SAF Nertinox 250P

[AndyStobbs]

Still not sorted out why the HF was problematic. Yesterday I removed the enitre HF generator unit to try and see if there was a wiring fault.

Am I right in thinking the first stage is power connected across a capacitor and resistor in parallel which in turn is in parallel with a transformer primary. The secondary is then across two more capacitors, in parallel with the spark gaps. It must jump first one spark gap then the next before being run into a hollow coil affair, through the centre of which the main welding current passes on a copper bar.

The contacts for the spark gaps where very blackened and burnt looking, so I faced them up on some 1200 wet and dry, and gapped them to 0.2mm.
Have only done a small amount of playing around with the set since - not enough to know whether its fixed or not - but it seems so very simple in construction that I don't see what else could be wrong with it.

 

[Jim Davey]

Did you ever get to the bottom of this Andy?

I'm not familiar with your machine but assuming you have a reliable supply voltage to the HF system (often 110 or 230 volts) then the problem is most likely to be the capacitors. (The transformer is less likely to fail, but can't be easily tested without specialist (ie. expensive high voltage test equipment). The caps are a very low capacitance but high voltage so not something that you are likely to have lying around but Tech Arc do a vey reasonable generic HF capacitor for sensible money. (HF caps from old Millers were over £200 if I recall so the £60 ish TAUK charge is a bargain)
If you've re-faced the caps and set them correctly then the only thing left to check is bad connections or dead shorts in the welding circuit. Melted dinse connectors that allow the brass core to come into contact with the metalwork of the front panel are a favourite place to look for a path HF can use to bypass the torch.
Or you could sidestep the problem, sling the existing HF system in the bin and fit an aftermarket solid state electronic HF system, the advantage is mainly that the new setup does away with points and their problems and gives you a more intense spark without the radiated HF that affects computers, telephone signals and so often fries the welding machines boards when the old suppression capacitors fail.

 

[AndyStobbs]

Hi Jim, you've actually pre-empted my next post. The HF is still intermittent, at first I thought it might've been me holding the torch too far from the work, but its definitely not that. I have been leaning toward the caps myself, comparing them in my mind to the condensor on an old ignition system - but at higher voltage.
The HF certainty seems to generate ok, which I think prooves the LT side of things and the transformer. I will have to remove the HF unit again and get those HV caps out and try to test them. If I can replace them I will.
I might have a working HF unit in the NewArc rover box, that could be salvaged if servicable.
Will keep you posted.
Thanks

 

[AndyStobbs]

Well I'm starting to get frustrated by the HF now, up until now I'vo only been playing with the TIG but now I'm using it in anger its annoying when it wont strike. Things came to a head earlier when this annoyance added to my non existant TIG skills, rattled me good style.
So, once again I have pulled the HF cover off the unit, and satisfied myself of all the LT/LV aspect of things, I stuck a multi meter across the big caps on the HF side and got open circuit on both, but not being familiar with them I don't know if that could be normal? - Hopefully someone can advise, but I was expecting they would charge up from the meter.

I have the newarc rover box, and all though the HF in that is untested, I may well look at fitting it. Is anyone familiar with the electronics that feed the HF on a newarc 300? There is a yellow and a green wire going from the control board to the HF unit, which is obviously its supply, but is that DC? and at what voltage?

Secondly, I could do with purging the pipework I'm welding, can I piggy back a second gas solenoid off the original solenoid already in the SAF, and use this second solenoid for a purge line?

Thirdly, is anyone well up on foot pedal schematics for the SAF unit? the plug is a 10 pin amphenol with a screw on retention ring.

Thanks

 

[AndyStobbs]

Pulled the newarc to bits, and took a guess that the HF is powered by 24VAC or pulsed DC. Blew a fuse in the SAF, having spent the day integrating the newarc HF into it.
Pulled it back out, but the fitment necessitated the removal of the inductor coil. It's nothing more than a solid copper bar helix, tightly wound, with a HV cable wound in a helix between the copper turns.
Copper bar is obviously ok, as when HF fails the tungsten is still live. Also proves all cabling to torch and torch itself. Which were never in question anyway as the hv circuit is electrically independent of the welding circuit.
Going to get the two HV caps on a megger to see if they can be evaluated.
Second gas solenoid is working well and giving me an auto purge set up.