90en making loud screeching noise

[mrjynx]

ive had this some years, finally got to using it the other day, worked fine. switched it on today to try use it again and it makes this noise when the triggers pulled.
-loudness of noise seems to be relative to power switch settings.
-doesnt matter if earths on or off, or wires in or not.
-set up for gas welding.

 

[voipio]

It could be that the contactor is not pulling in fully, or there's a loose transformer lamination, or possibly a loose part of the casing, that's influenced by the main transformer's magnetic field (though that seems unlikely, judging by the racket). If you have one, use a power meter, to try and see how much power the welder is drawing, when the trigger is pulled. It shouldn't be much, maybe around a couple of hundred watts, until an arc is struck.

 

[Hutcho]

When did you fit the torch ? Maybe check the wiring

 

[mrjynx]

It could be that the contactor is not pulling in fully, or there's a loose transformer lamination, or possibly a loose part of the casing, that's influenced by the main transformer's magnetic field (though that seems unlikely, judging by the racket). If you have one, use a power meter, to try and see how much power the welder is drawing, when the trigger is pulled. It shouldn't be much, maybe around a couple of hundred watts, until an arc is struck.

i dont know what a contactor is, and i dont know how i would test how much power its drawing. sound does seem to be coming from the transformer, and i came across the transformer lamination suggestion as i was googling causes just now. some suggest that can be fixed with varnish n tightening of bolts.

 

[mrjynx]

When did you fit the torch ? Maybe check the wiring

couple of years back, after reading the suggested upgrades on this forum. it was working okay couple days back. the wiring looks fine for that.

 

[voipio]

I've just had a look at this welder's operating and maintenance instructions, and the circuit diagram doesn't show any contactor. Images of the internals don't show the presence of a contactor, either, so we can rule that out as the source of the noise.

Has the welder received any rough handling, say enough to cause the casing to become distorted, or badly fitting? With the welder disconnected from the mains, check the transformer mounting bolts to the case, and also check the laminatons to see if there are any loose ones.

Measuring power consumption can be performed using a mains power meter. The easiest type to use basically plugs into a mains 13A socket, and has a 13A socket on the front, to plug in any device to be tested. Something like this:

https://www.amazon.co.uk/KETOTEK-Electricity-Monitoring-Consumption-Appliances/dp/B09WRHDSJF

If the welder draws excessive power when the torch trigger is pulled, but no arc is struck, then that would suggest that there might be shorted turns in the main transformer.

 

[mrjynx]

i have had to carry it around a bit, so yea it could easily have become a bit warped. ill give it a good inspection and tighten. if it comes down to voltage my brother in law might be able to help with that, he has the multimeters and stuff. ill update the thread when i either fix it or dont. thanks!

 

[steveo3002]

funnily last time i used mine it was doing a similar noise , didn't have time to investigate , mine is a pro 90

is it on a solid power supply or some dodgy extension lead?

interested to see if you fix it

 

[mrjynx]

ive tried it in multiple sockets to rule that out.

 

[eddie49]

I think that the nose could be due to a shorted diode in the rectifier, creating half-wave DC pulses across the secondary.
To check this:
With the wire pressure roller released and the torch trigger pressed, measure the DC output voltage from the torch tip to the workpiece clamp, at each of the "power switch" settings. It should start at about 15v and step up towards 30v.
Then switch off and disconnect the machine, open the case and locate the two connections from the main transformer secondary to the finned aluminium rectifier. Unscrew one of these heavy bolted connections, move the thick wire aside and insulate it so that it cannot accidentally short anywhere. Then plug in, switch on, and press the torch trigger again. There will be no wire feed and obviously you will not be able to weld, but if the noise has gone, then maybe the rectifier is at fault, and it can be further tested.

 

[mrjynx]

I think that the nose could be due to a shorted diode in the rectifier, creating half-wave DC pulses across the secondary.
To check this:
With the wire pressure roller released and the torch trigger pressed, measure the DC output voltage from the torch tip to the workpiece clamp, at each of the "power switch" settings. It should start at about 15v and step up towards 30v.
Then switch off and disconnect the machine, open the case and locate the two connections from the main transformer secondary to the finned aluminium rectifier. Unscrew one of these heavy bolted connections, move the thick wire aside and insulate it so that it cannot accidentally short anywhere. Then plug in, switch on, and press the torch trigger again. There will be no wire feed and obviously you will not be able to weld, but if the noise has gone, then maybe the rectifier is at fault, and it can be further tested.

ok thanks for the idea, will take me about a week or two now

 

[Ace Paul]

@eddie49

I was playing with one of these recently. I’m confident it is already half wave, centre tapped anyway.

 

[eddie49]

Even though it only has two diodes, a centre-tapped transformer still produces full-wave rectification. It is just not a "bridge" rectifier.
For a half-wave output from a single secondary, only one diode is needed.

 

[Seadog]

Often called "Bi-half wave".

 

[OJCar]

https://www.clarkeservice.co.uk/manuals/mig_welders/MIG90EN-151EN_rev5.pdf