air compressor magnetic starter/relay single phase

[disney]

I told myself I would just buy a new compressor and not have another project on my hands, but I didn't listen to myself when I came across this.
it's currently 3phase so I will need new motor, pulley, and starter relay. I have some (limited, but enough) experience with motor/pulley work, but the starter/relay thing is new for me. I will likely be installing a 5ph 230v single phase, although 7.5 might be possible. Suggestions on where/what to buy. Can I buy a 7.5 relay, and use it with a 5hp, or do they have to be size matched (I do understand that I can not use a 5hp switch, on a 7.5 motor....). I see some 'no name' items on flea bay, and I am a little worried about them. Oh and Happy new year to all! To save some replies: the writing (one of the 30 labels) on inside of the relay box state it is only rated for 3hp on 230v single phase, so I can not SAFELY use it...

 

[Industrial Toys]

I am not an expert on this stuff. But there are simple relays or contactors and there are overload relays. You can use a bigger contactor, like a 50 amp when you only need 30, but the overload part (if that is what you are using) would have to be appropriately sized for the load (motor). It drops out the contactor if the preset limit is exceeded.

Don't kick yourself. It's always nicer to get commercial stuff!

 

[LD1]

You can use a 3 phase contactor on a single phase motor. What you need to look at is how many volts the coil needs. Not familiar with that compressor, if you can take a pic of the contactor would help. But I am betting it don't need changed.

And what HP motor is the 3 phase in it now? Before sending a good chunk of money on a new motor, I'd buy a VFD. It would be alot simpler and quicker to set it up vs doing a motor/puller swap

 

[disney]

What you need to look at is how many volts the coil needs....
And what HP motor is the 3 phase in it now? ... I'd buy a VFD. It would be alot simpler and quicker to set it up vs doing a motor/puller swap

I will take and post pictures in a few hours, but from what I can tell the contactor appears to be 110v

I need to find out where and how much, but it appears replacement thermal reset 'strips' might be available in the amp rating needed for a single phase motor. But I (remember not an industrial electrician) still think the relay part (contactor?) would have to be replaced.

It is currently a 10hp 460v ODP configuration... although the motor and transformer coil show that 230 3ph is/might be possible

I am not familiar w/VFD and a quick google check did not mention them converting single to three phase, but maybe I didn't search correctly...

I have a 50a 230 single phase breaker avail. to power this.

From what I understand phase converters reduce motor hp, so pulley would need replaced anyway, but surplus has pulleys for around 20$, so no big deal.

If I can safely, and reliably use this motor for under 400$ I am game, but I have found a brand new 5hp usa made baldor w/shipping for 400, add pulley and belts; lets say 450 + cost to replace/modify relay box.

 

[LD1]

I dont think you are gonna have much luck replacing a 10HP motor with a 5hp motor. I dont think its as simple as cutting the speed in half. The large pulley on pump acts as a flywheel to help it overcome the end of the compression stroke. Cutting speed in half also cuts inertia in half and may require MORE than 1/2 the HP from the motor.

Contactors (at least the ones I am familiar with) the O/L's are an accessory and can be replaced separate from the contractor. You can use the 3-phase contactor for a 240 circuit, just use L1 and L2 and leave L3 empty.

As for the VFD, usually the smaller drives are listed as 1/3 phase. Usually up to about 3 or 5HP drives are still listed this way. Larger than they are listed only as 3PH because you have to de-rate same way you do with a static converter. IE: you would need a 15HP drive to power the 10HP motor. Just have to watch the input voltage. Cant use a 460v drive on 240v input. You would need something like this Hitachi WJ200 110LF Variable Frequency Drive 15 HP 230 Vac Three Phase Input | eBay

the problem with the drive then becomes the start and stop. If using a drive you would NOT need the contactor to power the motor. If the contactor is a built in part of the pressure switch, you would need to use it though to power the start stop circuit on the drive. the drive makes its own 24v power, in which case you would run a wire from that powersource to the contactor, and then to the start terminal on the drive itself. (terminal 2 on an allen bradley).

It really sounds more complicated than it is, once you have a book and follow the directions on start/stop control and see the wiring diagrams.

Not trying to talk you into a VFD, just saying thats what I would do. The single phase motor replacement, I am just afraid you are gonna need more than 5hp no matter what you do with the pulley.

 

[davesl708]

Have you opened the weatherhead on the motor? If there are more than four wires you may have a multi-volt motor and can simply rewire the motor to 230v single phase. Multi-volt motors are common in industry.
If multi-volt there should be a wiring diagram inside the weather head detailing the wiring configuration.

 

[LD1]

Have you opened the weatherhead on the motor? If there are more than four wires you may have a multi-volt motor and can simply rewire the motor to 230v single phase. Multi-volt motors are common in industry.
If multi-volt there should be a wiring diagram inside the weather head detailing the wiring configuration.

No need to open the cover usually, there will be a diagram on the outside showing the two configurations, as well as the nameplate being stamped something like 230/460 or 208-230/460 or something along those lines.

HOWEVER, if it is a 3 phase motor, it is a 3 phase motor. You cant run a 3-phase motor (EVEN wired for low voltage 230) on single phase 230 power without a phase convertor.

So you can still re-wire it to 230/340v, but you still need to feed it with 3 legs of power and not the 2 that come from single phase

 

[Mysfyt]

You can use a 3 phase contactor on a single phase motor. What you need to look at is how many volts the coil needs. Not familiar with that compressor, if you can take a pic of the contactor would help. But I am betting it don't need changed.

And what HP motor is the 3 phase in it now? Before sending a good chunk of money on a new motor, I'd buy a VFD. It would be alot simpler and quicker to set it up vs doing a motor/puller swap

Beat me to it. I run a 7.5hp 3ph compressor similar to yours using a VFD. I have it programmed to start over a 3 second interval (or 5, I can't remember) which eliminates the light dimming inrush you're going to get from a straight shot start up. Don't be intimidated from giving this a try. I think VFD's are some of the best technology to come along in a long time and I've been using them for years and never had one fail.

 

[buickanddeere]

Why not obtain a VFD and make true three phase power. It's even possible to vary the rpm to control flow to some degree.
Never mind, everybody beat me to the VFD.
A rotary or static phase converter are 2nd rate compared to a VFD.

 

[LD1]

Beat me to it. I run a 7.5hp 3ph compressor similar to yours using a VFD. I have it programmed to start over a 3 second interval (or 5, I can't remember) which eliminates the light dimming inrush you're going to get from a straight shot start up. Don't be intimidated from giving this a try. I think VFD's are some of the best technology to come along in a long time and I've been using them for years and never had one fail.

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.