New to me Miller AC/DC buzz box welder - hot temp at connector

[aribert]

I bought a new Miller AC buzz box back in '88, gently used. Recently I found the same model in an AC/DC version at auction. I bought it, tried it out with a few short welds. Then I sold my AC buzz box - might have been a mistake.

I was using the AC/DC welder in DC mode recently. I may have exceeded the duty cycle but there were definitive pauses between welds. Machine welded fine. Note images w/ cables shows how the leads were connected. About half an hour after welding I happen to look down at the floor in front of the welding table when I spied one of the insulated "nuts" on the high AC connector (Note: I was **not** using AC). The insulated nut got hot enough to melt off of the connector. I opened up the welder, looking for a loose connection (high resistance, high heat) and all connections are tight - including the high AC where the nut melted off. How do I trouble shoot this? I don't think just turning a new nylon "nut" is adequate. When looking at the images from inside of the box, the AC high is the one with dual leads. TIA for any insight.

[mickeyf]

"Tight" does not guarantee "clean". Long shot, but it probably wouldn't hurt to take the connections apart and send them shiny before re-tightening them. Unused connector getting hot implies it is not "unused". Maybe leaking to the frame where it passes through?

[loose nut]

I don't know if this helps but connector on welders can get hot. We used solder-on cable fittings, at work, for 02 or 03 etc. cable and when burn'in the biggada rod (1/4, 3/16, they get much bigger) the solder would sometimes melt out. Possibly if you over used the machines duty cycle it might get hot enough to melt the connector. Connecting nuts and cable connectors should be a tight fit to stop arcing which could cause overheating and erosion of the connector. Other then that I got nothin'.

P.S. what mickeyf said.

[Bob Engelhardt]

Since you were not using this connector, no current should have have been flowing in it. But some (a lot) was. To me that means that this connector is "shorted" to the case. Easy to check.

[Willy]

Since you were not using this connector, no current should have have been flowing in it. But some (a lot) was. To me that means that this connector is "shorted" to the case. Easy to check.

Or a very high resistance between the two leads that join at that connection.

It also looks like the + connector on the DC side is getting hot.

[Cheap Jon]

I had to replace one of the DC connectors that did the same thing. The aluminum wire was burnt and corroded so I cut it off and formed a new loop, then I relocated the hole because the wire was now too short and then installed a new connector from Amazon.

Jon
SW Mi

[JoeLee]

Or a very high resistance between the two leads that join at that connection.

It also looks like the + connector on the DC side is getting hot.

Yes, and I've seen that before. The pin gets all dinged up from being tossed around when they are plugged in they don't seat with full contact in the socket. Only the high spots touch and make contact. That becomes the point of high resistance. It becomes an electrical bottleneck.

JL...............

[Willy]

Joe you are right of course on the pins getting buggered up and then not fitting the jacks correctly and causing an improper or marginal connection which leads to heat, have seen this also.
What I was referring to though was a poor or corroded connection at the Hi AC jack and at the + jack on the DC side. If you blow up the photos you can see what appears as some signs of corrosion at the terminals. Also what appears as signs of heat at the + side of the DC jack.

[chipmaker4130]

I had to replace one of the DC connectors that did the same thing. The aluminum wire was burnt and corroded so I cut it off and formed a new loop, then I relocated the hole because the wire was now too short and then installed a new connector from Amazon.

Jon
SW Mi

For a long time, Miller didn't use any aluminum wires. That's one reason I stuck with them over Lincoln. If the machine in question has aluminum windings every connection so involved is suspect. Undo, clean, coat with anti-oxidation past and re-connect.

[J Tiers]

For my money, that double wire connection is suspect to begin with. It's not easy to make such a connection solidly, even with square wire.

I have no idea f the two wires are series or parallel. If series, then potentially there is current there even when it is not the connection in use, and a bad connection is likely to heat. If parallel, then if there is any difference in voltage, there is a current flow, and bad connections can cause heating.

If it is aluminum wire, then there is a good chance of a bad connection. Better to braze both wires to a plate, and screw the plate down under the nut instead of trying to get both wires to contact well. They didn't do that, and so there is an issue.

[aribert]

Since you were not using this connector, no current should have have been flowing in it. But some (a lot) was. To me that means that this connector is "shorted" to the case. Easy to check.

Bob: Exactly - no current **should** have been flowing. As I was driving home from my workshop garage after posting my question, I sort of came to the same conclusion. Since I was welding DCEP (electrode positive), the ground clamp was attached to the welding table, making the welding table negative. The welder sits on a steel shelf on the welding table. So the welder case was grounded. Does that make sense?

If it was shorted, as you and mickeyf are proposing, would the short not have been more obvious (like the connector arcing to the case) instead of just getting hot?


All the square wire is copper. As seen in the images, there are aluminum strips (buss bars?) interlinking the ground.

J Tiers: "Better to braze both wires to a plate, and screw the plate". I think that is a good idea. I should have some copper or brass that I can silver solder the wires to - had not considered doing so.

Thank you all for your responses.

[JoeLee]

Since you were not using this connector, no current should have have been flowing in it. But some (a lot) was. To me that means that this connector is "shorted" to the case. Easy to check.

Isn't the case a floating or isolated ground ?

JL.................

[J Tiers]

Shorting to the case probably would not do anything.

Most welders I have seen have the welding power isolated from the case ground, to prevent burning up external wiring or line cord. One contact to the case would probably not affect anything too much, so long as the work is not solidly grounded anywhere.

Who says there is no current flowing?

That connection is for higher current AC. It may be less total turns and thus lower voltage. The two wires may be a series connection in that case (with a few more turns for the higher voltage lower current connector), and the entire welding current may flow in them and the connection between them. A bad connection would then heat up that connection, and since it is right at the connector, could fry the insulator as we see happened..

The AC connections would be straight to the transformer, as shown, and the DC would go through a rectifier elsewhere in the unit. But wither way, the windings conduct current.

[Bob Engelhardt]

Isn't the case a floating or isolated ground ?

I thought so once, then was surprised to find that my mini-MIG's case was not. It sits on a rubber sheet on the steel cabinet. But, yeah, that was probably a bad conclusion on my part. Although aribert reported in his follow-up that his case had been accidentally grounded.

[Noitoen]

I once repaired a industrial high frequency car carpet plastic welder (it welded that small PVC mat wear protection by the pedals) which used high voltage vacuum tubes as the oscillator, some inductors and 2 square aluminium plates acting as a air dielectric capacitor. The connections to these plates was made by a 20 mm x 2 mm aluminium strip bolted to the plates by a 8 mm brass bolt. This was a high voltage capacitor and the fault was that, although the bolt was tight, it had formed a layer of oxide between these connections that it was completely isolated from each other. After cleaning and putting it back together with some neutral grease between them it came back to life.