Extra 12v battery in series ???

[mylo]

Hi' i am thinking of adding an extra 12v30ah pack in series with my 60v 25ah pack, i have made the 12v pack 30ah, so in theory it's voltage won't drop down low before the 25ah 60v pack does, the packs are identical lifepo4 cells 26650's. Have any of you had any experience in doing this or might it not be a good idea :? My wheel is an hs3540 and a 24fet 2000w 60/72v controller, i also have a ca fitted. If this is possible would there be a best way to wire it in series, ie small pack on neg lead then to controller or the positive.

Look forwards to you guys for some advise

 

[made_in_the_alps_legacy]

Hummm... I went through that story :

i have made the 12v pack 30ah, so in theory it's voltage won't drop down low before the 25ah 60v pack does

are u sure? in series, the current flowing through the booster pack (12v) will be the same as the 60V pack:
2000W/72V = 28A
30Ah in series of 25Ah : both packs voltages will drop low in about an hour at 2000W,
maybe you meant that the LVC of the 25AH pack BMS will kick-in first ? sorry if I misunderstood

this being said, I think it's a quite consistent lay out what you are planning, unless there are other things I am not considering

 

[veloman]

As long as you have something monitoring all the cells, you are fine.

 

[granolaboy]

I'm going to be doing basically the same thing in the next couple of months (once my bonus from work hits my bank account).

I'm going to connect the packs in series, and use big fat diodes to protect against one of the bms's tripping and the other seeing full reverse pack voltage.

 

[mylo]

That looks like a good idea