"Existential Angst" wrote in message
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"Winston" wrote in message
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Existential Angst wrote:
wrote in message
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Three phase induction? This looks promising:
http://ronja.twibright.com/exciter/
Though the most I could ever accomplish was 70 W for half an hour
a day, so I don't expect to run my house from one of these.
That's actually not bad.
How did you determine that it was 70 W?
At the time, I had an exercise bicycle that used a magnetic
'reluctance brake'. There was a knob next to the handlebar
yoke that I could twist to provide any amount of pedal
resistance. A meter next to it indicated the number of watts
I was converting. It probably wasn't terribly accurate but
it was good enough for a 'ballpark' figure and interesting
for a guy that is ~97% fat 
Between 'warmup' and 'cool down', I could keep the needle
above 70 W for a half hour, consistently without endangering
my health.
I was very impressed when I learned that world - class
bicyclists can generate over 480 (Four Hundred Eighty)
watts continuously during a one hour time trial!
Dayum.
I wouldn't be too impressed, just yet.....
480 W for a continuous hour is proly some laboratory confabulation, from
devices that are not measuring watts, but calculating/inferring watts.
A lot of these bicycle watt meters are "watt calculators" from piezo sumpn
strain gauges/load cells, not from true generated electrical power.
Dollars to donuts, if you tested these guys on a real generator, you'd get
far more modest results.
Here's why:
If you calc backwards from a 480 watt mechanical output, you wind up with
a VO2 of 100.
Keep in mind that the elite of the elite possess VO2 *MAXes* of about 95,
and VO2max is a semi-instantaneous value, NOT a sustained value.
I'll have to check, but I think VO2max need only be sustained for a
fraction of a minute to qualify as VO2 max.
Sustained (aerobic) VO2s are usually *maybe* 80% of VO2max values. And
that last 20% is almost exponential in its perceived exertion, ie, quite
unsustainable.
Iow, a marathon runner may win a race at 80% of his VO2max (2+hours), but
if he "miscalculates", and runs at 90%, he may crap out after 1/2 hour --
or sooner.
Marathon runners are toodling along at 18-20 cals/min, while your above
cyclist is calc'ing out at 34 cals/min -- which is unheard of, on a
sustained basis -- at least for 150 lb. guys. 300# -- mebbe.....
I'll post the calcs iffin inyone is innerested, basically just
conversions.
Was *your* 70 W really 70 watts? Hard to say.
I can tell you that I can run for a solid hour (if you pay me), albeit not
at any earth-shaking pace, but at 180# and with hills, that is some
effort/expenditure.
The point being, I couldn't keep a 100 W lite bulb lit up for more than 3
minutes, a few days ago, on my cycle-generator.
Now, I think I'm getting better quickly, as I haven't cycled in literally
40 years, but still, even with substantial improvement, 1/2 hour at that
output is proly beyond my wherewithall -- both physical AND psychological!
100 W calcs out to a moderate but still substantial 10 cal/min, but in
reality is certainly more, depending on the efficiency of a PM DC motor.
Inyway, just some perspective on some of these hyooge wattage claims.
A little more perspective:
Some cyclists claim 2000 W peak outputs, which I might believe, over a
second or two.
Powerlifters have been measured at near-10,000 W instantaneous efforts, no
doubt over fractions of a second, possibly milliseconds. Staggering, when
you think about it.
But, what you can do for second is a *whole* lot different than what can
be done for 10 secs, 1 min, 5 min, 10 min, 1 hour.
And then, of course, you have the HSN/QVC pod peeple, effervescing: Oh,
Oh, OH, I just burntid 500 cals in 1/2 hour, and dint even knowed it!!!!!
Not hardly, sweetheart..... If you burntid 500 cals in 1/2 hour, you
likely woudn't be goin to work the next day.....
--
EA
FWIW, when the Gossamer Albratross crossed the English Channel, which took 2
hours and 49 minutes, the power required in still air was said to be 0.4
hp -- about 300 W, on average. That assumed still air. Normal disturbances
increase the horsepower required.
Here's a quote from a cometitive cyclist and engineer. It agrees with what I
was told when I competed in road sprints, back when tires were made of cast
iron g:
"Most fit adults can produce 100 watts (0.134 horsepower) of mechanical
power on a bicycle for a sustained period. A world-class competitive cyclist
can produce up to 500 watts (0.67 horsepower) over a sustained period of
time."
Of course, you'll get a lot less from a small generator. IIRC, automobile
alternators are something like 60% efficient, and there is the mechanical
loss involved in driving them. Permanent-magnet alternators in the same
size, however, are said to be up to 90% efficient. Don't ask me.
--
Ed Huntress