Yes, I am cleaning the metal. The welds are basically all just sitting on the top of the metal.welcome to the forum, are you cleaning the metal first? looks like the weld is just sat on top of the plate in the second pic?
Capacitors are there to smooth the rectified DC output. They increase the open-circuit voltage ( OCV ), give a steadier arc, and less spatter.I believe there is a fault with the machine, would this be the capacitors?
Capacitors are there to smooth the rectified DC output. They increase the open-circuit voltage ( OCV ), give a steadier arc, and less spatter.
A faulty capacitor can go open-circuit, no longer working as a capacitor, so you would lose the above advantages. Alternatively, it could go short-circuit, which would damage the rectifier or trip the power supply fuse/breaker. I think the fault on your machine is low welding power, and I do not suspect the capacitors.
What voltage output, at the torch tip, are you seeing? I would expect the OCV to be maybe 16v to 30v DC, rising steadily as you step up the power ranges.
If the voltages are in that range, and are maintained when under load, then it is puzzling why the welds have no penetration, even on 1mm steel ( which would normally be fine on the lowest power setting ). I would usually suggest that there is a high-resistance connection somewhere in the heavy-current welding path, from the transformer secondary through the rectifier to the torch tip and workpiece return clamp and cable. A bad connection passes enough current to correctly drive a voltmeter, but drops voltage across it with high welding current. This type of error is ruled out if your voltage stays up even under load. However, it is still worth checking for loose, corroded, or burnt connections. The paralleled press-fit diodes on Migatronic rectifiers are joined by spot-welded thin brass tags with a small hole that tends to act as a fuse, and can sometimes burn through.
In the second picture it looks like the clamp isn't even on clean metal. Half of it is sitting on paint.
I think you need to start with a piece of spare metal that has been cleaned completely bare.
The Migatronic Rallymigs are good machines and there isn't a lot to go wrong.
I switched to the other contacts, one set had to be modified as they were up the other way as to be on when the contactor is off. Now it only arcs when turning off and is not buzzing.Good find ! Looks like the contactor has had a tough life, with lots of stop/start welding.
If the rest of the contactor is serviceable, you could use the two previously-unused sets of contacts instead of the burned ones ( although it looks like one of the contact pads may be smaller in diameter ). If you replace it, maybe you could parallel-up the contacts, so that in future all 4 contact sets are sharing the current.
A couple of ideas:one set had to be modified as they were up the other way as to be on when the contactor is off
Using that method one is ok and the other is open circuit.A couple of ideas:
- some machines ( Murex, Eland ) use normally-closed contacts on the Contactor to put the discharge resistor across the capacitor bank only when the Contactor is off, so that the resistor is only in the circuit when it is needed to bleed off the remaining charge, and it is not always dragging down the voltage and wasting power. It might gain you some power if you wire your resistor that way. I realise you have now had to use those NC contacts; you could maybe add a second medium-duty relay in parallel with the original, and wire the bleed resistor through a pair of NC contacts on that relay.
- maybe the capacitors ( or some of them ) are open-circuit? By smoothing the peaks of the full-wave rectified DC from the rectifier, capacitors do increase the voltage. I'm assuming there is more than one capacitor. You could test them individually with an analogue Ohmmeter, on the Ohms x 1 range. Initially the pointer should swing to the right towards zero Ohms, then drop back towards infinity as the capacitor charges. Note that when an analogue meter is set to Ohms, the black test lead is actually positive.
If you do not have an old-fashioned meter, you could just briefly charge each capacitor to a few volts using a battery, observing correct polarity, then remove the battery and check that the capacitor is holding the voltage.
So you were right after all, it was the capacitors!I believe there is a fault with the machine, would this be the capacitors?