Technical Shop Compressor Power Options

I bought this old Curtis compressor for $250. Don't know anything about it other than it's not frozen. I want to use it at my yard away from home which has no electricity apart from a 10KW, 220v single phase generator. The compressor motor is 3 phase, 39 amp (9KW). Would I be wasting my time trying to run it with the generator and a phase converter?

Or could I get a single phase motor that would power it?

Another option would be to put a gas engine on it. I see Curtis even sells one as such. Anyone ever done that?

 

You say you are running your shop off a generator? In that case it might be best to power the compressor with its own gas engine. Depends how much you use it and what other equipment you want to run, such as a welder.

 

Thanks Rusty. No my shop is at home, this is at an offsite yard. It would be the only thing the generator would be powering when in use. I have another smaller generator to run lights etc..

 

Compressors take a lot of juice to get them rolling. Converters kinda don’t like that. Gas engines give you portablality, but come with their own set of problems. Depending on your needs, a single phase motor might be the best bet. That’s a big compressor, it’s going to take a big motor, either gas or electric.



Bones

 

isn't the rule of thumb that you need about twice the generator KW rating, as the motor, to get it to start up a compressor?

but I could just be talking out my ass

 

Your generator might run your compressor, but it probably wont start it. Starting amps for motors like that are 5 or 6 times amperage draw and compressors are notoriously hard on motors.

 

OK sounds like a gas engine is be the best option. How does that work, there must be a clutch or something, they don't stop and start every time do they?

 

You're not.... A 10KW generator will have a max output of 43 amps which is barely adequate for the running current at 230V. But instantaneous starting inrush current can be up to 1200% of running current, with the 'average' being around 300%. Even a generator sized at 200% will be very iffy.

If you can get a three-phase 20KW generator with 460/480 output, that would be 'just' adequate.

Single-phase motors larger than 7.5HP are almost non-existent and horribly expensive if you can find one.

Installing a gasoline motor sized for the duty will be the cheapest and best solution. The gas motor will run all the time, you'll need to change some plumbing to vent the output when it reaches max pressure.

 

Here's the Curtis gas compressor but no description on how it operates. So the gas engine runs constantly at constant rpm and just bleeds off the extra air? What about startup? Is there a clutch of some sort? I do have my old v8-60 sitting around..

 

For start-up, almost all compressors have an 'unloader' valve to allow the motor to start not under load. I think I'd opt for the electric-start version…. LOL.

Talk to Curtis, I'm sure they'll be happy to sell you the bits you'll need to convert to gas.... It won't be cheap.

It may be cheaper to just buy a smaller compressor that your generator can power.

 

You have a 15 HP motor on it now. Do you know if the motor even runs? An equivalent single phase motor is going to be expensive. An equivalent gas engine is going to be expensive. Lots of extra stuff to hook up a gas engine. Typically, gas powered compressors are quite a bit more expensive than equivalent electric. No cheap way out of this one.

 

Yeah, so if the tank has no pressure why does it take so much current for the electric motor to start? Or is the requirement for starting at the set turn on pressure, like 60-80 psi?

I'd like to do some sand blasting, my experience with my smaller compressors is mostly waiting, with a little blasting in between.

Don't know if the current motor works. Don't see much of a way to use it anyway. Maybe I can recoup some of the cost of a gas conversion. Pretty sure I can come up with a 15-20 hp gas engine, got a friend who deals in riding lawn mowers and what not.

 

.... IF you can even find one. I spent 30+ years in the electrical trade and have never seen one that ran...

Here you go, request a quote... https://singlephasepowersolutions.com/product/15-hp-single-phase-motor/

They note that these are the worlds only large-HP single phase motors available. Let us know how much...

 

Most of the gas powered compressors I have seen use a blowoff valve that bleeds off excess pressure over the set pressure. The gas engine runs at governed speed all the time. Do you know if that compressor has head unloaders? Head unloaders let the compressor start with no load on it until it builds up oil pressure, then the compressor starts to compress air. It lets the motor start with very little load on it. You could also put a smaller pulley on an electric motor and spin the pump slower then it came from the factory. You could then use a smaller electric motor than it had originally. Of coarse it would not pump as much air as it did originally either.

 

ALL electrical circuits have current inrush, but on everything other than motor circuits it can usually be ignored. But even when starting a motor under no load, the inrush current still exists and the reduction isn't that great. This is inherent in the design, and would take a deep dive into electrical theory to explain.

 

Don't know if it has that. Guess I need to find a manual for it. I've hardly looked it over and I only get to the yard about twice a week in winter. Especially this winter..Good idea on the pulley sizing.

 

Could get a smaller motor and gear it down but it would take forever to fill that tank.

 

Use synthetic oil in gas engine and compressor. Install a valve to vent pressure manually for the first start of the day. You should have a governor to drop to idle speed when the set pressure is reached. And a blow off valve. If you can rig up a centrifugal clutch, so much the better.

 

You could always take it somewhere and test run it, then clean it up and sell it. Anything 10+ HP in compressors are big ticket but also a limited market. The simple fact is an old Curtiss like that will run nearly forever with regular care and feeding. New stuff is mostly import junk. Try shopping for one and see what I mean. With enough profit you can get something better suited to your limited needs. That one looks to be spalsh oiled and probably was a backup unit for a place with high air demand. The CFM output is probably intense at a minimum. I ran a single phase 10HP in my home shop for about 5 years. Electric bill was low because it didn't run much with a 120 gal tank piggy backed to the 80 base tank. Just under 7 minutes to fill 200 gal from zero to 150, about a minute 20 seconds to cycle from 125 to 150. Almost double the current demand but less than 1/2 of the "normal" run time of a typical 5 HP. Made sense to me. Let us know what you end up doing.

 

Will do. I have an old Suzuki 500 I never ride, maybe I'll chain that thing up to it.

 

We have five engine powered compressors: one with a Wisconsin V4, One with a 302 Ford (runs on 4, pumps on 4), an air cooled diesel. a diesel that starts on gas and switches to diesel, and a 4 cyl liquid cooled John Deere diesel. If it fits into your budget a diesel compressor is much cheaper to run and has rock solid dependability. They range from 70cfm to 850cfm and are used for everything from sandblasting (smaller cfm) to boring under a highway (huge cfm). Kinda favor the mid range John Deere powered unit.

 

Wow !
Did I read that correctly ?
Up to 100 hp on single phase.

 

Why not just replace the motor with a couple of pillow block bearings and the same diameter shaft that will hold the drive pulley, put a yoke on the other end of the shaft and hook a short drive shaft to some cheap but reliable engine& trans to drive it? With the engine and trans sitting on a simple stand with the matching radiator.
Farmers have used setups like that to run different things since Model T drivetrains were cheap and easy to get. Fire it up, kick it in gear or use a hand clutch to let the clutch out and a pull cable to work the throttle and set your rpm and blast away.
Since most tire shops with field service trucks have gas powered air compressors mounted on them the relief valves or what ever you want to call them should be reasonably common and not that hard to find. Well the photo was supposed to be on the bottom but study it a tad and the imigination might work.

 

5 hp is about the Max for single phase and it takes a bank of start capacitors to get it rolling

 

How much do you use air at your yard away from home? I have a friend who runs a stock car, he used to have a gas powered compressor on his ramp truck but he replaced it with a nitrogen cylinder. It does everything the compressor did like pump up tires clean parts etc but is a lot quieter, simpler, and cheaper. One tank lasts him all season. He made the change about 20 years ago. You get the nitrogen cylinder from welding supply outlets. A refill cost about $30.

 

That is correct , the start up is where your issue is going to be . You run that dude on single phase motor and you better get a new bearing kit to replace the ones your electric meter are going to toss out in the yard after about 5 minutes of use .

 

i have an old leroy portable compressor from the 50's i would guess, made for a jack hammer. i use it for sand blasting. cost about 300 bucks 20 years ago. put a fuel pump on once, and still running. your big 15 hp thing would be nice in a busy shop that needs alot of air, but to convert it over to what you want is a waist of your time and money. the big old thing like i have are common, as are small gas ones that the roofer and carpenters use

 

Don't know if the current motor works. Don't see much of a way to use it anyway. Maybe I can recoup some of the cost of a gas conversion. Pretty sure I can come up with a 15-20 hp gas engine, got a friend who deals in riding lawn mowers and what not.[/QUOTE]

I say sell it and buy something else. But if you are determined to use this, have your friend locate a 20-30 HP gas horizontal shaft engine from a mower with a PTO clutch and electric start. Wire the clutch to your pressure switch. My zero turn mower (Kohler engine) and others have this. Then, you will probably have to deal with gear reduction (possible jack shaft necessary) to get engine RPM matched to compressor pump. Another pitfall is that the engines mentioned will most likely only use one v-belt and that may not be adequate. Also, be sure that the compressor is good first. My granddad would call this a fools folly but he wasn't always right, oh wait....
Eddie

 

That would have been my guess, but they are advertising 100hp single phase motors.

 

Oh, the 7.5 HP single phase is not uncommon, and I've seen a few 10 HP, but nothing larger than that except for a few really old motors (teens/'20s).

They had no specs on the 15 HP single phase on their website (because it's discontinued?), but the 30 HP version weighs almost 1000 lbs!