UK v USA phase converter for spark eroder

Hi,
I have an old Agemaspark H300 which i am trying to get up and running in my garage. Due to the control system and spark generator as well as 2
separate 3 phase motors, which are all powered from 1 rather complex (415v 3 phase, no neutral) transformer, I am looking to build a 3 phase converter to power the whole thing. The rating plate gives 220/550v and 2KVA which is believe is well within the 240v supply. I have seen loads of USA designs for phase converters BUT it seems the USA has a 2 phase 240v supply unlike our single phase 240v supply. Having scoured MANY web pages I am unable to find a UK design. Does anyone have one or know of one I can beg, steal or borrow. I have the excellent book "electric motors in the home workshop" by jim cox, which shows some methods of converting motors and building a static converter for motors, but i am unsure if the resulting variations in voltages are ok to feed the transformer. I am sure someone has built a suitable unit and can help me out here.
With regard to my previous endeavors I also have 1 or 2 areas of doubt as follows.
Does a rotary converter "idle" motor need to be of the dual voltage variety? Some suggest using an older type of motor for this job, but the older type seem to be all single voltage types?????????
If i use a rotary converter will I get 415v, 440v or 480v ( i suspect this will depend on question 1?)
One of the motors (0.33hp 415v star) drives a pump for the flushing tank, it might be easier just to change this for a single phase (central heating) unit. The second (0.25hp 380/440v) is part of a hydraulic power pack.
The spark generator is rated at 10amps at i THINK 100volts.
The control system is an old analog type together with a moog hydraulic system.
Any suggestions very welcome. Regards, pete
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On Wed, 14 Sep 2005 12:00:29 GMT, Peter Gavin

If you want 440 or similar 3-phase you'll need a transformer to step up the voltage. The usual, though maybe not the safest, way is to use an auto-transformer (one tapped winding) . Then a normal 400+ V 3-phase motor will do as the idler.
Perhaps others here will come up with something more detailed, eventually.
Beware that 440V is *far* more likely to kill you than 240V if you touch it accidentally!!
Cheers Tim
Dutton Dry-Dock Traditional & Modern canal craft repairs Vintage diesel engine service
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wrote:

I've built a 10HP rotary phase converter; as Tim has suggested, I used a 240 to 415V autotransformer (rated at 8KVA); I couldn't find one surplus so I had it wound specially, it cost around 120 including a case. The motor is a 10HP TEFC 440 / 660V motor connected up for 440V (delta connected); don't do what I did and get a 2 pole motor as it runs at 3500RPM and the fan makes a lot of noise; look for a 4 pole 1750RPM motor. Motors of this size are often dirt cheap on eBay as no one seems to want them; postage is a bit steep though! Other bits you need are some contactors, various motor run and motor start capacitors, stop and start press button switches and either a voltage sensing relay or a timer relay to operate the starting contactor; note that 450V rated motor start capacitors are almost impossible to find so I have used motor run capacitors as start capacitors which works out somewhat expensive. I've got the circuit scanned somewhere on my disk, I'd be glad to email it to you. Martin
--
martin<dot here>whybrow<at here>ntlworld<dot here>com



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On Wed, 14 Sep 2005 20:09:14 GMT, "Martin Whybrow"

I managed to get a secondhand 10hp 6-pole 440V motor from the local rewind people for about 50 quid, OK not dirt cheap but they rewound it without a murmur when it failed after a month. *Far* too heavy to post! It's nice and quiet sitting in a 'dog kennel' outside the workshop.
Cheers Tim
Dutton Dry-Dock Traditional & Modern canal craft repairs Vintage diesel engine service
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I'm not sure i need the extra voltage? The transformer has a rating label which states "wired for 415v ONLY, if you want to use a different supply please consult the handbook" (i wish i had one, or just a schematic or wiring diagram!) so i'm trying not to "over" supply it.
I have the option of modifying the motors BUT its the control system that really worries me because that is also powered from the 3 phase transformer. I'm not sure if the spark generator uses the phases as some kind of timer between pulses.
I'll have to take the bull by the horns i guess and try to find out what the end voltages are/supply and modify the the control to single phase first and then worry about the motors?
Thanks for your input, Pete
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The USA doesn't use 2 phase 240. We use single phase 240 just like the UK. The only difference is that we are supplied with center tapped transformers that give us the option of 240 or 120.
To be technically correct there are some 2 phase systems in the U.S. but they are extremely rare, industrial only and are hold-overs from another age.
Cheers,
Kelley
On Wed, 14 Sep 2005 12:00:29 GMT, Peter Gavin
(Snip)

(Snip)
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Hi Kelly,
So am i right in thinking the diagrams of USA converters which describe "line 1 and line 2" of your single phase supply are the same as our "live and neutral", and your "ground" is the center tap to give 2 times 110v? and NOT neutral.
If this is the case it seems i can just copy the US design.
Many thanks for your input, Pete
Kelley Mascher wrote:

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I think we use the term neutral differently. For us, the center tap is the neutral. L1 and L2 are both hot with 240V across them and 120V is available between either L1 or L2 and the center tap/neutral.
It's possible that your 240V is derived in such a way that neutral is from a center tap, I don't know. I suspect it's just another case of Brits and Yanks using the same term to mean different things.
The bottom line, I think, is that you get 240VAC between the two lines that carry current in your electrical system. We also get 240VAC on the two lines that we designate L1 and L2 that carry current. In our terminology a neutral is only used to reference 120VAC.
The U.S. RPC designs should work on U.K. power as far as I can tell.
Cheers,
Kelley
On Thu, 15 Sep 2005 11:43:34 GMT, Peter Gavin

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wrote:

The U.K. system ( now harmonised with the rest of Europe ) uses 400 V 3 phase AC, this is centre taped to give three 230v supplies from centre tap, the centre tap we call neutral, and should be at earth potential.
--
Jonathan

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I've been through the process of building rotary phase converters, and have a list of links somewhere.
I originally started out with just a simple rotary phase converter giving me 240V three phase, but I eventually had to add a transformer (built to order) to get the full 415V three phase. I did have a wiring diagram somewhere, but I've not seen it recently.
I'll try and dig out all the stuff (links/suppliers/diagrams....) I had and post it up later.
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I now understand the differences in UK v USA 3 phase systems, I also now understand the limitations of the USA versions in the UK. If anyone is interested, here goes.
In the UK (and most of Europe) we have 3 phases each of 415 volts, (thats 415 volts phase to phase) plus a neutral which gives us 240 volts single phase when used with any of the 3 phase lines. I cant quiet understand why its not 207 volts which would be half the 415 and would be a center tap rating? but anyway.........
In the USA they have 240 volt 3 phase AND single phase.
If you only need to drive a UK 415 volt motor from our 240 volt single phase supply you must modify the motor to the USA 240 volts 3 phase system by re-wiring the terminals from STAR to DELTA. This is normally a simple task. You can then attach run and a start capacitors and the motor will work from a single phase supply. Note that the capacitor ratings for USA designs are not correct for UK use due to the difference in frequency (60hz in the USA and 50hz here in the UK).
The motor is easy to convert, the control is more difficult. Any start system attached to the motor will need to be looked at. If the system uses a neutral the solenoids and relays may well have 240v single phase coils so these should work OK, but if they have 415v coils you will need to change them.
If the control system (as is the case with my spark eroder project) is more complex things get more involved. What I needed in order to supply the whole machine is 415 volt 3 phase. In order to achieve this the 240 volt single phase needs to be lifted to 415 volts with a transformer. This can then supply a "normal" STAR connected UK motor which has the correct rated start and run capacitors. This "pilot" will then produce 3 phase 415 volts which i can feed to the machine. The other way to do this is to lift the voltage after a 240v DELTA wired "pilot" motor but this requires 3 transformers (1 for each phase) which does seem to be a bit of an expensive waste of money.
The good news is that the transformer on the spark eroder has 4 separate 3 phase inputs on the terminal strip (380v, 415v, 500v AND 220v) which is intended to allow connection in many places around the world (and is the last "expensive" option i gave above). This also means that if I build a USA type 240volt 3 phase rotary converter I should be able to feed the machine with the output from this and it will run everything including the 415v STAR connected motors.
Fingers crossed I don't blow the supply fuses, I'll update this info when its sorted (or not!)
Regards, Pete
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<snip>
Draw an equilateral triangle with sides of 415 units long, these represent the 415v phase to phase voltages. Now draw lines from the points of the triangle to the centre. These represent the phase to neutral voltages and will be 415/sqrt(3)$0 units long
HTH Mark Rand RTFM
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Vector/Phasor addition.
I remember the pain at college of learning Cartesian to Polar conversions.
Now seeking a dark room to lie down in. Aghhhh!
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It's no more difficult than the real-time calculation that you do when walking across the road from work to the pub on Thursday (or whichever day it is) lunch time... You know, the vector that gets the knee of your trousers torn out by the rear bumper of a car when the driver slows down :-)
Mark Rand RTFM
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