Chargery BMS balancing

cricketo

10 kW
Joined
Oct 23, 2018
Messages
523
Folks,

Has anyone been able to get Chargery BMS to balance reliably ? It seems like the BMS unit heats up so quickly that most of the time balancing is not active at all. I have BMS16T and BMS24T, and the first one does a bit better, but the second one gets hot just from sitting around (probably some weirdness with internal voltage reg, it's connected to a 22s pack)! Jason from Chargery is refusing to say what their expected duty cycle is, he just comically suggested to "put a fan" to it. Wondering what other people's experiences have been, but seems like the claimed 1.2A balancing current is nonsense if the unit is too hot to use it in the first place. I haven't seen any vendors to use "duty cycle" along the balancing current numbers though.
 
I would first fully balance the pack before plugging in the bms. Now use the bms to keep in balance. What cells are you using and where did you get them ?
 
Either your cells are mismatched

or past EoL

or not properly balanced manually before assembly

or you are going past the voltage shoulders in your usage patterns.

Balancing does not overcome the immutable fact that the weakest cell-group determines performance for the whole pack.

If you actually need an amp balance current on a regular basis, stop using a standard cheap BMS to do that job

get a dedicated active balancer, aka "non protective BMS" where the balance current does not vary with the delta.

And learn how to build / use your pack so re-balancing is only needed occasionally, ideally once a year is enough.


 
WRT to duty cycle, an hour or two should be the maximum needed, especially if top balancing.

 
Thanks for all the suggestions and alternatives. The pack is built using relatively large 80Ah cells (cells, not paralleled cell groups), so even the slightest mismatches in capacity result in the need to balance for a bit, especially when the charging current is on the larger side.

So for the other comment "hour should be enough" the fact is Chargery can't balance for an hour straight. Here is some simple math: 1.2A * 4.2V = 5.04W. 15 * 5.04W = 75.6W. So if in a 16S pack one cell is behind all others by whatever voltage threshold, and BMS tries to balance 15 of them at the same time, that's 75W right there. That's basically where I think the problem is - advertised current of 1.2A per cell for balancing is just unrealistic in practical applications. There will be some kind of duty cycle at play where say it will do 10% of that, but that means larger packs will never get balanced.

Again, I get the alternatives and I have them (active balancers, other BMS models) in other applications. I was just wondering if this problem came up for anyone else, and if anyone is aware of that percentage or duty cycle for the purposes of capacity planning.
 
I did not mean to imply the Chargery is right for the job, I meant use the right tool for the job.

80Ah is not large. Are you saying your charge rate is over 100A?

So long as LVC and HVC are based on cell level, differences in capacity can be ignored, so long as you accept that the lowest one dictates that of the bank as a whole.

Absolutely essential to actually see the cell level voltages accurately or you're flying blind.

Maybe if you atomize, manually parallel balance at 3.5Vpv or 4.15Vpc depending on chemistry , then re-assemble

Do not approach datasheet max cell V, CC only stop at 3.45Vpc or 4.10Vpc

Make sure your LVC is high, well above 3.0V or 3.4V isolated at rest.

And keep C rates low

then maybe the Chargery can keep up.




cricketo said:
Again, I get the alternatives and I have them (active balancers, other BMS models) in other applications. I was just wondering if this problem came up for anyone else, and if anyone is aware of that percentage or duty cycle for the purposes of capacity planning.

 
john61ct said:
I did not mean to imply the Chargery is right for the job, I meant use the right tool for the job.

80Ah is not large. Are you saying your charge rate is over 100A?

No, it's significantly less than 100A. I think 30A is the max I can do. But that BMS can't even keep up with a few amps it seems.

So long as LVC and HVC are based on cell level, differences in capacity can be ignored, so long as you accept that the lowest one dictates that of the bank as a whole.

Absolutely essential to actually see the cell level voltages accurately or you're flying blind.

Maybe if you atomize, manually parallel balance at 3.5Vpv or 4.15Vpc depending on chemistry , then re-assemble

Do not approach datasheet max cell V, CC only stop at 3.45Vpc or 4.10Vpc

Make sure your LVC is high, well above 3.0V or 3.4V isolated at rest.

And keep C rates low

Yup.


then maybe the Chargery can keep up.

That's basically the question in a nutshell: what can it keep up with :D
 
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