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Super old post bro. My method worked really well. I have managed 703rpm with a tin cam engine so don't try to sass on here mr newbie. I made the engine without plans and without true measurements(ruler) All by hand with zero knowlage of the science. I figured the displacer drop and cam throw distance, bent the wires, played with counter weight and presto more rpms than any predesigned unit or plan you can find.

Now you'v got to find if it has any power, Get a little DC electric motor, try and find one that normaly runs not too fast, some run at 5000rpm, others at 30,000 rpm, and make up some sort of pully system, big on motor , little on generator, start with say a 2:1 ratio, put an LED on the generator, and see if you can light it. A multimeter is quite handy. Ian S C

I thought about doing that actually but what confuses me if the "generator/motor" how can you tell if an electric motor will produce power in the opposite direction. Usually power is put in and spin is put out. I was thinking of building a larger version and using a car alternator.

Any small permanant magnet DC motor will generate if rotated, stick your tongue on the termanals, and turn the shaft(slowly), you can test if a dry cell has any power in it same way.
To drive a car alternator you will need at least 1hp, and be able to turn it over at 2000/3000rpm, I'v got one driven by a little Villiers 2 stroke of about 1hp, it will produce 250 watts continuous, if you put the load up to 400 watts, the motor starts to sieze up after about 20 miniutes, take the load off, let it cool a bit, then you can go again, the alternator is not too efficient. Ian S C

Well, if you put power in an alternator will it spin like an electric motor?

Insainhouserecords wrote:Well, if you put power in an alternator will it spin like an electric motor?

If one uses electronics to send appropriately timed pulses of current to the 3 different phase coils while at the same time supplying rotor power, an alternator can be driven like a motor. General Electric "electronically cummutated" motors are designed using this approach, but use permanent magnets on the rotor. I have one on a pole out front with blades attached.

R

An automotive alternator can run as a motor as theropod2 says, it needs electronics similar to a stepper motor, or like the brushless DC motors used in model aeroplanes. Ian S C

That is interesting. So, fixed magnet motor+spin=output but if brushless is more like and alternator than if seems that would work better. I guess scale plays a roll in why not.

Motor with brushes, DC output, brushless, AC output, or on the rare occasion if the motor had slip rings, it also would have AC output. Proberbly the most efficient would be a three phase alternator, but any small alternator looses some of its power if you require to rectify the output to DC. Ian S C

Ian S C wrote:Motor with brushes, DC output, brushless, AC output, or on the rare occasion if the motor had slip rings, it also would have AC output. Proberbly the most efficient would be a three phase alternator, but any small alternator looses some of its power if you require to rectify the output to DC. Ian S C

... which is why the diode blocks on most automotive alternators have large heat sinks since the voltage drop induced by said diodes is dissipated as heat.

R

I think I get the concept. Kinda like the striling, trial and error! I played with a amp meter and a few simple electric motors I had lying around. I never could get any volt or current back thru the wires with a brisk finger spin, not even a spike. Idk if the motors may be the wrong type or something. Can you give an example of some items a motor I'm needing might can be pulled from?

I also read on one forum that said normal electric motors you might have lying around the house, will usually need a diode removed Inorder to work this way due to most electric motors having a safeguard for reverse current. In other words, most of them have a "one way valve" or "reed" of sorts to prevent back charge.

Insainhouserecords wrote:I also read on one forum that said normal electric motors you might have lying around the house, will usually need a diode removed Inorder to work this way due to most electric motors having a safeguard for reverse current. In other words, most of them have a "one way valve" or "reed" of sorts to prevent back charge.

Only for some DC electric motors is a diode required. The diode serves are a one way valve so the motor will spin in only one direction and will only spin then if the current flows in the right direction (polarity). In most places all regular appliances use alternating current (AC) instead, so one of this applies.

This may be in reference to spinning an induction (squirrel cage) AC motor above its rated RPM to turn it into a alternator, but that requires adding a running capacitor and balancing the load accurately.

Removing the rotor in an AC motor and building a custom one with permanent magnets to match the coil windings will make a great alternator, but it takes some good tools when reassembly is undertaken. Those magnets will try to grab the coil winding laminations before the bearings can engage the axle and stabilize the rotor. This will still produce AC in as many winding fields as the motor has. A single speed motor will only have one set of wires to the coils whereas there are 3 phase AC motors will have up to six leads, or as few as 3.

Any regular brushed DC motor will make DC power when spun. Only a diode is needed if one wants to avoid some form of back EMF if the load is removed, or limit the current flow to a designated polarity.

In an application such as generating power with a Stirling I'd look at a dual disc axial flux 3 phase alternator rectified with a low forward voltage drop Schottky diode set and a large filtering capacitor for each phase. The stator could be made from the little field coils in a old floppy disc drive motor. I made a tiny little windturbine with just such a setup. I used rare earth magnets from old hard drive read arm control units on the dual discs. On the Stirling engine the flywheel(s) could serve as the axial flux planes.

There are several options available to generate electricity from rotational power.

R

Insainhouserecords wrote:I think I get the concept. Kinda like the striling, trial and error! I played with a amp meter and a few simple electric motors I had lying around. I never could get any volt or current back thru the wires with a brisk finger spin, not even a spike. Idk if the motors may be the wrong type or something. Can you give an example of some items a motor I'm needing might can be pulled from?

The motor from a printer that drives the print head back and forth is a little stepper motor and will produce AC when spun. These can "cog" quite a bit as the magnets spin past the coil winding laminations deep inside. That cogging is resistance to turning, which isn't what you want with a low power engine. This AC, of course would have to be rectified if DC use was desired.

A simple brushed DC motor is what I'd look for, and old VCR's had a great one for pulling the tape in and ejecting it. DVD/CD drives have load/unload DC motors, usually 5 volt. Test a little motor with a battery. Even a 1.5 volt "D" cell should spin one of these motors if the TWO wire leads are touching the battery terminals.

R

Ian S C wrote: To drive a car alternator you will need at least 1hp, and be able to turn it over at 2000/3000rpm, I'v got one driven by a little Villiers 2 stroke of about 1hp, it will produce 250 watts continuous, if you put the load up to 400 watts, the motor starts to sieze up after about 20 miniutes, take the load off, let it cool a bit, then you can go again, the alternator is not too efficient. Ian S C

What alternator did you use?
Years ago I took an 80 amp ford alt., rigged it to a 2 1/2 hp mower engine.
When I flipped the field on ,it killed the motor.
Had to go to 5 hp. Worked great then.
Pat