Topic: Running 3 Ph motor on Single Ph

[mick7504]

I've got a 3 Ph Air Compressor that I want to run on Single Ph. 415/240
Does the input need to be a10A or 15A or doesn't that matter?
There appears to be a few different ways of doing this.

The simplest way that I've seen is to change the connection from Star to Delta on the motor and then add in some running capacitors.

I'm no sparkie but have a very basic understanding.
Has anybody done this before or have any other suggestions?

[jgmmgood]

It can be done, and there are multiple ways to accomplish this.  A google search will point you to a few options, but it seems like you will be better off in the long run to just convert the motor to single phase.
Overall, I believe any conversion may be adverse to the 3 phase motor and will burn out the windings in short order.  You will also loose some HP in the orig. motor setup doing this and you may need to have a way to "start" the compressor motor turning on initial start up each time.  I would say if its probably safer and cheaper in the long run to switch the motor out to a single phase.  (this is without knowing if there is an advantage to having 3 phase in your shop for other things as well.....That may change the equation). 
Jim

[bill440cars]

     Whoa! Way beyond Me Brother, but I'd sure like to see what the outcome is. So, I'm tuned in here. 

[Duke McDukiedook]

Yeah, like jg said either change out the motor or you will need to get a 3 phase converter. Either option is going to cost you a few hundred dollars.

[mick7504]

Thanks for your replies and suggestions fellas.
I appreciate it and I'll do some more homework on this and keep you posted on progress.

My garage here at home only has single phase and I need more compressed air to run a bead blaster.
This compressor is in reasonable condition and has been in storage for quite awhile due to the 3 Ph power supply.
Thanks again.

[70CB750]

Mick, what is the electrical grid system in Australia?   Any chance of having 3 phases installed?

I quess because you are metric country, I suppose the installation makes more sense than in good ole USA:)

[Bailgang]

A guy I worked with bought an old compressor off our employer that had a 3 phase motor. What he did was talk to the man in our purchasing dept who got him in contact with a supplier that rebuilt electric motors and was able to work out a trade with his 3 phase motor for a comparable single phase motor.

[mick7504]

Mick, what is the electrical grid system in Australia?   Any chance of having 3 phases installed?

I quess because you are metric country, I suppose the installation makes more sense than in good ole USA:)

Mate our single Ph is rated at 240v and 3ph is 415v.
A mate has 3ph at his place and he's got 3 single Ph meter boxes on the power pole at the front of his place.
I don't know how they get 3 x 240v to equal 415v.

I heard that the power mob here in Darwin were putting restrictions on 3 Ph supply for domestic applications.

[70CB750]

I see. 

The 415 is between phases, 240 is between phase and zero.  In USA, 3 phases are limited to industrial zones, I would love to have 3ph in my shop

Over in Czech, houses get 3ph - there is nothing better than 3ph motor.

Anyway, it does not hurt to check on your options, you could pay for 3ph same money as for new 1ph motor.  And 3ph motor is superrior to 1ph, there is no question about it.

[scottly]

I was going to suggest picking up a used 3ph motor and making a rotary phase converter, but if the 3ph motor is a higher voltage than the single phase power, you would also need a step-up transformer. The 3ph spindle motor on my mill is 240V, and the single phase power is the same. The phase converter runs off the single phase power, and acts as a generator for the 3rd phase. You can sometimes find 3ph motors for cheap; I took a 25 HP to the recyclers last year and got about $45 for it.
If you decide to switch to a single phase motor, you may need to go a bit larger on HP. How big is the compressor?   

[mick7504]

G'day Scott
I'll dig the compressor out and see what its rated at.
The sun will be up here in a couple of hours and everyone out of bed by then.   

I was using it to supply c/a to a medium size workshop many years ago.
It's a single piston compressor with reasonable size reservoir.

I'll put some pics of it up here as well mate.

[kghost]

Watching.

Getting a decent air supply on single phase can be challenging.

In Texas on a busy day... I used to run 2 compressors in tandem lol.

[mick7504]

Mornin Tim
This bead blaster I have is a compressed air hog and I think if this motor can keep up to the task and a decent reserve of air it should work out ok.

My curiosity with this 3 to 1 conversion has got my head going.
We can only try mate.

[scottly]

Good evening Mick. Be aware that air compressors have higher starting torque requirements than say a mill, lathe, or drill press. The quick and dirty conversion to single phase most likely won't work.
According to the nameplate stamping, my 2HP 3ph spindle motor can run on either 230 or 460V, depending on the jumper selection; check your motor to see if it has different voltage settings.
Three phase motors are much more efficient than single phase (80+%) and rotary phase convertors are almost 100% efficient.

[mick7504]

G'day Scott

Your right about the phase convertors mate.
I think that it's time to get the crocodile out of my pocket and bite the bullet. 

I hooked it into the single phase and the motor spins up but it's nothing to write home to Mum about.
There was an old starting capacitor that I found in the shed but it made absolutely no difference.
It possibly was shot anyway.
Maybe a running capacitor might have been the way to go but I couldn't find one.

Here's a couple of before and after pics and also one of the ID tag on the motor.
It was worth a try I guess.

 3 Ph wired


1 Ph wired


Motor ID Tag

[scottly]

Looks like your motor isn't a good candidate for running off single phase 240V even with a phase convertor...

[70CB750]

Looks like your motor isn't a good candidate for running off single phase 240V even with a phase convertor...

+1

I think you would burn it soon running it on 1 phase.

Here in USA, due to grid limits is a good supply of strong single phase motors.  When I found out the 1hp motor in my new to me Walker-Turner cabinet saw is not strong enough, I was able to find 6.5HP compressor motor in farmer's store for under $200. 

[mick7504]

That is the only way to go with a single phase motor now.
When I saw the price on the rotary converters from 6.5 HP onwards, I changed my mind in a hurry.

I'll have a look around and see what's available from the US.
All that will need to be changed is the drive pulley which will be available locally.

The 3 phase motor that's on there at the moment has got about a 28mm shaft with an A section pulley.

Thanks for your help guys. 

[70CB750]

Good luck, Mick.

Pulleys can always be made, when hard to find.

Here is a place I used before:

http://www.surpluscenter.com/electric.asp?catname=electric

[mick7504]

Thanks for the link mate.
That will be a good start.

[scottly]

G'day Scott
I'll dig the compressor out and see what its rated at.
The sun will be up here in a couple of hours and everyone out of bed by then.   

I was using it to supply c/a to a medium size workshop many years ago.
It's a single piston compressor with reasonable size reservoir.

I'll put some pics of it up here as well mate.

Hey Mick, that must be a very large single lung compressor if it needs a 5 HP motor to spin it? My shop compressor is a two-stage unit, and the primary cylinder has a 4 5/8" bore. With a 3 HP single phase motor, running a compressor RPM of 514, it is rated for 15 CFM@ 125 PSI. With a 5 HP motor, spinning at 826 RPM the pump is rated at 24 CFM at the same PSI.

[mick7504]

G'day Scott
I'll dig the compressor out and see what its rated at.
The sun will be up here in a couple of hours and everyone out of bed by then.   

I was using it to supply c/a to a medium size workshop many years ago.
It's a single piston compressor with reasonable size reservoir.

I'll put some pics of it up here as well mate.

G'day Scott
I stuffed up mate and told a fib - It's a twin.
I've no idea what brand the compressor is but there "might" be a book on it somewhere hidden away in the files.

The other thing that I've been thinking about is whether a 5 HP single phase motor will do the job.

Here's a few photos of the single I mean twin. 








Hey Mick, that must be a very large single lung compressor if it needs a 5 HP motor to spin it? My shop compressor is a two-stage unit, and the primary cylinder has a 4 5/8" bore. With a 3 HP single phase motor, running a compressor RPM of 514, it is rated for 15 CFM@ 125 PSI. With a 5 HP motor, spinning at 826 RPM the pump is rated at 24 CFM at the same PSI.

[Terry in Australia]

Hey Mick, why not bolt a 5 HP Briggs and Stratton engine on that sucker and park it around the back of your shed? Won't be as nice as electric of course, but I doubt you'll get a single phase electric motor big enough to run it, and those phasers cost more than a good compressor!

I've got a 3 phase Brobo Saw that someone gave me a few years ago. I bought a single phase motor for it on eBay and I can machine up an adapter plate on my lathe, but I need to get a rotary speed control switch for it so I can use it for cutting both steel and aluminum. Cheers, Terry.  

[Retro Rocket]

I was going to suggest the same thing Terry just said, there should be a number of small petrol or diesel engines that would successfully run that compressor...

[trueblue]

I'm pretty sure you can only go up to about 3hp on 240v Mick.  Even then they need to run on a 15 amp power supply

[mick7504]

The petrol/diesel option crossed my mind but I'm still leaning towards the electric lad.
That's gonna mean running a 15 amp supply and outlet to the back of the shed which isn't a show stopper.

That surplus supply mob (reply 18 I think) has got some single phase motors listed with more grunt than a pig farm.

I'm giving the ol' girl a good clean up and a coat of jam at the moment.
Everything's in pretty good nic.
It's just been in storage for a long time and was working fine when it got replaced with a V Twin Atlas Copco years ago at the old workshop.

Boys and their bloody toys - I love it. 

[trueblue]

If you go over the 3hp mark you exceed 15 amps.  The 5hp motor on that site runs at 27.2 amps.  Might have a little trouble running that off your standard power supply.  You can go to 25 amps on 240, we have a few at work setup for that, to run our large single phase welders.  But that still leaves you a couple of amps short. 

http://www.surpluscenter.com/item.asp?item=10-2766&catname=electric

[mick7504]

Thanks Andrew
Electricity isn't in my vocab.
Faaarrrk what to do now.   

I've got a few spare Honda 4 donks.
That'll get the mongrel pumpin. 

Maybe I should just clean her up and flog her off and buy a new single phase lad and be done with it.
Otherwise it looks like this might turn into a WOFTAM.
Waste of fcuken time and money. 

[trueblue]

Have a chat to a sparky who deals with industrial sort of gear, and has half a brain, he should be able to tell you the best plan of action. 

[mick7504]

I think that's a good idea mate.
I'll have a talk with the ol' mate Willy.

He's an old dog who's been around the traps and knows his stuff.

[mick7504]

This idea turned out to be a WOFTAM - Waste Of Fcuken Time And Money. 
Aside blowing the arse out of a few capacitors and drinking lots of beer, it didn't hurt the ol' pocket too much.

What I'm gonna do is to give this compressor the once over and a coat of paint and flog it off.
You can buy a 3 HP single phase lad with a 150Ltr tank and 2 years warranty for 1200 bucks

Then the bead blaster can be fired up again. 

[70CB750]

Important to know when to cut your losses