7.5 Hp 3 Phz Compressor on 1 Phz power

CarlBoyd · Nov 1, 2020

I found a Quincy dual QR 7.5 Hp 3Ph compressor at a good price. I bought a tank an plan on moving one motor and pump to the tank and selling to offset the costs.
I don't really need 7.5 Hp for my home shop and can run at 5 Hp with smaller drive pulley.
Options in my small mind.
1) static converter on existing motor with smaller pulley, I can tune down shut off pressure if needed.
2) 5 or 7.5 HP single phase motor
3) digital phase converter like https://www.amazon.com/Phase-Conver...+phase+converter+7.5+Hp&qid=1604275106&sr=8-3

I have a 20 HP motor to make a phase converter, but don't what to have to start that up every time I want air. I am currently running a LaBlond 16" on a static converter with no issues.

Other options, experiences, advice, ridicule welcome.

CarlBoyd

mksj · Nov 1, 2020

Static converters do not work well on compressors, in particular with their high start-up loads and you loose Hp so would need to change the pulleys. The "DPC" mentioned are are junk, if they worked as advertised lots of people would be using them. Basically some capacitors and some digital circuitry , but not much more, the few people I heard that tried them with high loads something burned up in short order. I would go with a 7.5 Hp single phase motor, about $400-500, if you have a big air pump might as well get the most out of it.

CarlBoyd · Nov 1, 2020

mksj said:
Static converters do not work well on compressors, in particular with their high start-up loads

Quincy QR series pumps have unloaders to the motor starts unloaded except for inertia.

mksj said:
you loose Hp so would need to change the pulleys.

I don't need 7.5 Hp, 5 is plenty and was what I was really looking for. Smaller pulley is minor cost issue. The pump is rated for operation from 5-10 Hp.

mksj said:
The "DPC" mentioned are are junk, if they worked as advertised lots of people would be using them. Basically some capacitors and some digital circuitry.

Do you have first hand experience with DPC in general or the specific model in the link.

mksj said:
I would go with a 7.5 Hp single phase motor, about $400-500, if you have a big air pump might as well get the most out of it.

If I could find a good one for $500 that would be my choice. I would hate to replace a Baldor motor on the compressor with something less. Although maybe that does not make sense considering my other options are kind of cheap solutions.

Thanks for the suggestions.

CarlBoyd

dalmatiangirl61 · Nov 1, 2020

I had not seen the "digital phase converters", thanks for the laugh, from description, "The failure rate was even lower frequency operation" and "semi permanent life time".

Just get a 5hp single phase motor.

mksj · Nov 1, 2020

I worked with another person who tried one and it failed, opened it up and it was phase capacitors. They may be switched in/out digitally, but give it a try for $100 if you want. There are also those that use cheap 10Hp supposedly single phase input VFD's, they work for some and others they quickly go up in smoke. I have looked at those and the traces and terminals do not support their current ratings.

5HP or 7.5HP or whatever size floats your boat.
5 HP LEESON COMPRESSOR DUTY ELECTRIC MOTOR REPLACES 131537, BALDOR L1430T L1410T | eBay
5 HP 1-PH 1725RPM LEESON ELECTRIC COMPRESSOR MOTOR 184T C184K17DB31A 230V 131537 | eBay
https://www.amazon.com/WEG-INDUSTRIAL-COMPRESSOR-1760RPM-DIAMETER/dp/B07D2M95J7
NEW WEG 7.5HP 1-PHASE 215T 1760RPM MOTOR REPLACES BALDOR L1510T, LEESON 140155 685650080475 | eBay

beckerkumm · Nov 2, 2020

$500 will get you a single phase motor although you may need to swap the starter too. Quincy QR have a wide rpm range. I'd buy a gasket kit and take out the valves and dump them into some evaporust and then sand them on a plate. The QR will run forever with a little maintenance. If you ever plan to use air sanders like Dynabrade, you will want the 7.5 hp and faster speed so be sure you don't need more than 15 cfm when you go to the 5 hp motor. Are the pumps 340 or 350 ? 340 is more rare and a nice size so it should have a decent market value. 325 and 350 are more common but the weight of the 350 makes it cheaper on the used market. Dave

DDoug · Nov 2, 2020

I ran a 10 hp quincy on a cedarburg static box for years, used a smaller pulley for 7.5 h.p.

I used it for long periods of time sandblasting, no problems. The slow load time I think is key here.

I now replaced the pulley for full 10 h.p. and run it from an RPC

CarlBoyd · Nov 2, 2020

Dave

The pumps are 340's.

CarlBoyd

CarlBoyd · Nov 2, 2020

Doug

I am kind of leaning towards a static converter solution. I may set one up as a static and see how it works. I can sell that one if I am unhappy and try another option with the other.

CarlBoyd

CarlBoyd · Nov 2, 2020

mksj said:
I worked with another person who tried one and it failed, opened it up and it was phase capacitors.

I re-read the add for the DPS and it does sound like phase capacitors.

Thanks for the infor.

CarlBoyd

DDoug · Nov 3, 2020

CarlBoyd said:
Doug

I am kind of leaning towards a static converter solution. I may set one up as a static and see how it works. I can sell that one if I am unhappy and try another option with the other.

CarlBoyd

What I did NOT doo back then, but should have (now that I know a little more) is to add some balance
caps when running.

gustafson · Nov 3, 2020

You already own the 20hp motor, why not take the opportunity to set up a 3 phase system for virtually nothing
Get your lathe running on it too.

A little single phase starter motor and a couple switches and you are good to go.

CarlBoyd · Nov 4, 2020

gustafson said:
You already own the 20hp motor, why not take the opportunity to set up a 3 phase system for virtually nothing
Get your lathe running on it too.

A little single phase starter motor and a couple switches and you are good to go.

I'd prefer not to have to start an RPC to use the air compressor. I use the air compressor 4-5 time a week, the lathe once a month. I don't want to go out to the shop and need air, then have to start the RPC, then wait for the compressor to pump up, I want to grab the air hose and have air, period.

CarlBoyd

SomeoneSomewhere · Nov 4, 2020

Depending on how often you need large amounts of air vs just some air, it might be feasible to just put a small compressor in tandem and have them share tanks. Start the RPC and large compressor when using large volumes of air, or even throw some controls together to make it happen automatically when the tank gets below say 75PSI and shut off the RPC when the large compressor doesn't cycle for half an hour.

JST · Nov 5, 2020

The leakiest thing is probably the hose and couplings.

Put a quarter turn ball valve in the outgoing air line, and you should have air on hand for weeks. Put a shutoff on the electric to it, and when you go to the shop and need air, turn it on and open the ball valve. That ensures the compressor will come on when pressure falls.

Meanwhile the tank should have plenty of air still in it for immediate use.

My FIL does that in his gunsmithing shop (now hobby since he retired), it works well.

The 5 HP single phase seems like a decent plan.

CarlBoyd · Nov 13, 2020

JST said:
Put a quarter turn ball valve in the outgoing air line, and you should have air on hand for weeks.

I like that idea, thank you for that.

CarlBoyd

Garwood · Nov 13, 2020

I have a 7.5HP single phase QR-350. Runs about 500 RPM/175 PSI cutoff.

There's a pretty good starting load even without pumping air. That's a lot of shit to get spinning instantaneously.

I also have a pair of 325's with 5HP 3 phase motors running single phase through a pair of 10HP frequency drives.

The VFD works well and allows for a considerably more refined result.

Strostkovy · Nov 14, 2020

Phase converters get really annoying really fast. The only reason I used one for so long is because the motor on the press brake was some custom frame flange mount thing that would be impractical to replace.

That 7.5hp motor you'll have left over will make a nice phase converter for other equipment with just a potential relay and some start capacitors.

Balvar24 · Nov 17, 2020

I ended up with a "free" 10 HP compressor and a 25 HP 3-phase motor and 1 1/2 HP pony. I ended up sinking a couple hundred more bucks in wiring and parts/pieces to come up with a functioning rotary converter. The good news is that it works. I rarely use a lot of air. If I were running it daily, the Phase converter would be annoying. For my use, however it works.

7.5 Hp 3 Phz Compressor on 1 Phz power

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