Electric Bikes - why more volts?

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sevenhills
11-03-10, 05:06 PM
Hi

I have seen people posting about moving from 24v upwards to 36v and even 48v. Why are more volts better when most cars use a 12v battery? It would make things cheaper just to use what is already widely available, with batteries and lights.
So why is a 12v battery ok for everything from cars to minibuses, but not electric bikes?

S

rscamp
11-03-10, 05:16 PM
P=IV

Current is high at low voltages for the same power output.

Speed = Kv X V

Motor RPM is higher.

Maximum efficiency is achieved at a higher output power level.

Energy = Capacity X nominal battery voltage

More energy stored with a higher voltage battery
Sangesf
11-03-10, 05:20 PM
The 12v are for the accessories in a car like radio, lights, etc and not for running the car. In a car is an alternator which is "started" by the 12v battery and then on e the car is moving the alternator, recharges the battery.
The other voltages (24, 36, 48) you hear people talking about are for running the motors on the electric bikes and not the accessories.

sevenhills
11-03-10, 05:27 PM
A 12v battery starts quite big engines, I dont get all the "Speed = Kv X V", but the "More energy stored" is not the case. Because my batteries are 2 x 12v batteries.
Sangesf
11-03-10, 05:41 PM
"Starter Batteries" are just that. They provide huge amounts of energy for a very short time (about 5 sec). You can not "deep cycle" those kinds of batteries or they will die within a few recharges. They are also much larger than normal deep cycle batteries.
Storage capacity does not equal power over time.