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Old 07-08-2003, 10:00 AM   #1
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Dumb Generator Question #2

Ok, with all of this talk about using 30 amp outlets at home and elsewhere, what about the generator?
Mine is a 3100w with 2 120/20 amp outlets. How does this affect the requirements of the trailer. Seems to me it is a bottleneck in the system. Even though the generator is capable of more than 20 amps it is not available to the trailer, is it?

Second question: Where can I get voltmeter/hourmeter combo for the generator? I plan to fabricate a sound damping enclosure for the generator and may add temp and ammeter and put them all together in a panel. I hope the design of the enclosure will be inexpensive and repeatable and will post the results. Anybody want to chime in on possible readily available covers? Maybe an old window A/C enclosure? Nah, too many vents. Maybe a 55 gallon drum split lengthwise off-center and use the bigger half? Cover the inside with engine bay insulation, vent at the peak, drop it down over the genset and mount the panel on one end? Heck, paint it silver and it will look like the A/S's offspring! I know someone here used a job box, but that is a bit expensive and it would pain me to cut into it.
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Old 07-08-2003, 10:30 AM   #2
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Dave-O, there are some newer generator models, such as the Generac 4000XL that have full 120 V 30 amp outlets. Most generators, like my C/H 5000 watt model only have the full 5KW available through the 240 connector. The 120 V outlet is split into 2, 2500 watt connections, that CANNOT be hooked together, or the generator will self destruct.

I am not sure putting an air cooled generator into a "housing" would be a good idea, unless you can insure proper venilation.
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Old 07-08-2003, 11:09 AM   #3
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ventilation

Pick,
That is one of my concerns, how to vent air in/out, but keep the sound from doing the same. I found a thesis on the subject and vents were the prime sound leakage areas (obviously).
The guy built a wood enclosure for testing purposes, with minimal venting and stated that the small engine had a 450 degree limit (i think) and the operating temp with the cover got up to 370 before stabilizing.
The cover will have some form of mechanical ventilation. I have a bathroom vent/fan that I am currently eyeing.
Another thing I need to know is: Is it better to suck or blow? Do I want to suck the air off the engine and out or do I want to blow across the engine and have a passive vent for the outgo?

I have the pdf file of the Masters thesis for ME titled "Optimal Design of an Enclosure for a Portable Generator" if anyone wants to chew on it. It's a bit over my head.
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Old 07-08-2003, 09:15 PM   #4
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I don't know if a bathroom fan would be big enough. I have a 4kw Onan and it has a 480 cfm flow. As far as direction I would try and make the generator suck the air in and use the fan to exhaust it.

If you have a link to the enclosure thesis I would like to look at it. Probably wouldn't understand it either, but what the heck.

John
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Old 07-09-2003, 07:34 AM   #5
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Sure Pick, the address is:

PDF file on Generator Enclosures

Alternately you can do a google search for "Optimal Design of an Enclosure for a Portable Generator" and find it quick.

You're right on the bathroom fan, I think I may need to use a squirrel cage fan.

I have also found a source for the super trapp muffler for small engines at Jack's Small Engines
SuperTrapp Muffler

What can I do about the 20amp/120v outlets on my generator? Any way to have someone change one or both to one 30 amp outlet?
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Old 07-09-2003, 09:06 AM   #6
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Dave-O, there is NOTHING you can do to make it a TRUE 30 amp outlet. It is my understanding that generators with 30 amp outlets have a seperate 30 amp 120 volt winding on the generator.
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Old 07-09-2003, 02:27 PM   #7
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Ok, if I change the outlet to a 30 amp outlet, would it allow the trailer to pull the 25.8 amps (i think) that the generator is capable of?
I mean the generator won't put out 30 amps, but it puts out more than 20. Having the extra margin would be nice.

Nobody else is in the same boat? That is having a generator capable of running the A/C, but limited by the 20 amp/120 outlets that are put on?

One more question. If I am running the A/C with the current configuration, will the breakers trip on the generator if the A/C tries to pull more than 20 amps on start-up? Are does the voltage just sag? TIA

-David
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Old 07-09-2003, 06:03 PM   #8
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30 A from a 20A winding.....

Changing the receptacle rating won't allow you to pull a greater load from the generator. The capacity is dictated by the internal construction of the alternator. Whiel there is always a safety factor designed in, trying to push it will just create molten copper where once spun wire.

If you want to get 30A, then you'll need an honest to goodness BHG (that's Big Honking Generator). I would suppose such a one might be on teh market (i.e., 110V @30+A) but I've not seen one.
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Old 07-10-2003, 07:26 AM   #9
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Please read question again...

If the genset is capable of 3100w @ 120 volts, then there are 25.8 amps available. If I change one 20 amp outlet to a 30 amp outlet (or 25 amp if it is available) then this should allow me to get all 25 amps that the genset is rated for should I need it, correct?
I am not asking the generator for more than it is rated to deliver, I just want available to the trailer everything that it is capable of.

Does this make sense?
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