Cheap DIY 12S balance charger idea

I asked the producer before I ordered and they said I just need to write them when I placed the order and they will sent it for LiIon set up. I asked after they sent and they said they sent the right type. Let’s hope it is like this :sweat_smile: but AliExpress… you never know what you get :joy:

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@Andy87 Have you used your smart BMS yet? Does it work for you? I received mine about a week ago. Of course it’s 13S, even though the seller told me they would send 12S. :roll_eyes: Fortunately, I figured it can be easily configured for 12S. It’s a matter of shorting the BC3 and BC4 pins and configuring 12 cells using the PC app they provide. The seller even responded to my email and confirmed this is the right way to do it.

I’m still having some issues though. First, when I connect it to the computer and read the cell voltages in the PC app, the first cell is very flaky. It’s exactly the same problem as what’s shown in this video, so I assume it’s a bug.

I also tried connecting the BMS to my Android tablet using the Bluetooth module and that worked fine. However, I’m getting completely wrong cell voltages there. The first two cells appear as dead (around 0.5V) and the third cell voltage is flaky in the same way as the first cell in the PC app. The remaining 9 voltages look OK.

So the software seems buggy. I wonder if the MCU reads correct voltages and it only incorrectly communicates them to the computer/phone or if it has wrong voltages as well – that wouldn’t be good for cell balancing.

I had a similar experience with one there I reconfigured the series count. :frowning:

But I have multiple other units, unmodified, that work as expected.

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Unfortunately I didn’t have had a time before Christmas. Broken motors etc. took more time than expected. As soon as I have the bms installed i‘ll give you a Feedback

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@deucesdown Thanks for the info. Have you played with the UART connection to the BMS? I wasn’t able to get it working with Arduino.

I’ve not had a go yet, as the janky apps work well enough for me (barely).

But hey I’ve been thinking about that link you sent to Luuke’s stuff, with the isolated ac-dc 5v buck converters and TP4056 modules. I ordered up a bunch of stuff. I’m thinking, per channel, put in a voltmeter, TP4056 and a 5v dc-dc converter.

voltmeter something like this (There are 2 wire and 3 wire versions, and versions with a calibration pot. Gotta find one that has the required voltage range and has 2 digits precision):

This scary isolated buck converter running off mains voltage

And TP4056 modules. There are 3amp versions, also scary! I think 3 TP4056 in parallel, how is termination handled? (shoutout to @Hummie I think you found these first)

Hm or this, TP5000, 2A, includes heat sink. More likely to work than the 3A one.


Oo three amps. Nice find. Unfortunately someone said hooking 12 of these up to the battery to charge and balance at the same time would cause a short. Damn I want to do that. Who can tell me that’s a bad idea again @Blasto. Who else knows electronics? Maybe could add something extra?

If all the cells are inside a pack, you’ll need an isolated power supply for each.

you made me go through my old shit, this is what i found lol


I linked the isolated power supplies, under $2 per piece.

Im getting conflicting answers. Maybe linear supply vs switching?

You’ve seen this?

Isolated ac-dc 5v supplies, one per TP4056 charger.

It’s been done. It’s just crazy :slight_smile: I want one too.


This guy used a separate supply for each module. Hoping @Blasto explains how his buddy uses one supply for multiple. Smaller cheaper.

The cells are individual, not in a “pack”


Aha. Of course. Bummer. So need a supply for each cell. As said

I turned out the problems I had were due to the B- not being connected. I thought it’s the same rail as the BC0, but apparently not. Now it works like a charm. I started to work on intercepting the communication between the PC module and the BMS. It turns out the data sent by the PC module is exactly as documented here and that’s exactly what I used in my last attempt to connect an Arduino. I must have done something wrong. Will try again.

BTW, when I connect the charger, the voltage on the first and the last cell increases quite a bit. Without the charger connected, I have all cells pretty much in balance, say around 4.10V. When I connect the charger, all voltages go up a little bit, maybe to 4.15V, but the first and the last cell go much higher, like 4.25V. Measured by both the BMS and multimeter. Is that normal?

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If you hook up the charger without bms, does it have the same behavior?

yes 10char

Woohoo, looks like I’m getting somewhere. :slight_smile:




Sounds like a problem with the pack? Not the bms. As if the resistance of the series connetions varies (a lot?). Or weak cells in the first and last groups but that seems unlikely.

Ooh so exciting. 2 input vega coming soon?

That was my first thought, too. However, if that was the case, wouldn’t the cells get out of balance when charging/discharging? I do not balance the cells. I merely monitor the voltages. I only have the battery pack shortly, but there were at least 3 discharge/charge cycles and the cells apparently discharge/charge evenly. The first cell is slightly (~0.02V) higher than the other cells, but it has been like that from the beginning and isn’t drifting away. All other cells are within 0.005V difference.

I just needed something with display and UART and realized I have a fair amount of such devices on hand. :smiley: There have already been requests for displaying individual cell voltages on Davega. I said no to that, but I’m rethinking now. The problem is that there’s only one UART on ATMEGA328 and also not many people use the LLT smart bms. Instead, I’m thinking of making a simple I2C cell voltage monitoring module that I could hook up with the Davega I2C pins, which are still unoccupied. The module could be just a voltage divider and three ADS1115 on the same I2C bus. These are 4-channel 16bit ADC modules, so by using three, up to 12S would be supported. The resolution would be more than enough with 16bit ADC. I’m not sure how accurate these ADS1115 are though. I’ll probably buy some and do some testing.

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