Hello,
I was thinking about adding a 250w 10A dc motor to a bicycle, so i needed a battery pack. I was wondering if it would be possible to get a 12v 15A battery pack, and add a step up converter to make 24v? Would it work? What would be the difference from having a 24v 15A battery pack?
thanks
If your proposed motor is 250 W with a 10 A current draw, then presumably it is expecting 25 V (since 250 W / 10 A = 25 V).
If you draw 10 A from a 12 V battery you will have 120 W (since 12 V x 10 A = 120 W). This is about half the power needed. If you had a perfect converter that could step the voltage up to 24 V without losses, you would have 24 V and 5 A available (since 120 W / 24 V = 5 A). To get 10 A you would need 12 V and 20 A.
Since a 12 V, 20 A battery will weigh exactly the same as a 24 V, 10 A battery there is nothing to be gained from the step up converter, other than adding extra weight and increased power losses.
You should look for a battery pack of the right voltage for the motor. Put two 12 V, 10 A batteries in series if this works out to be more convenient.
How big the batteries need to be depends on the expected running time and range of the bicycle. Battery capacity is measured in amp-hours. So for instance a 20 Ah battery could supply 1 A for 20 hours, or 5 A for 4 hours, or 10 A for 2 hours (theoretically).
A convenient source of suitable batteries might be the lithium battery packs for hand-held power tools. They come nicely packaged in a robust plastic enclosure with all necessary safety features and matching chargers off the shelf. The motors from such power tools might even be good motors for electric bicycle applications. I even wonder if anyone has built such a thing? You could just plug a freshly charged battery into your bicycle and off you go, while another battery sits at home recharging.