48 volt BMS for 72 volt battery?

[johnnyz383]

I have a question...already have a 48 volt lifepo4 battery for my ebike. Adding more cells to make it 72 volts. Problem is that the bms only has 8 bms charging/monitoring wires (16- positive and negative) each pair going to 32 groups of cells...so each positive and negative wire wire monitors 32 cells...question can i increase each wire to 44 cells...(im adding 96 more cells), and in addition it would charge all these as well...

what do people think?

John

 

[DAND214]

Simple answer. NO!

But if find a why to do it, you will be a hero.

Dan

 

[dnmun]

a 48V BMS will not have only 8 sense wires. you should try to learn how they work first before attempting to use that BMS for a 72V battery.

 

[johnnyz383]

Thanks for the replies, but i havent heard a reason why...why the sensor wires cant be made to monitor 44 instead of 32..and yes i know how they work.


John

 

[dnmun]

then i don't understand why you are asking. i read that you had a set of 8 sense wires to use for a 72V battery. maybe there was something you did not say.

 

[d8veh]

16 sense wires is one per cell-string not two apart from the first cell, so you have 15 cells-strings of 32 cells . Each cell-string is 3.3v, so 15 x 3.3 = 49.5v. Each sense wire goes to a different monitoring channel on the BMS, so there's 15 chanels. If you want to increase the voltage, you need more cell-strings and more monitoring channels, so you need a new BMS. As the others have said,it's clear that you don't know how this works, so don't mess about with it until you have a good understanding or it might become expensive.

 

[johnnyz383]

Thanks for the replies...

John

 

[dogman dan]

Or you have 16 positive wires for 16 cell groups. The 17th and negative wire is the big negative wire, that also connects to cell number 1.

In any case a 16 s, 48v bms has 16 channels. A 72v lifepo4 bms would have 24 channels. So no way the same bms can monitor 24 channels with only 16 channel capability.

Just trying to clarify for other readers who might be still going what did that mean?

 

[alsmith]

Get either:
a 72V BMS rewire all cells, cell capacities should be the same

or a 24V BMS for the new cells, and wire the two batteries in series. Effective capacity at 72V will be that of the lowest capacity of the two batteries.