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Old 01-19-09, 06:58 AM   #41
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Good notes for those looking to build a similar project Metro. Thanks!

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Old 01-19-09, 10:23 AM   #42
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PS: just did calcs on "road speed" needed to generate useful power: 65 pedal RPM = 30.9 km/h or 19.2 mph on this bike in top gear (42 & 11 sprockets, 26 inch tire).
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Old 01-19-09, 01:34 PM   #43
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So, right now you're producing 50 watts an hour, or 50 Wh, or .05 kWh. How high do you think it would be reasonable to go up to with a better designed system? 100Wh? 200Wh? Would it ever be possible to generate 1 kWh per day? I'm guessing not if you ever wanted to do something else.

Kinda makes it sound like wimpy 60W solar panels actually do a descent job at collecting energy now, doesn't it?
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Old 01-19-09, 05:40 PM   #44
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It definitely puts power production into stark perspective when you see how much you can generate yourself vs. how much you use.

I'm sure with refinement, you could probably make a 75-100 watt system that wouldn't be ridiculously hard to use. But I think you'd have to spend many hours pedaling to generate 1 kW a day.

Here's the thing: I don't mind riding the bike to store a bit of power, but I don't want it to be a huge workout that requires a shower & change of clothes after.
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Old 01-19-09, 10:26 PM   #45
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I've been following this thread since I'm interested in pedal power for light hauling around my property and/or for powering a well pump.
This is a friction drive arrangement (not very efficient) in view of the need to keep the tire on the bike. It might be better to have another bike, or parts of one, that could use a chain drive to the generator.
The other thing is that wear on a sidewall will shorten the tire life.
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Old 01-19-09, 11:57 PM   #46
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Yeow! There is no way it takes this much energy to charge those batteries.
Let's see, optimally you would want this:

Muscle power ==> rotation ==> transmission (frictionless) ==> DC generator (correct rpm) ==> DC to battery (requires regulation circuitry for correct secondary battery charge)

But we have this:

Muscle power ==> rotation ==> transmission (lots of friction) ==> DC PM generator ==> automotive battery (charging) ==> AC inverter ==> transformer to DC ==> DC to secondary battery (properly regulated)

My estimate is that for every 10 power strokes, 9 are wasted. Compare your output to an emergency battery or radio that uses a hand crank generator and optimized charging circuitry.

What can be done to gain efficiency?

1) Muscle power ==> rotation
The bicycle is one of the most efficient machines ever invented. Hard to improve on this.

2) rotation ==> transmission (lots of friction)
The motor on the tire is turning a lot of energy to friction. A better method would be to use the wheel as a flywheel and connect the drive to the chain. Use a simple set of external lubricated gears to obtain the correct motor rpm.

3) transmission ==> DC generator
Motors will work as generators but actual generators are much better. Since you are using an automotive battery, consider a small alternator for the lowest resistance. Generators with permanent magnents make power at low rpms. Alternators like high rpms. You cannot produce enough power to drive either one anywhere near full output. But you can vary the field on the alternator to match your muscle input.

4) 12v DC to AC inverter ==> 120v transformer to 12DC ==> 12v DC to battery
A lot of wasted energy here. A whole lot. There are ways to bypass the inverter.

We don't actually use AC. All our stuff converts AC back to DC in a wasteful step. This is our energy infrastructure's crazy uncle in the attic. It's because Tesla lost out to Edison and died a pauper. He's dead but we're all still suffering.

Last edited by Ptero; 01-20-09 at 12:05 AM..
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Old 01-20-09, 12:49 PM   #47
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very interesting stuff.
I would not mind a sustem where i could get a little exersize ( maybe 15 min in AM and 15 in in PM) and recover some electricity.

Would it be possable to use this in place of an Alternator in the car?
30 min of Bike Time at the end of each day to recharge the car Battery?
( i would use a switch to turn OFF the alt in the car for longer triips of lack of charge )

using pedal power instead of Gas to recharge car bat. interesting..

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Old 01-20-09, 08:59 PM   #48
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Quote:
Originally Posted by fud2468 View Post
It might be better to have another bike, or parts of one, that could use a chain drive to the generator.
Definitely. If your goal is to generate useful amounts of power, instead of just playing around like I am, then a different design is needed.

Quote:
The other thing is that wear on a sidewall will shorten the tire life.
This is true! When I had the gen hub misaligned so the contact patch was too focused, it did start to show on the sidewall. I've since got it aligned better though (contact is approx 3/4 inch tall) and haven't seen any obvious wear since then.
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Old 01-20-09, 09:02 PM   #49
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Quote:
Originally Posted by Ptero View Post
My estimate is that for every 10 power strokes, 9 are wasted.
Well, it's bad, but it's not THAT bad.

By your estimate, if I'm feeding 50 watts to the battery (which I am, on a regular basis), then I'm actually putting out 500 watts! I'm not quite that athletic.

I'd say we're looking at more like 50% - 60% efficiency, not 10%.

Quote:
What can be done to gain efficiency?
Agree with the rest of your points though.
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Old 01-20-09, 09:10 PM   #50
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Quote:
Originally Posted by Doofus McFancypants View Post
Would it be possable to use this in place of an Alternator in the car?
Not with this setup. Back of the envelope calcs showed my car using an estimated 288 watts to run, with some accessories on.

The ghetto generator is good for a relatively comfortable (non sweaty) 50 watt output.

So you can see for each 5 minutes of driving, you'd have to pedal for probably 30 minutes or more (charging inefficiencies) to replace the energy used.

Better to bike and power your reading lights or something that can be "sized" to be replaced by 30 min of pedaling.

BTW, aside from attempting to recharge my laptop while it was on (doable, but too sweaty), and recharging my camera batteries (doable), I've just been using the bike to slowly recharge the used car battery I picked up. It arrived with 12.3v resting voltage, and so far this week (maybe 30-45 minutes a day) I've raised it to 12.43 resting voltage.

(I'm not sure what the battery's amp hour capacity is.)

Once I get to 12.65v, I'll start thinking about what I want to "spend" my energy on that can easily be replaced in a day or 2.

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