12v series connect not supported?

[Diemjoe]

I am wondering why some Lithium battery manufacturers support series connecting their batteries and others don't. I found this out the hard way with an mpp solar and 2 12v big batteries.

 

[sunshine_eggo]

The BMS must be able to handle the full series voltage.

 

[Diemjoe]

The BMS must be able to handle the full series voltage.

Thanks. That's a reason I can get my head around. Others do it so I am wondering what the decision factor is.

 

[sunshine_eggo]

Thanks. That's a reason I can get my head around. Others do it so I am wondering what the decision factor is.

cheap BMS vs. not as cheap BMS.

Limit risk due to most end users failing to properly deploy a 24, 36 or 48V battery using a 12V series string. Few folks realize that they need to fully charge each 12V individually and then in parallel before deploying into a series string.

 

[timselectric]

Just don't.
Buy the correct voltage battery for your system.

 

[GSXR1000]

The BMS must be able to handle the full series voltage.

I think this is the reason. yet any one BMS mosfets will only see one battery IE 12v so I can't really see how it matters.

 

[timselectric]

I think this is the reason. yet any one BMS mosfets will only see one battery IE 12v so I can't really see how it matters.

In parallel that would be true. But in series, each BMS will see the full system voltage.

 

[GSXR1000]

In parallel that would be true. But in series, each BMS will see the full system voltage.

no.. I you have 4 12v bms and you log into the BMS on each battery you will see ~13v... the only reference the BMS to positive is the balance leads..

 

[timselectric]

no.. I you have 4 12v bms and you log into the BMS on each battery you will see ~13v... the only reference the BMS to positive is the balance leads..

The BMS only reports for itself.
But the full system voltage must flow through it.

 

[TacomaJoe]

When things are working, each BMS sees its own voltage. In a series circuit (4 batteries and a load), each battery shows 12V and the load sees 48V. Now if you put a switch into the circuit and open it, then the load will see 0V. You can measure 48V across the switch. Same is true for a BMS that opens, the full voltage is across that battery.

 

[timselectric]

Yup

 

[GSXR1000]

When things are working, each BMS sees its own voltage. In a series circuit (4 batteries and a load), each battery shows 12V and the load sees 48V. Now if you put a switch into the circuit and open it, then the load will see 0V. You can measure 48V across the switch. Same is true for a BMS that opens, the full voltage is across that battery

well put .. I was only thinking when on.