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Priesthood
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Joined: 02/01/2012
Location: United States
Posts: 2

Posted: 01:29pm 02 Jan 2012

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Good day folks, my name is chuck
I hail for central Florida, I have been a electronics and robotic repairman for the last 8 years.(no exp in design)

The project I'm building is an exercise bike that turns a generator to send power back into the grid via a wall outlet. The motor I have is a 115vac that came from an old meat saw, i have 1 question, if I take the output of this AC motor attach a diode to stop back feed, will it feed back into the grid. My thoughts were that it would not until my generator gets over 112vac. Can you guys help clarify? If possible I would like to avoid rectifying it back to dc so that I can hook it up to an expensive inverter. Just doesn't make sence for me to do that. If it comes to that I would rather find a good DC motor to use.

Also if anyone has seen this done, please provide as much feedback as you can, I have seen it done on instructables and several other sites, but know one seems to do anything but charge batteries.

Thanks folks hope you can help.

Pretty excited to be a part of this forum, seems like there are some pretty knowledgeable folks on here.

Chuck

VK4AYQ
Guru

Joined: 02/12/2009
Location: Australia
Posts: 2539

Posted: 01:25am 03 Jan 2012

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Hi Chuck

To do what you propose you would need to pedal the motor faster than its synchronous speed then have a frequency sensitive circuit to control the attachment to the mains a diode is a one way device that wouldn't work on AC.
In my humble opinion it would be more trouble than it's worth unless you are an Olympic cyclist.

All the best

Bob

Foolin Around

Priesthood
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Joined: 02/01/2012
Location: United States
Posts: 2

Posted: 02:23am 03 Jan 2012

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Couldn't I step up the voltage? Wouldn't that mean I could peddle slower and still send pwr to the wall. If there is a better way to do it, please advise.

I guess I could rectify and invert but it just seems excessive.

Thanks for the reply

VK4AYQ
Guru

Joined: 02/12/2009
Location: Australia
Posts: 2539

Posted: 09:54am 03 Jan 2012

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Hi chuck

You could use a transformer but the losses on the system would use up a proportion of your energy, it would be OK as a little project for the interest of it but its practical application is limited. You would still have the issue of a controller and peddling to slightly above synchronous speed.

All the best

Bob

Foolin Around

MacGyver

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Joined: 12/05/2009
Location: United States
Posts: 1329

Posted: 07:40pm 05 Jan 2012

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Priesthood

You asked if anyone had ever seen this done and I have. I live on the west coast near San Diego and there was a small gymnasium that boasted it was "Eco-Friendly" or "Green" because all the exercise bicycles were hooked to small inverters and those plugged into wall outlets.

Personally, I don't think it did diddly, although I talked to the gym's owner and he assured me it spun his meter backwards. I did not actually witness the meter, so all I have is his word. That gym closed down only weeks after it opened, if that hints at anything!

I still don't buy it and the reason is this: Try this yourself. Hook up a 60-watt incandescent light bulb to your biycle's generator and start pedaling. Keep track of how long you're able to keep that light bulb burning before you pass out and die from exhaustion!

You'll soon find out it takes a lot of input to do any reasonable amount of work. Now, for a real heat breaker, figure out how that compares with your electricity usage from a wall outlet and you'll soon discover we are literally 'spoiled' when it comes to power consumption. You can pull several horsepower from a wall outlet. One horsepower is something like 700 plus watts; it's not even a kilowatt! Try pumping out one horsepower on your bicycle for any length of time and you'll get my point!

I'm sure you could have a burst of speed and make your meter run backwards for a nanosecond or two several times a day, but just that amount of effort would either magically turn you into Lance Armstrong or send you to your grave.

If you want a real lesson in raw power, build a steam or a compressed air engine and see how much effort it takes to spin it against merely its own internal friction much less an alternator!

. . . . . Mac

Nothing difficult is ever easy!
Perhaps better stated in the words of Morgan Freeman,
"Where there is no struggle, there is no progress!"
Copeville, Texas

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