Help on generator voltage controll : LUSENET : TimeBomb 2000 (Y2000) : One Thread

I have been working on a home built generator. I have a Lister diesel engine that I got for next to nothing. I have overhauled it and it is running great now. It is way over sized for the generator that I am going to use with it. The engine is 44 horse power, the generator is a 10 kw. It is recommended to have 16 to 18 horse power for that size of generator, so you see I have more then double the horse power. So I figure that I could run the engine at a low rpm and come out ok with the fuel economy.

I have the engine rpm set to run at 1200 and the generator turning at 3600 rmp which gives me 120 volts. My problem is with the engine running at a low rpm the governor is real sluggish, when I add a load I get poor response from the governor.

I need some one with the know how to help me out on this. Is there some kind of voltage regulator that I can use that will keep the voltage at 120 even if I up the rpm a little, Are there any electronic governors, Or do I change the pulley configuration so the engine will run at say 1800 rpm. But if I do this there goes my fuel economy. The engines top speed is 2200 rpm.

Or do I go to plan B get a smaller engine? I would like to keep this engine. It is a beautiful engine and is known for its fuel economy and longevity. I like the over size, it give the option of adding a compressor or hydraulics. Maybe I am expecting to much. What do you think? Thank you for any help.

-- Lyle (, July 05, 1999



Would check advance curve on your 44 horse. With a 3:1 step up your diesel should loaf happily @ 1200 but curve for demand load may well have been set for a different task and needs "push or pull".

-- Carlos (, July 05, 1999.

I doubt that you will ever solve your problem in that manner, because, in my opinion, your problem is with your engine and the torque band, which varies according to rpm. I have no idea about the specifications for that particular engine, but I do know they are good engines in general. But you must look at the specifications, find where the proper rpm for load is. Just as when you try to accellerate a car in 3rd gear at 15mph, rather than 2nd, when the eingine is running just fine, it loads up and is sluggish to respond, and you must feather the clutch to keep it from stalling, you have the same type of problem. You have to change your gear ratio, increase the rpm, and with that your problem will probably be solved.

You may really want to check this and your fuel consumption may get even better. I had a fuel flow meter on one my cars and the lowest fuel comsumption was at 35 mph, period, in high gear. Any speed, higher or lower, resulted in higher fuel consumption.

Put on a fuel flow meter and see.

-- xBob (, July 05, 1999.

Another idea. Put on a bigger generator, up the rpm, and sell the whole unit at a good profit. I hear that gen sets that size are in short supply. Then buy a smaller unit.

-- xBob (, July 05, 1999.

See if you can get a spec sheet for that engine. You might find running at 1800 will get you better "gas milage". Diesel genset's fuel consumption tend to be more affected by the load, which is the wattage used in your case.

All engines, gas or diesel will give the greatest efficiency at a particular given RPM and load, go above that or below that and effiency drops off. Please note that efficiency is NOT merely fuel per hour, but fuel per useable output. Figuring out or experimenting with what wattage load gives you the best fuel/watt is what you are looking for.

P.S. varying voltages is hard on electric motors, more fuel use and fewer motor burnouts would be my choice.

-- Ken Seger (, July 05, 1999.


If the engine has a top rpm of 2200, then I'm betting the torque curve is best at about 1800 rpm. This is probably where the engine is designed to run and respond to demands. It will also likely give you excellent fuel economy at that speed. Most portable diesel generators are set to run at 1800. Why don't you just change the gearing to 2 to 1 and then run some fuel consumption tests. Bet you will be surprised and happy with what you get.

-- Gordon (, July 05, 1999.


There are autoregulating transformers which will self adjust the voltage input from 90 to 130 VAC to 120 VAC. You will find these at surplus shops, check the net.

As far as motor speed you can go with an electonic governor but then you are into a technology issue (spare parts). The electronic governor will sense the frequency of the output voltage and move a solenoid lever to adjusat the throttle up to compensate for the underspeed. You may be about to get something like this through a wholesaler.

-- ..- (dit@dot.dash), July 05, 1999.


I agree with the other posts that you don't want to complicate this situation with exotic voltage regulators. Just put a pulley on the engine that is twice the diameter of the generator pulley and run some fuel consumption tests for a generator speed of 1800.

Now, one other thing. The frequency of 60 cycles is probably more important than the actual voltage, presuming you can put out at least 115 volts under load. You can put together a very simple frequency testing system. Go to any descent radio control hobby store and buy a digital rpm reader. These are about the size of a pack of cigarettes and cost about $35. They are designed to read the rpm of propeller speeds by pointing it at the spinning prop. Usually they have both a 2 blade and 3 blade prop selector setting. Use the 2 blade prop setting. Then buy a small fluorescent light, like the kind that are designed for wall mounting. These are usually a single tube unit about 18" long and sell for about $10 at any home supply store, or even Wal-Mart. Fluorescent lights actually flash at the cycle rate of the electric supply, but since the flashing is going on at 60 cycles per second or 3600 times per minute you can't visually see this, but the prop reader can. When you are ready to set the generator final speed for 60 cycle current supply, just plug the small fluerescent light into the generator plug, point the prop reader at the light and see what it says. It should read 3600 flashes or cycles. If it only shows 3500, increase the engine speed slightly until it reads 3600 on the prop reader and you've got it. Oh, and to calibrate the prop reader, first test it on that light plugged into house power to make sure it *is* showing 3600. The house power is always held very close to 60 cycles regardless of the voltage being supplied. Anyway, this will tell you if the prop reader is set dead accurate. If the prop reader shows slightly off you can either open up the back and fiddle with the fine adjustment, or accept the reading you are getting and use that as the base. If it shows 3500 on the house current, just accept that 3500 is actually 3600 and set the generator speed to produce the same 3500 that the house current gave you on the prop reader. Hope this makes sense. Anyway, it's a very inexpensive way to create an electric cycle *meter* that works real good, and can be taken anywhere you want to check the *cycles* being put out by either utility supply or any generator system anywhere.

-- Gordon (, July 05, 1999.


That sounds like a valuable tool, but I am confused on something.

If set at "two blade", doesn't that mean the tach reads two pings per revolution?

If so, would the florecent light indication have to be multiplied by two to get correct frequency (rpm), or 60 hz would indicate 1800 on the tach?

One more question. Would this tach work on a solid faced pulley if I put a piece of aluminum tape (or two, for "two blade") on the pulley and tried to vary the distance from the tach to get a reading?


-- Tom Beckner (, July 05, 1999.


The fluorescent light "pulses" twice per cycle, providing readings equivalent to a 2-blade prop.

-- Elbow Grease (, July 05, 1999.


I don't have the answer to the 2 ping question, unless the above comment is correct. I can tell you that the calibration procedure is straight from the owner's manual on this matter, so it works. And as far as reading the pulley directly, yes you can do as you suggest. In fact it is the recommended way to read a flywheel rotation on anything that is not producing electricity. Just put a piece of white tape or paint a white line across the entire diameter of the rotating item. Incidentally, if you set the prop reader to the 3 blade setting it will still work, but only give a reading of 2400 (I think that's right) instead of the correct 3600. Notice that you can use this to set rpm of anything that you can read a spinning line on, or any portable generator that puts out 60 cycle voltage by reading the fluorescent flashes.

-- Gordon (, July 05, 1999.

Hay: Thank you all for your response, this gives me some good ideas to start working on. I appreciate the help.


-- Lyle (, July 05, 1999.


Go for it! You'll feel justifiably proud of what you were able to put together, to make happen, especially in this critical electric area.

-- Gordon (, July 05, 1999.

Lyle: Good Luck.

Gordon and Elbow Grease: Many Thanks.

-- Tom Beckner (, July 05, 1999.

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