Britweld bovver

[jonrev]

Seem to be spending a lot of time here just recently! Picked up a Britweld 195 mig today which was described as having 'not much control at low settings'. Got it home and removed side panel and found a few wires have been getting warmish. Ripped out the burnt ones and replaced with the intention of then firing up the machine to see if anything promising happened. When I tried setting at the lowest power on the rotary switch it seemed to be siezed and just the 'knob' was turning. Reluctantly I decided to take it apart and see if it could be salvaged. Knowing full well how many springs and little bits can fly out of this type of unit I was suitably gentle and quite chuffed when all came apart and nothing shot across the room. Unfortunately I didn't realise that each switch unit (7 of them activated by a lobe running on a cam) could be placed either way up. In other words each of the switches had two possible positions. Maths isn't my strong point but the odds of getting seven switches in the right orientation by luck isn't good. There aren't any marks or indicators of where they were placed so I tried a logical approach and placed each in order one up, one down. I don't think I got it right and am not happy about connecting it up and causing more mayhem!
The unit appears to have power from the contactor applied to one side of each switch (they are all jumpered together). This leaves seven connections and seven wires. The seven wires all come from the 'chocolate block' connector as you can see in the photo's. Would anyone know if these seven connections are simply a line of tappings which should be connected in sequence via the selector switch or is it more likely they are connected in some more complicated way to select different combinations of primary windings rather than just a step ladder type of sequence.
Hope I've explained all this well enough for somebody to make sense of? I would guess the chances of finding a wiring diagram for this machine is slimmish- unless you know better???? Any advice appreciated.
Thanks
John

 

[penfold]

Those rotary switches can be very stiff; they will make mincemeat of ordinary plastic knobs. I vaguely recall Britweld were also available badged as Eland, but I could be wrong. You really will need a diagram to sort all that out! Let that be a lesson; never dismantle without either a manual or copious pictures, labels and drawings.

 

[jonrev]

Absolutely right. Maybe should have thought longer but since I couldn't turn the thing I couldn't test continuity to note what the switches were doing at each step so figured I had no option. Odd thing is once I'd put it back together without finding anything wrong (thought the innards would be welded together) it turned nicely. Can only think one of the cam followers had jammed somehow.
Think I'm going to start by taking readings of the transformer winding resistance at each tap just to be sure I've not got any burned out or shorted sections then try to set up the switch to select each tap in turn and see what happens.
Wish me luck

 

[Wedg1e]

I'd say you are correct: if each switch has a common side and the seven wires head off to the transformer via the choccy block, the switch will be selecting sequential taps of the TX.
I guess the worst that'll happen is that the output will be all over the shop; wild stab in the dark though... if it was me, the choccy block would have the wires in the correct order from one end or the other.
My Romarc has two range switches with 8 positions each: wiring looks horrific but each switch position brings in an entire winding - yours sounds more like my Oxford that has just half a dozen positions, each one being a sequential tapping.

 

[jonrev]

Yup thanks- you're absolutely right. Dismantled switch again and painfully slowly reassembled making sure each element switched sequentially as I went. Took readings of resistance from common connection on chocolate block all along the row and it increased at each connector. Wired the switch back in and all seems good with increasing voltages out of transformer at each 'click'.
I did have fears that the transformer primary could have been damaged by what would have been more or less shorted turns due to the burned out and fused together wires but it appears to be ok. I haven't welded yet as no earth lead and waiting on a couple of reels of wire but am hopeful I've got a decent machine. Another ebay buy and a pleasant seller. Got it for £37 and paid another £23 for the euro torch.Once I'm happy it's all ok I'll put the old Topmig 140 up for sale. Bit reluctant as I've invested time and money in it and it welds really nicely but have no use for two machines.
Thanks again
John