View Full Version : garage guys-generater/compressor ?

10-07-2007, 09:29 PM
I've got a 3000 watt honda generater and I need the biggest craftsman air compressor I can run with the generater. My question is: Is the formula "120 volts X Amps X 3 = Watts" ?
I think the electric motor on the compressor is going to draw a greater current at start up than at normal running speed. I'm having a difficult time getting this answered in the tool department.

10-07-2007, 09:47 PM
Power = Voltage X Current, so 120v Compressor at 3Amps = 360Watts

10-07-2007, 09:59 PM
3000 / 120v = 25amps. problem with compressors they can take a lot more to start them than running them. find a compressor you like and put a a/c clamp on it and see what the start up current is.

10-07-2007, 10:20 PM
If start up is an issue just trow on some big capacitors coming out of the generator, best bet is to get a compressor with max current rating of 20A

10-08-2007, 12:40 AM
Per below, Power = volts times current. Normally the generator is rated for continuous duty and surge. Compressors have a start up surge and then steady state power consumption.

10-08-2007, 10:03 AM
Start up current can be as much as 5 to 10 times the normal operating current. However, i think some generators can compensate for a quick draw on the current. Will there be anything else running off of the generator?

10-08-2007, 10:06 AM
Why don't you just buy a compressor with a gas motor?

Why does it have to be Craftsman? How will you be using it- general garage, car/truck/boat mechanical, inflatables (if you know what I mean) stuff?

10-08-2007, 10:41 AM
I have a 5hp 120volt Craftsman oilless compressor and a 5000/8000 watt genset. If the tank on the compressor is over 100 psi, and it needs to run the generator the compressor will not start without letting some air out of the tank. So if your running high psi's then your compressor may have a hard time starting. You would probably have better success with a belt drive (oil) compressor, since you allready have the generator.

Workin' 4 Toys
10-09-2007, 09:29 PM
Funny you would bring this up, Recently I have been running a 5HP craftsman (15 amps per the label at 120 volts) AND a Dewalt circular saw (15 amps per the label at 120 volts) on a 5000 watt gen(occasionally at the same time). And there is no power surges or fluctuations noticable.

Mind you, I am not concerned whatsoever about burning up the compressor or the saw. Hope this helps.

What size compressor are you considering? Portable, single stage, dual stage? Is there 120 volt cord with wiring potential for 220v?

Maple Leaf
10-09-2007, 11:03 PM
The start-up current is the only issue you'll have, but most generators can handle a short surge above their nameplate rating. Typically you can expect the start-up current to be 2-3 times the normal running current. If you stick to something around 1.5 hp, you should be safe.

On a related topic - a good rule of thumb: it's always better to run a longer air hose and as short an electrical cord as possible on a compressor. This is to avoid unecessary line loss on the electrical side.

10-22-2007, 09:05 PM
Great advice here-I was hanging around the Sears tool department today shopping for another tool box and asked the tool guy how big of a compressor I could get that would run off my 3000 watt generater and he pointed at a Craftsman 1.5 hp 27 gallon that sucked 15 amps. I remember everything that was posted here and asked him about the formula. There was another guy (painter) there shopping for a compressor and he said no way The generater could handle the volts X amps X 3 . The sears guy forget the formula and buy the compressor-drag it outside and hook it up to the painters' 3000 watt generater and if it doesn't run drag it back inside and he'll give my money back. we did it and the compressor ran like a champ-sears guy sold one to the painter too. No more excuses- I'm going to paint my boat trailer. thanks for the input gentlemen.

10-22-2007, 09:23 PM
the formula is Volts*Amps=Watts, not sure where the *3 came from... for your particular 3,000 watt generator the *3 might be if you were doing your calculations in kilo-watts.

10-22-2007, 09:50 PM
The 3 is the multiplier assighned to electric motors that pull more juice at start up then they use when they run normally. Since I started investigating this I've read this in several places including the Honda generater website.