3 Phase compressor, single ph service: What options?

[Fl_Key_Guy]

I just bought a Brownie's Yachtpro (Bauer with mods) compressor with a 7.5 hp 208v 3 phase motor and no VFD.

I have 240 volt single phase service.

I would prefer to run it with a 5 hp single phase motor on lower output, but Brownie's claims it can't be run with a smaller motor with smaller drive pulley. (True?) If it CAN be run with a smaller motor, would I just lose cfm and still get the pressure? Any other problem?

I am exploring a 3 phase generator, a replacement motor, various phase conversion methods. What is my best option for powering this compressor? (If you're just guessing, please don't answer.)

Thanks for knowledgeable input!

 

[pescador775]

Clark may be able to answer this as he is familiar with Brownie's equipment. Changing motors is not uncommon. As you said, a compressor can be operated with a smaller pulley (if available) located at the motor. There would be a reduction of cfm but not pressure. Some compressors have a minimum operating speed but I believe Bauer blocks will turn at very low speeds without problems. I wonder if there would be a problem with any of the auto controls when using single phase. I would not use mickey mouse stuff like phase converters as they will cause the feared power loss. I think that you will eventually get a more knowledgable answer since SB has several people who can talk to the subjects of VFD's, etc. Don't panic.

 

[wedivebc]

I did exactly that with a Bauer mariner and it has provided me with 6 years of faithful service.

 

[CraigAClark]

First you need to determine whether or not the unit has a Mariner or Mariner II block. The Mariner Block can run with a 5HP motor as long as the the compressor rpms are not less than 1100. I just converted a unit for someone because his new generators (even though they where the same size as the old ones) could not start the 7.5 HP.

I'm not sure what minimum rpms on the Mariner II are required. The older units had a high pressure oil pump and regulator for the final stage, so lower rpms weren't a problem, nor did incorrect rotation have an ill effect on the lubrication. However, the Mariner II has a low pressure feed for the final stage and running it with incorrect rotation will lock it up pretty quickly.

I also do a lot of work with VFDs.

Craig

 

[mike_s]

FL Key Guy.

check into what a Phase convertor would cost for your compressor. that's one option.

but just make sure you have enough amperage in your panel to budget for it. It'll suck up a lot more amps in single phase.

check out 3 Phase Converter Info- Sales- rotary phase converter, static 3 phase rotary converters. and google for other stuff.


also check out using a Variable Frequency Drive. you can use it in conjunction witha 3 phase motor with a single phase source. http://en.wikipedia.org/wiki/Variable_Frequency_Drive

 

[Fl_Key_Guy]

Thanks for the info so far!

My compressor is a 2003 Brownie's YP75DF 7cfm , max 5000psi spinning at 1200 rpm with the 7.5 hp motor. Brownie's Automated Marine Tankfill - Heavy Duty with the vertical configuration and no soft start.

I believe the controls run off one leg of the 3 phase 208v, so that should be solvable.

It appears that every economical means of phase conversion has nasty side effects, leaving only digital.

It appears that a Chinese digital VFD capable of phase conversion is about twice the price of a replacement motor- I'm not sure the soft start ability is worth the bucks- and then there is the questionable Chinese quality issue as well.

Good call on the possibility of inadequate oil pressure at 800 rpm... That's the kind of stuff that I don't want to learn the hard way!

 

[pescador775]

Is there space to fit a 7.5 hp single phase? It should draw only about 30-35 amps. I guess start up could trip a breaker, though.

 

[Fl_Key_Guy]

Size difference is a good question.

I had a tough enough time finding 7.5 hp single phase motors, let alone dimensions. I eventually found a 3 phase motor with dimensions and a Leeson "general purpose" single phase 7.5 hp and they were very close to the same size: about 11" across and about 18" long .

The single phase wants a 40 amp breaker which is not a deal breaker. It would be nicer to run a 5 hp as it could use a standard dryer outlet. At 300 lbs, the compressor is "sort of" portable.

I can get a 7.5 hp surplus 230volt DC motor cheap, but know even less about DC motors than AC. (Except that they are easy to reverse! ) Rectifiers are cheap. Anyone know if DC motors have enough butt to start the compressor? (might depend on the wiring type?)

Another question for a motor whiz: Does the motor have to be "compressor duty" or would "general purpose" or "agricultural" be okay?

 

[mike_s]

a 40 amp (or 50amp) single phase breaker is only like $10 bucks (or less). Easy to add to your panel.


You're gonna panic when you see what a 30amp 3-phase breaker costs....

 

[Fl_Key_Guy]

I have spare breakers on hand salvaged from a demolition so breaker cost is zero. Even have the correct wire!

I was just hoping I could safely run it on a dryer circuit using a 5 hp motor at a slower speed. The 5 hp motor is about half the price of a 7.5 hp single phase and it might save me a lot of tank hauling and truck miles if I could move the compressor to near the dive boats that we go out on.

I was investigating other options that would retain the 3 phase motor as it has some advantages, not the least of which is that we know it fits and works properly.