Inspired by the thread by Dave:
http://www.mig-welding.co.uk/forum/showthread.php?t=7007
I decided to buy a "PWM Speed Controller" from Maplin...
But this is only rated at 15VDC... after a bit of experimentation it was apparent that this was not enough ! (I was reading 30VDC on full speed with the original controller)
An email to the PWM controller manufacturer from Maplin resulted in zero help
A bit of research shown that the limiting factor was the timer I.C. - all the other components were rated at a higher voltage... so a simple mod to the controller PCB was in order - I added a 12VDC voltage regulator to power the timer chip alone.
Next was a dig around the "junk box" (well, junk room truth be told !) and a suitable transformer was found... 12-0-12 VAC @ 1.25A per winding, to this I added 4 1A diodes (as a "bridge rectifier") and a couple of 330uF capacitors as a reservoir - I used 2 because thats what I had at the time !
Once powered up, it seems the transformer was nearer a 15-0-15, as the circuit produced 34VDC !
I thought this might be a little too much, so wired the transformer for "12v" but this resulted in a VERY slow speed on low, and not really fast enough on high... so I put the secondaries in series to get that 34V again.
I stole Daves Idea of using the original motor wires to drive a relay - the junk box provided a 24vDC SPDT with nice fat contacts (probably over specced - but I had it, so why not ?)
I hunted Maplin for a plastic box in which to place the original controller - as I planned to panel mount the new one, in place of the old... but there was nothing to suit, so I did a bit of lateral thinking and found a small food container that fitted the bill.
The relay was wired so that the motor was "short circuited" when "OFF" and this has shown to be an excellent idea ! (again, pinched off the forum !
) as before, the over-run was producing a lot of waste wire, now there is about 1cm of stick-out !
All in all a very rewarding experiment - the welds are as if from a different machine
Heres a few pics of the Frankenstein SIP...
http://www.mig-welding.co.uk/forum/showthread.php?t=7007
I decided to buy a "PWM Speed Controller" from Maplin...
But this is only rated at 15VDC... after a bit of experimentation it was apparent that this was not enough ! (I was reading 30VDC on full speed with the original controller)
An email to the PWM controller manufacturer from Maplin resulted in zero help
A bit of research shown that the limiting factor was the timer I.C. - all the other components were rated at a higher voltage... so a simple mod to the controller PCB was in order - I added a 12VDC voltage regulator to power the timer chip alone.
Next was a dig around the "junk box" (well, junk room truth be told !) and a suitable transformer was found... 12-0-12 VAC @ 1.25A per winding, to this I added 4 1A diodes (as a "bridge rectifier") and a couple of 330uF capacitors as a reservoir - I used 2 because thats what I had at the time !
Once powered up, it seems the transformer was nearer a 15-0-15, as the circuit produced 34VDC !
I thought this might be a little too much, so wired the transformer for "12v" but this resulted in a VERY slow speed on low, and not really fast enough on high... so I put the secondaries in series to get that 34V again.
I stole Daves Idea of using the original motor wires to drive a relay - the junk box provided a 24vDC SPDT with nice fat contacts (probably over specced - but I had it, so why not ?)
I hunted Maplin for a plastic box in which to place the original controller - as I planned to panel mount the new one, in place of the old... but there was nothing to suit, so I did a bit of lateral thinking and found a small food container that fitted the bill.
The relay was wired so that the motor was "short circuited" when "OFF" and this has shown to be an excellent idea ! (again, pinched off the forum !
) as before, the over-run was producing a lot of waste wire, now there is about 1cm of stick-out ! All in all a very rewarding experiment - the welds are as if from a different machine
Heres a few pics of the Frankenstein SIP...
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