Running 3-phase gear off single-phase power.

As mentioned earlier, you can run a 3-phase motor on a single phase, but you have to have a means of starting it- e.g. pull start or capacitor- and it will only run at 2/3 rated power. There is a technique for wiring the third leg via 'run capacitors' as well as 'start capacitors' so that the motor will operate more smoothly (another form of white-man magic) but I think this still produces 2/3 rated output.

My 3hp lathe motor is actually running on a VFD rated to 2hp that was given to me by a friend. Not an issue in general use, but would not be able to run at full load such as heavy cuts on large diameters. I'm running it off a 20 amp circuit that I had installed for my welder. A lot of VFDs require 3-phase input for 3-phase output, something to watch out for if buying. One of the things with these gadgets is you can program all sorts of running parameters such as spool-up time, gradual slow-down to stop, emergency stop which uses electrical braking, forward & reverse, speed control etc.
I'm not by any means an expert in the subject, just did a bit of reading and internet research for my own purposes. I don't know how the current draw would compare between the various arrangements. The reading I did made it pretty clear that having switches between the VFD output and the motor input would be detrimental to the VFD, my understanding was one motor, one VFD.

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Originally Posted by rovercare

Phase convertors are the best, you can buy one just up the road in longwarry:D

With 2 phase you can "growl" a motor, but it's pretty crude, with one phase you ain't doing lick, without a vsd or converter

Single phase to 3 phase vsd's only go up in size so much

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In the 3-5HP range (which is all I could ever see myself using), what advantages does a phase converter have over vsd?

Ebay has Aussie made 3HP converters like this for around $1600, which is a LOT more than a 3HP VFD.
I note that you can run welders on them (up to 450A on that $1600 one), whereas internet opinion seems to be you can't run a welder on a VFD.

Still a high premium to pay for having that flexibility - there must be more to it than that...

Steve

I think the main thing is that with a phase-converter you can plug any machine, or multiple machines, into the unit up to it's rated output. Good for a workshop that runs several machines, including welders as you mention. A VFD is dedicated to one piece of equipment. Also with a phase converter, no modification is needed to the machine.

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Originally Posted by POD

I think the main thing is that with a phase-converter you can plug any machine, or multiple machines, into the unit up to it's rated output. Good for a workshop that runs several machines, including welders as you mention. A VFD is dedicated to one piece of equipment. Also with a phase converter, no modification is needed to the machine.

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That

Single phase to 3 phase vsd's have a high failure rate from my experience, that's Allen Bradley gear, so not rubbish

Running a 3 phase motor on star limits torque and trying to crudely make it growl will see another drop, then using a phase and neutral as opposed to 2 phases is even worse

Single Phase motors are extremely cheap these days also
Making a motor turn is different to making it do "work"

Matt,
My shed has two phases to it?
If I happened along some 3 phase gear - how much hassle is it to jigger the power to run it?
Just thinking thats all? Would most likely be a mill or hori bandsaw.

S

I've never understood what is meant by 2-phase power. I have single-phase power yet there is a bore pump (50m down a hole) wired from my shed that I've been told runs off 2 phases. This is a mystery to me. After a bit of reading, I kind-of understand the concept and purpose of 3-phase power, but that's stretching it.

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Originally Posted by POD

I've never understood what is meant by 2-phase power. I have single-phase power yet there is a bore pump (50m down a hole) wired from my shed that I've been told runs off 2 phases. This is a mystery to me. After a bit of reading, I kind-of understand the concept and purpose of 3-phase power, but that's stretching it.

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This website has a very good explanation.
What You Might Want to Know About Electricity Before You Talk to Your Electrician

Power companies in our area won't install 3 phase either for the reasons listed above, however, if you are planning to install a 3 phase air-conditioner to your house they will install the power for you. Hmmm, then have a source for 3 phase. ;-)

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Originally Posted by POD

I've never understood what is meant by 2-phase power. I have single-phase power yet there is a bore pump (50m down a hole) wired from my shed that I've been told runs off 2 phases. This is a mystery to me. After a bit of reading, I kind-of understand the concept and purpose of 3-phase power, but that's stretching it.

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I think a lot of old farms have this. It's not true 3phase. One of my mates has it on his farm. You can get away with far less current pull using "two phase". I pretty sure the phases are 180degrees apart... they must be the two sides off a center tapped trannie (I'm sure google would give the answer in seconds if you searched). I've seen old 240volt motors that have wiring instructions/tappings for 2phase.

I made myself a phase converter for a big grinder a while back. You need to have the correct 3phase motors. They need to be wired delta @ 240 across the phases from memory (check that, don't trust my memory). It worked ok, I just pull started the 2nd motor with a rope around it's pulley. Using cap start too run the 3phase motor ... it just didn't sound happy.

Honestly though?? 3hp motors are cheap in single phase these days .... it's probably going to be cheaper and less hassle just to by the single phase motor to suite. I did miss out on a 5hp single phase (monster sized ancient job) at the closedown of a motor rewinders a couple of years back. I'm still kicking myself for not grabbing it. Imagine the compressor I could run with that :twisted: I'd have to switch off everything in the shed to start it though .... could you imagine the startup current pulled by a 5hp motor :eek: The compressor used to dim half the street with a 3hp motor.

seeya,
Shane L.

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Originally Posted by POD

A third way is to wire the 3-phase motor via a Variable Frequency Drive (VFD) as mentioned in another thread. Like this one (incredibly cheap): eBay Australia: Buy new & used fashion, electronics & home d

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In a domestic situation be aware that using a VFD is likely to drive someone nearby nuts through the RFI getting into their radio or TV enjoyment.
Technically if you buy something like this from overseas you are now also the importer and responsible for all compliance issues like C-Tick.
Chances of coming unstuck legally are minimal, more likely to face the RFI complaints during the cricket.