# Air Compressor / Generator



## alex123 (Jan 12, 2019)

Hello Everyone,

I'm in the market to get a decent sized compressor to run air tools. Due to the nature of my living circumstances (moving multiple times, current landlord not okay with me rewiring to 220v, etc...), I am unable to get a 220V outlet setup at my house. Is it at all possible (and realistic) to run a 80 gallon 220v air compressor off a generator? I was considering this generator, and this compressor. Though, the compressor is rated at 230v and the generator is rated for 220v... Not sure if that matters? If there's anything else I should know, please feel free to share. Many thanks!


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## stevon (Mar 5, 2019)

Alex,

230 volts or 220 volts are basically the same, not true in a 208 vs 230 volt setup. In your situation, as long as the neighbors don't mind the noise of an engine, get a gas powered compressor. Compressors are very inefficient in transfering energy by themselves. A 5 HP electric motor compressor = about 1/2 HP air motor output. Why add even more inefficiency adding a generator? the wasted energy will be too much IMO. Besides when its time to move, you only have one item to move and store instead of two!

Stephen


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## stevon (Mar 5, 2019)

Alex,

Generators are poor at starting electric motors anyways. A 20.0 - 22.4 KVA generator is needed for starting a 7.5 HP compressor. Don't forget that the locked rotor at startup (0 rpm) is approximately 240 amps! The generator has to be able to bear this load for a fraction of a second every single time compressor turns on. To start a 7.5 HP compressor rule of thumb you would need 3 to 4 times the HP generator to overcome the inrush current or at least a 30 HP Generator. Call a rental place and ask them "what is the smallest generator" they recommend to start a 7.5 HP electric motor. 
On the other hand, gas powered compressors have an idle valve that lets the motor idle when not pumping air. It's easier to start pumping when the flywheel is already up to speed!

Stephen


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## alex123 (Jan 12, 2019)

stevon said:


> Alex,
> 
> 230 volts or 220 volts are basically the same, not true in a 208 vs 230 volt setup. In your situation, as long as the neighbors don't mind the noise of an engine, get a gas powered compressor. Compressors are very inefficient in transfering energy by themselves. A 5 HP electric motor compressor = about 1/2 HP air motor output. Why add even more inefficiency adding a generator? the wasted energy will be too much IMO. Besides when its time to move, you only have one item to move and store instead of two!
> 
> Stephen


Hello Stephen - Thank you for your reply. I'm still new to the air compressor world so forgive me if my next question seems a little silly. Almost all gas compressors I see are 30 gallons or less, whereas the electric one I was considering is 80 gallons. Is this possibly because the the gas powered ones have a high CFM rating? If so, what is the relationship (and effect on tool run time/power) between my CFM and tank size? Also, is it safe to have a gas powered unit in a garage (fumes)? I am totally open to gas powered if its safe and yield the same performance, but I'm not really familiar with them and don't know if I'd be losing performance? Many thanks!


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## stevon (Mar 5, 2019)

Alex,

The reason the tanks are so small is to provide ultimate portability, there are larger ones that are usually bolted in truck beds. I would not use a gas compressor indoors because of possible asphyxiation and fire hazard concerns. Theoretically it could be used in a cinder block garage with an exhaust pipe hole drilled to the outside but I wouldn't recommend that. Best bet is the 30 gallon on wheels stored close to the door and wheeled outside when in use or build a small thoroughly ventilated shed for the compressor. Just remember you need to double the gas HP vs the electric HP. A 13 HP or more gas motor would be the same as a 7.5 HP electric. The constant run feature of gas compressors is a nice feature, they can run at 100% duty cycles while most electric compressors are designed to run 50% on and 50% off to cool the motor in between cycles. The 100% run feature lets you get away with a smaller CFM compressor because pump demand is against a running flywheel and not from a 0 rpm dead start. What kind of work are you doing? spraying, grinding, bodywork? condensed water in the air is always something to deal with

Stephen


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## alex123 (Jan 12, 2019)

stevon said:


> Alex,
> 
> The reason the tanks are so small is to provide ultimate portability, there are larger ones that are usually bolted in truck beds. I would not use a gas compressor indoors because of possible asphyxiation and fire hazard concerns. Theoretically it could be used in a cinder block garage with an exhaust pipe hole drilled to the outside but I wouldn't recommend that. Best bet is the 30 gallon on wheels stored close to the door and wheeled outside when in use or build a small thoroughly ventilated shed for the compressor. Just remember you need to double the gas HP vs the electric HP. A 13 HP or more gas motor would be the same as a 7.5 HP electric. The constant run feature of gas compressors is a nice feature, they can run at 100% duty cycles while most electric compressors are designed to run 50% on and 50% off to cool the motor in between cycles. The 100% run feature lets you get away with a smaller CFM compressor because pump demand is against a running flywheel and not from a 0 rpm dead start. What kind of work are you doing? spraying, grinding, bodywork? condensed water in the air is always something to deal with
> 
> Stephen


Stephen, thanks again for your reply! Yes, placing it outside while in operation is a great idea, and thankfully that is an option. I plan on doing some body work, and spraying. Not sure if the 30 gal. gas compressor will keep up with disc sanding and die grinders? A disc sander needs a solid 20 cfm. You mentioned water in the air - I'm assuming a filter will take care of that issue?


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## stevon (Mar 5, 2019)

Alex,

For grinding sander I would go electric, air powered grinders waste far too much energy which is not cheap anymore not since the 1960s. A 7 inch buffer/grinder will work in most cases and a electric Makita 4" for smaller chores. 
A water filter will not completely deal with/separate the generated water. A fan forced radiator :
Air Cooled Aftercooler 15 HP, — Voltage 
or you could make your own from a discarded automotive A/C condenser
and some metal pipe would do it. I used 1" black pipe from a scrap yard bolted to the wall with a slope to collect water, with a drain at the end and added a "bulb" filter on the spray gun. A little water through sanders or other air tools doesn't seem to bother them as long as regular air tool oil is applied.

Stephen


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## stevon (Mar 5, 2019)

Alex,

One more thing, don't run the compressor anywhere near or in the same room as the compressor! Not only is there an slight explosion possibility but all oil lubricated air compressors release oil particles into the air while in operation and cause disastrous "fish eyes" in the wet paint, ask me how I know!

Stephen


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## alex123 (Jan 12, 2019)

stevon said:


> Alex,
> 
> For grinding sander I would go electric, air powered grinders waste far too much energy which is not cheap anymore not since the 1960s. A 7 inch buffer/grinder will work in most cases and a electric Makita 4" for smaller chores.
> A water filter will not completely deal with/separate the generated water. A fan forced radiator :
> ...


So if I've understood correct, I can get a regular water filter, but just regularly oil the tools and I'll be good?


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## stevon (Mar 5, 2019)

I mean don't run the compressor anywhere near or in the same room that you are painting in!


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## stevon (Mar 5, 2019)

Alex,

No, what I mean is that you need to do is more than just the filter alone. It's about managing the water generated which cannot be avoided. The 1 inch metal pipe cooled/dropped the velocity of air with suspended water then partially separated the water out, of course this had to be drained weekly. The air fittings on the top of the 1" pipe let air go out and at lower velocity water collects on the bottom of the pipe and runs down the slope. For me that was good enough _with_ the filter for my needs. if you use a smaller metal pipe/ rubber or plastic pipe, the water would remain suspended in the air supply. Air motors need oil to work efficiently any ways, side affect is water rejection/ corrosion prevention

Stephen


alex123 said:


> So if I've understood correct, I can get a regular water filter, but just regularly oil the tools and I'll be good?


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## stevon (Mar 5, 2019)

Alex,

I looked into a 13 HP gas powered compressor and they all weigh around 400 lbs! there is a portable 13 HP rotary compressor but it's over $6000! Looks like you will need to build a shed and get an electric start model. What is your budget for this compressor?

Stephen



alex123 said:


> Hello Everyone,
> 
> I'm in the market to get a decent sized compressor to run air tools. Due to the nature of my living circumstances (moving multiple times, current landlord not okay with me rewiring to 220v, etc...), I am unable to get a 220V outlet setup at my house. Is it at all possible (and realistic) to run a 80 gallon 220v air compressor off a generator? I was considering this generator, and this compressor. Though, the compressor is rated at 230v and the generator is rated for 220v... Not sure if that matters? If there's anything else I should know, please feel free to share. Many thanks!


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## stevon (Mar 5, 2019)

Alex,

This might work for you:






Toolots, Inc. - Reliable Equipment Fast.


Toolots.com is a one-of-a-kind international B2B online marketplace for factory direct industrial equipment, parts and supplies.




www.toolots.com





Stephen


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## stevon (Mar 5, 2019)

Alex,

I would not run gas motor without some sort of low oil level shutoff.






Descriptions, Photos and Diagrams of Low Oil Shutdown Systems on Generac Engines







outdoorpowerinfo.com





Stephen


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