Non bus related electrical ?

[goldgiter]

I have a chance to buy a mill and a lathe cheap.
My shop has 230v single phase service.
I have a 460 3 phase to 230 single phase step down transformer.
Can this transformer be wired in reverse to run these machines?
Both machines are fused at 30 amps.

Wes

[TedCalvert]

No.  You will need a single-phase to 3-phase convertor.  In the old days, about all that was available was a motor-like device called a roto-phase, IIRC.  I personally never installed one.  Nowadays, with modern solid-state electronics, variable-frequency drives are available; many will accept single-phase input and produce three-phase output of an adjustable frequency, which means variable speed for your machine, if desired.

Look on eBay for a VFD, you will need the next-larger size than your motor. (If your motor is 5HP, get a 7.5HP drive.)
It's a bit of a job, but very do-able.  Probably best to set it to 60Hz and use the gearbox/belt in the lathe/mill.

And I'd like to see a pix of that transformer and its nameplate.

[bevans6]

I solved similar problems in two different ways.  I have a bridgeport varispeed mill that was 600 volt three phase (normal in Canada).  These have a unique and very expensive motor with the varispeed pulley shaft as the motor main shaft.  I had it rewound by a specialty shop to 240 volt three phase and use a static phase converter to start it, and it runs at 2/3 the hp with the 240 volt single phase power I have in the shop.  My other mill  and my lathe I just bought single phase 240 volt motors for.

You can't convert single phase to three phase with a transformer, you need to use a phase converter.  You can't convert 220 to 440 without a transformer.  You could theoretically run a 220 volt rotary phase converter to create three phase power and then up-convert it to 440, but man, you are looking at a ton of code violations in any place I ever lived.   One thing to keep in mind is that if you get the voltage right, you can then use a rotary or static phase converter to run the motor.  But I found it a ton easier to change the motors than to change the electricity.

Brian

[brmax]

I would see if they are equipped with single side shaft motors, if so motor replacement is totally cheaper. If not a rewind, surprisingly their are people that do it and generally close to industrial areas.
I'm in agreement on not a good idea in faking the motor thinking there is a third line.
Sounds like some nice tooling if it can work out cheap enough for ya, good luck there.

Floyd

[luvrbus]

Wes,check posts by Boomer he had converter for sale not long ago he may still have it and he is a good dude

[goldgiter]

Thanks for replies.
Tom I will take a pic of the  transformer, it is actually 460 to 230 3 phase but the electrician changes an xo wire or something on the output that makes it single phase.
Thanks Clifford, I sent Boomer a PM.

Wes

[dvrasor]

I have a1953 Bridgeport. Starts with 2 capacitors on a momentary switch and single phase power.Runs on single phase after start up.It was set up like that when I bought it. I have owned it for 15 years with no problems.

   Dave

[TomC]

I had a friend that had a 120v 2cu/ft concrete mixer with a split phase motor. The starting coil was burned out. So to get it moving, two of us had to twist the barrel in the correct direction then quickly hit the switch. You could run it either way. Good Luck, TomC

[bevans6]

Dave, your setup is like mine, a "static" phase converter that is really a capacitor selected in size to provide the third leg voltage to get the motor turning.  As soon as it's turning it runs on two legs only, at 2/3 the original rated power.

I should point out that you can get single phase from three phase with a transformer, that is quite normal, but you can't go the other way.  You can run a three phase motor on single phase as long as you can get it to start turning, and it actually is the same as a rotary phase converter at that point.  Lots of home-made rotary phase converters are just old motors that have been wired up to single phase and have a little motor to get them to start turning.  As soon as they turn, they generate the third phase (all motors are also generators, of course).  There are even pull start rotary phase coverters that use a rope pull cord to get them to turn, then power is applied.  A bit dangerous because if the motor isn't turning fast enough when you apply the power, it stalls and you get full stall current, which usually hurts something or blows a breaker.

[brmax]

Sounds like we have all seen some types of these working, and as in my mention earlier faking one leg as using a capacitor is the standard.
Its seems to be used on many ac and other system motors for a long time and using the term I know "motor run capacitor" calculating this or these to MHz required to get a good start is the key.
Like mentioned a breaker trip design is important, I guess this design is efficient on single  phase somehow or they wouldn't design so many motor systems this way.
have a good day everyone
Floyd

[goldgiter]

I ordered a converter off Ebay today, 3 to 10 hp rating, I'm going to give it a try and if I'm not happy with it I have a 10 hp 3 phase motor that I can use to make a rotary phase converter.
Thanks again for the replies.

Wes

[goldgiter]

Just an update, I tried the static converter and it performed poorly.
I went to a friend of a friends shop that has a rotary converter and checked it out and this is the way to go!
I ordered a box already set up with everything needed except the motor for a little over 200.00. I already had a 15hp motor so I ordered the box for that size motor which will allow me to run several machines at once, even an air compressor.
Thought this might be some usable info.

Wes

[brmax]

Wes what hp rating is on you motor on the lathe and or the mill at the present.
I'm now curious do you plan a shaft over head with pulley system, your plan has me thinking, this guy is building a factory.
The 10 or even the 15 hp motors take a bit of amperage in a breaker setup I believe.
That 3 phase is already on your pole transformer, around here that setup is golden, though you pay for the ability no matter if used or not Ive always heard.
Keep us posted
Floyd

[goldgiter]

The lathe is 7.5 hp and the mill is 2 hp. Each piece of equipment has its own motor.
I do not have 3 phase power in my shop, that is the reason for the phase converter.
The rotary converter works by using single phase 230v with several start and run capacitors attached to 2 of the 3 connections on the 3 phase motor. When power is supplied to the motor and the motor starts running the 3rd connection becomes the 3rd leg of the 3 phase power, that is what powers the equipment.
It basically makes the motor a generator.
I THINK!!!!!!

Wes

[brmax]

Ok I thought you mentioned the transformer was changed outside eliminating the avail setup at the pole, just sounded real close n all.
And yes I'm understanding the capacitor leg thing, been doing that for oh 15 years, it requires more uhmp as in higher MHz of your motor run capacitors if not starting properly.
Many systems are electronic now but, I think the style circuit is today and has been well used prior to that electronic era many years.
Now for high hp ratings I can see one needs to consider options, I'm mean amps are amps and they use them.
good day
Floyd