Soup Dragon
New Member
- Messages
- 5
- Location
- Widnes, UK
Morning all – this is my first post on here (although I’ve lurked for a while) so please be gentle!
A friend and I have been learning the basics of ARC welding over the past few months or so with guidance and a borrowed set from a retired welder neighbour, and are now feeling slightly smug with a few practical projects under our belts (7ft high gates and frame, water butt stand, etc together with a few general repairs around the place). We’ve now decided to try and pick up MIG welding. As we are on a shoestring budget for this endeavour we spotted a second hand Clarke Pro 90 for just £20, advertised as “not working – spares or repair”. The seller mentioned that he didn’t have a clue why it had stopped working, but as it was an old set and he’d long ago replaced it he was fed up walking around it in his garage. It’s not the most exciting welder but for what we want at the moment it will do the job. Given that it was so cheap, we’re both mechanically minded and my friend is pretty handy with electrics and a multimeter, for £20 we decided to give it a whirl.
Having scoured this forum for as much relevant information as we could find we opened up the case to have a look. We’ve already spotted and fixed poor connections where both the torch and the earth clamp re-enter the case. We’ve checked that all the switches are working and cleaned the contacts. On squeezing the trigger the relay on the PCB can be seen working (we’ve also popped the back off the relay, cleaned up the contacts and replaced the cover), the wire-feed motor runs we’ve tracked voltages though the system to the rectifier. As far as we can see, everything else appears to be working as it should.
When the torch is triggered, the voltage at each of the heat sink plates is 25.1v (measured from the earth clamp), however the output from the rectifier only measures around 13v. We measured the diodes in-situ and got similar values for each, working in one direction only – then realised they should be isolated and measured separately. We’ve removed the rectifier and stripped it on the bench, measuring one plate (containing 2 diodes, press fit alternator type, soldered together in the middle) against the other we get differing values, so assume that at least one of the diodes has gone bad, although we haven’t yet desoldered them to test individually. As the existing diodes are a press fit in the plate like-for-like replacement would seem difficult.
Given the above, could anybody please point a pair of noobs in the direction of how to calculate the required diode size (4 existing diodes, 90 amp welder) to effect the repair, or somewhere to source a working rectifier? Any help or advice would be massively appreciated, and thanks for reading this far!
A friend and I have been learning the basics of ARC welding over the past few months or so with guidance and a borrowed set from a retired welder neighbour, and are now feeling slightly smug with a few practical projects under our belts (7ft high gates and frame, water butt stand, etc together with a few general repairs around the place). We’ve now decided to try and pick up MIG welding. As we are on a shoestring budget for this endeavour we spotted a second hand Clarke Pro 90 for just £20, advertised as “not working – spares or repair”. The seller mentioned that he didn’t have a clue why it had stopped working, but as it was an old set and he’d long ago replaced it he was fed up walking around it in his garage. It’s not the most exciting welder but for what we want at the moment it will do the job. Given that it was so cheap, we’re both mechanically minded and my friend is pretty handy with electrics and a multimeter, for £20 we decided to give it a whirl.
Having scoured this forum for as much relevant information as we could find we opened up the case to have a look. We’ve already spotted and fixed poor connections where both the torch and the earth clamp re-enter the case. We’ve checked that all the switches are working and cleaned the contacts. On squeezing the trigger the relay on the PCB can be seen working (we’ve also popped the back off the relay, cleaned up the contacts and replaced the cover), the wire-feed motor runs we’ve tracked voltages though the system to the rectifier. As far as we can see, everything else appears to be working as it should.
When the torch is triggered, the voltage at each of the heat sink plates is 25.1v (measured from the earth clamp), however the output from the rectifier only measures around 13v. We measured the diodes in-situ and got similar values for each, working in one direction only – then realised they should be isolated and measured separately. We’ve removed the rectifier and stripped it on the bench, measuring one plate (containing 2 diodes, press fit alternator type, soldered together in the middle) against the other we get differing values, so assume that at least one of the diodes has gone bad, although we haven’t yet desoldered them to test individually. As the existing diodes are a press fit in the plate like-for-like replacement would seem difficult.
Given the above, could anybody please point a pair of noobs in the direction of how to calculate the required diode size (4 existing diodes, 90 amp welder) to effect the repair, or somewhere to source a working rectifier? Any help or advice would be massively appreciated, and thanks for reading this far!