3 Phase compressor, single ph service: What options?

[Pura Vida Diver]

We have been running our 17 cfm Worthington with a 14 hp GE motor on a solid state phase converter for 3+ years at our dive shop. The converter was supplied by a company called Ronk Ronk Electrical Phase Converters - Run 3 Phase Equipment On Single Phase Power. Operation of this system has been flawless so far under commercial conditions. The initial cost was on the order of 3k for the converter and some wiring upgrades to the feed circuits but it beat the estimated $12,000 the Costa Rican power monopoly was going to charge for three phase. If you call Ronk with your application information (what you're running, motor info etc.) you will likely be talking to an electrical engineer who can make a recommendation.

 

[Fl_Key_Guy]

General information was sent to me by PM and I will share the meat of it for the group and others who may in the future be looking for this information:

Damage possibility:
It is very easy to damage a 1 phase motor if you have a power drop. (volts go down =amps go up = damaged motor.)

When starting or running it is good to make sure that no other significant loads are then turned on.

Power:
more PSI= more load= bigger motor required. So dropping the pressure will reduce the load and motor size required.

Tips:
1. Drop the compressor speed to 1100 rpm, and

2. Unload the compressor for start-up
a.) Make 100% sure all drains are open at start up.
b.) Cut into pipe exiting 1st stage & install a Tee with a tap that can be opened for start up.

All above will help to reduce start up load amps

(Note: Brownie's Yachtpro has an automatic timed unloader solenoid valve already built in between the first two stages)

What works:

5-5.5 hp 3000 rpm top quality motor for up to 3600psi/250 bar & a 7.5 hp for 4800psi/350 bar.
If it was just a few 4500 psi cylinders a day a 5hp motor is fine. For long runs over 2 hrs, use the bigger motor.[yes its overkill]

Don't get a cheap motor they don't last. WEG brand motors are excellent.

Bauer specifications:
petrol 8hp -6.1 kw
three phase 5.5hp-4kw
diesel 6hp-4.4kw


compressor output:
1300 rpm = 190 lt/min (at about 28 ltrs per cu.ft.= 6.8 cfm)
1100 rpm = 170 lt/min (6.1 cfm)

 

[pescador775]

I'll read more carefully later but all this looks about right. If you use a "3000 rpm" motor a different pulley will be needed in comparison to the Leeson 3450 rpm. Some time ago, at the Compressor Group, we calculated the extra power needed by a high pressure compressor as pressure rises. It was done out of curiosity and to check against any statements later that might be made by various experts. However, the issue of a 5 hp motor for your compressor is not so complex as to require that, there is adequate experience at hand for this situation. You were advised in this thread that the 5 hp motor will do fine at press up to 3500. The implication, if it was missed, was to check motor temp for sustained runs at very high pressure. If voltage is so crucial it makes one wonder how the problem is handled in various countries and islands. Perhaps that is the argument for over powering. Thanks for sharing.

Compressor_Team : Compressor

 

[Fl_Key_Guy]

This is just a follow-up in case somebody else faces the same situation and wonders what happened.

I bought a 5hp compressor duty motor that draws 25 Full Load Amps (FLA) at 230v.

Running a pulley that gave me a measured speed of 1220 rpm on the Bauer pulley drew the full 25amps and the motor shut off before I had 3300psi.

I reduced the pulley diameter by 1/4" and only draw 16 amps all the way to 4500psi, with the Bauer pulley speed measured at 1080rpm. Incredible the difference between a 6-1/4" and a 6" pulley.

I got away with using two poles of the three pole starter, even though it is supposed to shut down for lost phase. All of my control circuits were originally wired to run on one leg of the 208v 3 phase (120v), so that remained unchanged. I have my unloaders, auto-drains, and pressure shut down as before.
Everything works great! Thanks again to the helpful members that supplied information!