Battery Hookup 48V system balancing after the fact...

[Darren Orange]

Hey Everyone,

I figured I would post this question about my battery system.

I have 4 complete 16S 100amp hour batteries built using Battery Hookup Modules. I but them together added a BMS and started using them...well I did not balance anything and they did not come balanced. So after a while I was noticing issues with capacity and early cut off at the bottom and top of charging. So I got a balancer.
You can see my video on this here.

So if I go from 54.4V down to 48V in the pack I am seeing right around 102-103 amp hours per pack where as before 54.4V down to 47V I was only seeing about 96 amp hours. and I'm not hitting any BMS low cut off or anything. I am seeing some crazy stuff happening at the top still but I figure that is normal as you get close to 100% and close to 0%. Obviously I could likely run it lower an I will test that down to 45V and see even more over the rated amount.

So should I be happy with more than rated capacity from 54.4V to 48V does that seem pretty well balanced? It is hard for me to fully tell as it seems that the pack goes out of balance at near 0 and near top 100% so thats normal?

Sorry if my question is not super clear I just wanted to confirm that I've had success fully balanced everything. Thanks!

 

[sunshine_eggo]

Hey Everyone,

I figured I would post this question about my battery system.

I have 4 complete 16S 100amp hour batteries built using Battery Hookup Modules. I but them together added a BMS and started using them...well I did not balance anything and they did not come balanced. So after a while I was noticing issues with capacity and early cut off at the bottom and top of charging. So I got a balancer.
You can see my video on this here.

So if I go from 54.4V down to 48V in the pack I am seeing right around 102-103 amp hours per pack where as before 54.4V down to 47V I was only seeing about 96 amp hours. and I'm not hitting any BMS low cut off or anything. I am seeing some crazy stuff happening at the top still but I figure that is normal as you get close to 100% and close to 0%. Obviously I could likely run it lower an I will test that down to 45V and see even more over the rated amount.

So should I be happy with more than rated capacity from 54.4V to 48V does that seem pretty well balanced? It is hard for me to fully tell as it seems that the pack goes out of balance at near 0 and near top 100% so thats normal?

Sorry if my question is not super clear I just wanted to confirm that I've had success fully balanced everything. Thanks!

A proper top balance won't go out of balance at 100%, but may go nutty at the bottom. An active balancer throughout is only as effective as the ACTUAL current it can balance and the amount of current you use, so you may wonkiness at top and bottom. It will be more wonky at higher currents.

 

[Darren Orange]

A proper top balance won't go out of balance at 100%, but may go nutty at the bottom. An active balancer throughout is only as effective as the ACTUAL current it can balance and the amount of current you use, so you may wonkiness at top and bottom. It will be more wonky at higher currents.

Fair which is what I kind of expected, the behavior can kind of jump around and its hard to tell if there is a problem or not. So I guess I should just assume if I can get >100% rated capacity things are pretty good.

 

[offgriddave]

stupid question... but why can't balancing be done by just disassembling the batteries and hooking them all up in parallel, and leaving it overnight?

I was thought that is how you would do it.

 

[Darren Orange]

stupid question... but why can't balancing be done by just disassembling the batteries and hooking them all up in parallel, and leaving it overnight?

I was thought that is how you would do it.

My packs are kind of built and more or less not meant to be taken apart without a massive amount of work. I could in theory do that but the amount of work involved would be profound.

If these where the other cells not the battery hookup cells it would be largely easy. My goal was to use the active balancer to get it close and simply allow the BMS to slowly improve it if it gets out of wack. Regardless I can hit 54.6V without the BMS cutting anything off.

 

[offgriddave]

Glad you bought the battery hookup. They look like a great deal. How much did you end up paying for batteries + BMS per kilowatt?
Do you have a picture of inside of the tote or individual unit?

 

[sunshine_eggo]

stupid question... but why can't balancing be done by just disassembling the batteries and hooking them all up in parallel, and leaving it overnight?

I was thought that is how you would do it.

See this thread:

Paralleling LFP cells at rest to "balance" them

Hypothesis: Paralleling cells at rest does almost nothing beneficial. While voltages may be equalized, their states of charge remain dramatically far apart. I decided to do an experiment. Take two CALB 40Ah LFP cells. Fully charge to 3.65V Fully discharge to 2.5V Charge ONE to 3.65V Let them...

diysolarforum.com

While voltage is often emphasized during balancing, it's not what matters outside the context of state of charge.

Balancing is the act of setting all cells to the exact same state of charge. This can only be done at 3.65V (full) and 2.5V (empty).