10hp air compressor....how to power it.

[LD1]

If you want simplicity and have the current to do it, just get the single phase motor and the starter as it will be cheaper than any three phase solution. It will need plenty of power when you start it though so I wouldn’t do it if you have only enough power to run the motor. The inrush current will be very large as a compressor is a hard start. If power is limited a three phase solution with a VFD will use less current on start.

200a service at shop. Yea I have enough power.

Everyone keeps saying compressor is a hard start load....

No, not a screw compressor. Not any harder than starting a fan, or even a clutched machine like a lathe. It doesnt actually "load" the compressor til things are at speed

 

[Erik M]

Then you should definitely stick with the single phase solution. Easiest by far.

 

[LD1]

Then you should definitely stick with the single phase solution. Easiest by far.

Thats the conclusion I have come to.

But I am far from knowing everything. Thus the question as to a more economical solution if one so happened to exist before I pony up $800 for a motor

 

[Bingo9991]

I thought you meant engine, when you were talking about hp and rpms, guess I was just being a tard

 

[John Fitzgerald]

When I was advising consumers at the electric coop, this came up fairly often. I would advise to get a single phase motor. Many cooperatives in rural areas limit single phase motors to 10 hp and smaller.

 

[Industrial Toys]

I was reading an article this morning about oversizing conductors to save money in the long run. Had no idea a 100HP motor (costing 10,000) running 24/7 will use a hundred grand of power in a year!

Most time, one doesn't need much air. I would run a thing like that for sandblasting using a petrol motor and have a smaller compressor for filling up the tires.

I built a 10hp RPC years ago for a 3ph lincoln mig welder that I bought by accident. I think the power poles in the neighborhood jumped out of the ground every time I start that thing! I used to turn off all my sensitive electronics and appliances!

 

[bigdeano]

Yea, you basically made a static converter. And no they dont run full power. You are probably closer to 6-7hp rather than 7-8

It's a capacitor start, capacitor run motor. All three windings are energized while it's running, unlike the static converters which don't use run capacitors from what I understand. They're commonly used in submersible well pumps. The OP could change the pulley to lighten the load on the motor a little. It's the cheapest way to get the compressor running and should still put out a lot of air.

 

[the old grind]

.... this compressor airend is the exact same one used on 7.5hp/29cfm models......the 10hp/40cfm model that I have, and 15hp/60cfm models. they just did the speed change with pulley sizing.

....I cannot buy a drive big enough for any less money than a single phase motor.

.. also drives are fragile, as smoking when caps fail .. that said, you might could rebalance the RPC's legs, and that's often needed for largely disparate loads. Idling another connected motor might (a long shot, but sometimes) help balance, YMMV depending on what they are and what you have now (balance caps)

... Still trying to decide if I want to spend ~$800 for a 10hp and have a 40cfm compressor......or spend $400 for a 7.5hp and ~$25 for a new pulley and have a 29cfm machine? ...

Based on quote #1, gosh yeah. I suggest also that you set a much wider spread for your switch settings. Two stage piston jobs may set from 125 to 175 psi. I might use, or recommend on at 110 and off at 150. It's kinda like having a bigger well tank but using pressure vs volume to store-up because outlets are regulated, eg 90 psi for most small air tools 120 psi or so for tire changer or other high pressure OR volume tools. Fewer cycles is part of o'all efficiency, and I'd guess it's unlikely you use for long tools that need 20 cfm or more.

Thats the conclusion (confusion?) I have come to. ...Thus the question as to a more economical solution if one so happened to exist before I pony up $800 for a motor

I suggest you'd rarely need all of 5 of 7.5 hp you had on tap, and IMO you best explained why that would be a good choice. (you're good at that ... thanks, btw)

 

[LD1]

Was hoping you'd chime in old grind....rather than try to parse out quotes to reply to....I'll just do it all at once.

Tried balancing with another idler. 10hp. no load as it is a 10hp off another converter. That brought L1 and L2 down from 40ish amps to about 37...and added a few on L3 where it was at 20 and now 22. But didnt do me any favors for efficiency as single phase amps....feeding the main converter box...went from ~57 up to the lower 70's.

Regarding pressure....cant really up it any. Tank and compressor....according to Joy MFG....is only rated to 125psi max. And the L1 and L2 loads....the ones I am concerned with about the high amps....pull about 38A @ 100psi and is up to ~41A @ 120psi right before it kicks off. But those two legs only pull ~24A @ 50psi.....and a tad less under that.
Watching the Amp meter clamped on the leads....watching the amps climb just like watching the pressure gauge climb.

Now regarding my air usage......current compressor is a 11cfm 30 gal tank. Single biggest thing it cannot keep up with is my can crusher. 4" bore....6" stroke air cylinder @ 80psi. When I have a barrel full of cans at the house and want to crush....cannot crush more than 30 at a time without waiting on compressor. And the barrel holds ~150.

But I also do some sandblasting and painting, and running a die grinder which is an air hog for an 11cfm compressor.

Based on your reply....I am unsure if you are suggesting that I drop it to 7.5hp and adjust airend RPM's accordingly.....or stick with 10HP?

Do I think 29cfm/7.5 HP is plenty for now....sure. But dont want to regret spending ~$450 setting it up as such....and wish I had gone bigger if my air needs change.

Boy would I like to stumble on a use working 10 horse single phase motor

 

[Mendonsy]

Got any electrical equipment recyclers in your area? You can sometimes score a good deal on a used motor at those places.