big air compressor question

[Diggers4life]

I just acquired a Gardner-Denver compressor. It's a 25 hp 2 cylinder, single stage unit (bore = 7-1/2" stroke = 4-1/2"), model ACL1002. Obviously, I can't run the 25 hp 3 phase motor on residental power here in my garage. I was wondering, if I slow the pump down accordingly, would it work to use a 10 hp single phase motor as long as the oil pressure gauge says I'm making pressure? Original pump RPM is 870. I was thinking about slowing it down to about 350-400. It would be pretty quiet, and still make about 50 CFM at 100 lbs.

What do you compressor experts think? Will it work?

 

[W-Cummins]

Call up gardner-denver and ask them?? They can tell you if it will work. I have a Quincy that is a 20hp and it can be run at a slower rate with a lower HP motor (down to about a 7.5hp motor). A new 10hp single phase motor and starter is going to cost about 1k or so. On top of that your going to have about $50-100 in a new pulley sheve/belts ( I assume that it's at least a 3 belt drive).

At 10 hp you will be closer to about 35cfm or so...

William....

 

[Diggers4life]

Thanks W-Cummins, I have an e-mail out to a local dealer to see about a parts manual. Maybe it will have some info about minimum pump speed. I think I can get a motor cheaper than $1K. I'm a tool maker at a local job shop. One of the companies we do quite a bit of work for, repairs and sells Baldor motors. I think I should be able to get something used. Also, being a machinist, pullies won't be a problem. Hell, I figure even if it costs me $1k to get it running, it's still pretty cheap considering the amount of air it should make assuming the pump is in decent shape. My Quincy QT-5 cost me more than that and makes about half the air and probably twice the noise.

 

[Diggers4life]

Ok, next question.

Which would be better/cheaper?

Using a single phase 10 hp motor, or getting a phase converter and running a 3 phase 10 hp motor.

The plus side I see on the 3 phase is I don't need a starter, and I might be able to find a cheap industrial motor easier.

The plus side on a single phase motor is I won't need to purchase a phase converter.

 

[W-Cummins]

So I assume that you found out that you can run it at 10 hp??

After I answered the above question I had a brain fart Take the 25hp motor off the compressor and make a phase converter out of it. Then pick up a used 10 hp 3 phase motor for about $50-100 and use it to power the compressor.... That way it's low cost and your mag starter can be used for the smaller motor ( all you will need to do is change the heaters out) Probably get it all up and running for about $200 or less if your a good scrounger.....

William....

 

[Matti]

Oiling is usually the issue. A rule of thumb is 4 cm/hp although even the highest quality compressors don't quite deliver that IIRC.

 

[rsanter]

if you are going to make the 25hp motor a rotary converter, why wouldnt you go to a 15 hp motor to drive the thing

I would say 3phase and converter all the way

bob

 

[ron in sc]

I read somewhere that a single phase motor any larger than a 5 hp will have a significant reduction in life. Something to do with the amount of copper windings and the heat generated.

 

[Diggers4life]

I don't have the origional electric motor to make a phase converter out of. The prevoius owner got rid of it and made a hokey attempt of putting a gas engine on it. Needless to say he never got it to work. I don't want to go much more than 10 hp mainly because of the current draw. I think a 10 hp motor will draw about 50 amps of single phase 220. I just figured that was plenty.

 

[MLH]

I don't have the origional electric motor to make a phase converter out of. The prevoius owner got rid of it and made a hokey attempt of putting a gas engine on it. Needless to say he never got it to work. I don't want to go much more than 10 hp mainly because of the current draw. I think a 10 hp motor will draw about 50 amps of single phase 220. I just figured that was plenty.

Don't make a rotary converters!

From unique3phase.com | Let's say you have a ten horse invincible vacuum cleaner, a five horse compressor, and a quarter horse water pump. To run the vacuum cleaner you need at least a thirty horse rotary. (When I first started with this I tried to start the vacuum with a 25 horse rotary and it would not do it. It just wasn't big enough. So until you actually do it, it would be anyone's guess with a 30 horse.) Let's say we vacuum twice a week, and use the air compressor off and on all day, and the water pump is in the heating/cooling system, and runs when it's called for. You come in at 8 am and turn on the rotary. The shop comes alive and you turn on the heat and the air compressor. The air compressor fills the tank and shuts off. Guess what is still running? That's right the rotary. Does it use electricity when it idles with no load? You bet is does. How much? Well some manufactures publish the figures, some don't. Some claim that the losses are the kind of losses the power company can't measure. In any event for a thirty horse idler I would say at the minimum you are wasting 8 to 12 amps. This is 8 to 12 amps at 240 volts. That is 1920 to 2880 WATTS. Do you think the power company meter misses all that? Do you think the new digital meters miss it?

My $0.02

 

[kbs2244]

Single phase motors over 5 HP can have overheatitng problems.
It is easily solved with a small drug store fan wired in so that it blows on the big motor when it is running.
This can be real inportant if you hide the compressor away in a closet or in an attic with low air movment.

 

[Diggers4life]

I've done some research since I started this thread, and it seems like everything kinda points in the same direction. A phase convertor probably won't be the best idea (static or rotary) for the amount of juice I'm going to need to get this thing started. Maybe I should be looking into single phase motors. Or my other option: Anyone have any thoughts about using a VFD (assuming I could find a big enough one fairly cheap) with a 3 phase motor ( that I can find cheap).

 

[Steve in Mi]

If you happen to have a tractor with PTO you might consider powering your compressor with it. If you will only have need of the extra air capacity occasionally it could be an option worth consideration.

FLASHBACK;
I bought a used 4 cylinder single stage air compressor that sat on a trailer mounted 120 gallon tank and was PTO driven thru a gearbox. At 540 rpm on the PTO, with gearbox and belts, the compressor turns at 900 rpm. When I got it I didn't have a tractor with PTO to power it so I cannibalized the trailer for another project and removed the PTO and gearbox. Things have changed (they have a way of doing that) and I now have a tractor w/PTO to drive it. When I get to it (when oh when might that be?) I plan to mount the whole unit as a 3 pt. attachment (no trailer) and reinstall the gearbox and PTO drive for a portable sandblast air supply.

If I thought that the compressor would see lots of use I would dedicate an engine to it but more than likely this will see minimal service so rather than an engine setting idle for long periods I think the PTO drive will work best for my needs.

 

[Aceman]

Whatever motor you choose to go with you need a starter, single or three phase. Just an idea, I'm no motor expert, but if a 10 HP single phase isn't a good choice why not try a couple motors in tandem? Maybe two 5 HP or 7.5 HP motors. I'd bet they would be more common and possibly cheaper than one 10 HP?

We had an agitator for a manure tank on the farm with dual 7.5 HP single phase motors. When both motors were mounted up and ran, they were both amped to make sure they were running in spec and to verify proper pulley sizes.

 

[Diggers4life]

^^^I actually thought about doing that. I'd just never seen it done before, so I didn't know if it would work.

A pair of 7.5 hp or 5hp motors would probably work pretty well.