4S LiFePO4 as a 12V system

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ZeroEm   10 MW

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Location: San Antonio, TX

Re: 4S LiFePO4 as a 12V system

Post by ZeroEm » Nov 20 2021 10:40am

Now i'm hunting a 12V BMS, 4S lifePo4 3.3v.
Not that they are hard to find. Don't want to buy something that will have a short life span. Don't need any advance features just something that will protect the battery from abuse from me.

Played with the idea of not using one. Now realize that a BMS should cut off current if one Cell group drops to low even if the battery shows that it is not drained. Don't want to over charge a Cell group either. Will not really depend on the BMS to balance them as don't like to charge to 100%.

Don't really want a high end smart BMS over a $100, something in the lower end that will detour disaster.
2019 Performer E-Trike
2013 Nissan Leaf S 7 bars 331.5w/KM

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spinningmagnets   100 GW

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Re: 4S LiFePO4 as a 12V system

Post by spinningmagnets » Nov 20 2021 12:29pm

I'm watching the developments with "drain down" cell balancers. When a 14S lithium-Ion pack gets fully charged to 58.8V, a "dumb" charger would put one cell at 58.9V and another at 58.7V...and that's one of the reasons I charge to 90%, because of the variations in mass produced electronics.

So, I charge my 14S packs to 57.0V...and hopefully the BMS actively drains and charges the cells to the same voltage. A drain-down cell balancer simply drains the higher cells to the lower cells...or...drains the high cells to a resistor load.

4S LiFePO4 packs would be one of the first products that would sell well...

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ZeroEm   10 MW

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Location: San Antonio, TX

Re: 4S LiFePO4 as a 12V system

Post by ZeroEm » Nov 20 2021 7:58pm

I plan to balance the cells, could get a balancer but need to tend to my trike first. It may get a cell balancer first. My home back up will get left overs. Thought about going with out a BMS, as I learn think both a BMS and cell balancer is needed is this over kill?
2019 Performer E-Trike
2013 Nissan Leaf S 7 bars 331.5w/KM

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