Battery type and power

[ryanshane]

For the moment i am using a cyclone 24v cyclone 250w motor. For battery power, im using two 12v lead acid batteries.

I've noticed that e-bike dealers who want to make a sale, have tried to suggest to me that a 12v liPo battery will somehow result in a greater level of torque and top speed from my actual electric motor, compared to lead acid batteries.

Is it possible that there could be a correlation between battery type and motor performance, when the specifications are the same (24v delivered by either 1 liPo battery, or two lead acid batteries, both combinations having the same amp hours), or is it more to do with the fact that as the liPo battery discharges, it doesn't lose voltage as quickly or steeply as a lead acid battery?

 

[Ian]

I think, if the voltages were the same it's very doubtful that Li-Po batteries would actually give better performance than LA types other than the performance gain from the considerable weight saving, however the voltages will not be the same.

The voltage of Li-Po cells is rather different to that of LA, nominally 3.7V which is awkward when a 12V battery is required. The actual voltage starts at 4.2V when fully charged with a fairly linear fall off to 3.5V when almost discharged, as opposed to LA with a range of 2.2 to 2.0V. Therefore a 4 cell Li-Po battery would have fully charged voltage of 16.8V as opposed to the 6 cell LA battery's 13.2V. It could be this higher voltage giving rise to claims of better performance, however if the "12V" Li-Po battery had 3 cells (12.6 - 10.5V) then it's performance would be inferior.

A single 24V 7 cell Li-Po battery(29.4 - 24.5V) would be closer to two 12V lead acids, but would still have a higher voltage.

These days very few suppliers offer Lead Acid batteries for e-bikes, it normally being considered outmoded technology due mainly to weight and size.