Thread: How to make a mini generator??

1. Originally posted by Dima:
<STRONG>
Isn't 16v @ 10A is 160W? This is 0.2 HP... </STRONG>
Yep, it is. I'm an idiot.

Anyway, now that I've demonstrated my stunning lack of ability in mathematics, I will talk about the generator....There are several problems with this:

1. Engine is hard to start...I've played with these engines before, and it usually takes me a few minutes to get one going...Thi smay or may not be a problem.

2. Weird fuel. Won't run on regular gas...Might run on deisel once it is warmed up, but you will need to mix in oil.

3. High RPM. These engines run extremely fast to make so much power from such a small size. You will need extreme gearing to bring it down to a useable 3000RPM or so.

With that said, I'm not sure if a 0.5 HP engine will be able to drive an alternator producing 10A...The inefficiencies of the alternator may be too much for it...

2. Skinnyboy,

Use some high RPM high load DC motor. Like a RC car motor. If you can find a DC motor spec'd for the gas motor's RPM, great. If not the gearing for that high of RPM will need to be pretty good, although maybe you can use a gearbox out of a gas RC car? Use a flexible coupler for the DC motor shaft connection.

Hook the leads of the DC motor to a gel cell battery through a switch.

Use a SMPS PWM IC to output a PWM signal to a RC servo motor. Connect this servo to the throttle control. Set the throttle to only go down to idle, and you'll also need to limit the max RPM somehow I'd guess.

When you need to start it flip the switch. This will use the gel cell to start the motor, and when it gets going, it will self regulate with the PWM IC.

The DC motor efficiencies should be pretty good I'd think, although I'd shoot for 50%. You'll probably need to heat sink the motor, maybe put a fan on it. A fan would be great for the gas motor, as it is used to moving air across it's fins. Also you'll need to find the right DC motor winding for your application.

You could even come up with a glow plug circuit, and auto start/stop.

Just some crazy ideas, who knows if any of them will work..

Presslab

3. Originally posted by SkinnyBoy:
<STRONG>I would like to make a small generator able to give about 16volts @ 10amps, and power it with a small constant speed model airoplane engin, would this be possible??</STRONG>
Skinny,do you want this for your PSU with linear regulators? That's why u need 16v?

4. Aaron is right,
motors, designed and winded to work like motors are not the most efficient alternators. Considering that a stock automotive alternator, that was designed to be an alternator, has an efficiency somewhere between 40-60%... you get the picture.
Presslab,
Do you think that the most powerfull RC motor has the torque to crank an engine through the gearbox that is needed to reduce the engine's RPM? Have you ever seen how big the motor of a starter is?
And yes, diesel is an (cheaper) alternative to glow fuel, if you can find a conversion kit for your engine, and you loose the need for glow plugs and their power supply.

5. Presslab,
Do you think that the most powerfull RC motor has the torque to crank an engine through the gearbox that is needed to reduce the engine's RPM? Have you ever seen how big the motor of a starter is?
How much torque will it take to turn over a small engine? I don't really know for sure. I have seen how big starter motors are, I own one.

The better RC car motors can put out 1.5in/lb of torque and will spin at 20,000rpm. RC gas engines will spin at 10,000 to 30,000 rpm. So a gearbox might not be necessary. It would be easy to measure the starting torque of a gas engine.

A brushless motor would probably work better for this application but it is more complicated to work with.

Remember those vehicles that had the starter/generator setup? That's what I'm thinking of. A RC car motor might not be the best motor for the application though.

Presslab

6. if the motor is coupled to the engine with a 1:1 gear box/belt then maybe that torque is enough.
Even though theoreticaly electric motors have their torque constant through out their rpm span, practically they peak at certain rpm range.
Then agan, alot of energy will still be lost in heat (=low efficiency).

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