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Microwatt

Tue Aug 16 2011, 03:36AM

Registered Member #3282 Joined: Wed Oct 06 2010, 05:01PM
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Posts: 224

i am toying with the idea for a compulsator type of device which should definitely be in the range of amateur science. i think that an alternator could be used to put out tens of thousands of watts if you are able to excite the windings with enough voltage such as from a capacitor bank. The EMF force generated would instantly stop any automobile engine. So I propose to machine a key way into a manhole cover and attach it to the alternator. the theory being is that the spinning manhole cover has enough kinetic energy to turn a fully energized stator winding at ridiculously high voltages above 500v. a manhole cover properly balanced could easily field 50KJ of rotary energy or more.

Patrick

Tue Aug 16 2011, 03:45AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Manhole cover? Yikes thats a lot of kintic energy! Ive wondered what the maximum ouptut of a wellmade alternator would be capable of, ive attached them to a 16 horsepower 2-Stroke but moved into an apartment before i could test it. Try not to get hurt or killed by your manhole cover, if it ever flies loose!

I worry about saturation in the stator coils/steel. seems like your expecting to much power from to little steel.

Proud Mary

Tue Aug 16 2011, 10:53AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Microwatt wrote ...

The EMF force generated would instantly stop any automobile engine.

'The EMF force generated would instantly stop any automobile engine' in a way that made sure it would never start again. Something would have to give, shear off, disintegrate, burst apart, and with the crankshaft frozen, the whole engine might get it into its head to spin instead, breaking free of its mountings, and killing anyone who stood in its way.

Why not build a model using a small 2-stroke engine so you can thoroughly investigate the forces, stresses, costs, and hazards likely to be encountered in a larger machine?

Ash Small

Tue Aug 16 2011, 11:20AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Proud Mary is right. I recently did this myself, not for the first time.

Diesel engine stopped dead (siezed up) on the motorway.

Camshaft kept turning. cambelt jumped several teeth. valves hit piston. pushrods and rockers 'smashed to f%&k'.

Engine cooled down and 'freed up', but engine had turned into proverbial 'bucket of nails'.

Luckily I 'only' needed to replace the pushrods and rockers.

Microwatt

Tue Aug 16 2011, 02:17PM

Registered Member #3282 Joined: Wed Oct 06 2010, 05:01PM
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Posts: 224

Why not start at a lower voltage say 100V and monitor how much the engine stresses with that type of voltage applied to the stator causes. you could do this experiment yourself.

Patrick

Tue Aug 16 2011, 02:24PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Microwatt wrote ...

Why not start at a lower voltage say 100V and monitor how much the engine stresses with that type of voltage applied to the stator causes. you could do this experiment yourself.

I think current and voltage establish the counter rotational force that the pistons would see. And yes always start small.

Electra

Tue Aug 16 2011, 09:46PM

Registered Member #816 Joined: Sun Jun 03 2007, 07:29PM
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Posts: 156

I would imagine car alternators are quite lossy, as they need to be cheaply manufactured and lightweight, so copper losses I guess would tend to limit the maximum current, and I donâ€™t know how much you could increase the excitation voltage till it saturated as Patrick mentioned.

A vehicles engine could put out more horsepower than a small alternator could consume so Iâ€™m assuming it would just turn it until it smoked.

One of my first cars an old one, had the alternator regulator or rectifiers fail, it just gave out so much current that it melted a 60A lug terminal on the back right off.

If you want higher voltages a multi kilowatt mains generator set might be a more suitable option.

I guess the complusator would be a very much over engineered device to cope with very high peak current and mechanical shock.

Arcstarter

Wed Aug 17 2011, 04:22AM

Registered Member #1225 Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253

I agree, a small alternator would burn out before the engine would have a problem. What would actually happen is the belt would just slip. In the US, the typical small car is around 120hp or so. 745w is 1hp, so a 120hp engine theoretically outputs 89kw.

However, 120v is fairly easily achievable from a typical alternator. Enough voltage and high enough speed of rotation will allow you to get the voltage much higher than it was designed. It's reliability would be questionable at best, but it's doable.

Keeping the manhole cover from spinning on the alternators shaft would not be anywhere near easy. It would take one hell of a key. Even 5hp engines don't use a key to keep the flywheel spinning, they use the friction between a beveled shaft and a beveled hole in the flywheel at the same angle. The key just ensures the flywheel will be at the correct 'angle' in relation to the shaft to ensure the spark timing will be correct. I tried replacing a sheered key in a 5hp engine of mine with a much stronger steel, and it always sheered because i hadn't pushed the flywheel onto the shaft hard enough.

Microwatt

Wed Aug 17 2011, 08:53PM

Registered Member #3282 Joined: Wed Oct 06 2010, 05:01PM
Location:
Posts: 224

I understand that most keys are made of soft iron . maybe it is possible to add carbon to the steel and quench it. or a better way would be to simply braze the manhole cover to the shaft. Doing something to the rotor to keep it cool while the ends are red hot. How hard would it be for a machine shop to balance a manhole cover? Could it be theoretically possible to get 50kw out for a second?

Patrick

Thu Aug 18 2011, 04:26AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Microwatt wrote ...

How hard would it be for a machine shop to balance a manhole cover?

I doubt any of the shops that can do it, would do it for a single individual.

Microwatt wrote ...

Could it be theoretically possible to get 50kw out for a second?

Yes, this is a flywheel energy storage system for accumulating kinectic energy from a long time at low power, then using alot of that same power in a short time. Thus the laws of thermodynamics and laws of conservation remain in place without the universe exploding.

but the real energy in a optimized design is generally confined to the rim, not uniformly distributed as a makeshift man-hole thingy would be. What your trying to do is possible for a hobbist/DIY'er but you must not confine yourself to the manhole idea, though i respect your "man-hole" idea, its not what i would do.

when this has been done at physics labrotories/universities it is very specialized and well thought out. You will need to do the same. When i built my 16Hp motorcycle-engine-alternator combination, i relied on the inertia of the crankshaft, flyweel timer, some of the gears, the clutch was bolted permanetly, and the chain drive and alternator rotors. thats a lot of spinning steel! about 25lbs @ 2000 and 6000 RPM! I expected to get 8Hp "wasted" keeping the whole thing turning, then 8Hp would be left for the alternators, which i assumed at max generating power, efficiency would be 50% so 4 electrical horsepower would be useful, 4Hp x 746W = 2,984W. so for 105lbs of metal i would get 3kW, (400Vdc @ 7.5A) which means about 3000 Joules per second for as long as i had gas.

That was my system for generating power with out my father freaking out about me wanting a 240 Vac , 40A circuit for my personal use. He was afraid id explode the house or kill myself, or possibly both. Parents worry to dam much, you know? However, it should be obvious that the system i created is/was far more dangerous than just letting me have my own dam 240V socket!!!

Anyway, my system didnt store power, or time shift the input energy as you wish. my system was well built and conservativly down rated from what i knew it could do.

Also one last thing, dont exclude other options that arnt like your manhole idea, remember kinetic energy of a rotating body can be calculated with radius and mass with velocity and integration or some such thing. Ask yourself this: does it have to be a thin rotating wheel? or can it be a long slim rolling shaft? does it have to be light and spinning fast? or can it be massive and spinning slowly? one way may be easier/cheaper/faster to build than another way.

Ive been drinking and feel tipsy, so i should log off here shortly while i can still tYpe.}
Hope my ramblings have been useful. Try not to die or end up in the ER at 2 am bleeding.

EDIT: I forgot--one last thing. I made my system automatic (except for the kick start) and it was started and killed via very long corded control box, this way the device was far away from the house (on the farside of a hill), and far away from my own body (which i value greatly) then running power cables to the final device using the power. Any questions while running or comments like "what the hell was that !?" meant the E-stop was quickly activated.

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