On Wed, 20 Dec 2006 02:48:10 GMT, with neither quill nor qualm, "Tom Gardner" quickly quoth:
You're a real naturalist, Tawm. ;)
On Wed, 20 Dec 2006 02:48:10 GMT, with neither quill nor qualm, "Tom Gardner" quickly quoth:
You're a real naturalist, Tawm. ;)
Bob Pease publishes his email ( snipped-for-privacy@galaxy.nsc.com) at National Semiconductor, and does respond to questions (I've had conversations with him), so I would just ask him.
Joe Gwinn
Higher voltage motors have higher resistance and less current capability for given size and weight, though a higher voltage can easily be reduced (with consequent current increase) with lightweight electronics.
A smaller faster motor/generator can produce more power (for given size and weight) than a larger slower motor/generator. Torque is somewhat a function of motor size and weight, power is speed * torque. That's why a lot of 400 Hz electric motors are used in aircraft. A 4-pole 400 Hz induction motor runs at almost 12K RPM rather than the 1760 or so of the familiar 60 Hz 4 pole induction motor.
Ahh, they have a tiny speck of material on the head of a pin. You used to be able to buy this stuff in hobby stores. You can get an alpha source out of a smoke detector. I have a piece of the (in)famous orange dinner plates, and it is a pretty good source. Got a brick house and a Geiger counter? Check out your bricks! They are not a real dense source of radioactivity, but they are radioactive, too.
Natural Uranium is 99.3% U 238. It is the U 235 that is the weapons-grade stuff.
Jon
Hi Tom,
An AC Delco alternator isn't all that heavy. They can be set up to be self exciting I understand. You just have to figure out a small engine to drive it with. Their small alternator was good for 37 amps. The one on my truck is for 63 amps. Most of the stuff you want to charge up can be done with 12 volt adaptors. Figure out the heaviest engine you dare take, couple it to the alternator and maybe find a small deep cycle battery for the setup.
Another option might be an alternator from a motorcycle. It should be a bit smaller and lighter I would think. Lots of old Delcos around though.
Just musing out loud...
My choice would be a Stirling engine, but then I'd have to build it all myself. Ahh, yet another project.
Jon
Jon, do you know why all stirling engines are display only demonstration pieces. How come small power stirling engines are not used for real purposes. I am thinking of a small engine powering up a
20w generator, etc. How come nothing like this exists in real world. iOn this topic I have an Astroflite samarium cobalt motor and tons of nitro fueled model engines. Could I just couple them with a belt or gears and get say 12 volts out of this arrangement? These small electrics will produce about 20,000 rpm with a nicad pack at 9 volts. I once mounted a .35 model engine on my bicycle with propeller and it would get me around the block a couple of times on 3 ounces of fuel. I was only 13 at the time and 30 pounds lighter
Some of you may be interested in this little diesel engine. Perhaps running it at the low end of RPM would make it last long (though I have no idea if that is the case).
no affiliation
Enya builds very fine model engines. I have a few and the precision is great. Not touted up as much as OS and Supertigre but great nonetheless. These small engines are tremendously powerful and very easy to start.
How about a starter-ator from a small engine?
LLoyd
Doesn't that tell you what sort of voltage you might get (at load) at 20K rpm?
LLoyd
They do exist. It's just that their power to rate ratio isn't very good.
They are using them to create electricity from solar energy, and for cogeneration.
True, and what you wrote afterwards. But there are some _VERY_ tightly coupled motors out there designed for high(er) voltage that make quite efficient generators.
The motors typically used in 9-track reel decks (computer tape drives) are very efficient. I have a couple I keep around just for demos. You can barely turn the shaft by hand - even slowly - if the leads are shorted. If two of the motors are wired up, one as a motor, the other as a genny, you can get almost perfect syncronism between the input shaft and output shaft at finger-turned rpms.
These motors were designed to run up to 50V, but will run sweetly, powerfully, and silently on less than three volts.
LLoyd
That sounds really cool. Where can I get a couple of those?
Oh, wait a minute. I got a couple of CNC's with punch tape reels in them. Are they the same?
Would they last long if run at below their maximum RPM and power output?
i
Size. A steam engine of comparable size produces a lot more power. There are some Stirling engines in the British Science Museum that were once actually used as prime movers.
I doubt it. The motors are usually available from places that deal in computer and mil. surplus. They're designed for _vicious_ torque and reversing rates with applied voltage ramping up from zed to 50v in under 0.1 second.
Mag tape drives (modern ones) do (maybe did...?) control the tension of the tape by controlling current to the motor(s) so a "compliance arm" is kept centered in its spring-loaded swing. The motors have to react with great speed and precision to handle reverses in direction while still maintaining exact tension on the tape.
They're usually listed as "removed from equipment" from magnetic tape drives.
LLoyd
Using a brushless DC motor as a genny might be a bit dicey, unless you did a little surgery (pull the elex) and run it as a polyphase synchronous generator with external rectifiers.
The Astroflight 020 is a 250 watt motor with winding resistance of
0.07 ohms and rated current of 25 amps. It'd make a dandy little generator if you could spin it at or near rated speed.No load draw is 1 amp so its mech loss at rated speed and 12 volts is about 12 watts. At 8.3 amps (100 watts) IR loss would be 4.8 watts, total loss of 13 watts, efficiency = 100/113 = 88.4%.
I sold all my physics books and have forgotten many of the electricity formulas. If I run this little bugger at 5000 rpm might I expect 12 volts at 20 amps? I do have a biography of Tesla for sale and also a book about building nuclear bombs.
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