New to me Quincy 80 gallon 325 air compressor!

[averagef250]

A 325 is pretty heavy. The pump itself is around 200 or so. I poured a concrete utility vault at my dad's place for the compressor to sit down in out of the way, works real good, but the compressors been in and out a few times for maintenance and wiring changes. It's a heavy SOB. I used a 1/2 ton chainfall and really wouldn't dream of trying to lower or raise it by hand.

If you can't get it inside a building and use a truss to unload it you can build a wood tripod over the truckbed to raise the compressor and drive out from under it. Another way to get it out is to make some long wide skids that bolt to the bottom of the compressor so it can't tip. Make it long enough and you and some friends can slide the whole thing right out.

[mljjones67]

Well me and a neighbor strong armed it out of the truck last night. That was fun. Now I need to get the pad out by the A/C unit poured and see about getting it wired in. Then maybe I can start making some money too??

[mljjones67]

Well its been awhile since I updated this thread. I have started looking into getting it wired up and found out it is a 3 phase motor. Now I am not very good with electricity and wiring so I need some advice. I have been doing a lot of research and I cant run a 3 phase because my house is not 3 phase. I have two options, one is to get a converter which changes the it to 3 phase or two change the motor to 1 phase. 3 phase is the best as I understand because it give even pulses to the motor to make them last a long time. What is all your advice?? I would like to get it hooked up so I can make some money while I am out of a job. Any help or advice would be great.

[averagef250]

Doesn't a 325 at 200 PSI max out at 5HP? Why does that thing have a 7.5HP motor on it?

You can run it through a roatary converter, but you'll need a well made rotary, atleast 15HP to operate that efficiently. The nice part about Quincy's is the unloaders that don't load the compressor until it builds oil pressure. They start unloaded, really just the inertia of the flywheel and crankshaft that the motor needs to spin up when they start.

A better way to do it if the only 3 phase thing you have is that compressor is to buy a VFD. You can program in the acceleration rate to make it smoother starting. Having a larger motor HP than necessary on there would be a real advantage with a VFD if you choose to operate the motor at a different speed than 1750 RPM.

A new Baldor compressor duty 5HP motor is about $500. If you go that route make sure the magnetic contactor is rated to handle 5HP across only 2 legs.

[mljjones67]

Thanks Dustin. I will look into the VFD drive. That sounds like the best way to go! What VFD do you suggest?

[averagef250]

Thanks Dustin. I will look into the VFD drive. That sounds like the best way to go! What VFD do you suggest?

I had a terrible experience with an expensive Toshiba VFD and have used rotary converters ever since. My current setup is a 30HP rotary converter fed into 100 amp bus duct throughout the shop that feeds all the machines so no need for a VFD nor would it work for most of the machines I have.

VFD's are fine to supply power to one motor, but they can't really do two at the same time.

Practical machinist has a good forum section on motors and controls. I'd search there for suggestions on a VFD.

[MaxKlinger]

A Variable Frequency Drive is basically a rectifier-inverter that will change 60 Hz Alternating Current into Direct Current and then back to AC at a different, varying frequency. They're frequently used to "soft start" AC motors that are under load all the time by increasing the frequency slowly rather than just turning them on at 60Hz, improving longevity. Since the Quincy compressor has unloaders, it shouldn't actually go to full load until it's already spinning at operating speed, so a VFD is probably not necessary.

I just acquired a Quincy myself, with a gasket set for rebuilding. It's going to be a fun project. It came off of a PCC trolley car (the early ones had compressed air brakes). Since it has unloaders, I'm going to belt it to a 5HP Briggs and Stratton that I have lying around the garage. I have a smaller vintage compressor, an electric Montgomery Ward from 1954, for light duty stuff, and if I have a heavy duty project I'll just fire up the Briggs/Quincy duo and it will make a sh!t ton of compressed air.

[mljjones67]

A Variable Frequency Drive is basically a rectifier-inverter that will change 60 Hz Alternating Current into Direct Current and then back to AC at a different, varying frequency. They're frequently used to "soft start" AC motors that are under load all the time by increasing the frequency slowly rather than just turning them on at 60Hz, improving longevity. Since the Quincy compressor has unloaders, it shouldn't actually go to full load until it's already spinning at operating speed, so a VFD is probably not necessary.

From what I understand I need 3 phase converter or a VFD. I have 1 phase power at the house. Am I wrong?

[MaxKlinger]

Honestly I'd think about getting a different motor for your compressor. You'll probably spend way more on a rotary converter as you would on a new motor. That's because a rotary converter pretty much IS a motor without an output shaft, but instead with a set of output windings.

What kind of service do you have at your house? I'm assuming you have a 240V Single Phase service like most of us do. What is the current rating for this service (main breaker size, in Amps)? The reason WHY this is really important is that a three phase rotary converter is going to be a huge draw even at 240V. Take a look at this chart, which has sizing for 240V conversion:

http://www.phaseconverter.com/rotary-converter.sizing/

Your motor is a 7.5HP model that pulls 16.6 Amps at 240V. Even assuming it's an easy starting load, you need something that can sustain a 7.5HP, 17Amp load. That will easily require a 60Amp breaker on your single phase panel. As a point of comparison, most electric range/oven units are 50Amp, and most laundry dryers and HVAC Compressor/Condenser units are 30Amp. 60 Amps is a big load, dude. If you have a light duty service to your house (my house was built with a 60A service, I have upgraded it to 200A), this isn't going to work.

I would recommend finding a 240V single phase motor to swap onto this thing. I'll talk to some of the electrical guys at work and see if I can come up with some cost effective ideas here.

[mljjones67]

I'll talk to some of the electrical guys at work and see if I can come up with some cost effective ideas here.

Thanks. Appreciate it a bunch!!

[averagef250]

Tony, I don't understand your logic.

A 7.5HP 240 volt motor isn't a huge load. The 230 single phase capacitor start 7.5HP GE motor on my Quincy 370 shop compressor is rated for 30 amps max and doesn't actually get over 20 amps pumping up to 200 PSI. I have it on a 30 amp breaker with no issues. If a guy has a 7.5HP motor on a little 325 compressor it's not going to draw it's maximum rated amps.

http://www.aceair.com/PDF/QRSERIES.pdf If you scroll down to the bottom of page 5 you can see the table listing ratings for the QR-25 series two stage compressors. The 325 is a 3-5HP compressor at 200 PSI.

The right VFD with take a single phase input and convert it to a 3 phase output and allow you to control the motor's acceleration rate and frequency.

The premise that rotary converters are cheap is based on the affordability of suitable 3 phase motors. Mike, you used to work at a mill didn't you? Bet you had access to hundreds of old motors around 15-30 HP. capacitors are not expensive either. The most expensive part of a converter is usuaully a proper enclosure and a NEMA rated contactor to start and stop it.

[mljjones67]

Dustin, I used to work for a newspaper in the press room. We did have motors to run some of rollers on the press then we had the really big ones that drove the press. The motors when they were replaced no longer worked and would need a rebuild. They would send them out for a rebuild. It looks like no matter which way I go its going to cost me $500 to $800 to get the compressor running. Normally that wouldn't be a big deal but being out of work will make it one of the last things done unless I get a decent job soon. I appreciate the help from you guys. I will continue to research and look for cheap parts to get it up and running. I still need to get 220 out to the garage which shouldn't be to bad. I am just getting my auto detail and paint restoration business up and going so hopefully that will be my new full time career!!

[MaxKlinger]

The 230 single phase capacitor start 7.5HP GE motor on my Quincy 370 shop compressor is...on a 30 amp breaker with no issues.

Exactly. A single phase 230/240V capacitor start motor such as the one you've got is exactly what I'm suggesting that Mike should use. I would agree that in that situation he would be just fine with a 30A breaker and some standard 10-3 cable to hook it up.

The problem is that currently he has a three phase motor. If he were to install a rotary converter or a VFD, he would need the current capacity to run both the compressor motor and the converter itself. The 60A breaker (and corresponding heavy gauge wire) is probably required for safety and for starting, the steady-state current draw might be a lot less (30-40 amps or so) with both the converter and the compressor running. Remember, no conversion process is 100% efficient, so whatever converter you have is going to use electricity.

Dustin, thanks for the PDF from Quincy. I need to clean up this old Quincy compressor I just got and identify which model it is, and probably overhaul it. The one I have could have been built as early as 1951, but it looks identical to the other two-cylinder compressors in their catalog.

[averagef250]

The efficiency loss through a rotary converter isn't nearly as big as people think. On paper is one thing, but the reality is different.

I run my 100 amp 3 pole bus off a 100 amp 2 pole main breaker before the converter. I can load machines to the point of approaching 100 amps combined load and I've never had the main breaker trip. I have given everything a large safety margin though. All conductors (except the bus ducting itself) are upsized atleast one wire size for max load and I used oversized conduit to help dissipate heat better. One of my lathes even runs through a 45KVA buck/boost transformer after the bus to get 460 Volts and it runs perfect.

Something you have to be really careful of with a rotary converter is isolating control circuits from the wild leg. I've had to dissect both my CNC machine's internally and re-wire them to keep any control transformers isolated to just the two real legs of power. The generated leg suffers from voltage droops and spikes under changing loads and will cause brownouts and other issues that really suck.

[MaxKlinger]

I'm just going by what TEMCO recommended in their sizing chart, which clearly shows a 60A breaker on the single phase input to the rotary converter for a 7.5HP 240V motor. And that's assuming it's an easy starting load. If it's a difficult starting load, it would probably require an 80A breaker according to TEMCO.

http://www.phaseconverter.com/rotary-converter.sizing/

You're right about the "wild leg" for controls. Phase-a-matic specifically says never to install microprocessors on the third leg:
http://www.phase-a-matic.com/RotaryInstallation.htm

But none of that should really matter for a simple compressor motor, which should have no controls and should be perfectly balanced. Actually none of this matters if he goes to a single-phase motor.