Generator size

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New member
Jul 7, 2005
I just purchased a used class B that has roof air and a microwave but no generator. I need some advice on adding a generator; best to get a small portable I assume as my space is limited. How large a generator will I need to run the roof air? I assume the small microwave does not use much power. Any opinion regarding make and size of generator will be appreciated.

This class B is a Dodge with a 350 and single exhaust. Can I improve my performance and gas mileage if I got to dual exhaust?

Paul [email protected]

A small (9000btu) a/c would require at least a 2.5kw generator to run continuously. KWH=btu's times .000293. Even small microwaves use at least 500 watts, so you're looking at a 3kw unit to run both at the same time, and that's pushing it. Of course you could shut down the a/c when cooking. A 2kw genset will probably have a surge rating of around 3kw, but that's only for 10 or 15 seconds; not even enough to heat up a cup of water for coffee. Sorry I can't be more positive, but 'them's the facts'.

If your present exhaust system is too small, going to dual exhaust would increase power but not necessarily fuel economy. Best way to test is to take it to a facility and have it checked. They will drill a small hole in the exhaust pipe and measure back-pressure at various rpm's. Also be aware that exhaust systems are not just a way to get the exhaust from the engine to the outside atmosphere; they are part of the overall tuning of the engine/exhaust to get the best horsepower and torque within a normal operating rpm range. Too large an exhaust can seriously hurt your performance. Check with aftermarket exhaust system builders and compare the before and after performance curves before you make a decision. There are many out there. Google them. Also check out 'chipping' your engine - costly, but sometimes worth it.
Karl is right on.  Rv type roof a/c units are usually either 11,000 btu or 13,500 btu.  There are super-efficient models available that require as little as 8 amps (1.0 KW) when running, but the standard models are in the 12-13 amp range (about 1.5 KW).  And a microwave is a power hog also - the rating om a microwave is its output power, e.g. 600 watts or 1000 watts. The input power required to produce that is typically 1.5-2.0 times the output power.

A genset capable of putting out a sustained 15 amps will probably manage to run your a/c, but a 20 amp model would be a better bet. Shut the a/c off when you want to use the microwave. for a few minutes.
I guess this means I would need about a 3000 Gen? Any reccomendations as to where to shop or what brand? Since I have a classB (Camper Van) it will have to be a portable that I can put outside when being used.

Thanks for the info

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