air compressor magnetic starter/relay single phase

[disney]

heres two pictures

 

[disney]

here is two more

 

[disney]

ok and here is a picture of the motor label. Sorry I had a larger selection of better photos, but something just did not like them.

 

[Mysfyt]

What sized VFD did you get to work with the 7.5HP motor? In my experience, it a gamble as to weather you need a 10 or 15HP drive.

According to spec, you should have a drive 1.5x's larger than the motor wanting to be driven. (or you need a motor with no more than 2/3 the power rating of the drive.
Most common stuff that us weekend warriors play with work out even. IE, 5HP motor with a 7.5HP drive, and 10HP motor with 15HP drive. But 7.5 hp motor really only needs a drive rated for 11.25hp. Kinda on the bubble as to weather a 10HP will work. If you try to pull too many amps through the drive, it just faults. No worries of burning things up, it just dont work. For an air compressor, intermittent use, if you got a 10hp drive to work that would be nice, not having to make the jump to a more expensive 15HP drive.

I go twice the hp rating, so I'm running a 15hp rated VFD (Hitachi). The lathe in my avatar runs off of a 20 hp motor that is the size of a small block V8. I only fed my shop with 60 amps and the Spedestar drive (40 hp) starts it over a 10 second duration. I have programmed the digital readout on the drive to show the amp draw, and it only pulls 23 amps on start up and 19 amps idling. Most I've drawn is 28 amps on a deep cut. I have them on five different machines, all at twice the hp of the motor with zero issues so far. Note: there are some VFD's I've seen advertised specifically for single to three phase applications that are rated for the single phase motor hp.

 

[Mysfyt]

Just did a quick search and you're looking at about $1100.00 for a 20 hp VFD.

 

[LD1]

Here is a VFD for 300.
7 5KW 380V 19A VFD Variable Frequency Drive Inverter CE for CNC Hot Product | eBay

I was looking for that brand, however you pronounce it, as I have used them in the past with good luck. And currently am using a 5hp one on the logsplitter.

However, the one you linked won't work. That's only a 10hp drive and 380v. He needs a 220v-240v unit closer to 15kw /20 hp

 

[LD1]

Disney: based on the pics, the motor can indeed be converted to low voltage and ran off a vfd.

The contactor and overloads are separate. You can use the current contactor and get whatever else you want for overload protection based on motor amps if you do the swap.

Curious to see what literature you have that shows the pump being rated for multiple motors, and what else they require changing to make it work with half the HP?

 

[bigdeano]

I got a 10hp 3 ph motor to run nicely on 240 single phase by using capacitors and a starting relay. I used 220 uf run capacitors and 900 uf start capacitors. It's putting out about 8 hp near as I can figure, but would probably do more If I had more load on it. Motor takes a long time to even get warm. It cost a little over $100. I got the run caps at Surplus center, the start caps on Ebay. I had the relay.

 

[LD1]

I got a 10hp 3 ph motor to run nicely on 240 single phase by using capacitors and a starting relay. I used 220 uf run capacitors and 900 uf start capacitors. It's putting out about 8 hp near as I can figure, but would probably do more If I had more load on it. Motor takes a long time to even get warm. It cost a little over $100. I got the run caps at Surplus center, the start caps on Ebay. I had the relay.

You basically made a static convertor. 8hp is a bit optimistic. How did you "figure" you are getting 8hp.

If you want.to get 10 HP, you need a 15 HP pony motor, use the caps to start it, and run the 10hp motor off that. That's a rotary and good for the full HP if you need it. Just cleaner and easier in the long run to go vfd's if you need the full power, and more adjustable too. Only downside is you can only run a single motor at a time

 

[bigdeano]

You basically made a static convertor. 8hp is a bit optimistic. How did you "figure" you are getting 8hp.

If you want.to get 10 HP, you need a 15 HP pony motor, use the caps to start it, and run the 10hp motor off that. That's a rotary and good for the full HP if you need it. Just cleaner and easier in the long run to go vfd's if you need the full power, and more adjustable too. Only downside is you can only run a single motor at a time

I made a welder out of an alternator, I'm using the 10 hp motor to drive it. I figured the hp from the power I'm getting out of it, could be off some. My motor has a 1.25 SF, so could probably put out 8 hp.

The OP said he could drive the compressor slower, thus not requiring the full 10 hp of his motor. I thought he could save some money. This is pretty simple and works.