I have a 4000 watt generator, but cant run an 1800 watt air compressor. Why?
I have a 4000 run-watt Coleman power mate generator. Also have a Campbell-Hausfeld air compressor. The compressor is plugged directly into the generator. The first time the compressor starts, it starts and runs fine until it shuts off when the tank is full. When the air pressure in the tank drops below the preset pressure, the compressor comes back on but has a hard time (runs a little slow) and then trips the breaker on the generator after only a few seconds. The air compressor info plate states the compressor pulls 15 amps at 120 volts. That is 1800 watts. The generator outputs 4000 watts. Plenty of power to run the compressor. What gives? It works fine the first time the compressor comes on. It doesn’t struggle at all. The very next time, it has a hard time getting the compressor motor started and upto full speed. It always trips the breaker. Works fine on house power tho. I really don’t think its a generator problem but maybe someone else can tell me more? Any comments appreciated
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Tags: 1800, 4000, Campbell Hausfeld, campbell hausfeld air compressor, cant, Coleman, compressor, compressor motor, generator, power mate, time, watt
10 Responses to “I have a 4000 watt generator, but cant run an 1800 watt air compressor. Why?”
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You should probably check the amps. Although you have adequate wattage, the air compressor may require more amps than the generator is supplying.
Good luck.
The 4000 watts is available only under very special circumstances. That rating is close to, if not an outright, fib. If you had an unloader valve on the compressor such that the motor could get up to speed without pumping against pressure, the system MIGHT work fine. As a guess, the compressor starting against no pressure probably pulls (or tries to pull) 35 or 40 amps until it gets up to speed while starting against pressure, it pulls (or tries to pull) twice that amperage and the generator can handle the first load but not the second.
After the 1st time your compressor runs to full pressure and stops, do you hear air bleeding out of the cylinder relief? If not you have a bad valve. If the motor tries to start with pressure in the cylinder you will have high amps. The valve is cheep and is usually threaded in the tank at the end for the supply air line from the compressor.
Some high amp tools have a smooth start switch [easy-start] built into the on/off switch, so it doesn’t overload when it suddenly is switched on. It takes more amps to get something up to speed that to maintain it, just like a cars accelerator. My compressor has this, as well as my 12″ table saw, and it takes a second or two to build up to full amps, rather than instantly.
BTW, is the breaker on your generator a 15a, or a 20a?
A generator has a governor to control the engine speed, and it probably doesn’t have a chance to “catch up” before the breaker overloads and trips.
Check this out……..maybe this is the answer to your question.
http://www.chpower.com/webapp/wcs/stores/servlet/HelpView?langId=-1&storeId=10051&catalogId=10001&helpURL=help
It should be a link to Campbel-Hausfeld air compressor’s troubleshooting page dealing with a bad check valve.
The rating is 4000watts total.
Does it have multiple receptacle outlet types? 120V 240V 12V
If yes than the 4000 rating is the combined (independent) capacity of each outlet.
for example it may be equipped with:
120V 15amp (1800Watt)
240V 20amp (2400 watt)
Your compressor is at the maximum of the 120V 15amp outlet. Check the label on the motor, you may be able to convert it to 240V by moving a few wires or jumpers.
Once the compressor has built up some pressure, it’ll have a tougher time restarting against that pressure, so your startup amps, which can be as high as 250% of running amps, require more than the generator can provide. Startup amps should only peak for a second or so, but if the compressor has troulble coming up to speed with the available voltage/current, it’ll overamp and trip the breaker. Like one of the other responders said, the ratings on those generators are exaggerated a bit anyway.
The lock rotor amps is too high when the tank is partially full. Get a bigger generator
Your generator is rated at 2000 watts at from each 120V line. At 240V it will supply the full 4000 watts.
When the compressor tank is empty the motor can turn easily. Startup current requirement is within the 2kW rating of the generator. When the tank is partially full the motor requires more power to start turning. This higher startup current exceeds the generator’s rating. The motor is not supplied enough power to turn at the proper speed and current will remain high until the circuit breaker trips. It isn’t really a generator problem, but rather an inability to supply the required startup current which results in an overload.
When you are operating from house power the circuit is capable of supplying the extra startup currrent with the tank partially full.
If you want to operate the generator at 120V only and disable the 240V outlet, the electrical panel can be rewired. It would then supply the full 4000 watts at 120V and operate the compressor properly. You would have to supply proper outlets and overload current protection to ensure safe operation.
Alternately, you could rewire the compressor to operate at 240V to take advantage of the full 4000 watts available.
You are starting that compressor ‘under load`
on the second start. (Working against the
remaining pressure in the tank. The first start,
there is none. The motor never gets ‘up to speed’
on the second start and draws more current when
it’s in that ’stalled` condition.)
This raises the starting current of the motor.
If that genny is 4 KW. at 240V., you only have
about 2KW., (16.7A.), available for a single
phase load before the protection trips.
Can you wire the compressor for 240V. ?