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rp181

Mon May 26 2008, 03:12AM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
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Posts: 1529

I was reading up on cumpulsators and Flywheel energy storage systems (same thing?). I dont quite get how the work, from what i understand, there is a lightweight carbonfiber flywheel in a vacume on magnetic bearings, with a motor and generator attached to it. The motor would take it too high speeds, then the flywheel would be slowed down, and energy comes out. I dont get how the kenetic energy is converted too electrical energy.

Any hobbyists create a cumpulsator?

Quantum Singularity

Mon May 26 2008, 03:35AM

Registered Member #158 Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282

I don't know the finer details but the basics are pretty simple, and you've already said them so not sure what you don't get. A motor spins up a flywheel. Then the flywheel can generate power using a generator. Perhaps your getting hung op on the why not just drive the generator directly with the motor? Because the spinning flywheel can deliver a lot more power per time. Like say the flywheel weighted 10 tons. And they were spinning it up with a 2hp lawnmower motor. With enough gears in a transmission this is possible, it might take hours and hours to get it up to speed. But then when its at full speed, you could turn on a huge amount of load that draws millions of amps and spin it down in a matter of seconds. No way the 3hp lawnmower engine hooked directly to the generator could supply that kind of power. That is kind of an extreme, but you get the idea... using a relatively low energy source to 'charge' the compulsator, which is capable of higher energy discharge in a smaller time.

Just a note, I didn't happen to see compulsator in our HvWiki, this seems like something we should have. Here is the basic info on it

As far as hobbyists, IDK, not that I am aware of. I think the benefit to a compulsator over a capacitor is only on a much larger scale than hobbyists, like for example a >1MJ capacitor bank would be quite expensive and at those kind of powers a big flywheel isnt nearly as expensive, but thats just a guess, someone please correct me if I am off.

rp181

Mon May 26 2008, 03:54AM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
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I think i get it, but on a wikipedia entry, it said steel flywheels were replaced with carbon fiber flywheels, wouldn't they want heavier flywheels?

EDIT: ahh, so they eschanged weight for speed. Slower with heavy weight would be way more dangerous then Light high speeds.

Quantum Singularity

Mon May 26 2008, 04:23AM

Registered Member #158 Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282

Well, energy is a product of mass and velocity, its probably more efficient to have a higher velocity than more mass, or at least gets around the design problems of centripetal force like they said in the Wiki.

Bjørn

Mon May 26 2008, 12:23PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

E = 0.5 * m * v^2

So if you double the weight you double the energy but if you double the speed you quadruple the energy. So a lightweight strong material can store more energy.

There is also a a question about what happens when the flyeheel fails. A lightweight carbon fibre flywheel tends to break up into small bits and dust when it fails. Then the energy can be dissapated over a longer timespan.

A steel flywheel might break into two separate parts and is only safe deep under ground unless it is spinning fairly slowly. So in many cases even weak and cheap plastics may be more efficient than steel when safety is take into consideration.

rp181

Mon May 26 2008, 01:15PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
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So for a flywheel, im looking for tensile strength, right?

Bjørn

Mon May 26 2008, 01:52PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

Yes, higher is better because it can spin faster before it breaks. But you also want low density because that means it will spin faster for a given strength.

rp181

Mon May 26 2008, 04:00PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
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Posts: 1529

So i could find barely any info on cumpulsators, but aton of info on FES. Nothing i read says that FES can provide short high current bursts, i think you could, Whats the difference between these 2?

badastronaut

Mon May 26 2008, 04:03PM

Registered Member #222 Joined: Mon Feb 20 2006, 05:49PM
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Remember that just because your flywheel stores a megajoule of energy doesn't mean you'll get a million amps out of your generator. The compensating part of a compulsator reduces the alternator's impedance so that it can supply a large amount of power.

The first compulsators were iron cored, but they weighed several tons. They switched to air core, and these need to spin much faster to be efficient.

You can probably run a regular car alternator as a proof of concept compulsator by replacing the 3 phase bridge rectifier with something that can handle more current. The stator will act as the compensator, but they are designed to avoid this.

rp181

Mon May 26 2008, 06:07PM

Registered Member #1062 Joined: Tue Oct 16 2007, 02:01AM
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This seems like a good Science Fair topic for me, though ile have trouble getting the motor...

How do you find out how much speed u can get from a motor for givin hp using gears, no transmission?

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