Is there a duel BMS?

[Rapidrob]

After a couple of months running my battery pack of 8 ea - 38120S batteries, I have a question?
My pack is two packs of four batteries for 13.8 VDC, each pack with a BMS. I tie the outputs together in parallel for 13.8 VDC with max current to power my mobile HAM radio which they will do for many hours.
Each pack is charged separately now.
Is there a BMS that has two inputs to charge / monitor both four cell packs at the same time?
I'm using an AIR8 charger.

 

[sunshine_eggo]

After a couple of months running my battery pack of 8 ea - 38120S batteries, I have a question?
My pack is two packs of four batteries for 13.8 VDC, each pack with a BMS. I tie the outputs together in parallel for 13.8 VDC with max current to power my mobile HAM radio which they will do for many hours.

So 2P4S, two cells in parallel, 4 groups of two in series?

What BMS?

Each pack is charged separately now.

If they are connected in parallel, I don't understand how they are only charged one at a time.

Is there a BMS that has two inputs to charge / monitor both four cell packs at the same time?

Monitoring - not at a price point that won't piss you off. Batrium works with a central controller (Core) and attached monitoring units (K9):



Even if you whittle away the extras for added functionality:

I'm using an AIR8 charger.

Again, I'm confused how you are only charging one battery at a time when they are connected in parallel.

 

[Rapidrob]

The terminal block wiring is disconnected when charging. Each four pack is charged as a stand alone when charging. When done charging, wired back into parallel.

 

[TacomaJoe]

Why not charge them together in parallel?

 

[GuyG]

The terminal block wiring is disconnected when charging.

Why?

 

[ghostwriter66]

The terminal block wiring is disconnected when charging. Each four pack is charged as a stand alone when charging. When done charging, wired back into parallel.

WHY not Just charge them all at once ... ??

 

[Rapidrob]

Good questions. With the AIR Charger, how will it "See" the 8 cells to balance them or will that be done by the two BMS's?
Will the two BMS's talk to one another when connected in parallel?

 

[SparkyJJO]

The charger connects to more than just the two battery cables? It uses another BMS comm cable?

 

[sunshine_eggo]

Good questions. With the AIR Charger, how will it "See" the 8 cells to balance them or will that be done by the two BMS's?
Will the two BMS's talk to one another when connected in parallel?

No, but the BMS on the battery that's not connected to the balance will shut off current to the unmonitored battery if there's a problem. You shouldn't need to balance charge each time.

What BMS?

 

[TacomaJoe]

I looked at the AIR8 charger and see that it has the cell voltage leads for balancing. Seems like that charger is intended for charging a battery that doesn't have an internal BMS. You are correct in wondering how it could keep track of 8 cells if you charge the batteries in parallel. I'm thinking one at a time for charging.

 

[Rapidrob]

OK, thank you. I thought I was missing something. I'll keep charging the battery pack as two single packs. Not a big deal, the "battery" is not used every day.

 

[sunshine_eggo]

OK, thank you. I thought I was missing something. I'll keep charging the battery pack as two single packs. Not a big deal, the "battery" is not used every day.

If you have have observed cells during a charge, and they all hit the peak at roughly the same time, there is likely no balancing going on. If you don't observe any actual balancing when individually charging the batteries, you don't need balance charging.

Provided you are attaching the charger to the protected side of the BMS, then no balancing is needed. If you are attaching the charger to bypass the BMS, then yes, you need balance charging.