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Miller 452 Dimension contactor problem?

M. Moore

Titanium
Joined
Jun 8, 2007
Location
Vancouver Island, B.C. Canada
My really great 452 is giving us some grief. The main contactor is cutting in and out and it is quite random. Can happen with the machine on but not welding or when welding, it is happening more frequently now. When it welds it welds fine, no problems.

The main contactor sometimes clicks several times and then pulls back in or stays off. I opened it (contactor) up and the contacts inside all look quite clean and in good shape, no nasty blackness or signs of corrosion, the machine is 13 years old. I checked the resistance across the main contactor and it was 0.2 on all three legs, it is running at 208 three phase. The machine is labeled as 240, 480 or 600 volt.

The local repair shop suggested that it might be a low voltage fault causing the coil to drop out, if this is the case how to test for the fault? I did check the voltage at the main ON switch and it was 22.3 volts. The main contactor coil is rated at 24 volts. How low would the voltage have to be for the coil to drop out? 18 volts or less?
What is interesting is that when the main contactor shut off the light inside the main ON switch stayed lit, it appears the system is getting 24 volts without the main contactor pulled in.
I would have thought that the 24 volt transformer would shut off with the main contactor?

If someone were kind enough to walk me through some simple tests that would be much appreciated.

Thanks
Michael
 
I'd be looking upline to what supplies the voltage to lock it in first. If the voltage snaps in and out the contactor is likely fine. could be the coil in the contactor as well.
 
Tom,
The contactor is a Siemens/ Furnas, 42ef35ajagv.

Willeo.
I can test the 24 volt transformer, however I did mention that I had good voltage (22.3) at the main switch. How to test the coil?
Upline voltage? The supply voltage is quite consistent, what do you mean "lock it in"?


Is it possible that some kind of sensor is giving a false reading? Like the overtemp or something else?

Thanks,
Michael
 
Tom,
The remote switch is the switch on the front of the machine? I checked the voltage there when the contactor had turned itself off and I was getting 22 volts at the switch and the backlight was on. Turning the switch off and back on again and the contactor works properly, until it happens again.
Should I be taking that switch apart to see if the problem is inside the switch?
I am not sure what "check the wiring" means, you have to be very specific, I can do the tests but electrical work does not come naturally.

Thanks
Michael
 
My really great 452 is giving us some grief. The main contactor is cutting in and out and it is quite random. Can happen with the machine on but not welding or when welding, it is happening more frequently now.

If someone were kind enough to walk me through some simple tests that would be much appreciated.

Thanks
Michael

I am not an electrician or electronics guy but I can tell you what we have done when faced with similar intermittent problems with our Miller welders.

Forgive me if some of this has already been done.
I have my mechanic take compressed air and blow out the machine 100%. He then goes through and re-seats each connection. Each contactor screw is loosened, wire connectors tightened and screws re-tightened. Each stake connection pulled off wiped clean and re-seated. Every crossed wire checked for insulation wear. In most cases this takes care of the issue. If not then he starts pulling contactors cleaning and testing each one. Sometimes by pulling one he will find a coil that is starting to go. Some switches that seem good while mounted become wobbly when removed.

It's pretty amazing at what can be uncovered when parts and wiring are actually loosened and removed.

I'm afraid that all the help I can offer.

Walter
 
Walter,
Some good advice there, we can do those things easy enough.
I am unsure how a coil "starts to go", either they work or they don't?
Sorry for being so dumb but the only coil I have ever had to replace was just recently on a used machine, the coil had been connected to the wrong voltage, it lasted quite a while and then full burnout. No smoke but a very bad smell.
I have been installing new and used machines with mag switches for over 30 years and that was the first coil I replaced. Is it possible for a coil to lose some of its magnetic pull, getting weaker and weaker until it fails?

Thnaks
Michael
 
Walter,
Some good advice there, we can do those things easy enough.
I am unsure how a coil "starts to go", either they work or they don't?
Sorry for being so dumb but the only coil I have ever had to replace was just recently on a used machine, the coil had been connected to the wrong voltage, it lasted quite a while and then full burnout. No smoke but a very bad smell.
I have been installing new and used machines with mag switches for over 30 years and that was the first coil I replaced. Is it possible for a coil to lose some of its magnetic pull, getting weaker and weaker until it fails?

Thanks
Michael

Michael as far as I know you are right from an electrical standpoint. What we have seen though is mechanical issues like sticking movement or the actual contacts either coming loose or having excessive arc marks. In most cases there are no permanent fixes for these but temporary stuff can be done while you search on eBay for replacements.

It helps that I have a fellow working for me who is not only a great TIG welder but an excellent mechanic and electronic tech. He is equally willing to crawl under a forklift to replace hydraulic parts or tear apart a circuit board to replace toasted components. I wish I had two just like him!

Walter
 
Walter,
Some good advice there, we can do those things easy enough.
I am unsure how a coil "starts to go", either they work or they don't?
Sorry for being so dumb but the only coil I have ever had to replace was just recently on a used machine, the coil had been connected to the wrong voltage, it lasted quite a while and then full burnout. No smoke but a very bad smell.
I have been installing new and used machines with mag switches for over 30 years and that was the first coil I replaced. Is it possible for a coil to lose some of its magnetic pull, getting weaker and weaker until it fails?

Thnaks
Michael

The reason I asked about the brand of the contactor is that a few years ago Miller was using a Furnas switch with an open coil/magnet system which was standard construction. The problem was that magnet dust from grinding and whatnot was being drawn into the magnet and causing noise and poor operation. I designed a "shrouded coil" just for Miller that became the standard construction. The contactor you have is not the one that I was working on, but a newer design. It should not give you the same problems.

A coil can gradually fail by developing shorted turns within the coil body. This could be from faulty wire insulation or faulty coil construction. What happens is when a turn becomes shorted to itself, that turn will run hot. The heat from that turn will gradually degrade the insulation of the wires adjacent to it. They in turn will become shorted. The heat will escalate until massive failure and burnout. This make take months or years to develop. But it will not cause your kind of intermittent failure. What Walter A suggested is the best and most reasonable approach. Check each and every connection and wire. Since the function of that circuit is to allow for remote operation, there probably is a shorting plug somewhere that can be replaced with a remote cable. Make sure to look for that.

Tom
 








 
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