static 3 phase converter trouble shooting

[iain mackay]

Good Morning

This is my first post here but have been on the forum many times and have found some really useful threads so thanks to all.

I am looking for a little help trouble shooting a static 3 phase converter. Its a clarke pc40 which I bought on gumtree a couple of years ago to power a drill and grinder. Unfortunately the drill previously had a remote stop which had not been bridged and my mate who's an 'electrician' decided to disconnect all the wires and tell me he couldnt wire it. so to cut a long story short I bought a single phase drill and grinder and sold the converter to another mate with a money back guarantee.

He called me yesterday saying he tried to get it working on his mini lathe but no joy. he got someone to test it and all he got was 230v from 1 phase. I know it worked before because i manually pressed the contactor in (i know bad idea) and the drill fired up. Does anybody know what the problem could be or could somebody advice on further trouble shooting? I know theres capacitors inside and not to mess about with them. Any help would be much appreciated

 

[Wendelspanswick]

Is he measuring across the phases or between a phase and neutral?
I have an ancient Transwave converter, its basically a step up transformer and a load of capacitors.
240v L and N is fed into the transformer and approximately 400v comes out on 2 terminals, let's say X and Y, Y is then split and goes through a bank of switched capacitors with various tappings according to motor HP and is presented as Z.
This gives you your 3 terminals for 3 phase:
Measuring across X and Y should give about 400v as that's the true transformer output.
Measuring across X and Z should give about 380v as that is the phase minus the loss from the capacitor bank.
Measuring across Y and Z can give anything from 180v up to 360v as you are measuring the capacitor bank!
Under load the back EMF* from the motor under power levels out all these voltages to something around 400v across all 3 phases.

Its important that any switchgear, contactor coils etc go across the X and Y output of the converter as its a true voltage. Which makes it fun when having to swap phases to reverse motor direction.

There is normally a timer circuit in a static converter to kick in and out capacitors in the bank to aid motor starting.

*EMF is Electro Motive Force, the motor under load acts as a generator to smooth out the voltages. Thats all a Rotary converter is, a static converter with a large electric motor permanently attached to balance out the output voltages.

Just to add I am no expert, the above is what I have gleaned from tinkering with my converter, and BE AWARE, 415V KILLS.

 

[iain mackay]

Thanks very much for your reply. To be honest i'm not sure how it was tested but I will be able to have a look myself on friday. I cant see how only 230v came out on 1 phase unless something is knackered in the transformer. I am a mechanical tech on the rigs therefore Only have a basic knowledge of electrics but fully aware of the dangers (especially 415v) so I wont be messing with stuff outwith my capabilities. I'll pop the cover off and have a look for anything obvious (burned out, loose etc). Is there anything I could do to test the transformer?

 

[AdrianH]

In case it is of use here is the manual for the unit and it has wiring diagrams in it

http://www.clarkeservice.co.uk/manuals2/pc20_60.pdf

Adrian

 

[iain mackay]

that's great Adrian, thanks

 

[iain mackay]

Just in case anybody is interested, my buddy got the converter sorted before I had a chance to look at it. Unfortunately he doesn't know what was wrong with it since it was somebody else that fixed it but it didn't need any new parts. Thanks for the help guys