Energy Conversion Project

[zrjohnso]

I am working on a project to convert the mechanical energy exerted on an exercise bicycle into electrical power by using a DC generator and a DC to AC inverter. I was wondering if there is some way to apply the generated electricity back to the power grid by directly plugging an electrical cord into the wall outlet. What would it take to make this work? What kind of protection and reliability would be required? Anything about this in the NEC? And how would this affect the metering at the location?

Any thoughts on the concept would be appreciated.

 

[bob]

Before you do anything you would have to have approval from the utility.
They can give you the details as to what is required.

 

[mdshunk]

Depending on how your bike output waveform happened to match up with the utility waveform, backfeeding a receptacle would either work just fine or have dramatic and catastrophic results. Simply put, it's no advised.

 

[wireguru]

that would be a good way of converting a working inverter to a non working inverter

 

[coulter]

It's a workable concept. You will need an inverter that will sync with the utility. They are available.

You will likely have to hardwire the connection to the panel. Suicide cord connections are really not a good idea.

I don't know what your bicyclist can put out for continuous power - maybe 1/3hp to 1/2hp. Using 1/2hp and 70% efficiency, gives 260W, at $.10/kwh, that's 2.6 pennies per hour. It will take 38,500 hours to pay for a $1000 inverter.

The utility will likely require separate metering for back-fed power. But I wouldn't worry too much about it - unless you have less than four light bulbs in your house, you won't turn the meter backwards.

Unless it was me on the bicycle, then you would have to have one light bulb or less before you would have to worry about turning the meter backwards.

carl

edited one of the spelling errors

 

[coulter]

I checked your profile - engineering student. Good.

Consider this;
Couple the bicycle to a standard 3ph motor. Set the gearing to overspeed the the motor 1% - 5%. Connect directly to 3ph utility-fed circuit - appropriate GF, SC, OC protection or course. Be a good engineering project.

It's called an induction alternator - their asynchronous. No phase syncing with the utility required.

If you do this under NEC 590.3.C I doubt you would get any squawks from the AHJ. Talk to one of your buddies with a power option.

Could be you could boost your efficiency to 90%.

carl

 

[zrjohnso]

Just to expand a little more, the idea is to implement this concept with several exercise machines and exercisers working together. My group and I are trying to come up with the best way to store the energy we produce, and we were exploring how to plug our machines directly into the power grid, instead of storing it in a battery.

Carl, can you please expand on "set the gearing to overspeed the motor 1% - 5%?" I don't have much experience with motors yet. Thanks.

 

[nakulak]

why not expand the idea:

set up the experiment on a whole gym, use a transfer switch, and see if you can develop enough power to switch the whole gym on to bicycle/exercise machine generated power.

 

[coulter]

... please expand on "set the gearing to overspeed the motor 1% - 5%?" I don't have much experience with motors yet. ...

With your major, you may never get much experience. You're going to have to learn on your own. Hence the suggestion to get one of your power option buddies to give you a hand. However, it was third year/fourth year befor I got close to a decent power lab.

That was long enough ago, as Iwire alludes, I think we were still watching TV by candle light.

Motor speed for an induction alternator:
First this is 3 phase, not single phase - you're not going to connect this to a house circuit.

Induction motors turn slightly less than synchronus speed. At rated power they will turn 3% - 5% slower than synchronus speed. For example, consider a 4pole induction motor. Synchronus speed is 1800rpm. At full load, the motor will have a speed of 1750 RPM. This "slip is necessary for the motor to develop any torque.

If this same motor, electrical connected to the power source, has the shaft connected to a driver and the driver overspeeds the motor (same 3 - 5%), say to 1850rpm, a couple of things happen.
1. It takes torque to overspeed the motor - you have to put work into the motor to get it to overspeed.
2. This work comes out on the motor leads, as electrical power put back into the grid.

An induction motor used in this manner is called an "induction alternator".

So one would have to set the gearing between the driver and the induction alternator to operate the motor at 3% - 5% above synchronus speed. A 2pole motor would have to spin 3600 + 108 = 3708

I curious as to your purpose to want to "store your energy". If you are just screwing around to learn - great idea. If there is another purpose, we may needto know this to better advise.

If you are just after the learning, and the concept of an induction alternator is interesting, also check out a "double fed induction alternator". They are not so demanding on the speed they have to turn to produce power.

carl

 

[crossman]

Just to throw out some watt numbers for cyclists:

A fit amateur athlete bike racer can average around 200 watts for an hour long race. He could peak at around 700 to 1000 watts, but this is full out and he wouldn't last more than 30 seconds.

An unfit non-cyclist would be lucky to average 70 watts for an hour.

Of course, there are many variables which would affect these results.

 

[mdshunk]

I saw a news clip a good number of years ago where a man hooked a bike to his TV so that his kids would have to pedal to watch TV. It kept them from vegging out in front of the TV and getting fat. Not such a bad idea.

 

[Jraef]

I checked your profile - engineering student. Good.

Consider this;
Couple the bicycle to a standard 3ph motor. Set the gearing to overspeed the the motor 1% - 5%. Connect directly to 3ph utility-fed circuit - appropriate GF, SC, OC protection or course. Be a good engineering project. ...

Carl, can you please expand on "set the gearing to overspeed the motor 1% - 5%?" I don't have much experience with motors yet. Thanks.

Woah woah woah hold on there bunky! Aren't you forgetting something Carl? When he connects a 3 phase motor to the utility, IT BECOMES A 3 PHASE MOTOR!!! The only way he can then make it spin faster than it wants to is not just by gearing. He will also need to exert MORE HP than the motor is putting out, otherwise your feet on the pedals are just a slight load on the motor. He will need some sort of ratcheting / clutch arrangement in there as well so that he can get the assembly up to a higher speed than the motor BEFORE he engages it. But then even an unloaded motor it going to have some HP output, which must then be subtracted from the input power that a human can sustain (.16HP is what I have read for an average healthy human, .4HP for 10 minutes before they become exhausted).

All in all zrjohnso, not easy to accomplish with any degree of safety. You are better off with a DC generator going into a battery, then feed to the utility through an inverter. Lots of professional training treadmills have what are called "4 quadrant" DC motors and drives on them, That means they regenerate when the input (athlete) HP is higher than the motor HP. Find and gut one of those to connect to your bike, or just rig a means of running your mike on one of those treadmills!

 

[coulter]

...Aren't you forgetting something Carl? ...

No. I'm not designing it, my post was an introduction to induction alternators in 200 words (or less). I respectfully request you read the whole post before commenting.

... The only way he can then make it spin faster than it wants to is not just by gearing. He will also need to exert MORE HP than the motor is putting out,...

You lost me here. Connected to the utility, unloaded, the motor is ...ahhh ...unloaded. Our test 1/4hp motor will be very near synchronous speed. It only has to have sufficient slip to have the torque required to over come the losses - windage, friction, I^2R losses for the magnetizing current. So the only power that has to be input to the shaft to bring the motor up to synchronous speed is enough to match that. Since I'm not designing it, I don't care if he uses a ratcheting clutch or a flux capacitor. The requirement to input 1/4hp to the spinning motor shaft to get the shaft up to synchronous speed does not meet any physics known to me. Now, to turn the motor 3% over synchronous speed would take 1/4hp (plus losses).

...The only way he can then make it spin faster than it wants to is not just by gearing. ...

Don't like the gearing to get the pedal speed range to match the motor speed range - okay, I'll suggest the OP use a 72 pole 1/4hp motor. Then he can connect the shaft to the pedals.

... You are better off with a DC generator going into a battery, then feed to the utility through an inverter. ...

I'm not privy to the OP thinking. That fact would be part of what you didn't read of my post. Contrary to popular belief, I don't have sufficient hubris to tell the OP what is "best".

Woah woah woah hold on there bunky! ...

"Woah" (sic) - "bunky" That's demeaning. I would suggest that if you choose to be demeaning, at a minimum, you should get your physics right - buckwheat

carl

 

[rattus]

First things first:

First things first:

I would suggest scrounging an automotive alternator from a junk yard. I would think that one with an external regulator would be more enlightening. Be sure you understand the workings of these two devices, then hook it to an automobile battery. Now you can experiment with the gearing. A multispeed bike would be an asset here. You can experiment with the loading as well.

Remember, the battery is required to provide the field current, and a fully charged battery will present a light load.

Get all these ducks in order before you proceed.

 

[coulter]

Automotive alternators are fun to goof around with. But they are high speed devices. Most are geared up 2:1 or 3:1.

You could be looking at 3000rpm just to get minimal output.

Some will self start with just residual field magnetism.

Nice thing is you can short circuit them and they don't burn up - they current limit, even with full field.

New thought. I wonder if they could be connected as a double-fed induction alternator. Have to get rid of the diodes, but that's not hard. Interesting, but likely useless - except for goof off stuff. Have to work on this a bit.

carl

 

[dbuckley]

With your original plan of DC to AC, do a google for guerilla solar inverter, there are a number of inverter products that safely put power back to the utility, but that may not be strictly legal. These little inverters should be of the right scale for your initial project.

 

[Jraef]

No. I'm not designing it, my post was an introduction to induction alternators in 200 words (or less). I respectfully request you read the whole post before commenting. ...
Balance snipped for brevity

My apologies coulter.
1) I was not addressing my entire response to you, some of it was meant for the OP, but I did not clearly delineate, bad form on my part.
2) "Bunky was not meant to be disrespectful; more of an unconventional term of ill placed familiarity that I use in speech (probably too often there as well). Again, bad form on my part.
3) I'm all wet anyway. Bicycle pedals systems are inherently ratcheting! All he needs to do is make sure he is pedaling fast enough and with enough power to overhaul the motor.

 

[LarryFine]

"Bunky" means bunkmate, like the guys in the Swamp in M*A*S*H called each other.

It's certainly not derogatory or antagonistic, like "Bucko" from Happy Days might be.


Waddya mean I watch too much TV?! :roll: