While musing on induction motors I realized something interesting. A totally unmodified escalator should draw less and less power as more and more people pile on. At some point their energy should defeat friction. When lowering all those meat blobs over many meters, the Potential Energy has to go somewhere. In that case the current phase will reverse and the motors naturally become generators!
So, to power some of your mall lighting (or perhaps run the handicapped-only elevators), just provide lots of "down" escalators, but make everyone use the stairs going up.
(It's a way for corporations to steal your lunch more or less directly, and AFTER you've eaten it.)-- wbeaty, Jun 27 2003 People powered cities http://www.halfbake...idea/People_20power [wbeaty, Oct 17 2004] Squirrel cage motors used as generators http://www.qsl.net/...tion_Generator.htmlYes, it works just fine. [scad mientist, Oct 17 2004] I've heard that "down" elevators just throw away the recovered energy in brakes or resistor banks. They should be storing it in flywheels or something.-- wbeaty, Jun 27 2003 I don't know about "storing it in flywheels", but how about using it to power an adjacent up escalator?-- supercat, Jun 27 2003 Almost all motors used are "squirrel" cage motors. They work by having a rotating magnetic field. These types of motors won't generate squat when reversed because there is no permanent magnetic field within them. Don't know what types of motors are used in regenerative braking but they might work. Whatever you do you'll have to change the motor and balance the inefficiecies with the power gains.-- shazam, Jun 27 2003 What about having a transmission that can connect adjacent elevators (in reverse direction). Any time more passengers are going up than down, it would provide excellent energy recovery from the down side, and any time more passengers were going down than up, the up passengers would be nearly free.-- supercat, Jun 27 2003 [Shazam], squirrel cage motors do work just fine as generators. I seem to remember that state of the art permanent magnet generators will be a bit more efficient than state of the art squirrel cage motors used as generators, but in combarably priced mid-range units the efficiency will be very close because induction motors are cheaper to build.
If you have a squirrel cage motor running off the power line and you force the motor to spin fast enough, it will push electricity back onto the grid and mack your power meter spin backwards if it has net metering capability. If you want to run it stand-alone, you need to add some capacitance across the motor (see link).
To make these motors generate at 60Hz and feed the power back onto the grid, you need to spin them a good bit faster than the no load RPM. If loaded rpm is 1000 and no-load rmp is 1250, you might need to take it up to 2000rpm to get much power out of it, so the escalator would need to be fitted with either a transmition to shift the RPM at the motor, or a variable frequency controller that could run it as a generator at a frequency below 60Hz to genrate electricty without changing th RPM.
So you're right that it would take work to implement this, but I wanted to correct what you said about squirrel cage motors.
For what it's worth, most recent freeway capable electric cars with regenerative braking use three phase induction motors with a variable frequency controllers.-- scad mientist, Jun 27 2003 All electric motors are generators and vice versa.
Anything else would be a violation of Lenz Law (and a violation of energy conservation.)
That's the whole point of my entry: an UNMODIFIED escalator is already doing this. The "down" escalator produces electrical energy when enough riders are on it.
To make an induction motor generate, just hook it to an AC source and then forcibly spin it slightly faster than its designed zero-drag RPM. If it's an 1800RPM/60Hz device, then spinning it slower than 1800RPM makes it into a motor, and spinning it faster than 1800RPM makes it a generator. (I'm ignoring bearing friction here, i.e. if you spin it at exactly 1800RPM, it coasts, so it neither consumes nor outputs any energy to the AC grid.)
No AC power supply? Then just hook your induction motor to a capacitor (with the value of capacitance chosen to produce a 60Hz resonant circuit with the motor's inductor.) Spin the motor and any tiny noise currents will grow larger and larger. Add a resistor in series and the resistor gets hot. No permanent magnet is needed. (It's sort of like a magnetic version of the Wimshurst Electrostatic Generator, but rather than a small charge being inductively increased into a larger charge, a small current is inductively increased to become a larger one.)-- wbeaty, Jun 27 2003 hey you can use permanent magnet induction motors to have that constant magnetic field. so you can change your motor into a generator. but wait, you have to store or consume your electicity being generated...-- sridhar236, Feb 07 2005 random, halfbakery