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Rotary Phase Convertor

You will find bundles of stuff about building and running phase converters on Yank sites, the main differance is in the UK we have proper lecy, 230 everwhere and three phase is three lot's of that, quite what they have in the states I am unsure, whatever the setup they have around 200 volts three phase - someplaces seem to have 208 some 230- and i think they also have 440 and 600, gets weirder.

Anyway in 'blighty' we have three lot's of 240Volts so that's a phase voltage of approx 415Volts, from one conductor to another that is, no neutrals here- well there is but forget about them. The basis of the rotary converter is a transformer at approx 1.73:1. That gets 415 volts to wack across phase one and three in my diagram, then the motor generates the third phase, well a few caps to ballance it and thats it sort of it.

you can get a three phase motor, spin it and apply some 240 volt's to it, it will happily run and produce the third phase. the voltage will be low but it will run other motors. I gather some motors are rated for 230 volts three phase so no transformer needed, but an alectirician said he can't remeber seeing 230 volt's on three pahes motors and all the ones i have are 415/440, then there is the talk about they are alright wired delta, well all my old motors are wired delta the only ones I am not sure about - 3 wired- are modern motors.

The diagram is a bit confusing, so I can't draw. I did the whole thing off the top of my head, that's why I just spent ages wondering why it wouldn't balance;-) it was much clearer before I started to add the control wiring. the stop switch is a normaly closed switch, the start switch presses the conatactor in, I need to wire it to a switch so I can setup some remote on/off point's

The setup above has voltages of something like 457, 427 and 464 Volts unloaded. whan it's loaded with a running mill taking a cut I get 426, 427 and 427, first thing in the morning it did have all three at 429V. the current is 4.1, 4.2 and 4.2 amps.

I bought 100, 60 and 40 Uf caps. When I sat and figured out capacitances possible with these, I was quite suprised to find the number of permutations possible was so high. I am running L1-L2 fixed capacitance of 34.3Uf and the switched caps are the run caps from phase L2-L3 and the start caps on these phases, the start caps are 200 Uf, though I did have it starting with 100 - but I had drilled holes for two caps in the enclose;-)

I had a static converter, from which I copied the way they switched the start caps out. Simply a capacitor being charged with DC across the contacts of a relay, hence the bridge recitfier and resistor.

there is also a breaker, I am told it's an 'MCB', the whole caboddle is supplied via a fuse but the mcb means you can take liberties while playing with it and you don't need to have to keep replacing fuses...Suck it and see, electrickery..

I checked the voltages on the caps while I was fooling around and the ones 'burried' in a pack had several hundred volt's dc on them-days after turning it off-so I put resistors to bleed the voltage off, means you can stick your hands in it and move the wiring around without getting bitten - though I still check them first.

I put it together in an old computer case, it did the job but looked like something Victor [Frankenstein] would have had. I got this rather nice fire panel- with loads of relays and nice neat wiring, which i tore out- I mounted the contactors and relay on a DIN rail and put the switched caps in the enclosure. then knocked up a large box to put the transformer in, the other caps live with the transformer. The idea was to rubber mount the motor on top of the transformer box and mount the main convertor enclosure on the wall. The motor is on top of the trans' box but the box vibrates with the motor - it runs a bit rough when unloaded. So I might have to rethink that, I have the motor on a sheet of Plastezoate and the box is on adjustable feet and they are on rubber.

Anyway it works and I have power that runs all the motors on my bit's'n'pieces and even runs a 5hp type 30 Ingersol Rand compressor, though it needs some extra caps - the idler motor rocks in time with the compressor, starts it at 175lbs though....

I will sort out my voltages and capacitances, I wrote down all the voltages for a large number of capacitances, when you have a list like that its easy to see the trends and how to alter the voltages, I opted to tune the mill and lathe spindles as clean as I could, I will only need to add capacitace to the compressor.

Well it all got bolted to the wall.

Well almost done, it's amazing the number of little bit's you need to finish a job; I still need some more armoured cable or cable and conduit... hint hint young Maxwell. If you need any electrical testing try Max Knight Electrical, he doesn't touch conductive surfaces when he comes to my garage;-)

Anyway the box bolted to the wall with the two yellow buttons is the converter, the transformer and idler sit below, on the floor, The transformer weighs 40+ kg so i didn't want to put it in a box that i woudl have to lift, well i did but i didn't scrounge a big enough box.

I still have to tidy it all up, put a few more three phase spurs in and make a dc control circuit, so i can run a controll wire and buttons around to a few strategic point's - the places that you can usaully get at without having to climb over a motorcyle or a stack of old car bit's..

Of course the box came with a nice white engraved plate on the front, I spose I will paint 'on' and 'off' next to the relevant button, as I am the only one to use it it probably don't matter...Still it would be nice to find a bit of formica and cover the holes - formica do they still sell that?

       

 

 
     
  Cobbled together on the 6th August 2003
by
Richard

{last modified {15 th August}