"Ed Huntress" wrote in message
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"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.
I hope "a sustained period" = three minutes! LOL!!!!
Makes you wonder how one defines "most fit adults"....
Heh, you *could* make it foolproof/tautological by defining fit adults as
those who can generate 100 W for 1/2 continuous hours.... LOL!!!
A world-class competitive cyclist
can produce up to 500 watts (0.67 horsepower) over a sustained period of
time."
I'll believe dat **** when I see five 100 W bulbs at full brightness for a
solid hour.....
Previously, I managed 2:45. Just now I managed 3:30... that's
minutes/seconds... LOL!!!
Now, "manage" is really context sensitive... at what point does one
"quit"?
With no objective blood/lab values, that's really a dicey Q for true
reproducibility, so I use a kind arbitrary "pain threshhold": where I'm
whining for my mommy, but not yet screaming for her....
I suspect Thurs or Fri I'll be up to 5 minutes, and mebbe 10 minutes in
another week, but the point is, Goddamm, I fairly regularly run a hilly full
1/2 hour (2.5 miles or so), so if 100 TRUE watts is hard for me.....
Now, I estimated the driveline friction at about 12 W, and mebbe the PM
motor (perty old... how can I tell? cuz it's not made like ****....) is
80% efficient??
So ackshooly, that adds up to 137 W....
But proly other true bicycle generators would similar characteristics....
but not these "interpreted cycle watt-meters"....
So the comparison issue is still a begged issue.... Who really knows WTF is
up with internal losses, or even true wattage readings, eh? So how do we
really compare results, over the internet with diff setups?
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.
Funny, high efficiency motors are sposedly 98% efficient.... 3 ph, no
doubt.
--
EA
--
Ed Huntress