heat to electricity or other investigatory prjects

Jessica:

A Stirling Cycle free piston engine takes advantage of the heat-cold transfer phase of the kinds of gases used to run an air conditioner (freon of various types, alcohol, any other medium which readily transfers heat to/from itself, when pressurized or de-pressurized. Wikipedia shows this (http://en.wikipedia.org/wiki/Stirling_engine) for them, and How Stuff Works shows this (http://www.howstuffworks.com/stirling-engine.htm). Google videos have these as demos of the Stirling Cycle in many variants (http://video.google.com/videosearch?q=Stirling+Cycle+engine&ie=UTF-8&oe=utf-8&rls=org.mozilla:en-US:official&client=firefox-a&um=1&sa=X&oi=video_result_group&resnum=4&ct=title#)

(This link may break, as it is long. If so, google "Stirling Cycle Engine" and look for the google videos link.)

Finally, here is a source for ready-to-assemble Stirling Cycle kits, including steam driven, and several solar versions. (http://www.bullnet.co.uk/shops/test/stirling_engines.htm)

Note that it is possible to reverse the heat transfer direction of a Stirling Cycle engine, so that one might use a cold source (free flowing streams come to mind), with the hot side being ambient sunlight induced temperature. Again, as I noted earlier, all that is required is a fairly large temperature gradient.

Now on to the power generation side. Any permanent magnet motor (salvage one from your brother's battery powered car, for example) when driven by a mechanical power source, will deliver a useful DC voltage. It usually will not deliver a large amount of current (about 80% of what the batteries which powered it might deliver is probably a high limit), but for your purposes, it should do well. A motor designed to run at 6 VDC, at a no-load limit of 1000 RPM would probably deliver about 5.5 VDC out at the speeds you could get from one of the Stirling Kits, if you really pushed the Stirling for speed. Instead, it would be better to try to find a 12VDC motor. And for this purpose, since more capacity than you need is better than not enough, a larger frame motor (which usually indicates more power out, more current capacity, etc. and translates for your purposes to more current out at lower torque in, and more voltage at lower RPM) would be better. I would not try to operate an automobile windshield wiper motor, or anything of that mass, from one of these kits though, as I suspect you'd overwhelm the Stirling's available torque trying to drive the mass/internal resistances of the automotive motor.

Finally, for most cell phone chargers, a +5V Voltage Regulator chip, readily available online, which requires at least 6VDC in, and can handle up to about 18 volts in(some models can run up to 24, but for you to need that, even with a 12 VDC motor, you'd have to overdrive the motor a huge amount, probably destroying it in the process), with the regulator dumping the excess voltage as heat (above the 6 volt threshold) across a heat sink.

If you choose to charge a USB powered cell phone (many models, nowadays are powered/charged from USB ports on computers, and would be a perfect candidate for your experiments), +5VDC is all that is needed out, and the 5 volt regulator chip is perfect for the job. But for other models, you can get regulators online in many voltages, still cheaply. And adjustable regulators, though a little more complex and expensive, are also readily available.

A "SuperCapacitor" is also available online, and you can google for a source.

I googled everything I suggested to you, and found dozens of sources for both the operational theory of the device, and the device itself, online. The only exception to that statement is the 5VDC regulator, and I didn't google it because it is so ubiquitous, and I've used them for years, without EVER encountering difficulty in obtaining them online.

I didn't provide you ALL the links, because I wanted to leave you something to work on. I didn't try to draw the circuit, because despite all I know about how to use the pieces, I can't draw schematics online worth beans. I will give you this, assuming a +5VDC regulator:

SMPOut _DCMDriveshaft - Fm DCMotor Term + to +V on Capacitor to +V in on Reg

Fm DCMotor Term - to GND on Capacitor to -V in on Reg

Where SMPOut is Stirling Motor drive shaft out, and

DCMDriveshaft is the DCMotor Driveshaft

Couple these up physically, so that the output of the Stirling turns the DCMotor

and

DCMotor Terms are the solder or screw terminal tabs on the motor. Take your unfiltered, unregulated output voltage from them.

Finally, take your filtered (by the capacitor) and regulated (by the regulator chip) voltage to your USB connector from the +V out and Gnd pins on the regulator. It only has three pins, which are +V in, +V out, and Gnd. So it is simple to wire.

Google the USB Standard for the pinout on the USB device, and the only pins you'll need are for the plus and minus V, since you aren't designing for a USB signal. For minus V, use the GND pin output, and you should have no problem making the whole thing work.

Make sure to log back in here after you start on your project, and keep us posted. I'd love to know how its coming along. And if you have other questions, don't hesitate to ask.

Mike