How will a BMS-less battery die ?

[KirstinS]

Afternoon all

I have been waiting for my battery (36v 9ah bottle) to die for 6 months

I assumed that once I'd bypassed the BMS which had fried I'd get mere few weeks at best.

But it still it trucks on - charging to 42v and doing 15miles a day

I'm not complaining at all but interested to know how it will die - slow deterioration ? Suddenly ceasing to operate ? Unable to charge to 42v indicating an individual cell has gone kaput ? Or will a whole series go at once making it obvious ?

 

[Deleted member 4366]

There's nothing that should kill it. Sre you still charging through the BMS, in which case it should stay balanced? Ifyou've by-passed the charging as well, you need to check that it stays balanced, and adjust as necessary. The charger will cut off at 42v, which is the maximum 4.2v for each cell. If it went out of balance, you could have say some cells at 4.0v, but others at 4.4v to add up to 42v, which could damage them. Any more out of balance, could cause a fire.

so, if you've by-passed the BMS charging, you must check the individual cells every few charges. I've made an adapter that connects a 6S lipo charger to the cells' multipin connector so that I can charge and balance them. I just broke of 7 pins from this:
5x 40 pin Male PCB Header Connector for Arduino/PIC electronics project | eBay

 

[KirstinS]

Thanks but I'm afraid I don't get the last bit

Yes I had to bypass charging as well

The battery is 10s which is why 6s bit has lost me ??

 

[jerrysimon]

I think he means it enables you to check/charge up to six cells individually at a time i.e. first 6 and then last 4. Not sure but I am sure Dave will explain.

All my packs are home built with no BMS and I either split them into 2 * 6s or 2 *5s for ease of balancing.

I use cells that retain balance well without a BMS but do still need balancing after every 3-4 months of daily use to optimize their life. My oldest pack is nearly four years old with pretty much daily use.


Regards

Jerry

 

[Deleted member 4366]

Yes, you got it Jerry. The lipo charger can only charge or balance 6 cells at a time. It doesn't care which 6. Those cheap wattmeters can balance as well. Most of the cheaper lipo chargers charge through the power leads, which won't work because the voltage at the power leads (40v) would be wrong for the number of cells (6 or 4). You can still use them if you make an additional power lead connected to the top and bottom pins of the charger's balance cable, but you'd need two adapters - one for 6S and one for 4S.

 

[KirstinS]

Ah , gotcha

I have a IMAX b6 which I believe charges via main power cables not be balance leads

I will have to split power as you suggest

Thanks both - all makes sense

 

[KirstinS]

Hi there

Just wondering what the max amps I can safely put through the balance leads to charge is ?

2a I'm guessing as that's what the 8fun charger is rated at ?

 

[Deleted member 4366]

0.2C is the normal charge rate, so 2200maH x 4 x 0.2 = 1.76 amps.

The charger is probably 2 or 2.5 amps.

 

[KirstinS]

Thanks for confirming

Charger is def 2a but I am msnullay balancing via balance leads one s at a time at the moment

 

[KirstinS]

Ok I'm really confused

I bypassed the BMS totally - including charging through output leads . However , the cells are just not going out of balance. After 6 months of almost daily use !

How can this be ? I mean it's 10s 4p and every single S read at 3.75v after my usually commute

Happy - yet confused
Kirstin

 

[Deleted member 4366]

If you left the multipin connector in the BMS, then the balancing part will still work.