DIY Arduino Lithium Balance Charger - Page 1
Forum section: electronics / projects

author: apaxhud
author_rank: Newbie
timestamp: September 06, 2015, 01:03:57 pm
content: Hello everyone. Recently I thought about designing a lithium balance charger based on Arduino Nano, something similar to Imax B6, but not as complicated as B6, so here is test version. I want you to look at the schematic and say if it's ok and if there is room for imporvement.I think I need to make 1.1V voltage reference, thus it will be more accurately. I need to change resistor values for this, not a problem.PS: The main goal of the project is to make it as cheap as possible, so high cost solutions are not acceptable.PPS: There will be a custom PC software to display all data (beside LCD) and for communication with Arduino via serial interface, that's why I needed Nano version (actually compatible with all versions).

author: metri
author_rank: Contributor
timestamp: September 06, 2015, 03:10:20 pm
content: Nice looking project.First the Atmega line have internal 1.1V reference voltage, so no need to produce it. Just call analogReference(INTERNAL); and then the ADC will be comparing to 1.1VI've used a lot of chargers, and the best ones charge each cell separately. The benefit is it scales to any number of cells and each cell get's a perfect charge. The alternate, charging the battery and keep bleeding off extra on faster charging cells is less efficient but functional.Since you have to make a PCB anyway, I'd put the Atmega on the main board, program it with ISP header and forget the arduino altogether. The bare bones for adding the MCU to the PCB is the MCU, 100nF cap, 16MHz resonator and a 10K pullup on reset. You can see the arduino reference designs for reference. This isn't desirable if you don't have access to parts. If you do, it does make it cheaper.I don't know enough about the internals of chargers to know if your design is correct or not. I hope the other info is useful. Good luck, sounds like a fun project.

author: apaxhud
author_rank: Newbie
timestamp: September 06, 2015, 03:58:43 pm
content: Well, there is not much difference between an simple Atmega and Nano except serial converter. I need onboard serial converter for PC com which will run a Graphical User Interface displaying all the charging data, settings and so on, bbasically the same info fomr LCD but easier to work with.For now I need to know if there are problems with hardare parts in schematic.

author: eas
author_rank: Frequent Contributor
timestamp: September 06, 2015, 08:33:50 pm
content: Quote from: metri on September 06, 2015, 03:10:20 pmIf this is intended primarily for charging RC battery packs, then charging each cell separately at a high charge rate isn't really practical. The packs have high-current leads for the pack in series, and then much finer leads to sense and shunt each cell.One advantage of this arrangement is that it avoids incurring the bulk and weight of having thicker leads to each cell when the pack is fullfilling its intended purpose, powering an RC aircraft of other vehicle.

author: metri
author_rank: Contributor
timestamp: September 07, 2015, 03:44:11 pm
content: Quote from: eas on September 06, 2015, 08:33:50 pmCell by cell chargers are popular and better for your packs. In theory very fast charging is hard on your packs so fast charge with reasonable currents. That's really beside the point. I don't recall seeing battery balance leads smaller than 22ga and on my big packs are 20ga. I could charge at 10A and be within acceptable limits and that's pretty fast for most packs. I personally charge at 5A most of the time. You are correct, you can put more current through the regular battery leads, I just think it's not as healthy for your packs and you can charge at a reasonable speed through the balance leads.I think the point is that the designer wants to do pack charging with balancing, not cell by cell charging. No problem, but I do dispute balance leads are too small for charging.Quote from: apaxhud on September 06, 2015, 03:58:43 pmIf the serial is important you can use the Atmega32U4 (Like the leonardo) and have USB without a second chip. I understand it's easier to just plug in a nano and the nano design is very good. Anyway I see you need schematic checking and I can't help with that.I wish you all the best with the project.

author: apaxhud
author_rank: Newbie
timestamp: September 07, 2015, 04:46:00 pm
content: Quote from: metri on September 07, 2015, 03:44:11 pmWell, Nano clones on ebay are cheaper than Atmega32U4 itself, that's all about it. Thank you.Also, Atmega32U4 is available only in QFN/TQFP package, but my plan is to make an easy to make projectI've started a topic on the Arduino forum also, and already received some tips and errors on schematic. Here is the link:http://forum.arduino.cc/index.php?topic=346070.msg2385693#msg2385693

author: metri
author_rank: Contributor
timestamp: September 08, 2015, 12:56:51 am
content: It's amazing how cheap those Nano's are on Ebay. You're right the Atmega32U4 is a bit pricey and they are a small package. I'll follow the project as it progresses. I'm very curious to see how it turns out. Good Luck.

author: cncjerry
author_rank: Unknown
timestamp: September 08, 2015, 04:45:05 pm
content: I built a high function charger based initially on a uno, went mega and then used a Nucleo with a TFT. Went back to the mega for some reason, can't remember why.After all that work incorporating temperature control, various charge currents, delta V, current monitoring, timing, settle and wait delays, etc,etc, a fan, I had about $50 in it and it worked great. Then I found a charger on ebay called an Imax B6AC with shipping was < $35USD. Fully programmable balanced charger for < $$35. 1800 sold.I learned a lot about battery charging in the process but what I found most interesting (setting aside battery life) was that temperature was the best indicator of charge. I had someplace numerous charts that mapped temperature, voltage, charge current and you could clearly see the peak easiest on temperature. LiPO batteries are different though, only was doing NiMH at that time.

author: apaxhud
author_rank: Newbie
timestamp: September 08, 2015, 06:43:10 pm
content: Imax B6 series are no accurate, so you either need to change 1% resistors to 0.1% ones, or to calibrate, reflashing the firmware, and you basicall pay for non well working product, which I find not reliable. With a DIY charger, you first of all, learn how this thing works, and do it with your handsand also is cheapier than products on market.

author: microbug
author_rank: Frequent Contributor
timestamp: September 10, 2015, 06:56:26 am
content: Sorry to break it to you, but the Imax B6 / Accucel-6 / Several other HK chargers are easily accurate enough to be safe and effective. Even replacing the 1% resistors in a B6 would likely cost less than building your own charger, which would be an educational but ultimately necessary exercise.

author: apaxhud
author_rank: Newbie
timestamp: September 10, 2015, 10:43:56 am
content: Quote from: microbug on September 10, 2015, 06:56:26 amIts well known that B6 series are not accurate. Replacing resistors + unaccurate charger, that's the cost, not only the resistors. Also, 1% resistors are in 0805 package, they are very small and need some experience to solder.

author: mos6502
author_rank: Frequent Contributor
timestamp: September 10, 2015, 11:03:39 am
content: The B6 can be calibrated, and there is an open source firmware:https://github.com/stawel/cheali-chargerThe B6 hardware is perfectly fine. You're much better off helping to improve the software, instead of trying to reinvent the wheel and trying to roll your own.

author: mikerj
author_rank: Super Contributor
timestamp: September 10, 2015, 11:36:30 am
content: Quote from: apaxhud on September 10, 2015, 10:43:56 amYou don't need to change any resistors, the resistor tolerance can be calibrated out through the firmware. I have a Turnigy branded B6 clone that I have used for years to charge all kinds of batteries (often used for balancing old laptop Lithium-ion batteries) and it just works. The only issue I've had with it were the tactile buttons becoming intermittent, but a set of new buttons cost a handful of pennies.They aren't super accurate devices for sure, but they are accurate enough to get the job done if calibrated correctly.I'd be very surprised if you could build a charger with the same functionality as a B6 for less than the price you can buy one (unless you already have all the components). Don't forget that the B6 already includes a buck/boost switcher so it can charge batteries higher and lower in voltage than the supply, has all the balancing circuitry, and includes discharge capacity testing.

author: mrshirls
author_rank: Newbie
timestamp: May 13, 2018, 12:21:52 am
content: Hey, any update on this project?