino

I was very happy that I finally got one done and working.

Unfortunately, I screwed it up big time. It was charging the battery untill 4.05 volt then I took the battery out and hook up the wires trying to measure the amperage.

The meter showed some reading then 0. I smelled the smoke while I was wondering why. I then relized I connected the wire reversed. 

Now, I am very upset and feeling tired. I am going to bed now and hopefully tomorrow I can figure out which part burnt out and can be replaced. Wish me luck will you, my fellow CPFer.

Henry


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## djpark

I wonder which one went wrong, could that be your DMM probe fuse?. I wish you a good luck finding. I wasted quite a few 4054 till I got things working fine (or rather I found it working, I was tricked to see the led on when there is no charging).

If you want to measure the charging current, you can follow this portion taken from my original post.

[ QUOTE ]
For those who wish to measure and log themselves, please note that the charging current can be calculated by Ibat = Vprog / Rprog using Vprog measured between Rprog and ground. The low impeadance measuring equipment can cause erratic behavior of the charger and I suggest to use a 10K resistor in series to measure any voltage especially the battery voltage. 


[/ QUOTE ] 

If you insert DMM between charge output and the positive battery terminal to measure the charging current, you will likely get wrong value. With my DMM, I got just about 30mA with 400mA range and 300mA with 10A range. Dont trust those value and calculate it from the suggestion.

BTW, I requested sample charger controller ICs from Maxim and TI. I will put them up when I get them.

-- dj


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## balrog

djpartk, This is a way cool howto and a great little design. I love the USB idea to save on wall warts, power points and for excellent portability. /ubbthreads/images/graemlins/thumbsup.gif

Klaus, how long does it take to charge the R123 via USB power? I believe that from the USB bus you can only draw about 100mA max.


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## moraino

I think the max current from USB port is 500mA.


----------



## andrewwynn

This circuit is the bomb... I'm about to buy some LiONs and this will be just the ticket... I'm thinking of building the batts right into my next project, and just use an inky dinky power plug to get the charger connected. 

What's the best way to get a few of the chips, just order from them, or digikey or what?


----------



## djpark

I stay in Malaysia and Digikey is not an option. Neither Farnell nor RS Components carry them. The local LT representative was no help. They refused to give sample either. The only way to buy was from LT directly with $24 for shipping.

-- dj


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## Klaus

[ QUOTE ]
*balrog said:*

Klaus, how long does it take to charge the R123 via USB power? I believe that from the USB bus you can only draw about 100mA max. 

[/ QUOTE ]

[ QUOTE ]
*moraino said:*

I think the max current from USB port is 500mA. 



[/ QUOTE ]

Balrog - I think its the usual 2hours or so, probably less, and moraino is right - per spec USB ports can supply 500ma and the CM-4054 kit is set to around that charging current.

Klaus


----------



## balrog

Thanks. Well then the USB idea is even better than I could have hoped! Whilst on the topic, what voltage is the USB power at? /ubbthreads/images/graemlins/blush.gif


----------



## KevinL

5V 500mA max per hub (usually a group of two physical ports).

I have a GP NiMH charger for 4 cells, that runs off USB. I got tired of running out of wall sockets, this place is gonna start an electrical fire some day, so I thought I'd go USB. It's a medium speed charger, 7 hours usually. Charges everything from my 1300mAH GPs to 2100 Sanyos. A bonus is that since I place my computer in standby mode, rather than completely powered off at night in order to have it come up *FAST* the next morning, the ATX power supply continues to deliver a token amount of power to the USB ports, enough to keep the charger running. This is the standby voltage, because it needs to keep certain devices powered in order for wakeup to occur when an event happens, such as a key is pressed, or the mouse is clicked, or the Ethernet card receives a wakeup event yadda yadda.. 

The computer sleeps, and the cells are charged overnight or when I'm at work. No reason why you couldn't build a lithium ion charger out of this with suitable electronics.


----------



## andrewwynn

[ QUOTE ]
*djpark said:*
I stay in Malaysia and Digikey is not an option. Neither Farnell nor RS Components carry them. The local LT representative was no help. They refused to give sample either. The only way to buy was from LT directly with $24 for shipping.

-- dj 

[/ QUOTE ]

I ended up ordering 4 for a total of $15 with shipping ($7).. next time you need something so small talk to a guy in the states that might need something from LT.. for $7 you can probably as many little parts as you'd ever want shipped.. and it would probably cost about $1 to airmail you a letter that has a chip or two taped inside.

-awr.. 

ps.. 'for you'... i'd send one for free.. you solved several of my problems i had 'in the works'. oh oh i may have said too much (you didn't see that klaus.. mr private investigator you)


----------



## andrewwynn

OH.. ps... i bought a usb charge cable for my cell phone... for $2 off of eBay.. I only point this out... because the cable is about 1/4th the diameter of a typical usb cable, so might be much nicer for such a charger... 

I am tossed what i should do with this charger solution... i'm thinking of making an inline charger (like the inline amp concept)... that just has a micro plug... that i can plug into several different devices... such as a battery holder or a flashlight itself... i can have the charger inline inside some shrink-wrap (heat).. so that it looks a little like a snake that just ate something.. but the output is the charging ckt.. then i can use it to charge different devices... 

else.. i can just use a 5V supply (either from usb or from wall wart (powerbrick)).. and have the charger duplicated in the different devices... I like the idea of having a switch in-case i'm charging a bigger or smaller battery pack. 

ps.. i couldn't believe when i read the datasheet for the LT chip.. basically.. 

'here is a complete LiON charger... add voltage and battery'... and a single resistor to tell me how fast to charge

(thanks dj for sharing your project to save us all the time of figuring it out)


----------



## djpark

[ QUOTE ]
*andrewwynn said:*
I ended up ordering 4 for a total of $15 with shipping ($7).. next time you need something so small talk to a guy in the states that might need something from LT.. for $7 you can probably as many little parts as you'd ever want shipped.. and it would probably cost about $1 to airmail you a letter that has a chip or two taped inside.

-awr.. 

ps.. 'for you'... i'd send one for free.. you solved several of my problems i had 'in the works'. oh oh i may have said too much (you didn't see that klaus.. mr private investigator you) 

[/ QUOTE ]

It is great to know "WHOM" I need to talk in future. I really appreciate.

-- dj


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## djpark

*Asking HELP from Electronic Gurus:* 

This charging IC is working fine, but I am not happy with the led output of the status. LTC4054 employ 3 status on the output -- high impedance, 20uA weak pulldown & 10mA strong pulldown -- and this 3 status is fine. But my problem is with strong pulldown even without a battery to charge.

[ QUOTE ]
The CHRG pin can provide an indication that the input voltage is greater than the undervoltage lockout threshold level. A weak pull-down current of approximately 20mA indicates that sufficient voltage is applied to VCC to begin charging. When a discharged battery is connected to the charger, the constant current portion of the charge cycle begins and the CHRG pin pulls to ground. The CHRG pin can sink up to 10mA to drive an LED that indicates that a charge cycle is in progress.

When the battery is nearing full charge, the charger enters the constant-voltage portion of the charge cycle and the charge current begins to drop. When the charge current drops below 1/10 of the programmed current, the charge cycle ends and the strong pull-down is replaced by the 20mA pull-down, indicating that the charge cycle has ended. If the input voltage is removed or drops below the undervoltage lockout threshold, the CHRG pin becomes high impedance.







To detect when the LTC4054 is in charge mode, force the digital output pin (OUT) high and measure the voltage at the CHRG pin. The N-channel MOSFET will pull the pin voltage low even with the 2k pull-up resistor. Once the charge cycle terminates, the N-channel MOSFET is turned off and a 20mA current source is connected to the CHRG pin. The IN pin will then be pulled high by the 2k pull-up resistor. To determine if there is a weak pull-down current, the OUT pin should be forced to a high impedance state. The weak current source will pull the IN pin low through the 800k resistor; if CHRG is high impedance, the IN pin will be pulled 

[/ QUOTE ] 

The statement "strong pulldown" during the charge and weak pulldown when completed seems correct. When an led is connected from B+ (5V) to chrg pin through 1K resistor, it lights up very bright during the charge as expected. When the charging is complete, the led is hardly lit up, but still visibly on, so of 20uA weak pull down is correct.

The misleading part is that when there is no battery connected to charge it lights up quite bright though not as bright as during the charging time. I am hoping to turn off the led when it is not really charging with a battery since a user may not notice if the battery contact is no good since the led is on anyway.

*I don't know why LTC4054 is designed this way, but I am hoping that some gurus here can come out with a transistor circuit to cut off the led when not really charging in absence of the battery.* 

From my observation, I find this behavior of the chrg pin voltage when connected to B+ through 2K resistor (no led).

<ul type="square"> [*]1.44V during the constant current charging [*]1.78V when there is no battery [*]same as B+ when charging is complete [/list] 

That means to turn on led if the charg pin voltage is below 1.6V and turn off if above 1.6V using a PNP transistor, with different resistor value, the voltage would be different. Any suggestion?

Another point which I can take charging status is from the PROG pin.

<ul type="square"> [*]When it is in constant current charging mode, the voltage is 1V. [*]As the current start reduce, the voltage start going down as low as 0.1V (10%) [*]Once the charging current eaches 10%, the voltage drops to 0.01V to indicate no charging. [/list] 

So will it be easier if a NPN transistor is used to amplify this voltage to turn on led if above 0.05V?

Thanks a lot.

-- dj


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## MrAl

Hi there dj,

Did you try a cap directly across the output where the
cell goes? Value might range from 0.1uf to 10uf, you'll
have to try them.
This idea is to fool the ic into thinking it's got
a battery and that battery is fully charged 

Hope it works...

Take care,
Al


----------



## djpark

[ QUOTE ]
*MrAl said:*
Hi there dj,

Did you try a cap directly across the output where the
cell goes? Value might range from 0.1uf to 10uf, you'll
have to try them.
This idea is to fool the ic into thinking it's got
a battery and that battery is fully charged 

Hope it works...

Take care,
Al 

[/ QUOTE ]

Thanks a lot, Mr. Al!

I found this statement in the datasheet after reading your post.

[ QUOTE ]
The constant-voltage mode feedback loop is stable without an output capacitor provided a battery is connected to the charger output. With no battery present, an output capacitor is recommended to reduce ripple voltage. When using high value, low ESR ceramic capacitors, it is recommended to add a 1W resistor in series with the capacitor. No series resistor is needed if tantalum capacitors are used. 

[/ QUOTE ] 

Your suggestion works like a magic. The led blinks with a dim light. It looks like it is going through the trickle recharge cycle. With the capacitor, the output voltage without battery is 4.15V and without the cap, it is 3.8V. Maybe it is unstable between 4.2V and low voltage? I guess it thinks it is charging.

The led blinks slowly if bigger capacitor (4.7-10uF) and fast with smaller caps (0.1-1uF). Smaller caps gives almost continuos dim light from led. I find that using 10-22uF gives nice blink as indicator for the absence of the battery. So the led status should look like this now.

ON - charging process
OFF - charge complete
dim blink - no battery

I will add a 10uF cap to the basic circuit above.

* [edit] * _ Now the original HOWTO post is updated. _

BTW, do you think I need one series resistor with a electrolyte capacitor?

-- dj


----------



## andrewwynn

this is so awesome! i'm just about to build a ckt or two with this design, the timing couldn't be much more perfect.. i was just about to in a day or three solve this problem myself and you guys beat me to it, God i love CPF you guys are awesome... 

my initial thought was to just play with resistors or a pot on the LED.. perhaps just the right value of zener that would make it shut the current at the right place.. but the blink is awesome, what a cute solution.

-awr


----------



## MrAl

Hi there,

dj:
Oh, great news! Im glad it's working as expected now.
Seems like a good indication that the cell isnt connected.

andrew:
Hee hee, yeah 'cute' it is  I like the blinking too
as it's a very good indication about the cell. My LM317
based design has a shorted cell indication.

Take care,
Al


----------



## StoneDog

<deleted> nevermind /ubbthreads/images/graemlins/smile.gif


----------



## cypher2001

Anyone know of a parts house that has the LTC4054 in stock? It looks like Digikey has none. I'd order from them directly, but I will be stuck with a fairly hefty 7.00 shipping charge ( when weight isnt really an issue ). 
My real concern is not the 7.00 shipping. Its the fact that I need other parts anyways that I'd like to order.

Mouser doesnt carry it.


----------



## cypher2001

BTW. This is a good article on this type of technology... I found it an interesting read:
http://www.elecdesign.com/Articles/Index.cfm?ArticleID=2982&pg=1


----------



## vacuum3d

LT is only a few miles from where I work. If enough interest is there, I could go pick some up from them and send them off by snail mail.
I actually picked up 10 from them, but those things are so fragile, I managed to destroy three of them during testing. I located the rest of the parts from the local Fry's. I use surface mount parts to make the board quite small.

btw, I added the new Capacitor. The led light now makes a lot of sense.

Thank you dj and MrAl!!!

ernest


----------



## cypher2001

I'm sure your offer would save a couple of us some $$. I just wish I could find a supplier who has it in stock.

DO let me know if you get enough interest.


----------



## andrewwynn

whoo hoo.. my LT chips just came today..

HOLY CRAP are they SMALL..

did i mention... they are SMALL.

(not that i didn't know that ahead of time.. but theory vs. reality is a big thing)

Now i'm excited.. this chip will likely be quite a big deal for me over the next couple months... too bad i didn't realize 'til after the stores were closed that my chips were in.. now i have to wait 'til tomorrow to get my charger built. 

-awr


----------



## MrAl

Hi there andrew,

Hee hee, welcome to SMD parts 

How small are they anyway, like pin spacing?
I was thinking they were normal size but i guess not.

Take care,
Al


----------



## andrewwynn

the entire chip is about 3mm square.. and that INCLUDES the leads... i just looked it up.. it's 2.8 x 2.9 incl the leads.. and the chip alone is 2.9 x 1.5mm... in inches that works out to 0.11 x 0.06 inch.. and the leads are spaced just about 1mm apart. whooo hoo it'll be fun.

I'm actually thinking of wiring one up w/o a ckt just like i've seen recently for a flashlight micro pill... so i can incorporate it inline in a wire.. i'll pot the whole thing in epoxy when done for strength.

I certainly won't have a hard time fitting the chip into my designs.. the capacitor.. different story. 

-awr


----------



## djpark

Andrew,

It seems all the fun belongs to you. Enjoy!

When it is charging, the IC can get pretty hot. The heat is dissipated through the body and the leads. When the temperature goes up, the thermal control circuit will reduce the charging current.

So you will need to consider a bit of the heat sinking through the body as well.

-- dj


----------



## 4sevens

Dj,

I'm comsidering making a battery pack that consists of 3 D sized 
li-ions (5000mah!!!) but with a built in charger for each individual cell. Is it feasible to do this? That way, each cell gets individual charging... Also, would it have any drain from the battery
to the charging circuit when the charging circuit is not getting 5v?

This is the only way I'm going to pack my 3D HID lights forsale /ubbthreads/images/graemlins/smile.gif
With built in charger /ubbthreads/images/graemlins/smile.gif


----------



## djpark

4sevens, (personally I prefer 3sevens /ubbthreads/images/graemlins/wink.gif)

I don't really know if you are trying to put all of them (may be 9 or 12 * 14500) together in parallel or 3 sets in series. If you are trying to put all in paralle, 1 IC shall do with longer charging time (slow charge). If you put 3 sets in series with separate charging IC, you will have power supply common ground problem.

There are charge control ICs designed to handle more than 1 li-ion batteries. I chose LTC4054 for 1 cell and also SOT23 size so that I can manage with limited tools. If you search LT, TI and Maxim web sites or other semiconductor manufacturer, you will find many more chips supporting multiple cells at higher current if you are prepared for different size.

When there is no input power to LTC4054 or too low to charge, it will get in to low current mode and consumes 2uA.

Another thing you would want is to add over-discharge circuit protection circuit sitting together with charging circuit.

-- dj


----------



## andrewwynn

correct me if i'm wrong but you should be able to use just one charger set up with some fancy wiring so that when you plug in the charger... it'll connect to the cells in parallel.. but it might be a little too complicated.. but you need to disconnect the series connection to connect parallel.. it's something i've been trying to figure out how to do simply.. if i can figure out a good way to do it i'll post it here.

-awr


----------



## MrAl

Hi again,

andrew:
Wow, that is small. I guess i'll use the LM317 circuit
for a while although it does take up much more room.
If you want to change the arrangement in cell wiring
perhaps you can use a connector with two different
plug in's. Wire one with jumpers for series connections
while operating the light (or other device) and when
you are ready to charge, you can have the other plug in
wired so that the cells minus terminals are connected
together and the three positive terminals come out
to separate leads so they can each have their own
charger.
Doing this would mean to charge you'd simply remove
the dummy jumper connector and plug in the one
that connects to the charger(s). It would take
less than 2 seconds i think.
Drawback is there would have to be a connector
installed on the flashlight and a dummy jumper
connecter plugged in all the time when using it
normally.

Just one idea 

I dont think i would want to connect them in parallel,
however. If one cell goes very low the other cells
try to charge it VERY fast, which probably isnt a very
good idea because these things have been known to
explode.

Take care,
Al


----------



## andrewwynn

even a single cell charger is constant current to a single cell.. from what i've read it's best to charge in parallel... hard to get uneven charging... better i suppose to charge each cell individually.. but that gets very complicated, because you'd have to have a disconnect at each cell i'm thinking... bad news as far as resistance goes, etc... in any event.. i'll be toying with chargers.. if i come up with something cool, i'll be posting it.

-awr


----------



## 4sevens

If you charge them in parallel, you have to make sure that you charge AND discharge all of them all the time so that they don't have different voltages when you charge them. 

Say if you charge a pair of cells in parallel and one cell is 3.9v
and the other is 3.2v. Then even before you apply power to the cells,
the 3.9v is charging the 3.2v at a very quick rate and if the V differnce is big enough, you could get uncontrollable amounts of current going. Even if it's a small difference the 3.9 end up discharging before charging.

Not good unless you keep the cells together.


----------



## Hallis

David, what do you use to charge the 14500's?


----------



## 4sevens

I have a custom made charger that does the proper constant current /
constant voltage to 4.2v. Check out the DIY thread by djpark


----------



## 4sevens

djpark: I'm considering building chargers for my 14500's using standard AA holders. I would like to be able to charge 4AA's in parallel. Would it make sense to add standard diodes to each cell to
prevent reverse insertion? I know that would drop the V about .4v
but I can re-adjust the V up .4v

what do you think?


----------



## andrewwynn

Holy crap it works!

Well i guess you might say i 'improved on a design... I came up with a way to make it with no circuit board whatsoever.. i'll take some pictures soon as i get my camera back... I will describe it in the meantime...

I was going to copy Dj and carve up a piece of copper with a dremel and make a mini-enlarger.. but when i was at RS i saw something that jumped out at me... an 8pin dip socket... it looked like i could bend the 'leg' pins toward each other and they would get within 1mm of each other and be just right to solder to the itty bitty chippie.. 

Well holy crap it worked.. not before i managed to drop the chip like 4 times including once on the floor.. wowza.

Anyhow.. I stuffed some cutt off silver-tinned wire and stuffed the 5 pieces into the other side of the dip socket.. turning the thinsot into a dip6... with a couple unused pins.. i ripped them off..

so i could just plug it into my breadboard and wire it up.. and it started working first try... i first tried with a single AAA and then doubled them up.. and now it's charging 4 in parallel.. i put in a second 3.3k ohm resistor to get the charging current up a bit since the bat pack can handle 1.2A max charge rate.. the batteries were not very depleted.. about 3.85V and it was charging at 450mA or so when i left it.

So.. check this out.. i started trying to figure out how to wire it up in a tiny way.. and i realized.. duh.. soon as i take out the wire jumpers out the bottom... i can plug the parts in to the sockets ... several items can just be plugged right in.. and then other parts will be soldered to those legs. I think the whole thing will end up being about 1 cm square by 1.5 or 2cm tall.. including everything. I'm going to set it up so it can be plugged into a socket on a battery holder.. which can either charge 2 or 4 AAAs or 1 or 2 AAs.

I will pot the whole shabang into a block of clear epoxy, and the LED will just be buried in and it'l make the whole block glow.. it'll just be a fat bump in the middle of my cable... haven't decided if i'll make the first one from power brick or USB cable.

In any event.. i'm beyond happy with the results.. i've got my AAAs charging up and by tomorrow i'll have it NOT on the breadboard and not using alligator clips to connect to the batteries. 

Well another alnighter.. bedtime for bonzo.. what a fun project this has been.

-awr


----------



## djpark

[ QUOTE ]
*4sevens said:*
djpark: I'm considering building chargers for my 14500's using standard AA holders. I would like to be able to charge 4AA's in parallel. Would it make sense to add standard diodes to each cell to
prevent reverse insertion? I know that would drop the V about .4v
but I can re-adjust the V up .4v

what do you think? 

[/ QUOTE ]

Frankly I am no expert in the battery chemistry. But from my observation:-

If you add a resistance to the Vbat output (even a small one), it would drop the charge current dramatically if you are using LTC4054. Try putting a DMM in series and switch between 200/400mA and 10/20A, then you will see a great difference. Also it is not possible to increase the voltage output from the chip itself.

I'd rather go with 4 separate charge channels, cleaner and more practical. But if you insist on a single chip solution, I suggest that you just put all the batteries together physically and (permanently) wire them in parallel, so that they can be charged and discharged at the same time. Many LB-01 or CR-V3 has 2 14430 cells fixed in parallel.

The datasheet of LTC4054 provides the suggestion for the input reverse voltage protection using P-channel FET, but nothing is mentioned about the situation if the cell is connected upside down, I have no idea if it is safe. It does mention the short circuit protection, though. So I just add one red led with a small series resistor to light up very bright from the cell voltage if the battery is connected in reverse position. The charge status led is green.

Of course it could spell a possible disaster if you put multiple cells upside down in parallel. I suspect the gas leaked out of a li cell could be as flameable as gasolin vapor, then the battery may be quite warm or hot at the time.

-- dj


----------



## djpark

Andrew, you are going well with good energy!

I built my first LTC4054 on 4x4 holes perforated board and it is converted to PDIP8, it moves between the charger (with PDIP socket) and the breadboard.

Do you know that the chip can be used as 100mA current regulator for 8mm led or underdriven Luxeon? /ubbthreads/images/graemlins/wink.gif

I used a Nichia white led as the indicator and it was too bright. So I cut it off right above the die and smoothened it with the nail polish. So it is just a tiny dot of the light and it is nice to watch.

You will want to add 7805 with a small heatsink to provide the power instead of USB. Just give a little consideration to the chip temperature. When it is hot, the charge current is reduced.

If you want to measure the charging current, you can measure the voltage between prog pin and the ground and calculate backward using Ibat = Vprog / Rprog. Vprog is 1V during the constant current charge and it will go down during the constant voltage charging, then drops below 0.01V when charging is complete.

Have fun!

-- dj


----------



## andrewwynn

re: charg n discharge yup i know... actually I was an electrician in the navy... the 2V lead acid cells for a sub are bigger than me!

thanks for the note about charging current... i did notice it's very sensitive.. my first charge attempt i was monitoring current through my DMM.. and i think it cut out at like 4.10 or something.. I had to test them out a bit before continuing... they are amazing... i got some freakeyly scary DD currents through my Lux3s.. over 900mA from a single AAA... double the recommended dose.. so i only did it for a second. 

Well i have to get some sleep now.. thanks tons.. can't wait to take pictures.

-awr


----------



## andrewwynn

Did anybody say PICTURES?







here is the chip, mounted on the backside of an 8 pin DIP socket.. i simply bent six of the legs down toward where the chip would be.. i held the chip with a tweezers to get the first leg or two soldered... 

here's the ckt on the breadboard;






I made a webpage for them.. a few more pics.. check them out.

the circuit works beautifully.. it charged up a dead LiON pack i had from a dead cellphone.. amazingly. it took like an hour before it wasn't trickle charging and then went whole hog into charging.. nice chip.. i'm working to make the ckt itty-bitty.. maybe 1x1x2cm.

I think for the first one, though i'm building it into a project box that is about 7mm x 4cm x 5cm.. it will have a jack for power and a cord that plugs into multiple options (like single AAA double AAA single AA).. so i don't have to build too many chargers and can have multiple options


----------



## MrAl

Hi there,

Hey that's neat andrew! Thanks much for sharing the pics.

The three stage switch is really a good idea i think too,
as long as the contacts get a little wipe action, which 
i'd bet they do.

Im looking for a small switch myself, with two or three
positions (besides off). It has to fit into a 1/2 inch
diameter hole. Pablo from Argentina made me a nice
threaded end piece for my Minimag with his lathe so
all i need now is a switch that fits as i've already
got the electronics waiting. I wanted push on-on-off or
something like that rather than rotational for this
particular mod.

Take care,
Al



Take care,
Al


----------



## andrewwynn

the contacts do wipe a little because they aren't perfectly parallel.. the lowest contact doesn't move side to side very much but all the contacts are silver and with the amt of current going through them (they are designed for like 15A and will have to deliver 1/2A max).. i think they will work great. 

there are pre-fab clickie switches that rotate through positions... some are push some are rotate.. think of the classic lamp with the post and the rotating switch to turn on one lamp, two lamps and off.

I specifically wanted a no-machining retrofit as i have no lathe or mill.

-awr


----------



## andrewwynn

[ QUOTE ]
*djpark said:*
[ QUOTE ]
*4sevens said:*
djpark: I'm considering building chargers for my 14500's using standard AA holders. I would like to be able to charge 4AA's in parallel. Would it make sense to add standard diodes to each cell to
prevent reverse insertion? I know that would drop the V about .4v
but I can re-adjust the V up .4v

what do you think? 

[/ QUOTE ]

Frankly I am no expert in the battery chemistry. But from my observation:-

If you add a resistance to the Vbat output (even a small one), it would drop the charge current dramatically if you are using LTC4054. Try putting a DMM in series and switch between 200/400mA and 10/20A, then you will see a great difference. Also it is not possible to increase the voltage output from the chip itself.

I'd rather go with 4 separate charge channels, cleaner and more practical. But if you insist on a single chip solution, I suggest that you just put all the batteries together physically and (permanently) wire them in parallel, so that they can be charged and discharged at the same time. Many LB-01 or CR-V3 has 2 14430 cells fixed in parallel.

The datasheet of LTC4054 provides the suggestion for the input reverse voltage protection using P-channel FET, but nothing is mentioned about the situation if the cell is connected upside down, I have no idea if it is safe. It does mention the short circuit protection, though. So I just add one red led with a small series resistor to light up very bright from the cell voltage if the battery is connected in reverse position. The charge status led is green.

Of course it could spell a possible disaster if you put multiple cells upside down in parallel. I suspect the gas leaked out of a li cell could be as flameable as gasolin vapor, then the battery may be quite warm or hot at the time.

-- dj 

[/ QUOTE ]

This thought just came to mind.. since i like the idea of rev. voltage protection.. could you put a diode below each battery you want to charge as well as below the ground from the LC? that should raise your ground reference up .4V or whatever the Vf of the diode is and fool the charger into thinking it's only charging to 4.2V when it'd be say 4.6V to the top of the battery to ground.

Just a thought that came to me when i was pondering this idea.

I do like the idea of parallel charging circuits... that chip is only like $1.40.. maybe another $2 in parts and only $1 if you get them in bulk per channel.

-awr


----------



## MrAl

Hello andrew,

I think you 'fooled' yourself a little here 

A diode in series with the battery doesnt protect against
cell reverse polarity because the charge current is in
the same direction as the current through a reversed cell.
The only thing it does do is prevent reverse loading
if the input power goes away for some reason, which is
still a good thing for some chargers.

If you want true reverse cell protection you can use this
simple circuit (also see the new thread here)...

Take care,
Al


----------



## andrewwynn

that's an interesting ckt.. why the different values for the resistors? (different Vf of red and green LEDs? ) yeah you are totally correct about the oops in the thought i had about the cell protection, wasn't completely thought through.. i just was figuring out a way to deal with the other problem introduced... however.. would there be this use:... 

The point of my idea was that if you have multiple cells in parallel to charge. each one gets it's own diode (as well as the ground of the charging chip)... then if you put ONE battery in backwards.. it doesn't try to charge the rest at 20A. This was the intent of the concept i described above... or am i missing something, and it would still just try to draw a ton of current into the backwards battery (since it would 'see'.. what? zero volts ish)? I guess the 'easy' answer could be a 2C fuse /ubbthreads/images/graemlins/wink.gif

Also.. would it hurt to have a 4.3 zener in parallel with the charging ckt to avoid any chance whatsoever of an over voltage situation? 

-awr


----------



## MrAl

Hi again andrew,

Gee i hope i didnt sound too critical as the basic idea
was cool.

In your explaination of the batteries in parallel i dont
understand how the circuit is connected. If the batteries
all connect to the ground of the charging chip, where do
the 'diodes' go, or should i ask: what do the diodes
actually do in that circuit?

Unfortunately, i dont think a 4.3v zener will actually do
anything because if the voltage reaches 4.3v it's already
too high. Also, it's not possible to 'adjust' the zener
voltage or obtain a zener that has a voltage exactly
what would be required in order to protect something.
It would however be possible to build a back up circuit
or an 'electronic zener' (with more parts of course)
to monitor the battery voltage but it would take more
than a single zener to do so.
If all you're worried about is 'open circuit' voltage
and you've checked the chip and found the output
voltage might be higher and damaging to the chip
with no battery connected then a zener would help.

This circuit has to be borderline instrumentation quality
even though all it's doing is charging a battery. Strange,
i know, but the spec on the battery requirements is just
that exacting...within 1 percent.
Here's how i think of it:
It's not super simple, but it's still a heck of a lot
simpler than trying to charge a NiMH battery with real
simple parts (detecting minus delta V, that is).

You're on the right track i believe -- just have to think
along more and more perfect lines when it comes to the
battery's terminal voltage...
Try incorporating a low voltage relay? Low contact
resistance. Connecting the battery turns it on (?)
while the 'done' led signal turns it off (?).
Cheap comparator/op amp chips sense exacting
voltage levels. Mull it all over 

Circuit:
Yes, the different value of resistors is for the
different LED voltages, however it might be necessary
to use two red LED's until the next circuit gets here 
The next circuit will be a little more complex though 
im afraid. This one is about the simplest you can get
and yet very effective.
Im going to (at some point) add this to my full blown
Li-ion charger (1 amp charge max) and maybe my other
Li charger/Power supply (1.5 amp charge).
Cant beat it's effectiveness although you do have to
remember to turn the switch 'off' before connecting
the battery -- that's a downside maybe you can find 
a way around too. Maybe another green LED.

Good luck with it,
Al


----------



## andrewwynn

Ok.. here is the circuit i had in mind:






The thought is.. would this increase the safety in-case a cell is put in backwards.. by preventing the cells from trying to drain each other.. their effective ground reference would be raised by the Vf of the diodes, and so would the ground ref of the chip by it's diode.

helpful, pointless?

-awr


----------



## MrAl

Hi there andrew,

Oh yes i see what you meant now. That's a very interesting
idea for sure, but there's still a slight catch...

The diode in series with the chip conducts about 300ua
while the diodes in series with the batts conducts a min
of about 30ma. Since the diodes drop is dependent on
current flow they wont all have the same voltage drop 
and this will cause inaccuracies in the way the chip 
measures voltage getting to the cell. In fact, using
those 1N4001 diodes would result in a difference of
about 140mv, which means the cell wont charge completely.

I guess you could try a resistor in series with the
diode in series with the chip to drop a little extra
voltage, but that would only get the drop right at that
one battery current only, and once the cell(s) charge 
a little it's right back to inaccuracy city /ubbthreads/images/graemlins/smile.gif

I think you're on the right track however, just might
need some active devices to get to the final solution.
Maybe then you can get the reverse protection along
with it.

It's helpful even if it doesnt work exactly the way 
we want it to, because once we notice why it doesnt
work we have a better perspective to work from.

I happened to put a diode in series with a one cell
charger (concept) to prevent the cell from discharging
back into the charger if the power was removed, but
to get the zero reference voltage i used an op amp to
MEASURE the diode drop and apply that voltage directly
to the zero reference point. This is definitely accurate,
but still doesnt provide reverse protection :-(

More ideas would be good too...


Take care,
Al


----------



## andrewwynn

How about picking different diodes that have a different Vf at the current levels at hand? the important thing is the current level when the batts would be almost completely charged, not at full current... could always put a resistor 'around' the chip to give it a bias current of 30mA or whatever would match the batteries... at the expense of .15W

What does 'reverse protection' mean? I thought it meant.. protect me from my own stupidity... makes things not go boom if i put a battery in backwards... putting a LiON battery back to back with another would probably cause a 30-40A current.. 288W.. that's a scary thought. 

the chip seemed to be pretty smart.. i took a LiON cell out of dead cellphone that was dead for over a year... and measured zero volts... the charger spend a good hour putting like 25mA into the battery before it got enough charge and started charging 300mA... pretty sure that if a battery is loaded backwards, the load will be seen as a short and it won't charge... thoughts? 

-awr


----------



## MrAl

Hi there andrew,

You can do that if you wish, but the end result of biasing
the first diode to 15ma is almost the same as inserting
a 0.6 ohm resistor in series with each battery, which
extends the charge time.

Reverse protection referred to putting the cell in backwards.
Yes, it's good to have protection so that the batteries
dont try to discharge each other at very high current,
but it's much better to also protect the chip. Who wants
to replace one of those little things? If you're going
to do it, do it 

According to Doug S on here he stated that the chip blows
out if the cell is connected backwards.

When charging those little AAA cells i assume the charge
current is C/2 which works out to 150ma right?
This means if you're doing two in parallel you would want
the chip to put out 300ma and HOPE the two batteries 
share current equally. Better would be to use one chip
for each battery, that way there's no hoping, wishing,
or praying.

"Reverese Protection" means there is something built into
the circuit to protect the chip from blowing out if the
battery is connected backwards.

If in spite of all the pitfalls you still want to try
this it's up to you. Assuming 150ma charge for a 
single battery i propose the following experiments...

EXPERIMENT #1
Set the chip for 150ma output to charge a single cell.
No diodes, but insert a 0.6 ohm resistor in series with
the cell after discharging to 3.00 volts.
Time the charge cycle until it's done and record.
Compare this charge time to the charge time without using
a 0.6 ohm series resistor.

EXPERIMENT #2
We will attempt to charge one cell using two diodes as
per your schematic. We'll label the diodes from left
to right D1, D2, etc. This puts D1 in series with the
chip, D2 in series with BAT1.

Set the output current of the chip to 150ma.
Hand pick D1 and D2 to have voltages within 0.001 volt
of each other when biased to 15ma each at 20 deg C.
Make sure there's no fan running or drafts in the room.
Solder D1 and D2 cathodes very close together using
enough solder to make sure they are thermally well 
connected but not a big blob.
Cut all the leads short and attach thin wires like #24
gauge to form three leads, one for each anode and one
for the common cathode. Make the leads all about 4 inches
long and also label each lead. Wrap this construction
with some tape, then fold back the wires about 1/2 inch
from the end of the body and put another layer of tape
right across the end holding the leads firmly, then
fold the leads back out so they again extend from the
body. Put another layer of tape across the end to hold
the second fold. Doing this does two things: holds
the leads firmly and extends the thermal path along
the leads to the body of the diodes.
Next, if you want to ensure this acts more like a single
thermal node, wrap the construction in thin bare copper wire,
so that it's completely covered. Wrap with tape.
Next, cut a few pieces of thin styrofoam and wrap the
construction with these pieces, then a layer or two of
tape. Make sure at least 1/2 inch of the leads gets 
covered too.

Now you're ready to build the circuit.
Connect the diodes into the circuit and bias
D1 to 15ma with a resistor from the +5 volt supply.
Connect a cell that has been depleted down to 3.00 volts
and time the charge cycle. Record and compare with
Experiment #1 and with no resistor or diodes connected.


Take care,
Al


----------



## andrewwynn

how about a fuse? the chip can handle outputting 600mA.. i only have it set for 300... (i did have it set for 600 when charging 4 AAAs)... so wouldn't simply having a 500mA fuse be enough protection against putting a cell in backwards for the purpose of saving the chip... and... the same idea should work for the batteries.. but a 1A fuse on each battery... if you put on in backwards.. there will be a multi-amp surge between the bats and will open the ckt.. and the chip should be protected by a .5a fuse.. just a thought before we get all to fancy. 

-awr


----------



## MrAl

Hi again andrew,

Oh yes, maybe that would work. I'd hate to have to be the one
to test it though  but it could in fact work.
If each batt has it's own fuse (maybe one of those
real fast acting fuses) it would probably prevent an 
explosion but im not sure about the chip. 

How about this non-fancy idea:
Use the fuses as you were saying, then, also connect
a real heavy current Schottky diode (9amp) right
across the output of the chip! so that if the batt is
connecteed backwards, the diode conducts briefly,
then blows the fuse, all the while the chip only sees
about -0.8 volt maybe. This might be just enough
to protect it. You'd have to test this idea though.
Make sure to use fast acting fuses.

Hope it works.

Take care,
Al


----------



## Hallis

Can we sticky this thread?


----------



## MrAl

Hello again,

Doug S came up with a nice idea for protection using
a single N Mosfet and as soon as i can i'll have the
schem up. It's very simple:
gate goes to chip OUT
drain goes to (-) batt (only connection for battery)
source goes to ground.

The idea being if the cell is put in backwards it
sucks down the chip output just enough to cause
the gate voltage to lower to just above the
threshold point, where the Ron starts to rise and
limit the holding current to whatever the chip puts
out -- such as 150ma. There's also a red LED that
lights up so you know right away it's not right.

Take care,
Al


----------



## MrAl

Hi again,

Here's the solution for one cell protection.
We'll have to give the parallel cells more thought
i guess. If they are wired into a pack there's no
problem however.

Here it is:






Take care,
Al


----------



## Hallis

/ubbthreads/images/graemlins/bumpit.gif


----------



## MrAl

Hi Hallis,

That's funny /ubbthreads/images/graemlins/smile.gif

Take care,
Al


----------



## cgpeanut

Here's my version of the circuit using smd components /ubbthreads/images/graemlins/grin.gif Right now it does not look pretty (you should have seen the first version!) The actual charger circuit is in the middle where the led lights up. 













Below the 3mm led I'm using 2 10uF 16v tantalum caps my max input Vcc is at 3.5v anything more than that the cap gets hot! I'll try using 4v 10uF tantalums and a solar charger next time and try charging one aaa li-on see if can be done. 

Does anyone know what value resistor to use for the pin5 of the LTC4054 to charge up a aaa? I'm using 0805 resistors I will include the reverse protection circuit aswell.


----------



## andrewwynn

aaa charge: i use two 3.3k in series, gives me 150mA


----------



## cgpeanut

thanks andrewwynn! just wanted to make sure, will try to solder a miniature switch between the two 3.3k resistors so I can flip between aa,aaa and r123s.


----------



## andrewwynn

I'm going to do almost exactly same thing.. i want to be able to charge a four-pack of AAAA or a pair of AAAs.. but mostly i have to charge a single AAA... my charger is still on the breadboard and looks like this:






you can see my 'current setting switch' on the bottom.. one resistor = 300mA.. i put a second in parallel for 600mA and both in series for 150mA (one AAA)

I'm aiming to put it all in a package about 1/2 cm x 3cm x 4cm... with a 2.5mm jack input and a cord output... also with something like a 2.5mm plug.. then i can use either my usb cable or a wall wart to power.. and can plug into myriad choices.. AAA or AA holders, etc.


----------



## cgpeanut

Your circuit looks NICE! /ubbthreads/images/graemlins/buttrock.gif I was thinking of doing another version with regular components using copper pcb, ecthing stickers and solution from rat shack but I'm afraid I don't have the patience. I will layout the smd components again to conserve on space and add Doug_S's reverse protection circuit using the IRLML6401 I think I might be able to shrink into 1/2 inch cube.


----------



## Klaus

[ QUOTE ]
*andrewwynn said:*
(you didn't see that klaus.. mr private investigator you) 

[/ QUOTE ]

Hu /ubbthreads/images/graemlins/confused.gif

Klaus


----------



## si767676

Thanks to DJPark for this excellent guide.

I have made a few chargers using this method. On a couple of them, I have problems... The battery does not charge, and the status LED never goes off.
The circuit looks OK - no shorts etc, and it is definitely not the battery - same batteries charge fine with one of the other chargers.
So the only explanation I could think of is that I damaged the LTC4054 whilst soldering it. Does anyone know if they are especially heat or static sensitive. Datasheet says max lead soldering temperature = 300C for 10 seconds. I can't imagine I would have exceeded that. As for static - I generally have no problems with other components - I thought I took reasonable precautions to discharge myself.

If anyone can offer advice on possible explanations and how to avoid the problem, I'd be very grateful. It is not so much the cost of the parts that bothers me, but the hassle of unsoldering them and soldering on new ones as well as having to purchase new ones from the other side of the Atlantic if I run out. (by the way does anyone know a supplier of these LTC4054 in Europe, to avoid the high shipping cost from Linear USA?)

Thanks in advance for any help,
Simon.


----------



## andrewwynn

I'm ordering the LTC4054 in 3-digit quantities.. i think i'll buy and extra 25 or something just for people interested.. i'll send just in a letter envelope so shipping will be like $1.

I killed one of my chips by reversing the battery and yup not exactly a cake-walk resoldering.

I recommend getting this part from digikey: 






makes dealing with the sot-23 a cakewalk. 

Here's a computer model of my latest version of this charger:






that circle is 10mm... the charger is designed to fit into the head of an AAA light.

-awr


----------



## cue003

sweet. 

AWR, 

I would like to receive one of those little bad boys from you when you get them if that is ok. Or even better yet, I see you made a complete charger with selector switch etc. I would REALLY REALLY like to buy something similiar to that from you if at all possible. I just don't think I can find the time etc to put this together myself. I will want to charge R123 one or 2 at time is fine for sure and MAYBE AA, AAA two at a time. That is all the batteries I use. The other batts are Pila and I already have both an AC/DC charger for them. This will fill the missing link for me.

Thanks to all that did research and have tested this little marvel of electronics.

Curtis


----------



## andrewwynn

Cue: you are talking about my universal LiON charger thread i presume.

Yeah that charger is the 'bombigitty'. I have to add reverse cell protection it's no fun to replace the chip anytime you oops on that one (happened once, when i was wiring up a battery outside the holder)..

I have so far only made 'modules' for my charger to accept AAAs directly.. i just use jumpers when charging my AAs.. but when i get caught up a bit i'll be making the other modules so i can incorporate R123, AA as well as the AAA module i already have. (which can charge 1, 2, 3 or 4 at the same time). 

I would say that if you want to have a charger any time soon, i can help you out with the chip, and i'll even solder it onto a 'proto' board.. i don't know if i can spare the time to wire the rest up but i can show you the exact schematic, and modifiy it to match the pinout of the proto board.

The board and chip together are about $5. I think i'd solder it on and 'mail' it for the neighborhood of $10, as long as the demand is not nuts. I might just build up a dozen or so when i'm done making my chargers for the nano project and make them available on BST. Once on the protoboard it's a cake walk to build and fun to DIY.. and you can be creative how you want to solve the switching resistors (2 or 3 for binary is one possibility)... 3 resistors in series with 2 that short out two of them.. in a myriad of possible ways... or go whole hog with a big dial like i did.

send me an email: flashlight (at) rouse (dot) com. if not too many people ask for it, i'll make a couple protoboards with the LTC4054 ready to go. I can even test it on my bread board to make sure it works before i send it.

-awr


----------



## djpark

[ QUOTE ]
*si767676 said:*
I have made a few chargers using this method. On a couple of them, I have problems... The battery does not charge, and the status LED never goes off.

[/ QUOTE ]

Hi Simon,

You need to confirm if the particular charger has constant problem with any cells, or intermittent problem with certain cells.

If it works with some cells and some not, the LTC4054 may be still good. Physical problem may be the cause.

If the charger has problem with any cells, it could be the chip. Or check the physical connection of battery output from the chip.

*If you have the 10-20uF capacitor at output, the led will flash at slow speed (about 0.5-1Hz) when there is no battery. If the battery is having high voltage (full charge), it will turn very dim (20uA) which may be still visible with bright led. If there is no cap, no battery or no connection at all from the OUTPUT pin, the led will look like turned on at slightly dimmer level than charging status, but very much brighter than full charge status. One way to find out the connection..*

*If it continues, check the voltage of the PROG pin to confirm the charging status. During the charging, the voltage between chip pin 6 and gnd shall be 1.0 - 0.1V. 1.0V indicates the constant current charging and it goes down as the charging gets near completion. When the charge current is dropped to 10% of the programmed current, the voltage is 0.1V and the charging is terminated resulting the pin 6 voltage 0V. If there is output cap with no battery, or battery fully charged, it shall be 0V. If there is no cap and no battery or no connection from OUTPUT (pin 3), the prog voltage will be 0 yet the led looks on. From this measurement, you can determine if it is actually charging or if there is connection. (The DMM shows 0 doesn't mean really 0, it could have short pulses but not caught by the DMM.)*

I hope you can find out and fix it.

-- dj


----------



## djpark

Spent a bit of time to make a new charger some time ago. The new one has a jumper for dual charging current and has a small heat sink for the chip since I find that the heat can cause the charging current to drop due to the builtin thermal protection circuit and it slows down the charge.

Also I use new method of fixing the SOT23 LTC4054 chip on the perforated board directly without using the adaptor, it is fairly easy and simple. I will photos later.

Meantime, this is another charger I use regularly now. It is built on 4C battery holder with modular design.






Bottom left is the 7805 regulator with heatsink to drop down input (AC or DC) down to 5V. It takes most of the heat to reduce the voltage down so the heat generation by LTC4054. This helps longer constant current charge time thus reducing the total charge time. Green led to indicate the power.

Bottom right is the actual charger with toggle switch to select the charging current between 300mA and 750mA. The center position cuts off the battery connection as well as the program resistor resulting in LTC chip in shutdown mode. Blue led to indicate the charging status.

Upper portion is padded for 17680 cell, it can host various cells with a spacer.

Upper left is reverse battery indicator with red led using MrAl method. I chose this instead of Doug_S's FET solution since I use this to hold the battery for light testing, the toggle switch on the charging portion determines the connection. It also has 0.16 ohm resistor to measure the current flow. (Now I use MAX471 chip to measure the current with builtin 35 mili-ohm resistor instead.)










Here is some charts showing the charging characteristics with different max constant charge current (300mA, 425mA & 750mA). The higher charging current doesn't necessarily mean a lot faster charging.














To confirm the trickle charge feature of the charger with badly depleted cell, I drained an R123 cell totally (ab-use in the name of research) and got this charging result.






It clearly shows the trickle charge (actually constant 10% of max charging current) till the cell voltage rise above 2.5V. Good to rely on..

-- dj


----------



## andrewwynn

nice stuff i love the voltage regulator and reverse projection, very complete. I just figured out a mechanical interlock to prevent reverse connection in my charger.. I'm putting a brass ring in the bottom of the charger body, so the connection is only made on the outside edge of the battery. If a battery is inserted backwards, the center post of the positive side touches nothing. I will probably have to use foam or enamel paint on the ground surrounding the positive contact on the other side to make sure the battery wouldn't short out the charger output if put in backwards. 

-awr


----------



## RayO

Would anyone know if RS carries the caps and resistors for this project? Do I need 1/2w or 1/4w resistors. Caps available at RS are 10uf 35V. 

Thanks..


----------



## PEU

DJ: Bump on the Datalogger /ubbthreads/images/graemlins/smile.gif


Pablo


----------



## djpark

[ QUOTE ]
*RayO said:*
Would anyone know if RS carries the caps and resistors for this project? Do I need 1/2w or 1/4w resistors. Caps available at RS are 10uf 35V. 

Thanks.. 

[/ QUOTE ]

Any rating is ok, even 1/8W and 10V. I suggest to use 22uF instead of 10uF and it will give you about 1Hz flash without the battery.

PEU: It is coming. I need more time since I am spending much time for home improvement at the moment.

-- dj


----------



## andrewwynn

you can build with RS parts as i did... i've used 4.7uF and get a nice dim glow, the 10uF output makes a very quick blink occasionally, which also works fine.


----------



## vacuum3d

In the Reverse Connection Protection circuit posted by MrAl, does anyone know the part number for the MOSFET? Is it something I can find from RS?

thx,
ernest


----------



## djpark

[ QUOTE ]
*vacuum3d said:*
In the Reverse Connection Protection circuit posted by MrAl, does anyone know the part number for the MOSFET? Is it something I can find from RS?

thx,
ernest 

[/ QUOTE ]

There is another thread about the reverse battery protection here.

http://www.candlepowerforums.com/ubbthreads/showflat.php?Number=693440 

Dour_S who designed the FET protection circuit suggested using IRLML2502 which has Rdson = 0.045 ohm @ Vgs = 4.5V or Rdson = 0.080 ohm @ Vgs = 2.5V.

You can buy Si2302DS from RS which has Rdson = 0.115 ohm @ Vgs = 2.5V.

I bought Si2314EDS from NewArk which has Rdson = 0.040 ohm @ Vgs = 2.5V or Rdson = 0.051 ohm @ Vgs = 1.8V. This could be quite good.

But frankly speaking, I don't consider the reverse battery polarity protection a major issue. It is more of your discipline. Even though the cell's positive and negative is similar, it is not the same and if you train yourself to check before you power up, it is ok.

If you power the charger with the cell reversed, it may (or will) burn the chip, but without the power, the reversed cell does not kill the chip. So having a red led as reverse cell indicator is enough for me.

-- dj


----------



## Lynx_Arc

If anyone wants a bunch of used parts I just pulled a gob of them off a few circuit boards I have about 200 electolytic caps and perhaps 100 resistors most of these are circuit board pulls so leads are mostly short but I don't need but shipping reimbursed for the parts. PM me if you are interested with a list and I will see how many of what type I have.


----------



## vacuum3d

DJ,
Thanks for the info. The need of reverse protection is mainly because I'm building a charger for someone who can't tell left from right. It's just one extra insurance.

thx,
ernest


----------



## andrewwynn

vacuum... i have a design for a mechanical reverse protection for my charger.. on the negative side, the contact will be a 3/8 diameter tube that is about 1/32 thick.. so there is no contact in the middle. if the battery is put in backwards it makes no contact so it does nothing.

-=awr


----------



## Lux Luthor

This thread is great. Lots of useful info here, although I haven't gotten on board with this project yet.

There is one thing I need to do, which is charge off 12V. Can you guys recommend a good way to knock the voltage down? How about using one of the alternative LTC switching chips? They do look a lot more complicated to work with, though. /ubbthreads/images/graemlins/frown.gif


----------



## vacuum3d

andrew,
The 14450 that I have are flattops. I'm not sure how suitable your mechanical solution would be for such cells?


ernest


----------



## andrewwynn

mine are the same (the positive side looks like a negative).. but there is a mm or 1.5 or so around the edge... i built one it works perfectly, but part of why it works is my charger is built into a flashlight tube.


----------



## HarryN

It seems like a great setup would be if the charger could somehow detect the cell direction + / - (before) it starts to charge, and just stop the charge from happening electrically. I have seen mechanical interlocks beaten by people that thought they were doing the right thing.

A secondary over voltage protection / overcharging protection would also seem valuable, such as Doug S proposed. Last but not least, monitoring temperature would be handy, esp if we start using this thing on larger cells, like 18650. At that point, you might be able to get a UL or TUV listing.


----------



## djpark

[ QUOTE ]
*HarryN said:*
A secondary over voltage protection / overcharging protection would also seem valuable, such as Doug S proposed. Last but not least, monitoring temperature would be handy, esp if we start using this thing on larger cells, like 18650. At that point, you might be able to get a UL or TUV listing. 

[/ QUOTE ]

I have not tried Doug_S's FET protection yet. I am still trying to understand the theory of the protection.

But this LTC4054 chip (and other chips I tried) is rather sensitive to the output resistance and any extra (unnecessary) resistance can alter the charging current which will cause the chip functioning differently. Having a diode or a fuse in series is already bad idea.

There are other chips monitoring the cell temperature, this chip doesn't. But it does monitor the temperature of the chip itself and if it is too hot, it reduce the charging current.

-- dj


----------



## andrewwynn

I have to post a pic of my charger:






that is a 10mm disc it sits on. Almost hard to believe that's a complete LiON charger (just add battery and power of course). there are more complete pictures here


----------



## djpark

I needed to make a li-ion charger for my brother as I am sending a Q3 and PR123/R123. So instead of making an AA holder, I decided to mod the JSB123 charger for him. My initial mod was to put a li-ion cell protection chip and it did work, but why not modify it to house a LTC4054 based charger as used by this DIY charger.

As I am sharing the process of mod I did, it will bring some technical information on JSB123 (4.2V) charger and also other things such as LED charging status indicator and FET reverse cell protection. I hope it can be useful for others.


* JSB123 4.2V Charger*






This circuit is very cleverly designed buck switcher and transisotr based linear regulator combination to produce 4.25V DC output from input 12V (16V+ rectified) DC. The power supply sayd max 600mA and the charger says 350mA charging current. It is about 0.5C for R123, but the charger actually delivered 200mA only. Both battery holders are joined parallel, no individual control.

The green led is tied permanently to the output (on all the time) and the red led is turned on by a PNP transistor by sensing current passing through a diode. So at starting of the charging the red led is bright and as the charging current drops, the red led gets dimmer.

This is typical charging process. Since the charger output is just 4.25V, it may not trigger the over-charge protection circuit like Pila, so it takes a lot longer time to charge and you may not know when the charging is completed.






I did a few changes to the existing circuit to accomodate the LTC4054 charger chip. I didn't have time to prepare the detail circuit of the JSB charger change, but if many cpfers want, I may start a seperate thread about the JSB charger.






- changed input polarity protection diode from parallel to serial to the DC input
I wonder why it is designed this way.

- added 10k resistor to the feedback divider, so the DC output is now 4.65V instead of 4.25V
The reference voltage is 1.25V so it was easy to calculate.

- added 2 3.3 ohm (1.65 ohm) to the current sensing resistor hoping the max current will jump
I managed to get 300mA max but no more, maybe the inductor or the main power supply capacity?

- connected 15K resistor from PNP transistor base to LTC4054 charge status output pin
Since the LTC output is open drain, it is just so nice to find a PNP transistor based led driver already built in so that I can source the current to the bi-color led instead of sinking.

- added a capacitor and resistor to the DC output of the linear regulator
There is about 2V drop by the 2 transistor regulator and 1 current sensing diode and I find something funny which I can't understand with my limited knowledge. When the power is on, the buck chip didn't oscillated and the it did only when there was a slight output current draw. Somehow the LTC4054 chip didn't trigger the regulator and I had to add a 10K resistor to the regulator output to draw some current and it is stable.


* LTC4054 Charger *

Since there is some space on top of the existing board, I fixed all the components on top, the spider style.






I didn't have 3.3K SMT resistor, so hooked 3 10K resistor to get 300mA max constant charging current. Also added Vishay SI2314EDS N-channel FET as reverse cell protection as suggested by Doug_S, it works!

A typical charging of JSB123 with this charger is as follows. No major big deal, but just works as expected. Compared to the above charging data.







* Charging Status led *

Many cpfers asked me how to determine if the charging is complete with LTC4054 charger since the led seems on all the time.

The charging indicator pin of LTC4054 is open drain and it works like mechanical switch to allow current pass through, it does not provide current by itself.

While it is charging, the pin will sink as much as 20mA and the led is very bright. When the charging is complete, it still let 20uA current pass through instead of total cut off. The total cut off is done to indicate the shutdown status when the output voltage is higher than input such as battery is in but no power supply connected.

Even with small current such as 20uA, a bright led will still show some light and it may be mistaken as led on with charging. One way to overcome this is to use a dimmer discrete led display which will not show light at low current.

I and my buddy _cgpeanut_ (Roberto) have discussed about the desire to have red light for charging and green when charging is completed. We went further using a PIC micro-P to monitor the charging current and the battery voltage to indicate different charging statges with different led light pattern or color. I will write a program for PIC to do this sometime later.

Then I got wild to think of using the PIC to control the whole charge process without using a charger chip. It is possible and also feasible to make real intelligent charger. But I recognize it only suitable as school project, not really for a commercial project. There it goes!

Meantime, here is a PNP transistor based high side switch to source the current to led based on the signal from the LTC4054. It is especially suitable to provide current to common cathode bi-color led.






R1 (330 ohm) is used since it is already in the original charger and it gives very nice brightness red light, it may be increased.

R2 (2.2k) is also already there, sos didn't want to change. But the R3 (15K) is what I put and I find it working very fine to clearly distinguish between charging and complete. You may want to change value between 10K and 20K for best result depending on the transistor and R2 value.


* Reverse Cell Protection *

This N-channel FET based protection circuit is made by Doug_S and MrAl has drawn the circuit together with explanation of theory of working. Since I am not the one to use this charger, but my brother, so I thought a reverse cell protection is important.

As suggest, I used very low Rdson FET Vishay Si2314EDS and built in to the charger. Boy, it was really hard to buy this FET. Thanks to _Jay_ for helping me to get.






The reverse cell indicator led is built into the holder with 100 ohm current limit resistor. This low value gives quite bright red light even with much depleted cell when inserted reverse. It takes about 20mA from the fully charged R123 when inserted reverse without power connected.

Now the time has come for real test!

I connected power supply and with my fingers crossed, I inserted a fully charged R123 reverse. Both charging indicator and reverse cell indicator led were lit. The current measurement from the battery is 50mA only. Thanks God!

I shorted the both output terminal of the charger and measured the current and got 30mA. So total 50mA is correct.

The LTC4054 has output short circuit protection and I presume 30mA limited current is controled by the chip. Some brave souls may want to try this without the FET protection.


* Done *






It is done! I like it very much, but it is good to know my brother is going to enjoy it. It charges both 14500 and R123 with 2+ hours to complete.

I will update the main post with the new led indicator and fet protection when I find time.

-- dj


----------



## andrewwynn

BEAUTIFUL work DJ..

I am just about to mod one of those infamous 'exploding chinese chargers'.. 

It has two bays for R123.. and i'm going to make a dual channel charger .. it's tedius to have to make sure voltage is the same before charging pairs.. or not being able to pop on a second while one is charging by itself. In any event.. a lot of what you did here is similar to what i will do.. I want to get reverse protection in.. and a fancy LED feedback like tri-color red/green/yellow.. 

-awr


----------



## djpark

1) Most China made chargers I've seen including JSB123 charger have 2 battery slots joined together. So if you put 2 cells with different voltage, one battery will charge the other one before both get charged (I presume).

If you want to charge multiple cells with only 1 charging circuit, you can use LTC4411 chip for each cells. It is a low loss ideal diode and it switches Vin to Vout depending on the voltage of Vout pin with 140 mili-ohm FET.

So this chip can be used to charge multiple cells from a single charging source -- charge whichever cell with lower voltage till every cells have same voltage, then start charging together.

Likewise, the same chip can also be used for load sharing from multiple batteries of difference capacity as well.

Another good point of using this chip -- since it is also an ideal diode with very low drop, it will work as reverse cell protection perfectly. No FET needed, you may want to compare the price of this chip and very low Rdson FET.

$0.02 worth of consultation!

2) LTC4054 goes into trickle charge mode when the battery voltage is below 2.9V. That means it provides 10% of the programmed constant charging current. For the same reason, it allow only 10% of the programmed current when the output to battery is short-circuited.

My above experiments confirms that 30ma (10% of programmed 300mA) plus 20mA to led brings total 50mA of current to the battery when the battery is inserted reverse.

It would be interesting to try to put a battery reverse without FET.

-- dj


----------



## andrewwynn

the charger i have they are wired in parallel.. i will cut them apart.. i was just going to make two chargers in one.. double charger chips.. they are only like $1.88.. i'm about to make another order of 75 or so.

I love the idea of that chip though.. (load share).. that is much more clever. 

so.. you are saying to put the 4411 chip in series with each battery... and try and see if that alone will provide reverse protection? I think i like the idea of trying that. 

Ok.. just checked.. the LTC4411 is more expensive than the charger chip. I pay about 32 cents for the .045ohm Rsdon FET i'm using in my driver and buy them by the 100s, so i can build a dual channel driver with 2 4054s and two of the FETS for just about $4 in chips.

I want to figure out a cool way to implement a 2 or 3 color LED for charging status.. 

something like:

RED = reversed
YELLOW = charging
GREEN = charged. 

I have dual npn chips that are handy. 

I'm used to charged = off so it wouldn't bother me if 'green' was 'ready' and 'off' was charged.. but maybe 'dim' green was power on..

what is the mechanism that kills the chip if bat is reversed? 

-awr


----------



## djpark

I tend to go on a simpler way to display the led -- 3 independent leds in this case.

green - power on
blue - charging
red - reverse cell

If you want to be fancy with bi-color led, you can monitor the charge pin voltage and determine the charging current as % of the max constant charging current programmed, and display leds according to the charging current with different color or pattern.

1) red blinking - trickle charge (10% current)
2) red firm - constant charging stage (or above 90% current)
3) orange (red + green) firm - constant voltage charging stage
4) orange blinking - near completion
5) green firm - charge completed
6) green blink - no battery

Alternatively using a single color led (say blue), set the led output to 1 Hz PWM with duty cycle according to the charging current ratio. So during constant current charging stage, it will be firmly lit and during the trickle charge, 0.1 sec on and 0.9 sec off. Likewise for 50% charging current during the constant voltage charging stage, 0.5 sec on and 0.5 sec off.

Another $0.02 consultation.

Have fun!

-- dj


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## andrewwynn

hey i really like those two cents. I was going to use blue in the nano chargers. but YOUCH didn't really want to buy $100 worth of 5mm LEDs.. 

I like the idea of green blink for 'ready to go'.. and green solid is 'go'.. i think i'll be happy with yellow for charging... but i really like the progressive charge..

I'm thinking of this: how about a segmented LED.. where the segments light up inversely proportional to current (so easy to get off the prog pin).. It would 'fill' like a gas gauge... i would just have to figure out a reasonable way to do it..i do have some pics and a programer in the house collecting dust.

-awr


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## djpark

I have been busy with POP driver and decided to take a short break to cool down the head by making a few chargers.

The basic design is still based on the same Linear LTC4054 single cell li-ion charger controller, but now it has more indicator and I thought I would make a new post, here.

Simple DIY Li-Ion Rechargeable Charger Part-2

-- dj


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## JamesWong

MrAl said:


> Hi again,
> 
> Here's the solution for one cell protection.
> We'll have to give the parallel cells more thought
> i guess. If they are wired into a pack there's no
> problem however.
> 
> Here it is:
> 
> 
> 
> 
> 
> 
> Take care,
> Al



I have modified this circuit. The new circuit will better protect reversed battery insertion.
When the battery is reversed, the LED will light up. And the current drawn from the battery is only the current for the LED, no excess current. So the battery will be safe when inserted for unlimited time.

This circuit has not been tested in real life, just been simulated by SPICE. Should be 99% work.


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## MrAl

Hi James,

Oh ok, looks good. I guess you simulated it too then? 
Build one up yet?


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## AilSnail

I made a charger using the TI bq24200, which also works. Followed the instructions in the datasheet.
I was specifically looking for some chip that would not fault when the input is a weak solar cell array (10x15cm). Haven't tried it with the solar cells yet.
With some other chips you can adjust the timer, and some have power good status output, which would help to let me know whether the battery is charged or it is just too low power to charge, or if there is a faulty connection.


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## petebarchetta

Does this particular chager have the ability to cahrge more than one cell in parallel? I have two laptop battery packs giving me 12 cells 18650's.
I'm building a chargeable cell of 12 in paralell and output of 2x6 cells giving a 12v output. i have the output sorted, but cant find much in the way of charging more than one cell at a time.
THe cheapo ebay units hoof out from usb, but charge 1 cell, i cant tell if they have the "smarts" in them to detect over charging or are just based in timed charge.

I also have a LI-ion charger for my bike lights 4x18650 cell in parallell driving two cree, but thats just a wall wart and i dont want to sacrifice that unit as its fully sealed.

any help would be good


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## xeeshan

hay, i cant download the designs and cant open the next page where you write click here, any Problem in my account or from your side, please correct me.


Thanks


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