4=2x2: series then parallel, or parallel then series?

[viorel00]

I want to build a larger capacity higher voltage battery pack. To keep it simple, supposed I need a 2.4V 4000 mAh battery pack.

I could take 2 eneloop cells, put them in series (2.4V 2000 mAh) and then put 2 such groups in parallel to get me 4000 mAh

Or I could put 2 eneloop cells in parallel (1.2V 4000 mAh) and then put 2 suck groups in series to get me 2.4V

Which method is better? for now I want to take the cells out and charge them individually, but at some point I may try to charge the whole pack at once.

 

[Mr Happy]

Parallel then series. Join together any points in a circuit that are supposed to have the same electrical potential.

 

[kramer5150]

Parallel then series. Join together any points in a circuit that are supposed to have the same electrical potential.

Why is this better? Isn't the net result the same capacity and potential either way?

 

[old4570]

A = Simpler to assemble [ pack ] depending on how you want the pack configured , ??

So in the end , what space does it need to fit ? may dictate assembly method .

 

[Mr Happy]

Why is this better? Isn't the net result the same capacity and potential either way?

Which ladder is better:

This one?

Or this one?

 

[viorel00]

Thanks, keep the arguments for one method or the other coming!

I forgot to mention, 2x2 was a simplification, in fact the battery pack will end up with 10x10 (yes, 100 eneloops). Or I could just get a car battery, but then I have gases from charging I have to deal with....

I may end up with eneloops, even though nopt cost effective

 

[adnj]

It's just more effiicient to wire parallel then series. The batteries are conductors, taking the place of large gauge copper and you want the least amount of total resistance

 

[mvyrmnd]

I'm no expert in such things, but for what it's worth, any laptop packs I've stripped for 18650's have always been Parallel then series.

 

[old4570]

Thanks, keep the arguments for one method or the other coming!

I forgot to mention, 2x2 was a simplification, in fact the battery pack will end up with 10x10 (yes, 100 eneloops). Or I could just get a car battery, but then I have gases from charging I have to deal with....

I may end up with eneloops, even though nopt cost effective

End Voltage ?

If your after 12v , there are sealed 12v batteries , and no gas .

 

[fivemega]

I could take 2 eneloop cells, put them in series (2.4V 2000 mAh) and then put 2 such groups in parallel to get me 4000 mAh

Above method is 2S/2P and easier to build.

Following method is 2P/2S and better for equalizing each parallel group.

Or I could put 2 eneloop cells in parallel (1.2V 4000 mAh) and then put 2 suck groups in series to get me 2.4V

 

[gSPIN]

but at some point I may try to charge the whole pack at once.

if that's a requirement then that rules out parallel first since u can't reliably or safely fast charge NiMH in parallel.
the cell that peaks first will hog all the current leaving it's parallel mates unbalanced or worst case goes splodie from thermal runaway.
this isn't a problem for any chemistry that doesn't stoopidly decrease it's voltage once it's full.
for the most part u can get away with the getting benefit of overall lower pack resistance using buddy-pair, BUT ONLY ON DISCHARGE if ur using NiMH or NiCd.

the only other minor shortcoming on buddy-pair regardless of chemistry is that while it's true parallel is better for equalizing, the nature of physics being what it is, means that equalizing can only go down to the level of the weakest link.
i.e. if one cell fails short it will tend to take out the rest of the cells directly tied to it.
fortunately that mostly happens (tho not always) near the end of cycle lifespan so no great loss as the other cells were probably near dying on their own anyways.


as for which ladder is better?
i always ask 'better for what?', like which one takes up less space?
you've probably seen which ladder gets used up a mast or pole such as on a ship.

 

[mdocod]

100 cells?

Build 2 separate 10 cell packs. Each pack built with 10 D size LSD cells with 10AH rating. I'd suggest ordering a few extra cells and doing some cycle testing to break in and test each cell for capacity before grouping them into similar capacity groups for the pack.

Build a wiring harness of sorts that you can use to wire the packs in parallel when you need your 12V 20AH pack.

Buy a 2 channel hobby charger that can do 10 cell NIMH packs. Most of them can do even larger packs, so this won't be a problem. Pick one that can charge at a good rate, like 3-5 amps, with plenty of over-head power. Charge one pack on each channel of the charger.

That will only require 20 cells and 1 charger. The charging will be much easier, the reliability will be better, the complication of building the pack will be reduced dramatically.

Eric