High balance current BMS please help

Building a battery pack out of misc 18650 cells and need a BMS that can balance with a few amps instead of 50mA -_- I can't find anything at all. Needs to handle atleast 20s

Dont tell me its a bad idea, just want help with the balancer, thanks

http://www.bestechpower.com/balanceboard/JH-D131A.html

you can change the resistors and increase the current capacity if you really wanted to. just mind the limit of the transistors.

Typical BMS balancing circuits work by bleeding down higher voltage cells-banks.
Important to test for and remove self-discharging cells!
1 modestly discharging cell in 1 bank 20s20p will cause a voltage drop in 1 bank which will cause the BMS to discharge all the 380 (non-defective) cells not infected by self-discharge.

With no self-discharging cells, banks of equal capacity and similar IR, with moderate charge\discharge rates and voltages, there is no need for balancing! Cells and banks will return, identically, to starting voltages via bulk charging.

If your battery build requires substantial balancing, you have a severely defective build. Expensive BMS would be an expensive Band-Aid treating a symptom rather than curing the problem.

How much are you willing to spend? The BMS24T is a pretty badass system, but you need to buy a bunch of accessory items, like contactors, to use it. It can do 1.2A/cell.

It's about $330USD, that includes shipping.

BionicBlitz said:

Building a battery pack out of misc 18650 cells and need a BMS that can balance with a few amps instead of 50mA

Click to expand...

You need a charge transfer (bidirectional) balancer - either flying capacitor or flyback converter. The LTC3300-2 is a good multicell bidrectional balancer; you would need 4 of them for a 20s pack.

I strongly recommend testing and matching used batteries before assembling a pack from them. A BMS can't fix or lengthen the life of a poor cell, and as previously mentioned one bad cell can quickly make a whole pack useless with or without a BMS. Building from used cells is fine, and it's even possible to get several years of service if you put in the up front work to match up your best cells as well as treat your pack nicely with conservative charge and discharge. Throwing a BMS on a pack of just thrown together used cells that need and amp or two of balance current is like using a bandaid on a broken leg...ie a waste of time and money. Instead I'd suggest a minimum BMS for a cell-level LVC and a string of 1s chargers to top balance...and build the pack to be able to easily remove bad portions down the line.

Cell testing and matching procedure.
See - Bulk Capacity Testing