Re: Wind power generator to run radios
- From: "MattD.." <matt@xxxxxxxxxxxxxx>
- Date: Sun, 11 Jun 2006 16:34:29 +0100
After replacing Brian Reay with a small shell script on Sunday 11 Jun
2006 15:10, the following appeared on stdout:
Any ideas on a suitable motor source?
Not really. I was thinking of starting from scratch. A lot of designs
use surplus mainframe tape motors, but as I don't have a source for
those either, that's a pretty useless bit of information.
I found this design:
http://www.velacreations.com/chispito.html
(Nice idea for making the blades, I'm thinking maybe a bit of the
yellow gas pipe, if I can get a length of it.)
Yes, it is! I hadn't considered using sections of pipe as rotor blades.
My woodworking skills, well, aren't, so that is a useful idea.
The motor they suggest is 260VDC 5A, that is a 1.5HP motor or so. I'd
expect that to be a lot bigger (and heavier) that the design suggests.
I wonder if they mean 26VDC, although that would suggest the motor was
pretty efficient as a generator.
Not too sure on this. Motors aren't that efficient at making juice as
they are consuming it, which is why dynastarts were a flop.
I always sort of assumed the small 12V beasts would use an alternator
but I suppose getting 1500rpm or so could be a bit hard.
Most alternators in this category are multiple PM/coil jobs, which make
more power than a vehicle alternator at low RPM with the added benefit
of no field winding to energise. I'm looking at at least 18 rare earth
magnets, possibly 36 in a twin rotor setup, I haven't decided yet. They
are, surprisingly, not as expensive as I thought they'd be. The coils
are a doddle. They just have to sit there watching the magnetic flux
alternate. The more I read on this, the easier it becomes to judge what
will work well and what won't. It's really very interesting.
Also, they seem to have specified their 100W output a little
optimistically for average conditions. The mean wind speed is around 15
MPH according to the Weibull wind speed distribution histogram, which
means your 100W at 30MPH generator just became a 12.5 watter in average
conditions, assuming linear efficiency across a range of speeds.
0.6m radius, so swept area = PI * 0.6^2 = 1.13m^2.
Power available = 0.5 * Swept area * air density * wind velocity cubed.
So, ( 0.5 * 1.13m^2 * 1.23kg/m^3 (air density @ sea level) * 13.44m/s
(30MPH in m/s)) ^3 = 815W available. At 15MPH, this figure drops to
(0.5 * 1.13 * 1.23 * 6.72) ^3 = 102W
With decent efficiency, this should yield 30-35% of the available power.
That motor seems rather inefficient, about one eighth of the available
power turned into electricity. Far better to put that blade assembly or
better, a larger version, onto a decent low RPM PM alternator.
Of course, the advantage of this method is its simplicity and, if you're
just using it for radios, it should keep the battery topped up. ~1A is
a nice, gentle float charge for a large lead acid battery. On the boat
we're using a 250mA Savonius rotor type generator (commercial, of
course) to maintain the battery. Even with the skipper's 706 on most
evenings, we've never had a flat battery.
--
Radio glossary #44
Rotator: Someone who sits for hours twiddling the VFO knob but never
transmitting.
.
- References:
- Wind power generator to run radios
- From: Brian Reay
- Re: Wind power generator to run radios
- From: MattD..
- Re: Wind power generator to run radios
- From: Brian Reay
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