Arc-Tec MIG MAG compact

[Adam Craig]

Hi I am trying to turn this dual voltage machine from 415v back to 240v volts for my friend. When he bought it it had already been converted but now he wants it converted back as he is selling it. I have all the wiring diagrams etc but as you can probably see from the photos(sorry no scanner ) wires 91 and 92 are in different places in the 415v diagram and the 240v diagram at the main contactor. Unfortunately when it was converted to 415 volts the engineer removed one of these wires probably for convenience. Unfortunately for me this means that I cannot simply separate the wires and make it work. I think I need to add another wire which is fine but where do I connect it??? The remaining wire is connected to a three or four position switch on the front panel. HELP!

 

[Wedg1e]

As far as I can make out, wires 90-93 are the connections to a dual-primary transformer (see sketch). Each primary is designed to operate with 220v across it.
For 220v operation the 'start' of each winding (90 and 91) are connected together, and the 'ends' of the windings (92 and 93) are connected together. Mains is then applied across these two points (L1 and L3 on the contactor). This puts the primary windings 'in parallel' so they share the load presented by the output of the transformer.

For 415v operation, the 'end' of one winding and the 'start' of the other are linked 'in series' (using T2 of the contactor as an anchor point) and mains is applied across the two remaining ends (still at L1 and L3). So each winding sees 'half' of the input voltage, i.e. more or less 220v.

Which wire(s) seem to be missing? The transformer would tend to not work without all 4 connections...

Also, don't mix up the 'start' and 'end' as connecting say 90 to 93 and 91 to 92 would put the primaries in 'anti-phase' which will mostly cause smoke

 

[Adam Craig]

Thanks for your help wedg1e, has helped clear a lot up bringing me back to those years at college. Just to clear things up I am, or rather was (before the slump), an electrician and have no knowledge of welders etc, I've forgotten most of it tho... The wire that is missing is either 91 or 92. If as you say these are two end points of the windings then would it make sense to just connect the wire that was at T2 on the main contactor originally(415Volts) (91 and 92 together I'm guessing) to the live T1 on the contactor and then connect the remaining wires 90 and 93 together at the neutral T3? I know you said in your post that this would cause smoke but does it not mean that these two points are maybe connected together somewhere else? I traced the wire that was at T2 back to a switch on the front of the welder which has lots of different settings but which then has a few wires going from there into the windings(?) Hope this makes a little sense