Generator + Air compressor

[cathead]

I have an 80 gallon Sanborn two stage compressor that I would like to run on my Honda EM6500SX generator. The compressor
has a gas engine on it presently and I am thinking of removing the gas engine and installing a 220 volt electric motor(single phase).
From past experience, generators and compressors don't get along very well mostly because of the starting loads. My
thoughts are to change the ratio with a smaller pulley on the motor. If it would start, I would be happy with the slower
compressor speed and lower CFM output. My other option would be to come up with a smaller compressor that would
operate with the generator and feed into the Sanborn tank. I am hesitant to spend a lot of money on an electric motor
that would not run the compressor. Another possibility might be to use a 1725 RPM motor. At present, I'm using a small
compressor feeding the Sanborn but it takes at least two hours to air it up to 100PSI. It looks like it will take a bit of
experimentation to make a working system out of this. I think the original motor on the Sanborn was five horsepower
@ 3450RPM. What are your thoughts on this conundrum?

 

[Nutfarmer]

Why? Just run it as is

 

[Superburban]

What size is the intended motor? My work truck has a 4K generator/ welder, and it has no problem running the 3 HP air compressor also built in. I would think a 6500 watt generator could easily handle a 4 or 5 hp.

Something that can be done to ease the starting load is to increase the volume of the unloaded air between the compressor and tank, to give the motor a bit more time to spin up before the load starts building.

 

[cathead]

for Nutfarmer: I can't run a gas engine inside the shop area without getting asphyxiated with carbon monoxide. Putting the
compressor outside the building would render it useless in the winter months as it is way below zero and the effort to get
the engine started would not be worth it. The generator is in a small building that I can warm up and get it going.

for Superburban: I'm thinking of using a five horsepower motor. The compressor does have an unloader on it, not sure
if there is a small tank. I will try to take a photo of the unit today. It is a large cast iron compressor, probably 200 pounds.

Thanks for the comments.

 

[Bi11Hudson]

In a purely theoretical sense, since I haven't had sufficient coffee this early to make me fully functional, this is offered more to make you think rather than as a specific solution. The base function of a gasoline driven compressor has the prime mover running continuously, with an "external" load/unload function effectively seperating the compressor from the prime mover.

What I am driving at is that from a theoretical point of view, replacing the gasoline engine with an electric motor should not alter this particular function in any way. In that the prime mover, be it a gasoline engine or an electric motor, will run continuously. Thus eliminating the "starting current" of an electric motor to the initial start-up. It would be a matter of the motor simply transferring from an "idle" function to a "loaded" function. There will be a "shock" load on the motor supply, but the motor will already be up to speed so it will not be near as severe as a starting load at "zero speed".

The "up" side is that the starting current for the motor would be theoretically at the beginning of the shop session, before the generator was fully loaded. The "down" side of such a conversion would be a constant load on the supplying generator. In the event of an unplanned shutdown, there would be the matter of "stripping" the load until the motor had time to come back up to speed.

The concept is an extrapolation of having to deal with "ship's service" generators and specific loads waayyy back. I distinctly remember having to strip "unnecessary" loads before restarting the "heeling" pumps. During such operations, my duty station was on the aft generator (2@200KW) switchboard. Basicly I am speaking of a 50 year old concept from real time experience. it would be necessary for you to make the final adjustments as they pertain to your particular compressor. This entry is to make you think, not a solution.

.

 

[cathead]

Here's a photo of the two stage compressor with unloader valve.
I located a 5 hp 3450RPM compressor motor so giving that some consideration.

 

[RJSakowski]

A long time ago, I built an electric motor powered compressor. To reduce the starting load. I added a small chamber and check valve along with the unlloasfer valve on the pressure switch. The additional volume of the small chamber allowed the motor to come to full speed before having any significant resistance. In my case, the compressore was small so the chamber was made from a length of 2" pipe and two pipe caps. For a larger compressor, a larger chamber would be desirable, the volume based on the cfm spec for the compressor.

 

[JimDawson]

How about just exhausting the gas motor outside? Seems like the least cost solution.

 

[cathead]

How about just exhausting the gas motor outside? Seems like the least cost solution.

Well, it's a brand new insulated metal quonset building and I'm not too keen on boring holes in it. Not only that, it
would be pretty noisy to run a gas engine in the shop.