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Generators & Electric Motors General Discussion Antique Generators and Old Electric Motors: Questions and answers about restoring and showing old power generation systems.

Generators & Electric Motors General Discussion

Purposely running a 3600rpm generator at lower speed


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  #1  
Old 11-01-2018, 08:10:07 PM
K-Tron K-Tron is offline
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Default Purposely running a 3600rpm generator at lower speed

My brother needs a portable generator to run the block heater for his 7.3L ford diesel for about an hour every now and then during the winter months. I have a like new 7 horsepower 170432 Briggs powered 3kw Pincor generator that I would feel no real remorse if it was tossed about in the back of his pickup. The unit has about 30 hours of run time on it, and it like most 3600rpm generators run at the brink of destruction. Since the only thing that will be plugged into the generator is a 1000watt block heater, would there be any detrimental issues if I set the governed speed down to 3200rpm? That would save extra wear and tear on the engine, keep the noise down and shouldnt really effect the block heater performance one way or another. I do not think these Pincor contractor portable generators have any automatic voltage regulators in them. I will have to add a car muffler to this unit to keep the noise down. My brothers college will not allow him to run an extension cord to the trucks block heater, nor provide a power outlet. What do you guys think about this idea? Id hate to run it wide open with a big muffler, these engines already had trouble pushing the heat out of them.

Chris
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Old 11-01-2018, 09:00:10 PM
Vanman Vanman is offline
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Default Re: Purposely running a 3600rpm generator at lower speed

If the block heater is 120 volt, and the generator can output 120/240, you could slow it down until it outputs 60/120.
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Old 11-01-2018, 09:05:12 PM
Newoldstock Newoldstock is offline
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Default Re: Purposely running a 3600rpm generator at lower speed

Up here it get real cold.
I had a VW with a diesel and although it started it was hard to get it up to temperature and this meant I was cold.
Chum of mine ( and a mechanic ) installed a heater like this in his VW and was never cold again.

https://www.eberspaecher-na.com/prod...utomotive.html

I never got around too it.
Engine blew up in my VW.
Now I drive a Korean car with a gasoline engine....
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Old 11-01-2018, 09:39:44 PM
K-Tron K-Tron is offline
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Default Re: Purposely running a 3600rpm generator at lower speed

I am aware of the different style engine heaters on the market. I have a Webasto plumbed into the coolant on my truck with the Detroit Diesel in it. There is no reason to install such a unit on my brothers pickup, as this is the only winter he will need a generator to run the block heater, as he will be graduating in May. The last I ran this generator, about 5 months ago, it was running 3560rpm producing 59.2hz and 132.2volts. It reached 60hz right around 3660rpm, a little too fast for me! I can certainly test it out with the said load around thanksgiving and drop the governed speed until 120volt is met.

Chris
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Old 11-01-2018, 11:15:56 PM
Thaumaturge Thaumaturge is offline
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Default Re: Purposely running a 3600rpm generator at lower speed

No problem if a brush style generator. I typically back mine off 5% or so just to save on fuel and for the most part my loads are resistive heater elements or switching supplies good down to 90VAC input. Not so rosey with non-brush cap regulated gens. Their output falls off sharply too far from optimum frequency.

My suggestion is plug in killawatt meter or DMM and dial governor back to output reading ~112 VAC. (Note: Lower voltage will reduce heater WATT output. But not damage it. Watts = Volts x Amps. If 120 = 1000W then 112 = ~877W)
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Old 11-02-2018, 08:12:52 AM
armandh armandh is offline
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Default Re: Purposely running a 3600rpm generator at lower speed

a friend had an older 190 ish diesel and a second key for the door
he just let it run [small town]
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Old 11-02-2018, 09:42:43 PM
enginenut2 enginenut2 is offline
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Default Re: Purposely running a 3600rpm generator at lower speed

I think the life of a briggs or most other small air cooled engines is not compromised at 3600 R/M. If you look at the engines design/advertised HP rating you will find it to be almost always at 3600. The HP will be reduced below that speed and the cooling could be less adequate. The generator designer selected the engine size to build his generator set to, claiming a realistic output that would provide a reasonable life span-his company's ongoing success depends on that. Running lower speed with lower output might extend the lifespan a little but I think more would be gained by careful attention and periodical maintenance. I think there would be no compromise in adding a premium, quieter muffler, then it could sound like a Honda.
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Old 11-03-2018, 12:10:59 AM
richard.bessey richard.bessey is offline
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Default Re: Purposely running a 3600rpm generator at lower speed

I will chime in, yes I think you can run a resistor heater at a reduced RPM without much trouble.
I did this same thing except I was running a fan. I learned the hardway that the burned out, turns out the fan motor wants a certain frequency of AC power, even if it is 120 volts.
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Old 11-03-2018, 02:20:03 AM
Power Power is online now
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Default Re: Purposely running a 3600rpm generator at lower speed

I believe that Briggs engine is splash lubricated. The owner's manual on some engines say not to idle engine or run it at less than full throttle. I suspect reason for this is splash lubed engine does not get proper lubrication at lower speeds.

In my opinion, he will probably be fine running engine at slightly lower speed. Since it will only operate in very cold temperatures, reduced cooling airflow should not be an issue.

If it is just powering a resistance heater, gen end should be fine.

Eons ago, when I was in Marine Engineering school, we had formulas which I have long forgotten for calculating anticipated life of a diesel engine. Formulas were based on horsepower hours. RPM was one of the variables. If the RPM was reduced while holding load constant, engine life increased. Per formula, a 10% reduction in RPM at same load substantially increased engine life.

I suspect a 10% reduction on a gasoline engine would also substantially increase engine life. Without specific manufacturer's advice, 10% is the most I would consider on a splash lubricated engine.
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Old 11-03-2018, 07:19:17 AM
Kevin K Kevin K is offline
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Default Re: Purposely running a 3600rpm generator at lower speed

I suspect cooling would be more of an issue than splash lube by running a small engine less than 3600RPM. The small fins on the flywheel can't push enough air for effective cooling with the engine running at low speed. I typically run my lawn tractors at 1/2 to 3/4 throttle (but not under a heavy load!) and have never had an issue.

A lot would depend on the generator. A generator with a voltage regulator or a brushless capacitor regulated generator would never tolerate this. A brush type generator with a saturated pole or harmonic winding design may produce usable power at a lower speed. It would be an interesting test at any rate.
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