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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

general genny question


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  #1  
Old 06-03-2007, 02:07:27 PM
Economy Bob Economy Bob is offline
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Default general genny question

When I run my generator (30 kw single phase, propane ) and I use a load of say , 1500 watts lighting and 1500 watts electric heat, where are the rest of my watts going? Am I even making them , as I am not calling for them. And is this action causeing any damage to a pretty good size generator?
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Old 06-03-2007, 02:17:52 PM
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Default Re: general genny question

Your genset is just fine. You just have more power than you need.
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Old 06-03-2007, 05:21:54 PM
Economy Bob Economy Bob is offline
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Default Re: general genny question

And another question. If I am not useing 30 kw, does my fuel milage go down since the generator isnt struggling to keep up ??
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Old 06-03-2007, 06:46:10 PM
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Default Re: general genny question

Less work = less fuel used. the genny is still running at the same r.p.m. all the time. It just works harder as you put more load on it. Or draw more amps. The KW rating is generally only used to tell you what the max it can do. I use to know how to figure it but i am sure someone on here can tell you your total amps available. this is a more useable number. I get a kick out of the production truck guys that come along and ask me to give them single phase 208.
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Old 06-03-2007, 06:54:37 PM
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Default Re: general genny question

Yes Bob, your fuel consumption will be a lot less at 3KW than at 30KW. Your engine governor will control the fuel to make more or less watts. It will use a little more fuel at 3KW than say a 4KW generator at 3KW,however.
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Old 06-03-2007, 10:29:12 PM
Jim Rankin Jim Rankin is offline
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Default Re: general genny question

the voltage regulator controls the magnetic field strength to keep the output voltage at set point in the face of the electrical load you place on it. More electrical load requires more excitation from the regulator and more power from the engine.

On the nameplate of the generator, there should be a spec for voltage, amperage and kW. Voltage x Amperage (VA or kVA)tells you electrical capacity of the generator and watts (W or kW) tells you the engine capacity. These are not always the same. Frequently sets are built with an engine with kW equal to 80% of kVA. This is because some electrical equipment has a low power factor (kW< kVA)and takes less engine power per amp than high power factor equipment (kW ~= kVA)which takes closer to100% engine power per amp.

A diesel engine is always more efficient at part load than a comparable size gasoline engine because it can run with a "leaner" fuel mixture and doesn't have to pull air past a partially closed throttle. Fuel injected engines can more closely approach the part load efficiency of a diesel though even at full load, a gasoline or other spark ignition engine will still almost always be less efficient than the diesel.
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Old 06-04-2007, 09:05:30 AM
armandh armandh is offline
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Default Re: general genny question

power is power
if you take more power out expect to put more [fuel] in.
this is seen in the throttle position under various loads.

any system has a sweet spot, an area of the best efficiency.
if the designers had their heads screwed on....
it should be in the upper half of the output range.
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Old 06-04-2007, 07:07:31 PM
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Default Re: general genny question

Quote:
Originally Posted by Economy Bob View Post
...where are the rest of my watts going? Am I even making them
Nope, they never existed - the governor on the engine hasn't opened up enough to have allowed the generator to generate those 'extra' watts.

Quote:
Originally Posted by Economy Bob View Post
...And is this action causeing any damage to a pretty good size generator?
LP or Gasoline sets should be just fine. (Some Diesel engines don't fare so well under extended operation at light loading.)

Quote:
Originally Posted by Economy Bob View Post
...And another question. If I am not useing 30 kw, does my fuel milage go down since the generator isnt struggling to keep up ??
Depends by what you mean by 'milage'. Your fuel consumption per hour will be less at light load than at heavy load. But, your fuel consumption per kW-hr will be higher at light load than at heavy load, since the efficiency of the engine is lower at light load.
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