Do you really need a BMS, or could a cell balancer and LVD be used instead?

A.Justice

Swears he didn't start that fire.
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I found THIS active cell balancer on Amazon, and was wondering if it could be used to replace a BMS, as long as I safeguard my cells in another way. I already use a separate LVD on a relay for my large loads, and was wondering if I could add a cell balancer to that, and remove my BMS. I have been thinking about upgrading my 4s2p, to an 8s, and was looking at BMS's, and realized that you can do the same thing that they do, with separate components. I keep my batteries inside, so there's no risk of freeze, and I have a programmable Victron SCC, so that should keep it from overvoltage. Is there anything I'm missing?
 

snoobler

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Pretty sure Will has a video on that unit or at least references it. That's not a active cell balancer. It's passive.

Terminology-wise, I think you mean you have a 2P4S battery. 4S2P would indicate you have two separate 4S batteries in parallel.

LVD/HV limit on battery voltage does nothing to protect individual cells if they are out of balance.

A BMS exists to protect individual CELLS. You wont' have that ability.

Can it be used to manually monitor and balance a battery? Yes. Does it serve the same function as a BMS? No.

It's a monitor and a balancer. YOU become the BMS in this case.

$70 more for an overkillsolar BMS with bluetooth. Seems a trivial amount to get legitimate BMS function for expensive LFP battery.
 

A.Justice

Swears he didn't start that fire.
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$70 more for an overkillsolar BMS with bluetooth. Seems a trivial amount to get legitimate BMS function for expensive LFP battery.
It is in fact a 2p4s, my mistake. Makes sense, I'll just grab a BMS. Thank you for the reply, much appreciated!
 

zorlig

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Mar 12, 2020
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You want a simple bms for low voltage cut off regardless. An active balancer can do well on a charge because a cell jumping in voltage is going to slow down the constant voltage charge rate significantly. That doesn't work on a discharge though, the lower the cells go the MORE amps they pull, so you really do need a bms to cut the current.

I'm using daly bms at the moment due to the choice of understanding inverter (72v)
 
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