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Discussion Starter #1
I am having a hard time selecting the proper bms for my 32650 lifepo4 build 27s18p, 97.2 when fully charged and 300A discharge current peak for a 10kw motor with 30kw peak. I have little knowledge about the charger as well, but I understand the power balance current is related to bms-charger? will one BMS fit this build? or should i divide my build in 2, 3 or 4 battery packs? I really need some guidance on how to select the bms, for the charger, one with 25A charge current and 110v i have read is good...
I am planning on buying a good quality BMS from alibaba, aliexpress
the battery is a 32650 3.2nominal voltage, planning on a 3.6 charge and a 2.5 discharge
 

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Hi,
First, you need to know the job of the BMS.

A BMS is needed to make sure that no cell goes too high or too low, and alert you or shut off power.
When charging, if a cell goes too high it can explode.
When discharging, if a cell goes too low it'll die (but quietly).
So charging is where the BMS is most important, because it's for safety.

Try not to run the discharge power through the BMS. Use a voltmeter and when the pack gets low, go charge it.
Charge power should go through BMS so it can be shut off if a cell goes too high.

No idea about charger, anyone else have ideas?
-Isaac
 

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No need for charge current to go through the BMS, it can cut at the charger switch or its input with a contactor.

Besides cell-level HVC and LVC there also needs to be OCP and against shorts, could just be fuses.

And balancing cell-level voltages, dozens of philosophy and device choices there too.

Not a straightforward topic.
 

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No need for charge current to go through the BMS, it can cut at the charger switch or its input with a contactor.
This is just how the cheapest e-bike style BMSs handle HVC (and LVC too) so it's easy to implement :)
They've got a bunch of MOSFETS inside which are supposed to carry charge current and limit discharge current.

Actually you could use the signal for the MOSFETS to fire an optocoupler which could cut charge/discharge power (they are of course tied to the pack voltage, so the signal needs to be isolated).

-Isaac
 

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Discussion Starter #6
Ok, I discovered active balancers, BMS with passive balancing, BMS with active balance but only 14-24s :( so I was thinking my option could be:
1.BMS with passive balancing (the seller will shout down the passive balance) + 2 active balancer 14s
2. x2 BMS with active balance
3. Just use the active balancers and be my own bms, although i dont know how to avoidc overcharging the battery pack

300a 8s To 32s Ant Bms 24v 36v 48v 96v Ebike Li-ion Lipo Lifepo4 Lto Lithium Battery Bms Bluetooth Balance Pcm Pcb With Screen - Buy 4s Bms Lifepo4,21s Bms,Ant Bms 24v Product on Alibaba.com bms with passive balance
https://us-icbuim-file.oss-us-east-1.aliyuncs.com/file/40638c9b9bc185506215f6e2a2705ab6.pdf?Expires=1595711198&OSSAccessKeyId=LTAIxlzvmECyZvmX&Signature=cVESA744AGIZ3TxJVWQk7KcoHbs=&response-content-disposition=fileName=new BMS bluetooth Manual.pdf bms active balance
7s Li-ion Lifepo4 Lithium Battery Active Equalizer Balancer Energy Transfer Board Bms 1.2a Balance - Buy 7s Bms,Lifepo Bms,Lifepo4 7s 1.2a Bms Product on Alibaba.com active balancers

I also have concern, if stacking the lifepo4 32650 cells, will make the cells at the bottom of the pack crush due to a lot of weight, the weight of the battey pack would be around 87kg! that is why I was considering if it is good idea to better divide that battery pack in 2
 
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