Bus generator problems!! Any Advise for replacement?

Question

I have 6,500 gas generator to run two 12,500btu roof a/c units on my bus.Nothing but problem after problem with generator.I was advised to change unit out to diesel unit! Any advise on what size i should be looking for?

Answer 1

You don't say what the generator problems are. It may be undersized for the AC units you are trying to run plus other things you are trying to run. The AC unit may require all of the generator's capacity for about 2 seconds to start. So if one AC is running, there may not be enough capacity to start the second AC unit. What other things are you running off the generator at the same time? The 6,500 watt generator can only supply a maximum of 27 amps out of the 240 volt outlet or 15 amps out of each of the 120 volt outlets or any combination that does not exceed the 6,500 watt capacity of the generator.



A diesel engine has nothing to do with the capacity of the generator. Diesel engines are used on larger capacity generators or continuous duty generator sets. The generator itself doesn't care what type of engine is spinning the rotor.



Will the generator run just one of the units? If it does, then my thoughts are the generator doesn't have the capacity to run the loads you have.

Answer 2

When choosing a generator, you have to consider what electrical loads you may experience. If you are only powering the a/c units, then measure the amp ratings of each and muliply times a/c volts ...120 or 240...to get the watt rating draw.



For example, if each a/c unit draws 20 amps X 120 volts = 2400 watts per unit....X 2 units equals 4800 watts max load...assuming they run on 120 volt circuit....most units draw less than 20 amps. You also want to have a generator which is rated higher than the max load you want to run so that the gen is not running at full power all the time....usually figure a max load of 70-80 percent of the gen's max output. Another issue is peak load....electrical devices with motors or compressors... such as a/c units... can have much higher initial loads at startup...2-3 times normal loads.



So for 4800 watts max load, you want a gen rated at 6000-6800 watts normal operating load and perhaps 8000+ peak load rating to allow for higher starting loads.

6000 X 80 percent = 4800

6800 X 70 percent =4760



And if you want to add other electrical devices or future expansion, buy a larger unit.



Check the amp rating on the a/c units and go from there. A store that sells generators should be able to help you pick one out based on your usage.



Edit:

Excerpt from an RV site...

"A typical 13,500 btu RV a/c will use 14.5-15A and a high efficiency model about 11.5 amps. That's under full load (compressor running and fan on high). The tricky part is compressor start-up, when the amp load doubles for a few seconds and gives you a brief 3000-3600 watt load. If this passes quickly enough most small generator can ignore the overload, but sometimes the breaker will trip or the a/c won't start due to low current."



More info at the link...

http://www.rvforum.net/SMF_forum/index.php?topic=22899.0



Your 6500 watt unit should be right in the ball park but perhaps a little on the low side for high starting loads with two a/c units. At max draw of 15 amps and 120 volts = 1800 watts with perhaps 3600 startup load. With one a/c running at max load and the second at startup, the load would run around 5400 watts. ..well below the rating of 6500. Lights add very little to the load...perhaps 50 watts.



Does the generator engine quit when running with no load? If so, then I'd suspect engine problems rather than the gen pac. Small engines can have issues with fuel filters clogging or sediments in the fuel bowl which causes stalling...I've even seen cases where the fuel cap vent hole was plugged with debris or dirt on lawnmowers and caused stalling...the gas being drawn out when the engine is running causes a vacuum in the fuel tank and stops fuel flow after several minutes...stalling the engine. Unscrew the gas cap a little to allow air in the tank, start the generator and see if it still kills in several minutes. ...if not check the vent hole or replace the gas cap.



If the engine only stalls when load is on, then you may have a bad gen pac or overheat limit switch issues....is there good airflow around the generator unit? No obstructions? Check for damaged or clogged fans as well.

Answer 3

If you love the roar of a diesel engine and the smell of diesel fuel then I guess that's the way to go, places like Camping World have technicians that can answer all your questions and will also sell and install the perfect unit for you.