Help with Diesel to Electric Motor Swap on Air Compressor

[Mud]

I've got an industrial duty air compressor that was given to me due to a non-running diesel engine on it. The other components are in very good shape so I'm wondering if it's feasible to install a 220v motor to replace the diesel engine.

It's a skid mounted horizontal 60 gal tank unit with a Duetz(sp?)/Rugerrini MD-150 15 hp 2 cyl diesel engine. The air pump looks to be pretty good size, connected to the diesel with a 16" diameter pulley belt drive. The air pump is a 2 cylinder unit and turns fine. The engine is rated 15 hp at 3600 rpm and runs CCW, which seems to be compatible with most electric motors.

I have tried to diagnose and fix the diesel, but have gotten fed up with it. It will turn over but will not start. I would prefer something that I can run indoors anyway, thus the idea to install an electric motor. I have 100 amp 1ph service to my shop so installing a circuit capable to handling 20-50 amps is not a problem, nor are any fabrication needs for mount plates, etc.

Is this feasible? How do I figure out what hp motor is needed? Any advice is appreciated.

 

[tom slick]

Without doing some research I can't tell you exactly what size motor to use. A quick look in the baldor catalog says a 15hp single phase 220v 1725 rpm general purpose motor will use 70 amps at a full load. 15hp is a big single phase motor. just as a reference a 3 phase motor will use about 40 amps. that is a big compressor for home/small shop use.

 

[Steve S]

I would try to look up a compressor with similar specs "output" and see what size motor it has .Usually internal combustion hp compared to eletric hp is different, then also the cutoff switch.

 

[Mud]

From what I remember, I think that when looking at hp comparisons of gas/diesel and electric, you don't need the same hp with an electric motor as you do with the g/d engine. So I don't think that I need a 15hp electric as a replacement, especially if I'm looking at 70a service. Man that meter would be flying.

In looking at equivalent units of tank size (60-80gal) even the largest non-commercials don't typically go over a 5hp electric motor, using a 2 cyl pump. That's why I thought about the 5hp motor. They are also available at the approx rpm range (3600) where the diesel was producing its 15 hp.

I will take another look at the pump to see if it is a 1 or 2 stage unit, maybe I can dig up some cfm ratings or it.

Another comparison - with my small 1hp compressor, there is a pressure switch that cuts the electric motor on and off. With this big compressor, the diesel engine runs continuously because I see pop-off type valves to limit tank psi. So now I wonder if I install an elecric motor it seems that I should install a pressure switch to avoid the motor running continuously to avoid using electricity when not needed.

Thanks for your help - additional comments are welcome. Sorry to be long-winded, just trying to figure this out.

 

[CBR.worm]

I would think that you would definately want to use a pressure switch to start and stop the motor, I would be worried about an undersized motor not having the torque to restart. Maybe by changing pulley sizes you can slow down the speed of the compressor to run with a smaller electric motor.

 

[dkcase]

I had occasion a number of years ago to specify an engine-driven fire pump. The diesel engine manufacturer said the guideline was to use an engine rated at twice the horsepower of the required electric motor.

 

[car54]

The cost of the electric motor and pressure switch might actually approach the cost of a new compressor. Somthing to consider with the trouble of converting.

 

[Shannow]

Find out how the compressor works.

Hooked up to a diesel, it will have (most likely) an unloader, and should start unloaded i.e. free breathing. Once at speed, it should load up as required to keep the pressure up. If that's the regime, then equivalent power output would prolly be OK, or maybe a bit less.


Just running the thing through an on-off pressure switch wouldn't work on something of significant size.

 

[frankiee]

Find the tag on the compressor and give the serial and manufacturer of the air compressor.
And the size of the pistions. (should be on the tag)
Post that info and it will be better.
Also, if you have the info you could contact the manufacturer and get a specific hook up for your application.
I work on ships as a marine engineer and have read of exploding compressors taking lives.
DO IT BY THE BOOK.
Have non painted, good condition, non tampered with (anti tamper wire still intact) safety valves installed.
I wish I had an industrial compressor for my shop.
I would hook the diesel to a generator if it were fixed.
Whats up with the engine any how.
Is it hand crank or starter motor??
What kind?

 

[Mud]

Yes, the compressor is equipped with several unloader valves. They are all clean, wired, and appear to be in good shape.

I will look for a tag on the compressor as you mentioned.

Frankiee, please see the initial post for info on the diesel - it's electric start. Really a nice setup, just can't get it to run. Will turn over and that's it. However, we have a friend that works on the big stuff - Cats, dozers, etc, that said he would take a look at it. Maybe he can bring it to life...

Happy new year folks - stay safe!