18650 Battery Management Systems for non-18650 use??

Hi all,

I'm hoping I'm about to get some ex-commercial 3.3v 300Ah LiFePO4 cells from an old solar connection. I'm hoping I'd be able to use them for a nominal 12V system (4S)... What I'm wondering is what on earth I do for a BMS here? Do I use a standard 18650 one? Do I need a custom one? Am I missing a whole slew of 'high capacity cell' ones?

If anyone would like to recommend, I'd like the maximum possible protection (voltage, temp, short circuit, anything else good?? haha!) since the system will be largely without supervision, ~200A discharge rate, and if there was some kind of connectivity (Bluetooth etc) for monitoring that would be swell too... Am I dreaming?

Cheers in advance!

the shape of the cell has nothing to do with the chemistry.

i would just buy a balance board and nothing else if you are going to use it in a car.

flippy said:

the shape of the cell has nothing to do with the chemistry.

Click to expand...

I don't really mean the shape, so much as 'a pack made of lots of small capacity cells in parallel, versus a single cell of high capacity'. I assume your response remains true here, however I can't afford to take the risk of not asking with cells that cost this much haha!

Any recommendations for a suitable BMS?

flippy said:

i would just buy a balance board and nothing else if you are going to use it in a car.

Click to expand...

Why's that, out of interest? Because the alternator should protect its output voltage anyway?

It will be used for an offgrid system with generator and solar input, as well as high and low amp outputs, so protection seemed important... Am I just paranoid?

phazaar said:

flippy said:

the shape of the cell has nothing to do with the chemistry.

Click to expand...

I don't really mean the shape, so much as 'a pack made of lots of small capacity cells in parallel, versus a single cell of high capacity'. I assume your response remains true here, however I can't afford to take the risk of not asking with cells that cost this much haha!
Any recommendations for a suitable BMS?

Click to expand...

BMs only cares about voltages and currents. and those are dependant on the chemistry.

check the bluetooth bms thread for a suitable bms for you. considering the currents you might want to do some upgrades.

phazaar said:

flippy said:

i would just buy a balance board and nothing else if you are going to use it in a car.

Click to expand...

Why's that, out of interest? Because the alternator should protect its output voltage anyway?
It will be used for an offgrid system with generator and solar input, as well as high and low amp outputs, so protection seemed important... Am I just paranoid?

Click to expand...

no, because a bms on a car battery will trigger when you dont want to. and the currents can go into the hundreds of amps discharge and well over 100A charge.

for offgrid i would first see if you can crank the voltage. go to a 24 or 48V system in order to lower the current and increase efficiency.

what have you already bought or is fixed?

flippy said:

BMs only cares about voltages and currents. and those are dependant on the chemistry.

check the bluetooth bms thread for a suitable bms for you. considering the currents you might want to do some upgrades.

no, because a bms on a car battery will trigger when you dont want to. and the currents can go into the hundreds of amps discharge and well over 100A charge.

for offgrid i would first see if you can crank the voltage. go to a 24 or 48V system in order to lower the current and increase efficiency.

what have you already bought or is fixed?

Click to expand...

Thanks for the prod in the right direction - the Bluetooth BMS thread does help but finding anything that could be delivered in days in the UK rather than months would be good. Any suppliers I should know about, even sans Bluetooth? By upgrades do you mean mosfets for higher current etc?

Can I confirm, do I need to find a 4S 200A BMS, or would any number of channels > 4 be fine?

Unfortunately I'll only be able to get 4 of these cells, and already have 18V panels and lots of 12V equipment, so it's 12V all the way!

Make sure that the BMS is made for LiFePO4 chemistry. The cell voltages are different.
Estimate the maximum current draw you will require and size the BMS to handle it.
Make sure the BMS has balancing capability.
Some BMS's can be used for a smaller cell count than they are capable of managing, but not all. Finding one that is made for 4s shouldn't be difficult.