Strine

Why use Phase converters

26 posts in this topic

This subject was raised elsewhere but I've started it again here to seperate it out.

I have gone to a lot of trouble bringing to life a large bandsaw that was run on 3 phase. I don't have 3 phase but can see the usefulness of a 'converter'. There's a lot of heavy duty machinery out there that generally goes for a song. (32" wheeled bandsaw = $200) and would be very handy in the shed.

So what's the go with converters. Are they easy to build? Do you need a degree in electronics? Are they pocket sized or will I need to extend the shed. At what point should the electrician become involved. Or will he have to do the whole lot negating any saving of some hard earned.

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Not sure what kind of power you have in Oz, but here in the US, this will work with 220 single phase.



 

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There are some books floating around that describe the various ways to do this - Lindsey Publications used to sell one. The basic summary is that you can build or buy a convertor to either generate the third "ghost" leg with capacitors or combine them with a three phase motor. In my experience (that and $.50 gets you a Coke:-), the capacitor-only units won't handle much HP. I can't tell you why that is - maybe it's the rating of the caps but it seems easier to gain HP by putting a suitable 3-phase motor in the circuit.

On the other hand, I bought a 10hp Rotophase for a very good price from a farmer who eventually got real 3-phase electricity so you may want to check around in rural areas for used units rather than take the time to build one from scratch.

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If you look at the diagram, the capacitors only start the static 3 ph motor that generates the 3rd leg.

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whatever you do, put the output of your converter to a 3 phase breaker panel. any load you hook up to this is thus protected from over load. size these breakers according to the load, and have fun. the idea of bringing an electrician on board, at least for consultation, is a good one. we do this for a living, so we know how to do it right.

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I know I have seen the starter cct and capacitors, for sale on ebay, then you just supply your own motor. Alos like mentioned above look around farm magazines etc, around here quite a few farms run them.

I just picked up a used big one,good for up to 145 amps combined load or up to largest single load of 30hp motor, for $500 canadian, but I got the good guy deal from an electrical company I used to work for. I have seen a few for sale in washington state, one was $900us capable of running up to a single 15hp motor. just to give you a few ball park prices for used ones.

You can run into problems trying to run larger 3 phase motors/converters if you have bad power coming in to your shop, such as large voltage drops, undersized wiring etc.

If your cofortable in reading electrical diagrams and in your wiring skills its fairly simple to build your own, just watch out for the capacitors because they will hold a charge and zap you even with the power off.

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Strine,
I have 2 in my shop that I have built and use alot. One is a small 1 HP for a lift table and the unit is incorparated into the table. The other is a 7.5 hp unit I use for a belt sander and a lathe. They are rotary converters and have been relatively maintenance free. I Scrounged most of the parts so I really can't tell you what they cost to build. I have been happy with mine.

These links are still good and tell you what you need to know. I used the balance capacitors also, with the balance capacitors I am running a 1hp motor on a hydraulic pump with a 1hp pony motor with no problems. These are links to the info I used to build mine.

Also if you have a electric motor rebuild shop in your area they can be a good source of info and good used capacitors.

Hope this helps.


http://www.metalwebnews.com/howto/ph-conv/ph-conv.html
http://www.homemetalshopclub.org/projects/phconv/phconv.html

JWB

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Hi Strine
I would love to get any info on this subject as I hope to set up some 3 pH motors in the future.
Cheers frankw.

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My Little Giant 50# power hammer came with a 3 phase low rpm motor. After reading up on building a converter, I went to a local electrical shop and had it done for $175. It's mounted right on the side of the motor in a real nice box and they even put on an extra long cord for the starter switch so I could place it anywhere I wanted. A far better job than I could have done and a lot quicker and safer. For such a contraption, unless you are an electrician and have all the parts and pieces handy, I can't see a better way than to go to a good shop and let them do it. I consider the money well spent and probably cheaper than running around trying to find the pieces. The converter is the new gray box on the side of the motor.

333.attach

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Hi Richard.
Thanks for that info.
What you did is a good idea electric's would not be my strong point.

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This was one of those times when I probably couldn't have done it myself any cheaper and certainly not better. The box is actually larger than it has to be based on the components inside, the guy said his big hands wouldn't fit into a smaller one...lol

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Hi Richard,
Would it be possible to take a photo of the inside of the box safely

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Sure, but I won't be able to for about 4 hours when I get to the shop (about 2300, 7/16/2006). At first, it was wired to go CCW, so I went in and rewired it to go CW, so no big deal. Just make sure it's unplugged.

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Thanks heaps fellas. There is a lot to absorb here. Jr, The Electricity supply company graciously allow us to get 240V. and I'm guessing here, I think it's 50 Hz...whatever a hertz is.

By all accounts it's as easy as making a cuppa :rolleyes: BBB what are you doing this weekend, praps you could pop round...I'm only just around the corner....of the globe

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hertz is a measurement of how many times alternating current alternates ever second.

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Sorry FrankW, it'll be awhile before I can post a picture of the phase converter insides. My digital camera got broke tonight. It was just sitting there on the layout table waiting patiently and when I got to it, alas a couple pieces had been knocked off somehow. Maybe it shouldn't have gotten under that pile of hinges I was working on :). Oh well, to the store tomorrow.

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In addition to the information here and the links provided, you might want to peruse the discussion group dedicated to this topic on the Practical Machinist.
http://www.practicalmachinist.com/ubb/ultimatebb.php/forum/3.html
With almost 12,000 posts, you should be able to search and get an answer to anything you want to know. And you will get a pretty good reply to any questions in very short order. Home shop machinists deal with this issue as a matter of course. The cheapest and best performing machines are almost always 3 phase, so thousands of folks build their own routinely.

I have a 5 hp RPC I bought from someone else. It will run my 5 hp 1945 metal shaper with no problem. That is because the power is the same; it's just the leg that the power shows up on that changes.

The static converters aren't the same thing. You really should match them carefully to the machine. So even though they are cheaper, they aren't as flexible, and their performance can be erratic. In several tables I've read, the real output hp is about 2/3 the stated converter rating. (I'm guessing technically it is probably 70.7%?)

RPC's are all over ebay. Just search on "Rotary Phase Converters". Or you can buy a kit from a place like this: http://www.rotaryphaseconverters.com/kits.htm

An excellent description of three phase power is available here:
http://en.wikipedia.org/wiki/Three_phase_power Within the paragraphs on phase converters, you can click on links to rotary and static converters and see examples with a writeup on each.

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look at this link, or go to the ebay link,
http://home.isoc.net/~generic/
this guy lives close by me . and from what i have read he is very helpful thru e-mail and the price is right too, i think the plans are $2.00 US for an e-mail plan and $10.00 for the CD i have the CD matter of fact i just picked it up this morning
i also built my own 3phase converter from an old 2hp motor hooked up to 220v single ph, and a small capacitor to start it, it runs fine with no other caps, all 3 legs or 220 are within 15 volts of each other, it runs a 1hp 3ph milling machine just fine

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Hi Richard,
Sorry to hear about your camera there is no hurry I wont be using all this info and help from you and other members for a while as I will have study it all first.
Cheers Frank.

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Hi Richard,
Thanks for the pic they are a great help.
What size motor are you running .
Cheers Frank

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I have an old 3 hp 850 rpm 220V, 3 phase converted to single phase. The electrical shop said it was in good shape and better for the hammer than anything they could come up with any time soon.

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I have an old 3 hp 850 rpm 220V, 3 phase converted to single phase. The electrical shop said it was in good shape and better for the hammer than anything they could come up with any time soon.



Thats a little guy :) The bigger converters can get a bit more complex with timing cct's and aot more capacitors but pretty much the same thing, I'll see if I can get a photo of the inards on my converter.

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