Gererator problems


  #1  
Old 12-31-03, 06:25 PM
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Gererator problems

Ok, here's one for ya. I have an air compressor that I need to run from a generator but it won't hold it. It will drag the generator down and kill the engine. I know the generator is working correctly as I can run my whole house on it, with exception of the central air unit. The air compressor works like a champ on any normal 15 amp circuit. Here is what I have:

Generator: Generac 3500 XL series - mod 09441-5 - volts 120/240 - amps 29.2/14.6 3500watts
Air Compressor: Porter Cable - mod c3151 hp Peak 3.5 - 120v 15amp w/time delay fuse

The generator has a 30 amp 3 prong round receptacle (along with the 220 and 15amp outlets) which I made up a cord for to use everything the generator has and it still won't run the compressor. Any ideas???
 
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Old 12-31-03, 07:02 PM
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The startup load is very high on an air compressor. I see this alot on job sites with small generators like yours. It's because the compressor is starting under full load. As the compressor starts it pulls down the generator, as the gen pulls down the voltage drops, as the voltage drops it makes the compressor starting problem worse. Get the scenario.
This is the idea behind a time delay fuse. The house voltage stays relatively constant but the amperage is very high for a short time as the compressor starts. Once running the amperage levels off to the running amps.

One thing you can try is to pull the air bleed to relieve some pressure when the compressor starts. This may help.

You may be running your whole house on this genset but it is not nearly enough to run many things at once. You must be very disciplined with what's on when under gen power.
 
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Old 12-31-03, 07:14 PM
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Thank you! Good explanation as to what is happening as the compressor tries to start. I'll try to bleed it as it starts...

Re: running the house: I'm not running the Empire State building for sure

Thanks again!
 
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Old 12-31-03, 07:23 PM
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Good luck!

Try and post back. It's nice to see if our advice is acurate and what other remedies might work.
 
  #5  
Old 01-01-04, 09:09 AM
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If that compressor can be changed over to 240volts then you will have better results. You will be drawing from both phases of the generator and at lower amps. Your compressor should already have pressure relief valve that relieves the pressure on the compressor head when the switch shuts off.
 
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Old 01-01-04, 11:33 AM
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Welp...I went and tinkered with starting the compressor and was able to get it to run on the generator IF I bleed it down to 0 psi and run on the 30 amp plug. I have to do this each time it starts. Pretty much renders the unit useless to get any real work done.

Quick question, I can't remember, but doesn't 1hp equal like 25amps? If that's the case I need like 87 amps peak (3.5hp) to get the the thing cranking? If I bust down and get another generator I want to be sure it runs the compressor. Thanks

Oh, the compressor is 120v only.
 
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Old 01-01-04, 11:59 AM
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A one HP compressor will require about 8000 watts at start-up. Which can be sustained for a few seconds. More then your 3500 genny can handle. You may want to invest in a "hard start kit" for you compressor. May help.

A one HP compressor motor needs 8000 watts at start-up. 746 watts per horse, about 10.5 HP
 

Last edited by weebee; 01-01-04 at 12:54 PM.
 

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