First I thought about using an car alternator for this, but have since found perhaps an even better alternative, namely high-end radio controlled helicopter motors. It turns out alternators weigh a lot and are clunky and heavy, while BLDC motors from modern RC helis are not.
So how would I go about finding the correct BLDC for my project? I got some help here and ended up with the following:
- Lead-acid batteries have optimal charging voltage of 13.8 to 14.4 volts.
- The GX25 motor has optimal RPM (RPM with highest torque) @ 6000 RPM.
- The GX25 motor has an effect of around 0.7kW.
With this as input finding a motor for our project is easily calculated as follows:
- Desired kv (rpmvolt) = 6000 rpm/14.4 volt ~= 417 kv
- Desired continuous effect is above 700 W. We will go with at least the double to put the least amount of strain on the generator.
- Desired continuous amp is 700/14.4 ~= 48 A
(disregarding all the voltage losses etc).
Next I just chuck these parameters into hobbyking's motor finder to get some alternatives, for example the Turnigy SK3 5055-530kv with the following specs:
Turns: 12TVoltage: 5~8S RPM/V: 430Internal resistance: 0.019 OhmMax Loading: 70AMax Power: 1750WShaft Dia: 6.0mmBolt holes: 25mmBolt thread: M4Weight: 378gMotor Plug: 4mm Bullet Connector
I must investigate this further to ensure that I don't go buying one of these motors that wont work because of some parameter I did not think of.