I recently bought 16 x 3.2V LiFePO4 cells, they were top-balanced before assembly into a 48V battery and then connected to a Axpert 5kVa Inverter/charger. The Axperts' settings are 55V max (3.44V per cell), 48V cut-off (3.0V per cell) and monitored remotely through a Pi with ICC. A 2A active balancer is permanently connected and currently there is a variance of about 0.085V or less between cells. Temps below zero are not expected. I've been told that this is not sufficient and that a BMS MUST be used and that an active balancer should NOT be connected permanently. Is this correct?

This is what my voltages look like throughout the day.

Thank you 87, what BMS would you recommend? From either in SA or from one of the chinese online retailers? Daly and JBD seem to be popular options.

Something like this: https://www.lithiumbatterypcb.com/product/13s-to-20s-li-ion-or-lifepo4-smart-bms-relay-solution/

or this:

https://www.aliexpress.com/item/4000445091437.html

or

https://e-glow.co.za/collections/battery-management/products/ant-smart-bms-8s-to-20s-150a

Edited November 4, 20214 yr by Graham

Then perhaps this: https://www.aliexpress.com/item/1005002608874846.html

Not many options out there where the shipping costs less than the item.

Quick question: if a cell goes out of range then does the BMS cut the power to the entire system? Which in my case would include monitoring and comms.

@Graham https://a.aliexpress.com/_mqFwX4q you can check this.

3 minutes ago, Raj35 said:

@Graham https://a.aliexpress.com/_mqFwX4q you can check this.

Thanks, 300A though is a bit overkill though, more than 3 x my inverters capability and 4 x the demand of the house.

Thank you, I really appreciate the advice and get what you're saying. The house is a off-grid holiday home so the demands are relatively low and not likely to increase in the foreseeable future (unless the lottery strikes). So 100-120A would be totally suitable from what I understand.

Looks like I will choose this one: https://www.aliexpress.com/item/1005002650532071.html in the 16S LiFePO4 UART option. Cost apparently R2200 delivered by Fedex.

52 minutes ago, Graham said:

Thank you, I really appreciate the advice and get what you're saying. The house is a off-grid holiday home so the demands are relatively low and not likely to increase in the foreseeable future (unless the lottery strikes). So 100-120A would be totally suitable from what I understand.

Looks like I will choose this one: https://www.aliexpress.com/item/1005002650532071.html in the 16S LiFePO4 UART option. Cost apparently R2200 delivered by Fedex.

100 Amps at 48v is 4800watts.  You should assume total losses in the inverter to be equal ~85% usable power so call it 4000 watt usable power.

Your battery needs to be sized to your systems maximum demand, at the very least. If you size it smaller than the system, it is the sign of an amateur.  I say this because what is preventing the system from being used up to 5kW?

Considering I paid R2700 for a 300amp BMS (with delivery), it just seems silly to try save R500 on the overall cost of the system for something like that.

The link is the 200A version.

39 minutes ago, Graham said:

The link is the 200A version.

Ah, I didn't click but yes that makes more sense.

Won't be choosing this shipping, me thinks 😅

@87 Dream - so with one of these BMS's, if one cell goes higher than 3.65V during charge, will it disconnect the entire system, charger and load (ie the entire house)?

And, if it turns everything off, when does it turn it back on again? If it does turn it back on again will the same thing happen again as soon as that cell goes high again, going into a loop? If it does turn everything off and not turn back on then apart from protecting that cell it is not going to be useful.

Edited November 7, 20214 yr by Graham