Anyone with electrical hints on Squarewave problem?

[mic_hviid]

Does anyone have any idea what this problem might be:

I have an Esab DTA 200 (AC/DC squarewave tig). Its transformer-based. It worked perfectly and now suddently trips the ground fault relay. Every time I switch it on - but only after 6-10 seconds. I have tried to clean it very thoroughly with dry compressed air because I suspected it might have been stored a bit too moist during winter - but to no avail.

When I switch it on the water pump starts and I have checked the return: water is flowing. Then the pregas shuts of and 2 seconds later it trips the GF relay. It does this on both AC and DC, stick and tig. Also with no welding cables attached.

I could understand if it set on fire, or just didnt work at all but that it starts up fine and then trips the relay leads me to think it might be something simple.

Anyone have any idea before I get someone to pick it up for repair (which probably wont economically viable considering the age of the machine).

Kind regards

Michael Nielsen

 

[rtbcomp]

Has it got a supressor on the main input? If so this may be getting warm and leaking.

 

[eddie49]

Following on from what rtbcomp suggested, the problem may be a leaky capacitor. That could be a small, low-value capacitor, tied to ground, anywhere in the circuit. If you have electrical skills, I would suggest isolating the functional units ( e.g. main, HF, control ), and powering them up independently. Or, could your earth-leakage protection be over-sensitive ? Do you have any power sockets available that are not on the GF-protected circuit ?

 

[mic_hviid]

Yes there is transient protection (if that is the same as suppressor in english). But there is not active thermal cutout on that one it seems (if that was what you ment).

Unfortunately I have no mains without GF protection. Last year I welded on exactly this very same electrical outlet equipment.

I will try measure all the capacitors connected to ground. This also makes some sense in that it takes a few seconds before cutting.

Thank you for your input both of you - keep the suggestions comming ;-)

I am not super strong in elec myself but I will get assistance from someone who can fiddle with this in a safe manner but has no specific knowledge on welding machines. So you will do not have to fear that I suddently becomes a part of the main cirquit because of your help ;-)

Michael

 

[eddie49]

Michael, I think that rtbcomp was suggesting that your welder may have a leaky mains input supressor, especially when this item warms up. The purpose of this supressor, or filter, is mostly to prevent electrical noise from the machine going back into the mains. It will have a couple of capacitors and a choke, and could be in a sealed tin box close to where the power cable enters the welder. If present, you could bypass it, and test without it.

 

[rtbcomp]

Yes Eddie, that's what I was thinking. The capacitors go to earth from live & neutral so if one leaks you'll trip the RCD. The fault will most likely be on the primary side of the transformer.

 

[mic_hviid]

Ahh, now I understand (I will naturally mask my problems of a dim bulb with limited foreign language skills )

Yes it has this kind of suppressor. And yes, it is build as a sealed unit with the mains switch on the front, so I have to bypass it with another switch. So I have to find something else to take apart since its easter and everything is closed until tuesday, hmmmm ;-)


Michael

 

[madkayaker]

could be a fault on the transformer it is quite normal for then to be "leeky" to earth. Only above a certain value (10mA here) does t become a problem for safety. Not sure on regs with you but you can put in none RCD circuit for an appliance of this nature

 

[big_d]

Hi there, I notice that there is a lot of focus on the suppressor to ground and ths should be checked, but I notice in your first post you mention that the unit is a water cooled system. Is it possible to disconnect the water cooler as a waer leak could cause the problem? If you have the welding current pretty low, you won't really need the water cooler (at least for testing purposes). This would prove if the prblem is in the water cooler or the main welder.

 

[mic_hviid]

Unfortunately I cant put it on a non RCD line - not allowed anymore ;-(
But I will try disconnecting the watersupply. Its on a seperate transformer inside the welder. It shouldnt be a problem though cause the water is safely routed in channels underneath the welder.

I have also now got some power resistors to discharge the larger capacitors, so I can happily measure away in there. I really hope its not the transformers themselves leaking. I will also try bypassing the supressor tomorrow.

Thanks guys, I will let you know how it fares

Michael

 

[Jake SS]

Was or is there a lot of metallic dust inside?
You would have to use a IR/Meg meter to test the transformer properly
Check all the earth wires and connections inside machine for heat etc
May have to disconnect components to try and isolate the general area that is causing the problem
Have a good look under the transformer, basically everywhere for bits of wire or similar that may have worked there way in somehow
I have had lots of cases where this has happened, have worked there way in between windings causing all sorts of problems, even though the panels should not allow this but it does happen
LOTS of things to check and test
Hope you find it first up !

Cheers
Jake

 

[mic_hviid]

Thank you all of you!

I cleaned the inside even more. Found two pieces of snapped ziplock under one of the main transformers - shouldnt have caused any problems since made of plastic?
Dismounted all the electrics to the waterpump (since this was the easiest suggestion). Turned on the welder - worked fine. Ahh, so the pump it is then. Reconnected the pump just to be sure. Welder worked without problems. So probably an intermittend fault with the pump - which will be nice to know next time it cuts out.

But me learning to weld alu in 3 hours - no can do. It worked fine welding flat position but not under an overhanging lap weld looking down into an upsidedown wheelarch with the helmet comming off my head every 10 seconds.

Also, trying to cut corners I had a couple of aluminium pop rivets I thought I could "weld away" and then grind. The collar melted fine but the pin that pulls the rivet just turned black and wouldnt melt. Strange.

But again, thanks alot for all your suggestions!

Michael Nielsen

 

[rtbcomp]

............. The collar melted fine but the pin that pulls the rivet just turned black and wouldnt melt. Strange.

Michael Nielsen

That's because it's made out of steel which melts at a much higher temperature than aluminium.

 

[mic_hviid]

Ahh, I thought that might be the case. But I also thought that it would be stupid, because the steel will make the alu corrode. So "this pop rivet will selfdestruct in T minus....."

Michael