Using a 3 phase compressor in a 1 phase shop?

[Ipassgas]

I have a lead on an IR T30 60 gallon 5hp 3 phase compressor from 1996.

Do I:
1. Get it and a 5 hp rotary phase converter
2. Get it and swap the motor for a 5 hp single phase
3. Not get it and wait for a single phase to come my way
4. None of the above, and do something I haven't yet considered

The compressor is $250.

I have an intermediate term need for a compressor (next 1-2 months), but am not sure I'm feeling the love for this one.

What do you guys think?

 

[apollo11]

 

[theoldwizard1]

#2

If the motor that comes with it is in decent condition, you might even make a couple of bucks on it after buying a good used 5hp single phase.

 

[Paperman]

You will have as much in a decent 5HP compressor motor than you do the compressor. Don't bank on getting much out of a 3ph 5hp motor as they aren't in high demand. T30 are pretty bomb proof if its a good running unit, just be sure the capacity and tank volume work for your needs.

 

[slow]

Single phase input to a variable frequency controller and 3 phase out. Side benefit you can lower the speed.

 

[malibu101]

I have a small pony motor that I had laying around to start a 10HP 3Ø motor that a buddy got free for me to run my 5HP compressor.
I've been doing this a few years and dealing with the extra used floor space since it's cheaper than a 5HP 1Ø motor.
It has worked perfectly for me.

Clumsy but cheap. Maybe the electric bill ain't cheap but it only runs a total about 1/2 hour a month so I'm fine with it.

If you can get a little motor and a 3Ø motor cheap. do it.

 

[930dreamer]

Find a 10hp 3 phase motor and build your own converter.

 

[matt_i]

My opinion is a rotary converter is not the path you want. Now you have to have controls (or grey matter recall) to make sure the rotary is started and running before you attempt to start the main compressor. The simple little control circuit is going to get a lot more complex if you desire automatic operation.

I would get the frame size of the 3ph motor and go about trying to find a good used equivalent version in 1ph.

 

[malibu101]

My opinion is a rotary converter is not the path you want. Now you have to have controls (or grey matter recall) to make sure the rotary is started and running before you attempt to start the main compressor. The simple little control circuit is going to get a lot more complex if you desire automatic operation.

I would get the frame size of the 3ph motor and go about trying to find a good used equivalent version in 1ph.

That motor would cost twice of what the OP can get the compressor for.
I have my setup since I too got my 3Ø compressor very cheap.

 

[Bottlecapdigger]

I did #2. Figured down the road if you ever want to sell it, it would be worth more then if it had the 3ph motor on it. I looked on our local Kijiji and found a good used lesson for half price of a new one. Start by posting a wanted ad for a 5hp single ph motor. BCD

 

[cj7jeep81]

If you do go the phase converter route, you'll need a 10hp phase converter to start it, a 5hp won't cut it. And then you can start buying lots more 3 phase stuff for cheap, and use it more

 

[rnscustom]

#2 5hp baldor can be had on eBay new for about &300 that's what I paid for my 1725 +/- motor . Came right out of a weco in Boston

 

[MEngineer]

I would suggest to make this guy an equitable offer and forget the whole project you were on about earlier. Here is a 30T with the 5hp single phase in Columbia:
https://columbia.craigslist.org/tls/d/ingersoll-rand-air-compressor/6318242947.html

 

[sberry]

I can and don't,,, find a plug and play unit that runs on single and get on with it.

 

[wyliesdiesels]

If you do go the phase converter route, you'll need a 10hp phase converter to start it, a 5hp won't cut it. And then you can start buying lots more 3 phase stuff for cheap, and use it more

This, though a 7.5HP MAY work.

Idler motor needs to be larger than what youre powering.

 

[matt_i]

This, though a 7.5HP MAY work.

IDLER motor needs to be larger than what youre powering.

Fixed it for you

The pony motor can be a 1/4hp if it can spin up the rotor of the 10hp under no load...

 

[rnscustom]

That compressor looks tough , paid $400 for my t30 with a motor issue but looked new and well taken care of ( well maybe not well taken care of or wiring issue ) . New baldor motor and runs like new . If you have a nice unit just replace the motor . Those on eBay are new compressor duty baldors . They even have ones they call surplus which are removed from new compressors for alternate power sources ( bid on those ) . Some great buy it now prices from that weco seller

 

[rnscustom]

For a compressor that runs randomly is it wise to use a converter . I understand machines that you fire up the converter to use then shut it down when your done . ??

 

[wyliesdiesels]

Fixed it for you

The pony motor can be a 1/4hp if it can spin up the rotor of the 10hp under no load...

Yeah whoops. Brain fart...

For a compressor that runs randomly is it wise to use a converter? I understand machines that you fire up the converter to use then shut it down when your done . ??

Why wouldnt it be? Done all the time without issue....

 

[matt_i]

Yeah whoops. Brain fart... :will_nil



Why wouldnt it be? Done all the time without issue....

I would prove out via manual intervention, that the 3 phase compressor motor will quickly trip out the overload heaters if the idler fails to automatically start in such an unattended operation. If this happens when unattended you are going to lose the idler and the compressor motor most likely because of a single phasing condition where the motor is sitting humming drawing max amps with a locked rotor....only the overload section knows this although presumably you could reference voltage on the generated leg to pull in a contact as confirmation its OK-to-start.

 

[wyliesdiesels]

I would prove out via manual intervention, that the 3 phase compressor motor will quickly trip out the overload heaters if the idler fails to automatically start in such an unattended operation. If this happens when unattended you are going to lose the idler and the compressor motor most likely because of a single phasing condition where the motor is sitting humming drawing max amps with a locked rotor....only the overload section knows this although presumably you could reference voltage on the generated leg to pull in a contact as confirmation its OK-to-start.

I dont know about heaters but almost all the solid state overloads Ive worked on have phase loss protection. That would prevent just the scenario you describe...

 

[Norcal]

Perhaps a time delay relay to allow a RPC to start up & then the compressor to start afterwards, not quite that simple but doable.

 

[fordcragar]

I have the same compressor; which was three phase too. I had the same question that you have and ended up buying a 5hp single phase motor. That was over 10 years ago and it is still going strong.

 

[Norcal]

I dont know about heaters but almost all the solid state overloads Ive worked on have phase loss protection. That would prevent just the scenario you describe...

Just a note, heaters/thermal elements have been going away because of RoHS, Reduction of Hazardous Substances, regulations, some of the metals used in them run afoul of international regulations, the adjustable O/L relays are a major improvement & one of only 2 things I like about IEC style starters the other being DIN rail mounting. NEMA style are still the most rugged.

 

[sberry]

Now that we come up with every version ever invented is this something you really want? I could do this for near free and dont. Other than a big fig I don't really use I don't own anything that would overload a number 10 wire or can't plug in a common outlet.

 

[rnscustom]

Ok, do phase converters start up automatically or do you start the converter first

 

[laser3kw]

I did #2. Figured down the road if you ever want to sell it, it would be worth more then if it had the 3ph motor on it

^^^^ answer x2

Ok, do phase converters start up automatically or do you start the converter first

edit : whoops! I misread the question and responded to a vfd install! Coffee hasn't kicked in
Simpler to do the single phase motor swap. The RPC would be next simplest. RPC has to be "running" before other load is applied.

 

[wyliesdiesels]

Ok, do phase converters start up automatically or do you start the converter first

RPCs can be wired to be automatic but that requires quite a bit of know how.

Would need a separate pressure switch to energize a pony motor that would spin up/start the idler motor.

Would have to experiment with pressure settings to figure out where the optimal setting is.

 

[rnscustom]

For a compressor that runs randomly is it wise to use a converter . I understand machines that you fire up the converter to use then shut it down when your done . ??

If the converter doesn't start automatically that means you leave it running all day while your working . Seems like you'll wipe out the cost of the single phase motor in a couple months . ??

 

[nsula_country]

Vfd...

Ct

 

[malibu101]

Below is a link to a simple little YT video of me starting my RPC and compressor.

First I plug the 120V little motor into an outlet next to the panel.
When it's up to speed I unplug it while simultaneously turning on a 50A breaker.
You then see me manually disconnecting the 120V motor.
Then turn on the compressor.

 

[930dreamer]

I think the vfd will need to be larger then the motor its needing to start/run, ie its sized to the full load amps of the motor its starting.

 

[Norcal]

I think the vfd will need to be larger then the motor its needing to start/run, ie its sized to the full load amps of the motor its starting.

50% derating,is normal over 3 HP.

 

[Dagny]

Just get the right single phase motor.

 

[Matt Matt]

50% derating,is normal over 3 HP.

This is depending on normal being buying a three phase input VFD.

I normally buy single phase input VFD's that are rated for the output motor size in three phase. No Derating.

I can get single phase input to three phase output up to 15 hp. This is what I consider normal.


I just finished building my air compressor with a 5 hp VFD on a five horse power motor. I just received the automatic drain on Wednesday and installed it yesterday. I'll add a picture.


It really comes down to your electrical Comfort zone.

If you do go to single phase route, you're probably have to go with a single phase pressure control switch and take out the three phase contactor.

 

[wyliesdiesels]

This is depending on normal being buying a three phase input VFD.

I normally buy single phase input VFD's that are rated for the output motor size in three phase. No Derating.

I can get single phase input to three phase output up to 15 hp. This is what I consider normal.


I just finished building my air compressor with a 5 hp VFD on a five horse power motor. I just received the automatic drain on Wednesday and installed it yesterday. I'll add a picture.


It really comes down to your electrical Comfort zone.

If you do go to single phase route, you're probably have to go with a single phase pressure control switch and take out the three phase contactor.

I am not aware of a different pressure switch for single phase vs. 3 phase since pressure switches on 3 phase only switch one side of the contactor coil.

And many times one can use a 3 phase contactor on a single phase motor. Depends on ratings...

 

[Matt Matt]

I am not aware of a different pressure switch for single phase vs. 3 phase since pressure switches on 3 phase only switch one side of the contactor coil.

And many times one can use a 3 phase contactor on a single phase motor. Depends on ratings...

The difference is a three phase pressure switch is it only switching and designed to only switch low current. The low current pressure switch only switches a magnetic coil in a contactor that is rated (for this particular 5 hp) with a Nema size 1 rating. When you switch the contactor from three phase(7.5hp) to single phase The Nema rating is adjusted to only 3 hp. So, the contactor can no longer be used under single phase situation. It will arc itself welded usually under the first hundred shut downs.

If the pressure switch has NEMA rated contacts (size 1) which then control the motor, these would be rated at about 27 A three phase. Or 14 A single phase . A 5 hp single phase motor needs a size 2 contactor.

A Nema size 1 contactor is rated for 3 hp single phase or 7 1/2 hp three-phase.
A Nema size 2 contactor is rated for 7 1/2 hp single phase or 15 hp three-phase.

So generally a compressor manufacture will not just willy-nilly throw a size 2 contactor on a 5 hp three phase motor. They're just wasting their money.


So, good chance being if you swap out the motor for a single phase, you'll probably have to swap out the contactor too, as it is probable that the pressure control switch is not rated for this size contact, and neither is the contactor! If it does have four contacts like the A.B. contactor I have shown below(left), there is ways around this where you can run the two hot legs through and splice them through in parallel through the four contacts. But this is a rare situation. This is contact amp sharing, and usually needs to be approved.

Here is a size 1 and size 2 contactor made by Allen Bradley.

Here is a single phrase pressure switch with Contacts for switching load. The second picture has a pressure switch with Contacts design for single phase and pressure unloader. It is rated for 26 FLA, which encompasses most single phase 5 hp motors. (It will need to be hardwired without a plug to a disconnect, as there is no plug rated for 5 hp under single phase 240v applications) .

Overload heaters or fusing need to be prior or after each of these contacts to prevent Motor overload.

Now I as for my thoughts on IEC versus NEMA, NEMA Contactors are generally are best set up for industry (or industrial use). They are the most robust contactors built in the world. IEC have a very narrow and complex set up. Usually any changes made to an IEC require a whole new contactor. But the nice thing about IEC is there usually about half the price, but usually half the quality. The nice thing about Nema, they are, pretty straightforward for most North Americans.

As for an RPC for rotary phase converter starting a 5 hp air compressor, it's been on the market for a few years. Just watch this video. I've done many work jobs with these guys, and I have absolutely no affiliation!

Now that I'm done writing this, I look back, wow, what a waste Rant. Nobody's going to understand what I just said, except for A half-dozen electrically sound . 99% of electricians I run into just think I'm speaking Spanish. The worst part is is I'm not electrician by trade!

 

[fordcragar]

When I was researching what to do with mine, I considered a VFD for a few minutes. When I realized how big the VFD had to, it became a deal breaker. It's a lot cheaper and easier to just put a 5hp single phase motor on it.

 

[wyliesdiesels]

The difference is a three phase pressure switch is it only switching and designed to only switch low current. The low current pressure switch only switches a magnetic coil in a contactor that is rated (for this particular 5 hp) with a Nema size 1 rating. When you switch the contactor from three phase(7.5hp) to single phase The Nema rating is adjusted to only 3 hp. So, the contactor can no longer be used under single phase situation. It will arc itself welded usually under the first hundred shut downs.

If the pressure switch has NEMA rated contacts (size 1) which then control the motor, these would be rated at about 27 A three phase. Or 14 A single phase . A 5 hp single phase motor needs a size 2 contactor.

A Nema size 1 contactor is rated for 3 hp single phase or 7 1/2 hp three-phase.
A Nema size 2 contactor is rated for 7 1/2 hp single phase or 15 hp three-phase.

So generally a compressor manufacture will not just willy-nilly throw a size 2 contactor on a 5 hp three phase motor. They're just wasting their money.


So, good chance being if you swap out the motor for a single phase, you'll probably have to swap out the contactor too, as it is probable that the pressure control switch is not rated for this size contact, and neither is the contactor! If it does have four contacts like the A.B. contactor I have shown below(left), there is ways around this where you can run the two hot legs through and splice them through in parallel through the four contacts. But this is a rare situation. This is contact amp sharing, and usually needs to be approved.

Here is a size 1 and size 2 contactor made by Allen Bradley.

Here is a single phrase pressure switch with Contacts for switching load. The second picture has a pressure switch with Contacts design for single phase and pressure unloader. It is rated for 26 FLA, which encompasses most single phase 5 hp motors. (It will need to be hardwired without a plug to a disconnect, as there is no plug rated for 5 hp under single phase 240v applications) .

Overload heaters or fusing need to be prior or after each of these contacts to prevent Motor overload.

Now I as for my thoughts on IEC versus NEMA, NEMA Contactors are generally are best set up for industry (or industrial use). They are the most robust contactors built in the world. IEC have a very narrow and complex set up. Usually any changes made to an IEC require a whole new contactor. But the nice thing about IEC is there usually about half the price, but usually half the quality. The nice thing about Nema, they are, pretty straightforward for most North Americans.

As for an RPC for rotary phase converter starting a 5 hp air compressor, it's been on the market for a few years. Just watch this video. I've done many work jobs with these guys, and I have absolutely no affiliation!

Now that I'm done writing this, I look back, wow, what a waste Rant. Nobody's going to understand what I just said, except for A half-dozen electrically sound . 99% of electricians I run into just think I'm speaking Spanish. The worst part is is I'm not electrician by trade!

you completely missed my point.

If you have a single phase motor with a motor starter and a pressure switch from a 3-phase setup, you can use the pressure switch to switch the coil on the contactor since the coil amperage should only be an amp or 2.

 

[Matt Matt]

you completely missed my point.

If you have a single phase motor with a motor starter and a pressure switch from a 3-phase setup, you can use the pressure switch to switch the coil on the contactor since the coil amperage should only be an amp or 2.

Very true. I was just trying to cover all of the comments made. I quoted you on on the fact that there are pressure control switches designed specifically for single phase applications that double as a motor starter. And possible if swapping out the motor, this might be a cheaper Avenue then sourcing a new motor starter/contactor.