generator governor

The cheaper 2 pole alternators run at 3600 rpm. the more expensive 4 pole alternators run at 1800 rpm. Each pair of poles spun 360 degrees produces the sine wave 60hz output. 3600 rpm /60 = 60hz or 1800 /60 x2 = 60 hz The 4 pole units have more wire, cost more, run much quieter, have much better life. 2 pole units are cheaper, match up well (both hp and speed) with 1 and 2 cylinder indutrial engines.
I don't know all the specifics of the Geo engine but I'd assume that it has a relatively wimpy torque curve below 2000 rpm. Proably is geared to cruise (?? smirk!!) at 60 mph at about 2800 rpm. So the dilema is: run the engine at 1800 rpm where it will have a very long life but delivers very little power or run it at 3600 rpm where it has max horsepower but will tear itself apart. Imagine driving a Geo at 85 mph for as many hours as you plan to run the alternator. Imagine a rod tossed through the side of the block.
In order to get decent fuel economy as well as reasonable engine life, the engine should be turning around 2200 to 2800 rpm. This means about a 3:2 ratio. You can do this with a belt drive but this adds some more issues: the rear bearings on a Geo are not likely to like the side loading of a belt setup. Vehicle engines plan on delivering the load axially. It would probably work ok with a notched belt, a double row 'V' belt would not be my first choice.
You never mentioned how big the alternator is that you plan to drive. The textbook answer is that 746 watts = 1 hp. Add in some surge capacity and you can figure a bit under 2 hp per kw at full load. So the Geo engine would probably match up reasonably well with a 25 kw alternator. You could put a bigger one on but it might stall under heavy loads, especially trying to start a large motot. 10kw or less, use a 2 cylinder industrial engine that likes to run at 3600 rpm and has a decent governor built in.
Cheers.
Jerry Martes wrote:

On Mon, 26 Jul 2004 04:22:06 GMT, "Martin H. Eastburn" calmly ranted:
$170-250. $9.99-150
Speaking of which, I wonder if J.C. Whitney has been decimated by the availability of parts via Ebay.
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Jon, There is a mechanical governor used on older Gravely walking tractors. It is an "aftermarket" unit built by someone else and adapted by Gravely to the tractor. They worked pretty good as I recall. I cannot remember the manufactuer, but check with a Gravely dealer. He might have one on the shelf.
Bob

I bought a "universal" cruise control on eBay earlier this year for about $40. The going rate for newer units is somewhat higher. The neat thing about this ancient unit is it has a pot (like radio volume control) for setting speed. So, it could be locked on the right speed and left there. A modern (digital) cruise control would need to be "re-trained" for the right RPM (1800 or 3600) every time you started it up - a major hassle.
Jon

Yup!
Ideally, yes but due to winding resistance and magnetic losses the voltage will drop as the load increases even if the rpm is absolutely constant. Voltage regulation usually is done via the field current.
Ted

I have designed engine speed controllers, now in production. For a one-off like this, I agree with Jeff and Jerry that an aftermarket cruise control is the way to go. These are PI (proportional-integral) controllers so steady-state error is about zip. They come with a speed pickup (stick magnets on a rotating shaft) and a vacuum throttle actuator. Some tweaking of the gain control may be necessary to tune it so it doesn't "hunt", since the rotational inertia of a generator is probably considerably less than the inertia that governs acceleration of an automobile.
A wind vane governor, as on a lawnmower engine, might work reasonably well here. Another possibility would be an eddy current drag cup pulling the throttle against a spring, rather like a speedometer. With permanent magnets rotating in a stationary conducting cylinder free to rotate against a spring, torque is proportional to speed so rotary displacement (hence throttle position) would be proportional to torque and spring constant. If speed drops, throttle opens. Tighten spring to increase speed. A small DCPM motor with it's wires shorted together would also serve as a speed-to-torque transducer. This, a spring and a throttle linkage could comprise a rudimentary governor.
These are P (proportional) controllers so they'll have some "droop" at full load, but they're easy to make and might work acceptably well.

Thanks to all for the great ideas! The purpose of this project is to be able to run an air conditioner during the summer at our beach house in Baja Calif. It would also be used to help the PV panels charge banks of 12v batteries. I really don't need much more than 20 amps. max but it must run quietly, hence a small multi cyl. gas engine not working very hard instead of a more efficient (and noisy) diesel. Thanks especially to Don for confirming that a cruse control is probably the most workable solution, although I'll look into the other options. Thanks again!
Jon

Be sure you look into the 1800 RPM RV genset units. The Onan 'Emerald' series come to mind.
J> Thanks to all for the great ideas!

On 26 Jul 2004 21:07:09 -0500, Jon L. Eiserling vaguely proposed a theory ......and in reply I say!:
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May I step in?
Aircons are hard on gen sets. They not only start motors, but often under load. I have used a gen set that _ran_ an aircon easily, but would struggle to start it. In fact it would bog down at startup (and I have run a welder off this same genset) and never get up to speed, not because the governor was no good, but because the engine would drop in revs, to the point where no amount of throttle would rev it up. We used to have to start the aircon by _over_revving the gennie, then plugging the aircon in, then rapidly releasing the throttle. One hot day my wife failed to understand this needed technique yet again, and in spite of my screming and running for the plug, held the throttle open. No aircon.
We were in the postion where (a) the temp was such that the aircon was _always_ on "cool" once started (b) the aircon fan motor was _just_ enough to load the genset so thatn it was already throttled up and could kick in to start the compressor.
So a cruise control will only work on a gennie engine that has good reserves over the required power.
There is one possible solution; a huge flywheel. This would help carry the start load.
AND.
A petrol engine is unsuitable for what you want. Silence the diesel. Petrol engines running a charging system will make for very expensive charging, unles you have a really good inhjection system.
Airtcons are also hard on petrol engines.
Having said that, if you can get a petrol engine for Xhundred bucks and the same powered diesel probably cosost Xthousand, that's a lot of fuel at a holiday shack.
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What was the steady-state rating on the air conditioner, vs the steady-state genset rating? If one wanted to avoid this problem, how high up would one have to oversize a gasoline genset?
Jim
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Good point, Nick, but at steady-state load of 25 amps or so he may be OK. 25 amps at 220 V is about 5.5KW or 7.4 HP. Figure some inefficiency in the genny, call it 10 HP. Start surge on a capacitor-start motor can be 10X steady state, but the engine flywheel will soak up some of that. More flywheel would be good.
Running the engine too slow may put it so far down its torque curve that it bogs down and can't recover even at WOT, like trying to accelerate at low speed in 4th gear. I think 1800 RPM would be too slow for a gas engine.

But no alternator can provide 10x overload current. Look at the peak specs on consumer quality ones; probably more like 10%.
I personally build a 8kw genset with a 2 cylinder diesel engine.
My engine is a VM 292; made in Italy. It has 92mm bore and is rated at 27HP at 3k. Alternator is a 8KW Leroy Somers direct drive single bearing with SAE bell housing; rated 3x starting surge current. This genset weighs over 500lbs and can make 9KW at 1800RPM. Above 9kw the motor bogs and starts loosing RPM.
This genset will start a 4 ton central air or a real 5HP air compressor. Both of them pull less than 1/2 rated power but start so hard that the diesel lets out some black smoke and a heavy grunt. The waveform looks likes a clipped sine wave approaching a square wave. I doubt I could start either one of them if the genset was also running another heavy load. Another concern is the affect of the surge on other things. ie how is the frig going to react when the line voltage drops, the wave form clips and the freq drops at the same time?
I took the same motor and belt drove a 15kw alternator. Motor RPM was now 2400 and I could make serious power (about 12kw). I went back to the 8kw configuration because the noise level was too high at 2400RPM and I really didn't need that much power. I suspect the fuel consumption was high too.
chuck

No alternator can do it ,,,, but yours does???
I suppose motors vary in start current. The one I measured was 10X for less than 1/2 second. With a smaller start cap (or a droopier voltage source) it would draw less peak current but take longer to reach speed.
Compressors usually have unloaders, don't know about A/C pumps.

No mind does not. I tried to give an example of a industrial generator rated at 300% surge current have difficultly starting a load that is only 1/2 the rated capacity of the generator. Maybe that didn't come through..
I believe the range is 5-10; depends on motor type such as cap start, cap run, etc.
chuck

has a governor for $28.95, item 28-1201. Site is down for maintenance right now. Another source might be early sixties GM cruise controls. Speedometer cable driven, mechanical.
The engine he is using is about 60 HP. He could probably get 10 HP at 1200-1500 rpm.
And why worry about radial loads with belt reduction? There is a belt on the front of the engine driving the accessaries. With the exception of the 25 hp Kohler, I believe all small engines with oil filters and pressurized oil systems use plain bearings.

On 27 Jul 2004 08:54:41 -0700, jim rozen vaguely proposed a theory ......and in reply I say!:
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hmmmm...many years ago. 3KVA genset. Aircon was only for a caravan. Maybe 1...1.5 KVA? I know I was pushing my luck, but the aircon could definitely be started by blipping the throttle first. It was just tricky, and ultimately fatal to the aircon (and nearly our marriage! ):-<
I never tried starting a 1-1.5KVA motor on some other machine using that genset.
Don't know. It was the combo of the fact that the genset is virtually "idling" under no load, because its throttle is way down, the engine speed having no momentum, and the heavy inrush current of the aircon's motor. We were living "away from it all" with bugger all money. A possible solution would be a resistive load applied just before the aircon was attached (hah! A heater! ), and removed immediately the aircon had stabilised. This would load the genset's engine up into its power zone more, and apply some throttle. The amount of "preload", if it worked, would be very "cut and try".
***************************************************** It's not the milk and honey we hate. It's having it rammed down our throats.

A big-ass idler motor might even be better.

On Tue, 27 Jul 2004 17:27:35 -0700, Jim Stewart vaguely proposed a theory ......and in reply I say!:
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What part of "bugger all money" don't you understand? ***************************************************** It's not the milk and honey we hate. It's having it rammed down our throats.

Maybe I didn't think enough about what you'd written. The info was there. Yup. The one I tested was cap-start cap-run.