# Running a Compressor on a Generator



## DeckPros

Hey guys. Deck builder/remodeler here with an electrical question.

Last week, due to the heat, we had power outages where we were working.

So I fired up my 8000 watt generator and plugged in a small 10 amp compressor. No problems at startup. But the compressor would blow the genny's breaker after about 30 seconds. 

Since this generator has no problems running two 15 amp miter saws at the same time, I figured there was something wrong with the compressor. Tried my larger Makita 12.3 amp compressor. Same thing. It would start up fine (when it takes the most juice) but blow the breaker on the genny after 30-40 seconds.

I tried both 120v outlets AND the 30 amp 120/240 with the proper cord.

Is there something different about a compressor motor and a saw motor? What gives?


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## 480sparky

Compressor motors usually run longer.


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## DeckPros

> Compressor motors usually run longer.


True dat.

But my 14 amp table saw can run for 30 minutes straight on the generator with no problems....


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## 480sparky

DeckPros said:


> True dat.
> 
> But my 14 amp table saw can run for 30 minutes straight on the generator with no problems....



That 14 amps number comes from where?


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## DeckPros

> That 14 amps number comes from where?


My mistake. 15 amps...

http://www.dewalt.com/tools/machinery-portable-table-saws-dw745_2.aspx


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## 480sparky

DeckPros said:


> My mistake. 15 amps...
> 
> http://www.dewalt.com/tools/machinery-portable-table-saws-dw745_2.aspx



That means nothing. I need to know what it really draws, not what some Madison Avenue ad agency wants to tout.


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## woodchuck2

What 480 is saying is there is a difference in the load between the tools. What a tool states for amp rating does not mean that is the amp draw that it uses. An air compressor is under load from start to stop where a saw may be free wheeling or under very little load. You put a dull blade on that saw and drive it into a long cut and you will see the generator trip off again. I myself think it is the generator. My Honda 2000I will power up my porter cable pancake compressor with no issues although it will not run my 30gallon craftsman. It is tough to find a good generator that will power any good size air compressor. Some generator manufacturers will over rate the output of the unit and some manufacturers are more accurate. This is one reason why Honda's are so popular, their output numbers seem to be more accurate.


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## boman47k

Don't electrical motors pull something like 3x rated amps on start up? Have no idea have much amperage a compressor pulls in relation to rated amps, when it kicks back on when it may already have 80lbs or whatever of pressure in it.

Wonder if a higher rated capacitor could be used to help in those situations.


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## Framer53

We have had no problems in the past with a 6500 Yamaha generator running any compressor, in fact we used to run 2 off one.


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## Morning Wood

I'd say something is off. An 8k genny should run a 110 volt compressor just fine. I might try changing the breakers on the genny. could be bad. Or wait for some better advice from this thread.


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## SLSTech

Stupid question (maybe), but was someone trying to run a saw while the compressor was running? an 8000w compressor is generally only rated for 4000w continuous if memory serves me correctly


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## nailkiller1

I dont know anything about this technical stuff
But I have wrecked 2 generators with what I believe to be electric comp related(this is not scientific)

Since having a no comp on gen rule I have had zero issues with premature gen retirement?


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## DeckPros

> Stupid question (maybe), but was someone trying to run a saw while the compressor was running? an 8000w compressor is generally only rated for 4000w continuous if memory serves me correctly


It's rated for 8000 watts continuous power. And we turned everything else off and just tried the compressors...


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## boman47k

Shouldn't that generator handle at least 72 amps for a 110 volt tool?


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## flashheatingand

I would think that if you are going to run a compressor off a generator, it would be easier on the generator if you used a 240v compressor versus a 110 compressor


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## Cole82

This may sound odd but I had this problem with a smaller 3500 watt gen. So I called the manufacturer and they asked if it was grounded how the instructions say. I never read them so no.
They want a minimum of a 2' grounding rod and 10gauge or greater wire to the grounding post. After that it wouldn't trip the breakers running the saws.

Cole


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## boman47k

Cole82 said:


> This may sound odd but I had this problem with a smaller 3500 watt gen. So I called the manufacturer and they asked if it was grounded how the instructions say. I never read them so no.
> They want a minimum of a* 2' grounding rod and 10gauge or greater wire to the grounding post*. After that it wouldn't trip the breakers running the saws.
> 
> Cole


 
Do people actually do that? :whistling


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## frenchelectrica

Cole82 said:


> This may sound odd but I had this problem with a smaller 3500 watt gen. So I called the manufacturer and they asked if it was grounded how the instructions say. I never read them so no.
> They want a minimum of a 2' grounding rod and 10gauge or greater wire to the grounding post. After that it wouldn't trip the breakers running the saws.
> 
> Cole


Ya gotta be kidding on that one.

The main issue is the generator interal bonding I know some portable generators they will have floating netural and grounding system but some will bond both netural and ground at the generator.

Merci.
Marc


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## frenchelectrica

DeckPros said:


> Hey guys. Deck builder/remodeler here with an electrical question.
> 
> Last week, due to the heat, we had power outages where we were working.
> 
> So I fired up my 8000 watt generator and plugged in a small 10 amp compressor. No problems at startup. But the compressor would blow the genny's breaker after about 30 seconds.
> 
> Since this generator has no problems running two 15 amp miter saws at the same time, I figured there was something wrong with the compressor. Tried my larger Makita 12.3 amp compressor. Same thing. It would start up fine (when it takes the most juice) but blow the breaker on the genny after 30-40 seconds.
> 
> I tried both 120v outlets AND the 30 amp 120/240 with the proper cord.
> 
> Is there something different about a compressor motor and a saw motor? What gives?


What brand name that genny it is?

with cheap one when it get loaded up pretty good the HZ and voltage will drop unless the engine govner is right on the track with it.

For most generators for unloaded it will run about 62 or 63 HZ once it get loaded it will drop to good 60 HZ but once you drop below 60 HZ you will run some issue with it.

Most portable genny are set up to run at 3600 RPM loaded unloaded it should be about 3700 or so.

And most of cheap one they have kinda pretty crappy voltage regualtion { 2 V per HZ } so if running right you should have good 120 volts at 60 HZ anything else you may have weak voltage regulator or bad capaitor.

Merci.
Marc


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## Magnettica

Uh, maybe, hey you never know -- the generator's circuit breaker might have shut off prematurely because it was basking in the sun and was hot. Try keeping it a cool place. I know that's hard to do out on the job but heat plays an enormous factor on electrical equipment.


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## woodworkbykirk

if were heavy framing we run two generators, one for saws, the other is dedicated to teh compressor. currently were building a 6000 sq footer for our excavation contractor and he has a gas operated compressor which hes letting us use


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## jimbo82

What about a petrol-engine powered compressor? Cut out the middle man?


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## world llc

my compressor always trips the 15a plugs but rarely trips the 20a or 30a plugs with adaptor cord. and my compressor is that old (8 years) yellow cambell housfield twin tank. sais it's 14 or 15 amp.

i have heard of the breakers in generators going bad, not sure if that mees prematurely tripping or not tripping at all, but maybe look into that?


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## Kengine7

*Compressor never reaches speed*

Impressive that the compressor starts.

More than likely the compressor is running underspeed/high amps. Within 30-40 seconds the cb opens.

Over speed generator governor to get compressor up and it will sustain speed.

Only works until set psi is reached


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## ckseppa

Had that same issue trying to run my compressors on a honda 3500. I've got 4 compressors, tried them all & the Porter Cable pancake was the answer. Didn't overload the breaker & runs a framing gun to boot! I know the question wasn't about compressors, just my 2 cents.


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