Bulk charging 3s cells

[whereswally606]

I have been thinking about bulk charging my lipo packs for a while now. I have loads of identical modded server power supplies to do it at the pack voltage in this case 18s. But to do this i need to current limit the power supplies as they will output upto 32 amps.

Anyway some crazy (or not) idea i had was to charge the lipo packs in parallel. ie. my zippy 3s 4000mAh 40C rated batteries. Of which in my pack their would be 12 (im running 18s2p). So my idea is create some study solid bus bars with the 4mm bullet connectors on to parallel all 12 there by giving a 48Ah 12ish volt battery. I figure that if this was hooked up to a single server powersupply that 32amps would be less of a problem (current limitwise) since it would be 32/48 ie a less than 1C charge.

I dont know enough at the moment to know why this is potentially stupid and near sighted of me and ive not tested it (nor will i till i get some expert feedback).

My guess is the danger lies at the end of the charge cycle but if i keep an eye on the voltages of the cells with my cell log and its clones bvm8s then am i going to have issues?

Thanks for reading hopefully it made sense.
regards Andy

[whereswally606]

Is no one going to have a stab at calling a wally a wally?

I dont mind critism but no comments in two days? was the idea that bad?

[SamTexas]

Is no one going to have a stab at calling a wally a wally?

Probably because no one understood your question. I certainly am confused.

I have loads of identical modded server power supplies to do it at the pack voltage in this case 18s. But to do this i need to current limit the power supplies as they will output upto 32 amps.

A) So you have a power supply that can output 75.6V (18*4.2) at 32A.

my zippy 3s 4000mAh 40C rated batteries. Of which in my pack their would be 12 (im running 18s2p). So my idea is create some study solid bus bars with the 4mm bullet connectors on to parallel all 12 there by giving a 48Ah 12ish volt battery.

B) You want parallel all your twelve 3s packs together to create a 11.1V (3*3.7), 48Ah battery.

C) Now you want to charge your B)battery with the A)charger, correct? If so here's what'll happen:

1) As soon as you make the connection the charger (A) and the battery (B) will try to equalize immediately.
2) The 75.6V charger voltage will drop SIGNIFICANTLY and the current will shoot up to possibly 6 times the rated current (up to 6*32A). What this means is that the wiring will get hot instantaneously and will possibly melt in a short time.
3) The A)battery voltage will rise quickly (if not instantaneously) and might very well exceed the MAXIMUM 12.6V (3*4.2V) in less than 30secs.

[whereswally606]

ok not very clear.

No I would use one server power supply ie 12v 32amps with all 16 3s batteries in parallel.

Im not so stupid that i would attach a 72v powersupply to a 12v battery.

basically my question is that the powersupply has no current limiting, so will it be okay to charge at the 32amps which is its max rating if the battery is big enough i.e. the 48Ahs

thanks for having a stab at it. There is obviously a bit of skill in writing a clear explanation.

[SamTexas]

basically my question is that the powersupply has no current limiting, so will it be okay to charge at the 32amps which is its max rating if the battery is big enough i.e. the 48Ahs

Perfectly ok. Just make sure that the battery voltage never gets above its max, 4.20V per cell.