Batteries in Serial

[Mattjenkins1990]

Question for my own education.
Hypothetically if i build my own bike using a kit, got two 48v 10ah batteries and wired them up in series to double the voltage what impact would that have vs doubling the ampage (providing my controller and motor could take the extra voltage).

 

[flecc]

In series doubling the voltage doubles the speed in theory, though in practice it can be a bit less than doubling due to other factors like wind resistance.

In parallel doubling the amperage doubles the range in theory, but in practice it's usually a bit more than double. That's because the higher capacity battery is more efficient in delivering current, raising the performance a little too.
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[Mattjenkins1990]

So if i doubled the voltage with a 10 ah battery would the range decrease relative to using a 48v 10ah on its own ? Thanks for the prompt reply

 

[Deleted member 4366]

Your range would go to zero because you'd blow your controller apart if you doubled the voltage. Two 48v batteries in series go over 100v, which is more than enough to electrocute yourself, which is why the standards state 48v maximum for DC.

 

[Mattjenkins1990]

Good point, i personally have not seen a controller that would be able to handle that voltage, it was a purely hypothetical situation as to what would happen to range if i upped voltage substantially by wiring in series.

 

[flecc]

I'd say the range would decrease a little due to the other factors, like the increases in wind and rolling resistance at the higher speeds attained.
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[4bound]

Do you mean would two batteries go less far than one, or would they go less than two parallel? I would say somewhere between.
The extra power available would not always be required so you would reduce throttle ( compared with 1 battery) in order not to go faster than you needed, this would reduce drain on battery and so extend range. If you were able to cope with the power without throttling down then you would go faster for the same output from battery one and hence go further, so still increasing range.

On the other hand the greater speed would mean more losses so you would not achieve the range available to the parallel set up.

I don't think I have said that very clearly, but I know what I mean!

 

[flecc]

I understand too. I do mean less far than one battery alone if they were in series, but only if the extra speed is used. If you are not using the extra speed, there's no point in having the two batteries in series, adding unnecessary weight which itself entails losses.

That loss of range due to extra speed is because the capacity has not been increased at all, capacity determining the range. Since the travel would be at much higher speeds, the wind resistance increase would soak up additional battery current , shortening the range by more than the gain in speed could compensate.

Wind resistance increases by four times with each doubling of speed, so the loss in range capacity is greater than the gain in distance due to speed.
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