Power in remote area's when operating portable is often a problem and not easily solved. Solar panels are too big and their usefulness depends on the weather, a wind generator is a little over the top and a small petrol generator is often too big for what it has to power.
A while back, i was given the engine end of a small 40cc petrol strimmer, very economical with fuel although a little noisy, i wondered if i could use that for something. I had in my junk box a small 3 phase motor of the type used in model planes and multi-rotor aircraft (an abandoned hobby) and wondered it these could be used as an alternator. They run at a pretty high speed, anything up to 30,000 rpm.
I fitted the motor shaft into the end of my Dremel drill chuck, held things down and switched on, definately producing a voltage but what about the current?
As the motor is 3phase, there are 3 leads coming out of it, i just connected a 55w car spotlight bulb across two wires and switched on. Taking the dremel up to full speed, 30,000 rpm blew the bulb! The bulb was rated at 55 watts, the dremel motor 170 watts. a quick calculation tells me that at 12v the current was just under 5 amps.
So what about a load on all three? 2 more spotlight bulbs were connected to the other wires in Delta connection and the dremel turned back on. Unfortunately, the load was too great for the dremel and all i could get with 3 bulbs was 9.8v
This was enough to tell me that i could use one of these brushless motors as an alternator. Creating a 1:6 drive from the strimmer engine i was able to get a little over 16 amps from this small motor. Next thing i will need to alter is the gearing. 16 amps load doesnt even start to slow the engine down and i could run the engine at a lower speed for better fuel economy and quietness. A better silencer would improve the noise problem.
Whats next. Ive plans to add an automatic speed control, one that delivers full power during transmit to save the battery, and then goes back to a much lower speed to trickle charge the battery.