DIY Lithium Battery Balancer and monitoring (BMS)

According to DHL my PCB samples should be here today, so perhaps wait until I’ve got it working!!

Thanks might wait and that is an impressive delivery time, i nearly pulled the trigger on them this morning as well. Will wait a little while. Mind if i post some mods on your code to github as it would be great to get it to post into grafana.

Feel free to branch, as you can see it’s only bare bones code, going for another session on this tonight!

Gosh we really are doing very similar things!

In my case there are 8 series connected cells per arduino but the basic idea is the same.

I don’t know if this will help but my code to correct the inevitable measurement error using EEPROM to store calibration data is working very well so I have provided a link to a source code text file containing the functions to deal with the battery.

Any comments appreciated.

How bizarre I just spent a couple of hours writing EEPROM code!

My PCB’s have arrived, I ordered from (China) about a week ago, they made 10 boards, in white/black silk screen air-shipped with TNT to the UK in 8 days - cost £4.20 !!

That is crazy cheap!


I guessed you might be.

Thanks for the PCB info’

I have just ordered 10 PCB’s from allpcb for my cell balancer. These are 85mm X 70mm X 1.6mm 2 layer. I expected to pay about $5 each based on Stuart’s message but it was $5 total!!! Including shipping from China.



Thats what I thought as well - the boards appear to be good quality to. I couldn’t post them down the road for less than £4 let alone half way around the planet!

Sorry about the picture quality!

I have a couple of suggestions for your footprint problem.

  1. Don’t draw your own 3D shapes but import a validated 3D Step file from one of the open source sites and then lay this on the footprint you have drawn.
  2. Print the PCB 1:1 and put the physical component on the footprint you have drawn to check

I received a response from allpcb. They do not like Altium gerber file format. They require the old file extension formats of .gtl .gbl etc

The file content is RS-274-X so all I have done is change the file extensions for them.

I also suggested they indicate their preferences on their website.

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Thanks BrianD, I’m new to PCB design and the printing at 1:1 is a good idea. All the existing footprints I’ve used are from the KiCad libraries, but looks like I may have picked the wrong sized ones.

SOIC-8 instead of SOIC-8 Wide!

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Using other peoples footprints is not as dangerous as it was because you can validate the footprint against the 3D shape. However, the time it takes to check against manufacturers recommendations is comparable to making your own footprint and then you only have yourself to blame if it is wrong :slight_smile:

Another thing to watch out for is pin numbers. The SOT23 is probably the worst example. A lot of engineers have burnt their fingers on that one (including me).

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curious what are your prices you are paying for lithium cell for your power wall… I built a “power wall” i few years ago already- using these lithium batteries - and I had no issues with it so far

they are intelligent lithium batteries everything built into them… if you build anything that 48 volts and under a master BMS is not really needed as the slave BMS( found within the battery will handle everything ) all you do is connect the batteries together as you would a normal battery. if in parallel no need to connect the BMS cable if in series then connect the BMS cable and it keeps each battery in balance. - the run cycle is 2000 to 100% DOD If I remember correctly 6500 cycle @ 50% DOD

I checked my computer for old docs all i find is the master BMS doc

11LiFePO4 BMS user’s guide.pdf (287.9 KB)

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They look good - so far my PowerWall has been constructed from recycled cells, think I’ve spent about £100 so far.


I have recently self installed a couple of PV arrays so no FIT (current rates so low it did not seem worth the added cost of using an installer as I was able to get panels and inverter pretty much at trade prices). My ultimate goal is also to add AC connect battery.

Has any one found a regular source of recycled cells in the UK?


Hi Stuart, Did you order your boards before you split the design as it’s confused allpcb, did they also complain about a missing drill mask for you? I’m away from home at the moment but shall check the file i uploaded once i’m back.

Hi Colin, I didn’t bother getting the boards split in the end (just for this batch) but no problems with the drill mask - the file I used is on GITHUB.

You’ll need to speak to recyclers although in the UK its difficult as technically you need a waste carriers licence to trade in scrap.

If you look at the Facebook forums, Glynn and Kaspar are two UK people who have lots of cells for sale.

@Colin_Hickey do you think we should swap the connection daisy-chain cables to RJ45 sockets instead?

Small ethernet cables are very cheap to purchase and the sockets are around 50 pence - seems that a lot of the cost for my existing design is for the sockets!

Like this?

That could be a good idea, less fiddly when connecting also. More bulky but that wouldn’t be the end of the world.