All alternators consume energy in their field windings creating the magnetic
lines of flux that must be cut (passed through) by the stator to generate
energy. For example, look at that schematic referenced on the web page
above. My numbers may be way off, but after you build & run the circut,
you can measure and tell us where the energy is going. Let's say 2 Amps
flow in the field winding of the alternator to create the required magnetic
field. So that's 2A x 12V = 24 watts. That's 24 watts NOT being delivered
to your batteries. (Purists - Yes I know that there's energy being lost in
the darlington pass transistor, but we're still looking at 2 Amps in a
series circuit feed by 12 volts.) If you're getting 100 watts to your
load, then your efficiency is 100 watts out/ 124 watts in = 80%. And
there's plenty of other losses that aren't factored in here (like IR
losses, eddy currents.)
Good questions. My experience fails me. But you can't beat 0 field current
for a permanent magnets. Haven't I convinced you alternators are not the
most efficient way to go??? Cheap, available, yes. Efficient, not
usually. Google for do it your self permanent magnet generators.
I think it's because they have to run in dirt, and crud, and shock,
and heat, and vibration, and noise, and NOISE, and keep running for
years.
You left out the socially redeeming factor of cost. My guess is even a 100%
efficient alternator (Impossible, see above) would help gas mileage by a
minor amount, so manufacturers aren't even trying. In addition to the
factors you list above that are competing factors against efficiency,
weight & size probably rank high.
I was thinking it'd be interesting to see if you could rewind one;
I don't remember if it was here or some other thread or NG - but ISTR
somebody said even rewinding it, although it would help, still falls
way short of one designed for efficiency in a living room environment.
It has something to do with pole gap spacing or some such Magnetic
Black Magick Arcana.
<AOL>
Me, Too!
The bicycle powered alternator system I built was from an article in Ham
Radio magazine. (Not _a_ Ham Radio magazine, that was _the_ name.) It
suggested, and I used with great success, a couple of bicycle chains to
loop around the alternator and the rim of the bike tire. Attached to the
shaft of the alternator was a 5 speed gear cluster. The chain drive meant
you didn't have any pulley belt slippage, at least at the alternator.
Surprisingly, black electrical tape wrapped about the rim held up for many
hours of operation. Now you may have to use leather or rubber to last
longer, but there's so much contact area on the rim that there's really no
slippage to speak of to rip up your "rim pad."
Borrow somebody's panty hose for the first smoke test. ;-)
Good Luck!
Rich
OK, now for the "flames." ;^) Unless I missed what the Original Poster
eventually said, there's 3 - 75 Amp-hour 12 Volt batteries in this system.
Let's see --- that's 75 Amp-hour * 12 V = 900 watt-hours. Times 3
batteries = 2700 watt-hours. If you can produce 100 watts of power from
your bike power system, that's 2700 watt-hours / 100 watts = 27 hours of
pedalling. Oh, don't forget, there's charging inefficiencies. So it's
probably more like 35 hours to fully charge dead batteries. Fortunately,
your batteries will & should never be dead, but we're still talking serious
hours pedalling. Man, 3 - 75 Amp-hour batteries. I know I'd be dead after
pedalling to charge 'em, even to 25%! IIRC, with my bike generator [sic -
bike alternator] system I could power a 100 watt load for say 15 minutes.
50 watts, over an hour. 175 watts, expect to pass out in about 2 minutes.
It was a steep power curve. I never did an efficiency estimate or
measurement on my bike system, so YMMV. Good luck, I honestly think you
may need it.
Seriously, please do some power budget calculations. See
www.homepower.com.
How much KWH per day do those radios take? Can that power be replaced by
humans each day? Not enough data given to tell.
Thanks, Steve