FridgeFreezer Posted June 27, 2007 Share Posted June 27, 2007 Just before finishing the 109 my welder's control transformer let the smoke out. It's an NBC Autoweld2 from before time began, Butters were very helpful on the phone but couldn't afford to hire Tony Robinson and co to dig that far back into their archives for a manual for it. They actually phoned the retired guy who used to be the MD to see if he'd kept the manual in his loft - now that's good customer service for a 30 year old lump of electronics! Basically the main transformers are fine, the control gear is fine, but the transformer that supplies it has given up. Now, if I knew what voltage the thing put out (my money is on either 115v or 24v) I could sling a small replacement unit in there and bring it back to life. However, without doing a lot of prodding about and reverse-engineering the thing (admittedly not hard but time-consuming) I was wondering if anyone has any info or a similar unit they could wave a multimeter over to save me a lot of time. All info greatly received! Quote Link to comment Share on other sites More sharing options...
simonr Posted June 27, 2007 Share Posted June 27, 2007 John, I'm surprised an enterprising chap like you hasn't figured it out? If it were me, I'd use a varable transformer or variac. You've probably got one lying around at work - but if not they are cheap as chips on eBay E.g. http://cgi.ebay.co.uk/Claude-lyons-ltd-var...1QQcmdZViewItem For those who don't know what a variac is and can't be arsed to click on the link - it's a transformer with a variable output voltage - typically 0 to 240v output. They are fantastic for 'testing' stuff you have built but are worried about it tearing a hole in space-time if you just plug it into the mains. With this you can wind up the power slowly and stop before your TV turns inside out. All you need to do is plug it in and wind up the power from zero until it begins to function properly. Measure voltage, round up to the nearest likely figure and there is your answer. They are also handy if you fancy yourself as Jack Bauer and wanted to torture your flat mate for example? Si Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted July 7, 2007 Author Share Posted July 7, 2007 Well, after a day spent reverse-engineering the thing I think I've gotten to the bottom of it... It wasn't the transformer that let the smoke out, it was the wire feed motor just above it It's a DC shunt-wound motor so it seems what they do is leave the field windings connected to 110v DC all the time and then energise the armature to make it spin. Unfortunately the field coils didn't like this after a long period of being energised with no motor action to cool them down and have gone toasty. To find this I also had to repair one of the rectifiers (the one that supplies the motor) as two of the diodes in it had gone s/c, I don't know which caused which but with the rectifier back I could power it up without the panel fuse blowing, at which point the motor made a crackly noise and let some more smoke out So, not an ideal result but at least it's not the transformer, a motor can be replaced or possibly even re-wound (if it lasts another 30 years I'll be happy!), Monday's job will be a call to Butters or Parvalux who made the motor in 1972 and are amazingly still around and boasting about their reliability New rectifier with shiny heatsink: Not good : Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted July 9, 2007 Author Share Posted July 9, 2007 Well Parvalux are shipping me a brand new motor, from the technical drawing of the old unit so it should bolt in. A bit pricey at £125 but if you average it out over the 35 years the old one lasted it's not bad value and cheaper than buying a new welder. BTW if anyone needs the circuit diagram for an NBC Autoweld2 I have it scribbled on a bit of paper now One thing that did come up in discussion with Parvalux was the idea of fitting a current limiter to the motor to prevent the coils getting hot when left on for a long time. I know such devices exist (thyristors?) does anyone have any thoughts on this? Quote Link to comment Share on other sites More sharing options...
simonr Posted July 14, 2007 Share Posted July 14, 2007 A simpler solution would be to switch the field windings on & off with the Armature via a relay. It may be that the field windings remain powered intentionally to heat up the motor. A hot motor will run slower than cold so keeping it warm means less variation in feed speed on long weld runs. If the diodes feeding it have gone short circuit, I guess the field windings were being fed with AC? If so, the amount of power they would have to absorb was doubled. That may explain why the motor cooked itself. With new diodes and motor, I suspect it will be fine! Si Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted August 14, 2007 Author Share Posted August 14, 2007 Well Parvalux took their sweet time but then this was basically a one-off custom jobby. The motor arrived, exactly to spec. Had to: - Remove reduction gearbox from old unit - Remove drive gear from old motor - Drill shaft of new motor to take roll pin to hold the gear on - Enlarge and tap the pre-drilled holes in the top of the new unit - Cut the shaft down once the gear was on (the old unit had had this done too, presumably the factory method) I've just installed it... and it's ALIVE! I'm a happy bunny - excellent service from Butters, slow but good service from Parvalux. And I am back in the land of fabrication, which is a good thing. Now to get a new Speedglas that hasn't been run over... Quote Link to comment Share on other sites More sharing options...
james4x4 Posted August 7, 2017 Share Posted August 7, 2017 Hello, I know it is 10 years on but I have an Autoweld 2 that has done exactly the same thing with the drive motor, I understand now why it was smoking while not actually welding, because the field windings are powered all the time. I was wondering if your new motor/welder was still operative, whether it is worth me repairing, as it is a bloody good welder. Any info on the welder would be gratefully received. Quote Link to comment Share on other sites More sharing options...
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