Battery Wiring question

[tmstacks]

I'm currently running 10S2P Lipo (37v,10Ah). I bought two more of the same Lipo's with the idea of making a removable booster pack. I would like to parallel the two together, then run them in series with my current pack to give me 15s2P (55.5v, 10Ah). Does it work like this? Does 10S2P + 5S2P = 15S2P? Or would I have to rewire it so that it's two 15S1P packs paralleled together? (15S1P + 15S1P).

Thanks!

 

[dnmun]

you can do either way. you can parallel them at the cell level and then use a 15S BMS to handle both of them together or use a 15S BMS on each string and put them in parallel at the outputs.

if you put them in parallel under a BMS on each then you have to separate the two BMSs when charging at the P- terminal. the drains of the output mosfets on each BMS cannot be connected while charging.

i just bot three of these to build three individual 5Ah hobbyking lipo 15S packs from 6S packs. $19+$5 shipping for each.

http://www.bestekpower.com/48v15spcmbmspcbforlifepo4batterypack/PCB-D126.html

 

[tmstacks]

Can it be done without a BMS?

 

[dogman dan]

Sure, easier without a bms actually. One of the beauties of lipo packs is the way you can quickly, easily, and conveniently change both the size in capacity or the voltage of it. It's just depends on how you plug them together whether you have 36v or 48v.

IMO, the best way to wire it would be 2p first, then start series connecting to the voltage of your choice. But you could also do 1p 15s, if you wanted to use the lighter 1p- 5 ah pack at times for shorter rides.

What you will have to do, is get fixed in your mind what voltage is your new stopping point if you are only looking at pack voltage. If your stopping point was 36v when you ran 10s, It would be 54v at 15s. Both stopping with about 3.6v per cell.

What you can't do, is discharge your 10s till it's empty, then add the 5s boost pack and keep riding. This is obvious if you think it through, but if you just look at "stop at 36v" you could fool yourself that you could keep going after adding 18 more volts.

So if you were using the boost pack for less than the entire ride, you'd still need too stop when the 10s part of it was empty.

 

[tmstacks]

My thinking is 37v for the weekday commute, and 55.5v for weekend fun. But I have to lug this thing up and down 3 flights of stairs, so less weight during the week when I don't need the extra speed is what I'm aiming for.

I have a harness for 10S2P. I'd like to splice in the 5S2P, but not sure how to do it.

 

[tmstacks]

This is the schematic I drew up for what I'm trying to do. I'd like to run 10s the majority of the time, and 15s occasionally.
When I hooked this up on the test bench, I got a big spark and a melted connector. Not sure where I went wrong...

 

[wesnewell]

Look at your drawing again. If you don't see the problem, never touch another battery as long as you live. BTW, your drawing is really about as confusing as you could make it. Good thing you weren't working with a higher voltage. You'd have some holes in your fingers.