Big Battery Kong 48V Problem COV CUV

[Collin ev/solar]

Good day all!

I am looking for some guidance. I have been helping my dad with his off grid solar system for a few months now. The short of it is, he has a Big Battery Kong Elite Max 48v that continues to go into cell over voltage (COV) around 53.5v and cell undervoltage(CUV) around 48.5v. I have confirmed the inverter settings multiple times with Big Battery. It is charged by solar at a max of 50amps up to a max of 56v. Big battery has sent me a new BMS and a new balancer. I installed them with now change. At the recommendation of BB I have tried to draw the battery down to 47v then charge to 56v which is difficult because i keep getting the COV and CUV. I have done this many times with no success. It is regularly Cell 1 that is the problem. The only next step i can think of is send the battery back and leave my dad without power for at least a month. Any suggestions would be greatly appreciated. See attached pictures. Also the percent meter is never accurate.

Thanks!!!!

 

[sunshine_eggo]

I hate Big Battery.

With cell 1 hitting full first and empty first, that means it's the lowest capacity cell, and it's limiting your capacity.

The question becomes, what is your actual tested capacity?

If you're meeting rated capacity, well, not much you can do.

If you're not getting rated capacity, is it bad enough for them to warranty it?

3.1-3.2V is also a relatively low state of charge - about 10-15% SoC.

This tells me that your battery may be undersized a little if it's actually consuming >80% of its capacity every day.

If the battery doesn't meet spec there is an alternative to not having power:

Robot or human?

Yeah. It'll suck, but some power is better than none.

 

[Collin ev/solar]

I hate Big Battery.

With cell 1 hitting full first and empty first, that means it's the lowest capacity cell, and it's limiting your capacity.

The question becomes, what is your actual tested capacity?

If you're meeting rated capacity, well, not much you can do.

If you're not getting rated capacity, is it bad enough for them to warranty it?

3.1-3.2V is also a relatively low state of charge - about 10-15% SoC.

This tells me that your battery may be undersized a little if it's actually consuming >80% of its capacity every day.

If the battery doesn't meet spec there is an alternative to not having power:

Robot or human?

Yeah. It'll suck, but some power is better than none.

Thanks for the reply. I am not sure what the actual kwh vs rated capacity is. The voltage in that picture is that low because big battery wanted me to get the battery that low to bottom balance the cells (whatever that means). At the end of the day the battery is normally around 60-80% SOC.

 

[sunshine_eggo]

Thanks for the reply. I am not sure what the actual kwh vs rated capacity is. The voltage in that picture is that low because big battery wanted me to get the battery that low to bottom balance the cells (whatever that means). At the end of the day the battery is normally around 60-80% SOC.

okay.

This model?

https://bigbattery.com/wp-content/uploads/2023/01/Spec-Sheet-48V-KONG-Elite-Max.pdf

It's clearly imbalanced at both ends, but since cell#1 is the trigger at both ends, it doesn't matter that it's imbalanced - cell #1 is the turd. I would expect that you're not going to get over 350Ah. It's important to establish the actual capacity. Repeat the charge/discharge and confirm you get 372Ah per the display. If you have a secondary means of measuring current, like a clamp DC ammeter, it's a good idea to confirm the reported current value.

 

[Collin ev/solar]

This is the battery today. Seems weird that the COV is on a different cell. The battery was charged from nearly dead.

 

[Collin ev/solar]

okay.

This model?

https://bigbattery.com/wp-content/uploads/2023/01/Spec-Sheet-48V-KONG-Elite-Max.pdf

It's clearly imbalanced at both ends, but since cell#1 is the trigger at both ends, it doesn't matter that it's imbalanced - cell #1 is the turd. I would expect that you're not going to get over 350Ah. It's important to establish the actual capacity. Repeat the charge/discharge and confirm you get 372Ah per the display. If you have a secondary means of measuring current, like a clamp DC ammeter, it's a good idea to confirm the reported current value.

Yes that’s the battery. I’ll let the cells hopefully balance over night so it’s fully charged tomorrow and I’ll discharge the battery. What should i discharge it to?