Creating a battery that can be used as 5s or 6s?

[footloose]

Need advice, please.
Is what I'm proposing reasonable, or is it not?

Currently I have 3 hand-built battery packs, each consisting of 6 A123 cells in series yielding a nominal 19.8V / 2.3Ah.
They are then connected in parallel, creating a larger pack that yields 19.8V / 6.9Ah (6s3p config)
I use it to drive one of Adrian's Commuter Booster setups... works great.

I'd like to repurpose the packs for another build, but in a way that allows me to swap them back into Commuter Booster config easily.

Design goal of the new build is 49.5V / 2.3Ah.
Will be a very short range setup, but also very light if it works.

Could this be as simple as adding new + leads between cells 5 & 6 on each pack?
Voltage on the new leads would be 16.5V. (5s1p config)
Then connect the modified packs in series, yielding 49.5V. (15s1p config)

Effectively, in the new configuration cell #6 of each pack would become "invisible" to the circuit... but would remain available for use if I want to swap config back to original setup. If I want the higher voltage then use the original + lead... If I want the lower voltage, then use the new + lead.

Assuming this works... any issue with charging the 5s config simply by using the new lead, charging the 6s config simply by selecting the old lead?

If sensible idea, cool. If bad idea, I'll stop being a cheapskate just buy a new battery for new build :wink:

 

[dogman dan]

Just disconnect it at the break between 5s and the 6th cell. In other words, build 5s and 1s. Add the 1s in series if you wish, but don't carry it if you aren't using it.

 

[footloose]

Because each 6 cells are already built in a nice glued-together 2x3 block, I can't physically remove cell #6.

But I think you are right, the sensible thing is to at least introduce a physical break in the bus,
between #5 and #6, with ability to jumper #6 back into the pack if I want it in future.
Fortunately, the way I built them, I think that will be reasonably easy.
I'll give it a try!

 

[dogman dan]

That's info I didn't have. Then you can just add the single plug at the + of cell 5 and just tap into that for 5s. Just be careful about voltage, so you don't end up adding cell 6 at a different voltage, then put on a charger for 6s.

See what I mean, If you have 1-5 depleted, but 6 is more fully charged, you'd end up overcharging the 6th one if you put it on a 6s charger.

So I was thinking in terms of a complete break in the circuit, and always charging the 6th cell by itself. That would be the best method IMO. Then you never attach cell 6 to the other 5 unless all 6 are fully charged. With the complete break, you can charge both the 5s and the 1s at the same time with two chargers.

 

[footloose]

Thank you, it's good advice, I'm going to take that approach: 5s, plus an electrically separate 1s.

Believe I can wire this in such a way that it will be easy enough to go back and forth between configs.

The charging piece was worrying me. Makes sense to charge them independently as 5s + 1s, then hook them
together only when they are both at full s.o.c. After that, while they stay in 6s config, can charge
them as a single 6s unit.

Thanks again!