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Old 02-04-08, 01:35 PM   #1
BIG-E
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How many watts can a fit cyclist produce?

I want to build a pedal powered generator. Does anyone know how many watts a good fit cyclist can produce? Both peak and steady.
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Old 02-04-08, 01:50 PM   #2
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Steady for how long and peak for how long?
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Old 02-04-08, 04:28 PM   #3
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100-200 watt/hour for an sustainable level, 500+ peak for very short bursts of 20 seconds to a few minutes depending on fitness level. This means if you cycled on your generator for a whopping two full hours at a nice 160 watt clip, you'd generate 0.32 kw/hour of electricity. You'd likely burn something like 1000 Calories in the process. I can imagine you'd spend at least a few dollars to eat enough food to replenish the 1000 Calories burned. On the other hand, here in Arizona electricity costs about 10 cents per kw/h, so you're looking at it costing you around 3.2 cents.

If you were thinking more of an off-grid setup, you can do a 160 watt/hour solar panel with inverter and battery backup and stuff for something like $1000 and have a generator that produces power for 4+ hours a day, plus battery backup, for no further investment. Humans really aren't very cost effective power generation stations.
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Old 02-04-08, 05:23 PM   #4
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100-200 watt/hour
I think you mean 100-200 Watts... not watt/hour.
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Old 02-04-08, 06:26 PM   #5
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You should think about the excessive green house gases you'll be producing while pulling that generator. You'll be contributing to global warming by exerting yourself. Just find a comfortable couch, turn on the TV, watch indoctrination shows that convenience people were causing global warming, and only ride your bike to go somewhere. Producing your own electricity also avoids paying taxes on the power you would have purchased reducing revenue to the government.

If I offended anyone with my satire I must be doing something right.
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Old 02-05-08, 09:59 AM   #6
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Humans really aren't very cost effective power generation stations.
Which is why The Matrix made no sense to me. Just kill all the humans, and install ground source heat pumps everywhere.

Back on topic: yeah, 100-200W is about right. Considering the speeds you can reach with such a small amount of power (compared to a car), it makes a cyclist a very efficient mode of transport.
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Old 02-08-08, 08:06 AM   #7
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You call it satire, but I just came to here from a youtube thread where people were arguing exactly what you were jesting about without a hint of irony.
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Old 02-08-08, 08:09 AM   #8
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There is a combo trainer/generator that is commercially available on the internet. I think the whole setup, including batteries, costs somewhere around $1000. Or it did a year or two ago when I was thinking about buying it. You should google bicycle generators or bicycle trainer generators to see if you can find it. You may still want to build the DIY generator, but at least you can see what other have done for inspiration.
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Old 02-08-08, 09:58 AM   #9
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Originally Posted by BIG-E View Post
I want to build a pedal powered generator. Does anyone know how many watts a good fit cyclist can produce? Both peak and steady.
A rec road cyclist who doesn't race? Under 200w, probably closer to 100 if you're looking at the non-dedicated types.

Lance armstrong sustained over 6w/kg, 400-500w for about an hour. So there's the top end.
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Old 02-08-08, 12:58 PM   #10
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If you're looking for an instantaneous peak (not sure how they measured that)

the maximum for a sprinter (track racer) is said to be 2000 watts.

http://en.wikipedia.org/wiki/Bicycle_performance

I'm guessing that amount is actually sustainable for about 1/4 revolution of the pedals.
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Old 02-09-08, 09:35 PM   #11
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If you were thinking more of an off-grid setup, you can do a 160 watt/hour solar panel with inverter and battery backup and stuff for something like $1000 and have a generator that produces power for 4+ hours a day, plus battery backup, for no further investment. Humans really aren't very cost effective power generation stations.
Start the hundreds of gerbils wired up.
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Old 02-09-08, 09:44 PM   #12
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Can I ask what your reason for the generator is?
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Old 02-09-08, 09:50 PM   #13
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I'd think it'd be cool if you could power a small TV/DVD with it. Think about it: instead of just making heat on a trainer during winter months / training sessions, you could power a TV and watch Buffy the Vampire Killer instead! [Actually, you'd be making just as much heat, if not more, if you count in the killing of brain cells from watching TV.]

I'm sure there are some low power TV's and DVD players out there. Maybe not many at the 100W level, but maybe, just maybe...
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Old 02-10-08, 11:19 AM   #14
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All you need is an automobile alternator, a deep cycle marine battery, a rectifier, and some additional hardware to connect everything up to your trainer....costs...maybe $200.00. Then you could use an LCD TV made for RV's/Boats whose electrical systems are often 12V DC. You could charge the battery while riding the trainer or you could run the TV directly (using the Battery to stablize the output for the TV's electronics).
If you are really strong, you might be able to charge the battery while watching the TV, but I don't think most of could do that.

Basically, an average cyclist could produce about 150 Watts in a steady state for about an hour maybe two....at 14V, this would be about 10.5 amps of electricity.....check the current requirements on the electrics and match everything up, and it should work fine.
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Old 02-10-08, 11:24 AM   #15
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I'd want to use some sort of smart controller on the battery controller--in addition to making sure the battery is properly floated when its fully charged, I wouldn't want to have to power 400W out when the battery is low. A smart controller that I could dial the output power from the generator, so that I could set it to my comfort level.
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Old 02-10-08, 11:26 AM   #16
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Originally Posted by monkey_boy View Post
I think you mean 100-200 Watts... not watt/hour.
No, he meant kilowatthours. Multiplication, not division.

160 W for two hours = 2 x 160 watthours (Wh) = 320 Wh = 0.32 kWh
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Old 02-10-08, 11:38 AM   #17
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No, he meant kilowatthours. Multiplication, not division.

160 W for two hours = 2 x 160 watthours (Wh) = 320 Wh = 0.32 kWh
I think the poster meant that the average rider could do 100-200 Watts per hour -- that is, a person could comfortably output 100 to 200 Watts continously for an hour or two. Wrong units, yes; but right concept. Most riders could not kick out 320W for an hour, but they could do 100W for 3.2 hours -- both are 0.32kWh.
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Old 02-21-08, 11:21 AM   #18
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Originally Posted by ModoVincere View Post
All you need is an automobile alternator, a deep cycle marine battery, a rectifier, and some additional hardware to connect everything up to your trainer....costs...maybe $200.00. Then you could use an LCD TV made for RV's/Boats whose electrical systems are often 12V DC. You could charge the battery while riding the trainer or you could run the TV directly (using the Battery to stablize the output for the TV's electronics).
If you are really strong, you might be able to charge the battery while watching the TV, but I don't think most of could do that.

Basically, an average cyclist could produce about 150 Watts in a steady state for about an hour maybe two....at 14V, this would be about 10.5 amps of electricity.....check the current requirements on the electrics and match everything up, and it should work fine.

I am not sure of using a car alternator. I thought about doing this. First a car alternator is designed to put out current at idle of the engine, Say 800 rpm (at crankshaft) most car altenators I have seen have a much smaller pully then what is on the crankshaft. So I would say the altenator is running twice as fast. (1600 or more) This would mean you would have to be running to very tall bike gear. Consider your "crankshaft" RPM would be 100 (cadence).

Next, I don't know how low of a wattage car altenator is out there, but a small one these days I have seen is 60 AMP @ 12+V. 60X12=720 watts. This would be max of the altenator. But a very large load (big hill) in a very tall gear.

I suppose if you limit its current out put in the 200w range it might be doable, but I don't know if you would get a good output at a slow alternator speed.

Has anyone done this?

Jeff
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Old 02-21-08, 11:38 AM   #19
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I am not sure of using a car alternator. ...
Has anyone done this?
Looks like the internet to the rescue!

http://www.pedalpowergenerator.com/

From that website, it looks like they use a car alternator, but only with modifications, one of the pages specifically states that you'll waste a huge amount of efficiency if you try to charge a battery directly from the alternator, but it appears it can in fact be done with modifications. That website rates their build kit at just 40 watts of output though, so it looks like there's a ton of mechanical/electrical loss from the human output to get usable, stable electric output. The other method listed is to use a DC generator instead of an automotive alternator.
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Old 02-21-08, 12:33 PM   #20
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I am not sure of using a car alternator. I thought about doing this. First a car alternator is designed to put out current at idle of the engine, Say 800 rpm (at crankshaft) most car altenators I have seen have a much smaller pully then what is on the crankshaft. So I would say the altenator is running twice as fast. (1600 or more) This would mean you would have to be running to very tall bike gear. Consider your "crankshaft" RPM would be 100 (cadence).

Next, I don't know how low of a wattage car altenator is out there, but a small one these days I have seen is 60 AMP @ 12+V. 60X12=720 watts. This would be max of the altenator. But a very large load (big hill) in a very tall gear.

I suppose if you limit its current out put in the 200w range it might be doable, but I don't know if you would get a good output at a slow alternator speed.

Has anyone done this?

Jeff

You can use a car alternator, or conversely use a permanent magnet motor. Either one will work, both have their limitations.
Do a search on Google, you will find lots of information. I've seen recommendations of using old VW 6V systems, as they are apparently easier to work with, but I'd be worried about battery options then.
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Old 02-21-08, 12:45 PM   #21
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You should be able to use an electric bike motor, as long as it's the brushed type (brushless won't work). Theoretically it could output as much as its max input, about 300-400W. In practice it would only be the power your legs could muster minus a few losses. It should be easy enough to rig up mechanically, but the tricky part will be transforming that DC voltage (anywhere from 24V to 48V) into either 14V DC to charge a battery, or 120V AC to power a TV.
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Old 02-22-08, 01:38 PM   #22
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Looks like the internet to the rescue!

http://www.pedalpowergenerator.com/

From that website, it looks like they use a car alternator, but only with modifications, one of the pages specifically states that you'll waste a huge amount of efficiency if you try to charge a battery directly from the alternator, but it appears it can in fact be done with modifications. That website rates their build kit at just 40 watts of output though, so it looks like there's a ton of mechanical/electrical loss from the human output to get usable, stable electric output. The other method listed is to use a DC generator instead of an automotive alternator.

I saw this site after posting. Also, looking at the "riders" I can see why they only wanted 40 watts of output. In fact if charging a big battery lower wattage and longer ride time might make more sense.

Another thing, I believe a alternator puts out a full wave rectified output. The bottom half of the sine wave is on the top making DC current with lots of humps (ripple). I wonder if you cut out half the diode then it would only be half wave, thus only have the output of the alternator and half the load. If you put this into a car battery it would it charge it ok?

I was thinking of doing this if I go the burningman this year to charge up batteries for cameras and night lights. Would be kinda fun, but photovoltaics sound easier.

Jeff
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Old 02-22-08, 01:41 PM   #23
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You should be able to use an electric bike motor, as long as it's the brushed type (brushless won't work). Theoretically it could output as much as its max input, about 300-400W. In practice it would only be the power your legs could muster minus a few losses. It should be easy enough to rig up mechanically, but the tricky part will be transforming that DC voltage (anywhere from 24V to 48V) into either 14V DC to charge a battery, or 120V AC to power a TV.

So if you turned around a electric bike hub and spun it would it be a generator? (or ride backwards )The difficulty here though is voltage regulation. That's nice think about an auto alternator, plus I have a half dead one to try.

Jeff
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Old 03-05-08, 11:16 PM   #24
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FWIW, I did a double century last summer and managed just a hair over 18mph. My avg. watts during the 11 hours of riding was around 180. I've sustained 220 over 56 miles @ 21mph, but that was in race setting. And I'm far from the fastest guy out there.
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Old 03-06-08, 12:16 AM   #25
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I did a double century last month and avg. 215 watts for 12:46. Last weekend's ride was 253 for just under 3 hours.
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