High Efficiency Power Generation for Hot Air Engines

[VincentG]

For reliable, simple and efficient diy hot air engines, low rpm is likely easiest. That doesn't necessarily go hand in hand with efficient power generation. I think the ideal generator should be in direct drive or close to it. Unfortunately I could not find a readily available commercial option, so I finally tried out an idea that's been kicking around for a while. I had hopes of being able to directly produce DC power, and in a way that came to fruition. However there's a bit more going on here than my limited knowledge of electronics allows me to understand.

Not very good at editing and so there is a repeat segment in here, although it repeats a significant point of an odd combined AC/DC power characteristic. From what I can gather, this type of power is known as reactive power and typical efforts go towards mitigating its negative effects on the standard flow of electricity. I'm trying to source an affordable high end oscilloscope to help me better understand how to fully harness this energy. I'll make another video soon to explain a few things further, including an odd situation where when overloaded, the generator no longer works and instead acts against itself causing high shaft load at even low rpm. As long as I don't do anything dumb(like arc the wires together at max rpm and 45 volts), this does not happen. After the passage of time, and some odd combination of playing around with the wires, it returns to normal operation.

https://www.youtube.com/watch?v=511ag9Ei--o&t=

[Fool]

However there's a bit more going on here than my limited knowledge of electronics allows me to understand.

Reactive power...

Whenever I hear those two things in a discussion, my stomach starts getting a little queasy. I suddenly feel like explain things. Two things come up at first glance, and a bunch more explaining needs to follow. The first two things are easy, 1: Reactive power is not real power, it will power nothing, zero, nada. 2: Reactive power can not be generated. Any attempt to generate reactive power will either power nothing, or will create real power that is all lost to resistance, wire losses, called line losses.

Sorry. Reactive power adds little load to the generator, zero to any motor, and is all burned up by the resistance and the transmission lines. So the more reactive any AC system runs, the less efficient it runs.

What you've built is an air core, ironless, permanent magnet, inductive, generator/motor. It operates similar to all the other motors. And that is awesome. Cudos...

The reason you are getting DC with the LEDs and not when open circuit is that the LEDs are diodes and are rectifying the AC somewhat. I say 'somewhat' because LEDs are poor diodes and have a low PIV rating. Meaning that in reverse they breakdown at a low voltage. Power them up with a resistor and battery. You will find one way will be .7 to 1.4 Volts, the other way won't be much higher than 5 to 7 volts. Exact values I don't have. If you looked at the waveform it would be AC with a DC offset.


I like the thought of lining, gluing to, a flywheel a ring of small magnets. Then having a series of stationary coils, a ring, called a stater, that could be moved closer for higher power or further away if it tended to stall.

A stater ring of magnets and soft iron flywheel, called a rotor, could be used as a hysteresis brake. Smooth and easy applied by moving closer.

Magnets need to alternate North South North South. Probably best to have them axially oriented.

[VincentG]

You are quite right. I had 2 leds in series with reverse polarity light easily and got excited, but the triple set appears to reverse flow VERY easily. I've since fried them lol. All a relief really as I just wanted to make AC power and rectify it to DC. I've since connected 2 parallel leds in either direction and an AC flash pattern is the result. Good call. I'll carry on testing other rotor configurations. The aircore is all the rage with DIY wind power guys now due to low starting torque and it seems well suited here too. Retesting with this in mind and I'm still getting very good output.

[VincentG]

The basic concept for this idea was similar to the Newman generator, but with the addition of nearly 180 degrees of unidirectional eddy current generation before a flux change, followed by another near 180 degrees in the reverse direction. The Newman generator is very efficient, and I think I can build upon that design. I think some kind of bypass capacitor can be used to store the eddy current and align the discharge along with the flux change. That, or a hall effect switching system. I may even try a mechanical brush arrangement to isolate the eddy current phase. I'm open to suggestions.

This video is an amazing demonstration of how electricity propagates out like waves in a fluid, and can so be directed, delayed and aligned just as any other flow.


https://www.youtube.com/watch?v=2AXv49dDQJw

[VincentG]

High voltage back emf is used by the joule-thief to boost low voltage. Simple solid state commutation is used by the Newman motor to produce mechanical power. Brushless permanent magnets motors can use diy Arduino control to produce mechanical power. All of these air core permanent magnet alternators are relatively efficient despite an uncontrolled/untimed power collection method. Step one is to time the collection of the electrical power. A brushed DC motor does this mechanically, there's surely a way to do this solid state. Step two is to use the back current in a forward direction, like the joule-thief, while it typically fights against the system or is dissipated into separate windings.

https://www.youtube.com/watch?v=vAtjaRvjNXg

[matt brown]

This video is an amazing demonstration of how electricity propagates out like waves in a fluid, and can so be directed, delayed and aligned just as any other flow.


https://www.youtube.com/watch?v=2AXv49dDQJw

Interesting video and "information" buzz.

[VincentG]

Here I am running the generator as a motor on a depleted 9v battery(only reaching 6v while running). A single cam driven contactor powers the coil through less than 180 degrees of rotation, drawing .2 amps and reaching 1000rpm with great torque, especially considering it's coasting through over 180 degrees of rotation. With a switched transistor setup I think the ac output voltage could be above the dc input voltage. Maybe useless, but a cool mechanical voltage booster I think.

The angle in which motive force is produced is separate from the angle in which ac power is generated. So it's possible to simultaneously run as a motor and generate ac power. More importantly, that means the coil can be switched off when it is not generating power, reducing eddy current losses. Or ultimately, the collapsing field of the coil after being switched off could be turned around and used to provide motive force to raise generator efficiency.


https://youtu.be/pjWmfA5e5FU?si=xawCpJt-NyITOewH

[VincentG]

I've rewound a new stator with 50 turns of 27ga wire(.015") from the previous 100 turns of 30ga(.010").

I was able to power an 1156 25 watt automotive bulb to full brightness at over 12vac and over 2 amps with just my little cordless Dremel, rated at 8 watts output, just before overload shutdown.

This is still being driven through a small length of silicone hose acting as a coupling. Previous attempts with the other stator would cause the Dremel to shutdown after just a dull orange glow. Time to get some real equipment to measure efficiency. It's much more powerful as a motor now too.

I was also able arrange the contactor to both run as a motor and output an isolated dc pulse to drive a LED at the same time while running on the 5v power supply. The same arrangement also allows driving as a generator and outputting the isolated dc pulse.

[MikeB]

Sounds like you need to measure the actual power draw of the Dremel, since you seem to be getting over 24watts out from only 8watts in ...

[VincentG]

Agreed, I'm not suggesting more power out than in. Just that the tool is rated at 8w, so I must be getting some pretty good efficiency at least. I imagine it can sustain short bursts of more than 8w.