BMS: inexpensive programmable balance points?

timmy66

100 mW
Joined
Jul 11, 2016
Messages
42
Seems great being able to double or quadruple battery packs by charging to 4.0 or 4.1V per cell group,

but it seems almost all the normal (<$30) BMS'es out there don't balance unless going all the way to 4.2V -- and perhaps the bulk charging is not perfectly precise, and then a specific group is never even seeing the 4.2V level to trigger the BMS'es balance function.

It seems that having a configurable balance point (either a hard switch/jumper) would solve this -- otherwise, you'll unlikely be working the pack correctly and then stressing some cells more than others.

Ideally, you'd want the BMS to see the "bulk charge rate", divide this by the series count, and say : each cell group stops at this voltage, and properly starts saturation once getting to this, throwing the rest of the energy away or to the other cell groups. Balancing down via resistance seems stupid.

I see the bluetooth BMS that some have linked to ~$40-50 on AliExpress with a configurable balance point. Not all that fanciness needed for a normal battery though.

Thoughts?
 
Good question... pretty much every BMS I have looked into that was available (given that's not too large of a list) balances right around 4.2v. Of course I understand why balancing on the high end vs low makes sense, but would be great if that was adjustable. But a simple solution is to charge your battery to 4.2 (or slightly above to make sure it is balanced) once in a while, assuming you are using decent/good cells, they should not get out of balance too quickly. Just a ballpark number, but I'd suspect that if you did this every 10th charge, you'd probably be in good shape. Of course your best idea is to monitor your parallel groups individually, and see when it's necessary (or just get a good idea of how often it is).

On the other hand, as I mentioned I did not know of a BMS currently available that you could adjust that value... but I do know of one that should be instock next month I'm actually waiting for bestechpower to get in stock their programmable BMS models HCX-D328 (http://bestechpower.com/communicationbms/BMSD328.html) and HCX-D338 (http://bestechpower.com/communicationbms/BMSD338.html). Actually, I only care about the HCX-D338 right now... but I've been told both of them should be instock sometime next month. But I expect them to not be cheap... while I'm no expert.. I've heard a number of people recommend Bestechpower for High Quality BMS, though they were never mentioned as the most economical, but if willing to spend the money, very recommended. Sadly, ordering from them is not as easy for consumers looking for small quantities. BTW, those 2 models have A LOT more than just the balancing voltage as adjustable.

I'm very interested in hearing if anyone else has any they would recommend.
 
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