Variable frequency driven compressors

[MLH]

My 'plan' - I plan on buying a new 3hp compessor (portable - maybe from IR - don't know what model yet) and doing a conversion from a single phase motor to a 3hp three phase VFD controlled motor. I want to do this so i can take this around and plug it any standard 10A 240V socket.

Any thoughts / recommendations on this?

-Mike

 

[CraigFL]

I'm not sure what you are trying to accomplish. The VFD is typically used for changing the speed of the motor. A compressor is typically off or on with the maximum air flow. What are you looking for that a cheap 240V, single phase motor won't do?

 

[goodfellow]

My 'plan' - I plan on buying a new 3hp compessor (portable - maybe from IR - don't know what model yet) and doing a conversion from a single phase motor to a 3hp three phase VFD controlled motor. I want to do this so i can take this around and plug it any standard 10A 240V socket.

Any thoughts / recommendations on this?

-Mike

Doesn't make sense -- most likely the portable IR already has a 115v motor on it -- why change over to VFD and 240V. With 115v you get ultimate flexibility.

 

[Steve in Mi]

Save your money. Most any 3 HP motor on a compressor will already be dual voltage so I see no gain, just more expense. A VFD on a compressor can give a soft start but seldom needed on a 3 HP unit.
BTW, "standard 10A 240V socket" what is this? And what size breaker do you put it on?

 

[timgr]

I know there's a 15A 240V receptacle - I needed one for my air conditioner install.

NEMA type 6-15R

A 10A 240V receptacle wouldn't make much sense, since you can deliver the same power with a 20A 120V line, and cheaper.

 

[MLH]

Oh... ok then i won't need to get one then

 

[Stuart in MN]

As mentioned, you should be able to get a single phase 3hp motor without any real problems. For the others who questioned it, a variable frequency drive (VFD) can be used to operate a three phase motor when single phase power is all that's available. Obviously for an air compressor you wouldn't need to vary the speed of the motor, but it will provide a nice soft start feature. Typically the VFD has to be oversized by about 50% if it's used in a single phase application (so for example, to operate a 5hp three phase motor off single phase, a 10hp VFD is required.) However, it's best to talk to the tech support people for the VFD manufacturer to explain your situation, so they can recommend the right model.

 

[W-Cummins]

Obviously for an air compressor you wouldn't need to vary the speed of the motor, but it will provide a nice soft start feature.

Actually that's why I'm running one on my large compressor. I wanted to be able to run the motor ( and pump) at 1/2 speed. The soft start is great too I can start the pump on a 20 amp breaker now. w/o the VFD it spiked the 500v lines to 135 amps for about 1.5-2 seconds. ( now the VFD amps vary from 18-24 when it runs from empty to 175psi) The breaker will still trip if I cycle it from empty to full as it nears 175psi but I have no intention of running it normally on only a 20 amp breaker!

William....

 

[heavychevy454ss]

If you have too much compressor for your usage, it a vsd/vfd can be used to drop the peak electrical load as w-cummins mentioned. This can be very important when your utility company charges you on peak usage rates.
I work for a fortune 100 company and we are evaluating all our compressors for the applicability of this technology.

 

[ddawg16]

I use a lot of VFD's.....Single phase is not exactly an ideal use for them. And when you factor in the cost....and power loss through it...I can think of better ways to solve the problem.

I would be willing to be that you could buy another smaller compressor and motor that will operate just fine on a 20A 110/220 ckt. Basically, it's cheaper to operate a smaller compressor longer than a larger one for shorter periods of time. If you don't have enough capacity, add another small comperssor.

Tanks are cheap. You can usually pick up just a tank for about $50....find an old dead compressor with a tank on it and you might get it for free...nothing wrong with having 2 or more tanks around the garage.

BTW....A common decision point on using VFD's (besides needing variable speed) is when the motor size gets in the 50-75hp range. And unless you have the need for variable speed...softstart is a cheaper way to go.