VFD on a 3phs air compressor, tips?

[Badasssapper67]

I got a variable frequency drive to hook my three phase air compressor up to my single phase power and was wondering if anyone has done this and has tips or advice.

I see that some people set theirs up to run at higher frequency when empty and slow down as pressure builds and all kinds of crazy stuff but I need to start out simple.

Do you hook an on/off switch in between the wall outlet and the vfd? What kind of on off switch have you guys used? How did you wire the pressure cut off switch?

As always, your advice and help is greatly appreciated.

 

[930dreamer]

How big of an air compressor?

 

[Badasssapper67]

80 gallon two stage five hp motor

 

[930dreamer]

The vfd is used for speed control, not sure on the rest?

 

[larry_g]

Can you link to the manual for the VFD that you have in hand? There are some basics and some specifics to the various VFD's available. If you link to a generic manual then list the specific part number of your VFD.

lg
no neat sig line

 

[JoeFin]

You'll need better then a 10 Hp VFD to drive that compressor.

 

[vga]

The VFD will not work on a old school piston type compressor, these load, unload and shut down as they hit a static preset set point for pressure control. If your compressor is of modern construction using gear, vanes and slide valves to control disch air pressure. As the compressor reaches the H set point it will unload and the motor will slow down based upon a signal the VFD receives from a pressure transducer located on the tank. Stay above 30 Hz min as motors do not like to be run below 30 Hz. As to timing, if the compressor run for 5 min or more unloaded at reduced speed then it should be shut down by this timer.
What brand VFD are you using.?

 

[rockwithjason]

The VFD will not work on a old school piston type compressor, these load, unload and shut down as they hit a static preset set point for pressure control. If your compressor is of modern construction using gear, vanes and slide valves to control disch air pressure. As the compressor reaches the H set point it will unload and the motor will slow down based upon a signal the VFD receives from a pressure transducer located on the tank. Stay above 30 Hz min as motors do not like to be run below 30 Hz. As to timing, if the compressor run for 5 min or more unloaded at reduced speed then it should be shut down by this timer.
What brand VFD are you using.?

why wont it work? He gets his start and stop signals from the pressure switch and configures the drive like a soft starter. No big deal at all. The op needs to read the manual carefully for the vfd he wants tho. And beware that the vfd will have to be oversized.

 

[Badasssapper67]

Well. Did not know the vfd had to be a lot bigger than the hp rating of the motor. Back to square zero.

 

[454ragtop]

Might have to be bigger, might not. Post up the amp draw of the motor, and the specs of the VFD. A single phase to 3 phase 5HP VFD with enough capacity for a 5 HP compressor is likely a pretty expensive item, which is why I recommended getting a single phase motor instead when you asked in your earlier thread. I still think that is a better way to go for a compressor. If the VFD would work, you would probably wire the pressure switch to the low voltage controls of the VFD.
Good luck, Jim

 

[Badasssapper67]

454, I have two compressors, one that I had motor trouble with recently and one that is a "project". The project is a big older compressor that has a 3phs 5hp motor on it. It's just sitting there daring me to get it running.
With the changing of the seasons Im uber busy and brain dead so it's back on the back burner, but it still sits there laughing at me while I get my shop chores done. It had better enjoy it's vacation though because Im going to put it to work as soon as I get my jacks rebuilt, and my farm truck running, and my Cat clutch discs unstuck, and run bigger wire to the shop and build raised garden beds, and build feed troughs for the pigs...etc.

 

[zkling]

You'd be better off building an adequate sized rotary converter allowing for future addition of other 3ph machines...imho

 

[Packard V8]

FWIW, air compressors are the most difficult application for rotary converters and VFDs. A couple of shops I know who are very experienced with running all their other machinery off rotary converters have given up and buy single phase air compressors.

jack vines

 

[Boilerhouse]

We have a large (+150 HP) variable speed screw compressor and it works great. We normally size our VFD based on existing motor size unless there are some unique circumstances. We also have large single speed reciprocating compressors that are not candidates for a VFD. Slow speed will screw up their lubrication.