how to switch 3 PH back to 1 phase

Joe Miranda · Jun 4, 2008

I have a rotary phase converter and the generated leg fluctuates wildly (yesterday I measured it between 247 and 281v). My CNC lathe is capable of running off single phase current. If I pull the generated leg am I back to single phase or is there more to it than that? The current measured on the other two legs runs pretty consistently around 120v. Thanks,
Joe

metalmagpie · Jun 4, 2008

Joe Miranda said:
I have a rotary phase converter and the generated leg fluctuates wildly (yesterday I measured it between 247 and 281v). My CNC lathe is capable of running off single phase current. If I pull the generated leg am I back to single phase or is there more to it than that? The current measured on the other two legs runs pretty consistently around 120v. Thanks,
Joe

Um, 120v is a voltage, not a current.

Why not just unplug the machine from the RPC and plug it into where the RPC is plugged into?

Grant Erwin

Joe Miranda · Jun 4, 2008

Um, 120v is a voltage, not a current.

"Why not just unplug the machine from the RPC and plug it into where the RPC is plugged into?"

Grant Erwin

Because the machine is already in place and so is the 3 phase wiring! Can you answer my question or not?! This is not a vacuum cleaner we're talking about - it's a 3 thousand pound machine!

Joe

jim rozen · Jun 4, 2008

1) what kind of phase converter is this? Store bought or
home-made?

2) are the fluctuations in the manufactured phase in response
to load changes or are they there all the time, at random?

Without the converter yes you will only get single phase.
The exact details of what your load will see when the
converter is not active will depend on the internal details
of the converter itself. Simply turning a store bought
converter off will probably remove all power from your
load.

So a bit more information is needed before anyone can
supply a definitive answer. The question you posed
was a little on the vague side so it cannot be easily
answered in a single line.

But if one had to, the answers would be "yes" and also
"yes, there is more to it so you need to look at the
details."

If the fluctuations really are not in response to load
variations but occur at random I might almost think there
is some sort of wiring problem unrelated to the converter
operation.

Jim

Pierce Butler · Jun 5, 2008

Joe Miranda said:
My CNC lathe is capable of running off single phase current. If I pull the generated leg am I back to single phase or is there more to it than that?
Joe

Joe,

There is a little more to it than that.

As far as your CNC lathe goes, you really need a copy of the installation manual, the motor nameplate data, and possibly the service manual to make a determination if the lathe is truly capable of operating from single phase power.

If it is capable from running from single phase power, I would hook it up before the RPC, not after.

JunkyardJ · Jun 5, 2008

People really are trying to be helpful here.

You're really NOT providing adequate info on how to address your question. If the lathe REALLY will run off single phase, it makes me wonder why it's on 3 phase. You'll need to post some specific data in order to answer your questions fully. If I were you, and the lathe really would run on single phase, I'd bypass the RPC alltogether, whether you have to re-wire or not. It's POINTLESS to convert to 3 phase if you don't have to, so long as it doesn't reduce the output capabilities of the lathe.

wippin' boy · Jun 5, 2008

my guess would also be that if machine is setup now for 3 phase that more than just
pulling one leg is needed to swap it to single

Joe Miranda · Jun 5, 2008

Gentlemen,

The wiring is already in place. I don't want to have to pull additional wiring if I don't have to. Please forget about the machine control. Leave that aspect to me. All I am asking is whether or not if you pull one leg off the three phase if it reverts back to single phase. When I check the voltage I am getting 120v from ground to either of the two stable legs. Does that mean I am ok or is there more to it than that. As far as the manufactured leg fluctuating so much I really don't know why. I have been using this phase converter for 9 years and it has always worked fine with the other machines I have, but because I am concerned about the sensitive nature of the CNC electronics I want to take precautions. You guys are saying you need more information to answer my question. What else do you need? All I want to know is if by pulling one leg off the converted three phase power if it reverts it back to single phase.

sundermm · Jun 5, 2008

3 phase to single phase

Joe,

The short answer is no. You cannot make 3 phase into single phase by disconnecting one leg. The phase angle between the phases is 120 for 3 phase and 180 degrees for single phase.

Heres the wiki link.

http://en.wikipedia.org/wiki/Three-phase.

Marlin

J Henricksen · Jun 5, 2008

This is all conjectural. You need to get with the machine builder.
You may be able to change back by pullin gone leg of the 3 ph. It depends on what all is being driven and how the machine mfg has it set up.
If the drive is all that is requiring 3 ph or 1 ph, removing one leg and putting a jumperon the correct terminals may be all tha is needed.

Pulling new wire shouldnt be needed,

wippin' boy · Jun 5, 2008

========================
" Please forget about the machine control. Leave that aspect to me"
=======================

if that's the case then you should also be able to figure out how to bypass the rotory device in its box with a couple pieces of wire

someone tell it's him it's ok so he can let the smoke out and get it over with :rolleyes5:

Lloyd H · Jun 5, 2008

single phase from 3 phase

If you have 120 volts to ground from each of two wires(not the manufactured phase) AND 240 wire to wire you have 240 single phase. Sundermans answer is only correct if it is 120/208 3 phase which is not likely with a RPC. Your 3 phase is most likely 120/240 with a HIGH leg ie. the mfg leg. If you trace your 2 regular legs back thru your RPC they should be right accross the supply line to the RPC which is single Phase

Joe Miranda · Jun 5, 2008

Lloyd H;907158]If you have 120 volts to ground from each of two wires(not the manufactured phase) AND 240 wire to wire you have 240 single phase. Sundermans answer is only correct if it is 120/208 3 phase which is not likely with a RPC. Your 3 phase is most likely 120/240 with a HIGH leg ie. the mfg leg. If you trace your 2 regular legs back thru your RPC they should be right accross the supply line to the RPC which is single Phase[/QUOTE]

Lloyd,
Thanks. It is as you said - the mfg leg is the high leg. I have 120 volts to ground from each of the wires and 240 volts wire to wire.
Joe

Joe Miranda · Jun 5, 2008

For those who may be following this thread, just to let you know, I have talked with the tech dept at Milltronics and they are the ones who told me the machine can run on either power source and that it can be done without any jumpers. You just connect the single phase power to L1 and L3. Since I already had the machine wired for three phase it seemed like the simplest solution to me that if all that was necessary to convert the three phase power back to single phase power was to dissconnect one leg (the mfg leg) then my solution was very easy. So I pulled the wire from L2 (which was the mfg leg). I turned the machine on and it seems to run just fine. The tech at Milltronics said that if the machine was set up to run on either voltage it would either run or not run when I switched voltage and that it wouldn't hurt anything if I switched it to single phase and it wasn't set up to run that way. He said it just wouldn't run and then I would have to go about balancing the 3 PH voltage. But it does run. I just wanted to make sure that I am back to single phase voltage. So thanks to everyone who has contributed. I hope I don't fry something and let the magic smoke out like Wippin Boy said.

I'll try to remember to report back here from time to time so everyone can learn something from this as it seems like there are a lot of opinions regarding this issue.

Joe

Pierce Butler · Jun 5, 2008

It sounds as if the Milltronics already has a VFD built in so it is phase flexible. You are good to go by disconnecting one wire.

You likely won't let the magic smoke out.

Joe Miranda · Jun 5, 2008

Pierce Butler said:
It sounds as if the Milltronics already has a VFD built in so it is phase flexible. You are good to go by disconnecting one wire.

You likely won't let the magic smoke out.

Pierce Butler,

Thanks. That's interesting about a built in VFD. I never asked how they accomplished it.

Joe

JunkyardJ · Jun 5, 2008

Check the wire guage VS current draw.

There's one concern I have. Removing the manufactured leg means it will draw MORE CURRENT through the other 2 wires. Make sure you have the proper wire guage for the SINGLE PHASE current draw of the machine. If it was originally wired according to the 3 phase current draw, it MAY have been wired with wire that's too skinny to carry the current. Thought you should be aware of that.More information would have been a schematic/picture of the wiring inside the RPC, and seeing if any wiring changes would be needed. I wasn't thinking about ripping all the existing wiring out, unless it was too skinny. :cheers:

Gackman · Jun 20, 2008

Joe,

Never heard of any CNC lathe running off single phase power. If I knew this 3 years ago along with all my BS problems with running 3 phase CNC equipment off single phase converted to 3 phase via Phase perfect I would of never been down this road!! Now that I've got things running.......well I guess that's my luck. What model, year and size is this lathe? Curious minds want to know!

Greg

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