Compressor help

[barrmust]

So I have a compressor that does not have a moter with it. I am looking to get it going but need some help with figuring out how to go about it.

I have a eagle aircompressor that I picked up without the electric motor. It uses a davy style 4 stage 15 cfm compressor. It came with a 15 hp 3 phase electric motor. I dont have 3 phase at the house so I am looking to put a single phase motor on it. The price for a 15 hp single phase unit is crazy so I really dont want to go that route. I was wondering if I can put a smaller motor on it and still have it work?

I could also put a 18 hp gas engine on it (that was a option and I have one) but would prefer electric. I looked at phase converters and they are expensive and generally inneficient so I would prefer to stay away from that choice.

I am open to any suggestions and could really use some advice.

Russ

[Wookie]

Even a 10 HP single phase motor is stupid expensive. I would say your only choices are the phase converter or gas engine. I don't like either option. Don't you have a friend with commercial property where you can put it that has 3 phase juice?

[mike_s]

You said you're open to suggestions...

I say sell it and buy one that is better suited for single phase power.


While a 15cfm for "home use" seems nice, it's really kinda overkill if you're only going to fill a few tanks at a time.

chances are you can sell it and pick up one better suited for home use than trying to convert that one.

[dannobee]

We just helped convert a 15 cfm Eagle (Bauer block) to 10 hp single phase power because there wasn't 3 phase power anywhere near the dive shop.

The motor was ~$1100, IIRC.

The project worked well and the compressor is up and running.

[barrmust]

So I am assuming that I cant power this thing with something smaller than a 10 hp motor?

If I go with gas power what do I need to be concerned about? Obviously not getting exhaust into the intake but what else?

I looked at 3 phase motors and they can be had dirt cheap. So what are the draw backs to a phase converter. How inefficent are they and what would it do to my electric bill?

What i really have is 1 compressor minus the electric motor and a spare compressor pump, intercooler and drains. basicly everything spare except the frame and guage assm. I also have a 4 tower filter system that is rated for 84,000 cf of air.

I appreciate all of your replys.

Russ

[miesemer]

If you are willing have reduced output (cfm), I believe you could reduce the rotational speed of the compressor and use a smaller HP motor.

[Peter_C]

From what I understand a phase converter draws more amps, than a single phase motor replacement. Plus the phase converters themselves are expensive.

Leeson is an affordable motor. I used one for changing my compressor from three phase to single phase. Ebay will have other types of motors including used, but they may or may not be adaptable. Craigslist would be worth watching too.

The idea of putting it into someone Else's building, that has three phase, would work great!

[adelman]

I worked with Dan to convert that Bauer/Eagle to single-phase. This is roughly how we ended up where we did..

We were looking for a cheap solution, and evaluated the static phase converters first. The problem with these as compared to a true rotary-phase converter is that you only get 2/3rds the horsepower out of the motor, so you would need to put a smaller pulley on it (and new belts). When we factored that into the equation, and considered the age of the 15HP 3ph motor we were replacing, we decided to go with a new motor.

Single phase electric motors are common in 7.5HP at 1800 RPM and 3600 RPM. They are available in 10HP at 1800 RPM (you likely have a 15HP 3ph 1800 RPM motor). Since we needed to transport this motor to the third-world, small was as much a factor as cheap. I started by looking for 7.5HP 3600 RPM motors, but realized that we couldn't get a small enough pulley (it would have been around 2.25 inches) to run the compressor at the right speed. Next we looked at 7.5HP 1800 RPM motors, but for the price difference, we decided to go with a 10HP 1800 RPM motor (this is being used in a dive shop high-volume operation, so we were interested in getting everything we could out of the compressor). As long as we were hauling a 10HP (>100 pound) motor to the third world, I wanted to be sure that we were going to USE all 10HP, so we ended up buying an adjustable-diameter pulley for it (more money) so that we could measure the running current of the motor and set the diameter to draw exactly 10HP. The 10HP motor has a different mounting-bolt hole pattern, so we added a set of adapter-rails designed specifically to mount a 10HP 1ph on a 15HP base. The total cost that Dan quoted includes the few hundred dollar pulley, new belts, and the adapter rails. All new, from Grainger. The motor ended up bolting right in, but we needed to, uh, "relieve" the sheet metal belt shield that sat between the motor and belts to allow the new motor to stick through a bit. We did this with third-world tools and gusto.

If you want to do this on the cheap, I'd look for a used 7.5HP 1800 RPM motor (they're cheaper and you're more likely to find one used). At half the horsepower, you need to spin the compressor at half the speed, so buy a pulley which is half the effective diameter (in other words, save money by not getting an adjustable pulley). One thing to remember is that these motors are not internally protected -- if you go 7.5HP, you'll need to replace the heater elements in the external thermal protection device appropriately. If you use a 10HP 1ph motor, that would use the same heaters as the 15HP 3ph motor. Just wire two of the wires straight through and leave the third unused.

About spinning the compressor slower -- If you have less horsepower available, you MUST use a smaller motor pulley to spin the compressor slower. There is, however, a limit on how slow you can go; if you go too slowly, the compressor won't develop sufficient oil pressure. I know the Bauer block is good at 7.5HP, but I wouldn't go slower than that without talking to someone at Bauer about it.

Sell it and buy a smaller compressor? I wouldn't. A de-rated compressor block with a smaller motor will last forever. (Of course, I'm running a 20cfm for "personal use".)

[oxyhacker]

There are a bunch of electric motor and surplus places that carry leftover and industrial surplus motors for considerably less than list price. They turn up on ebay too. Watch out for 7.5 HP specials made for home shop compressors, they usually put out closer to 4 hp. Go by amps not claimed HP. If a motor is suspiciously light, that's another sign it may not be up to the job. If you aren't going to be moving the compressor around, a heavy motor is almost always better than a light one.

You want to check with whoever made your compressor before you derate it (there is a limit to how slow they can turn and still lube and cool themselves.

You can find a lot of info on DIY 3 phase converters at woodworkers forums since they are always trying to adopt old industrial machines to home workshops.

If someone gave me that compressor, I would probably derate it as far as I could, then look around for a good deal on a real 7.5 or 10 HP single phase motor, and if I couldn't find one, make a homemade DIY phase converter using a junk 3 phase for an idler motor.

Scrap metal yards, electric motor shops and machine tool dealers will often have large collections of used pulley sheaves at reasonable prices.

[captain]

If you could run the gas engine exhaust outside through a wall it would be the cheaper but noisier and less convenient option.