I hope this is not in the wrong place or OT.If so I apologise.

I took home a arc welder yesterday, it worked for 5 minutes gave me a arc then died. I have a minor and I mean minor understanding of some electronics, and so I did a bit of probing on the transformer with my fluke meter, I found that the secondary winding is open circuit, this winding is in fact what I think is 2 series windings with a join between them. It is this join that has come apart, the windings are aluminum and look like they were soldered together before age corroded the solder etc apart.

I would like to re solder them and then re tape them, can someone tell me what varnish I would need to cover the winding ends with and what flux or solder type I need to achieve this and then what tape I would need to cover the windings once finished.
Please note I live in the UK so any items needed would by neccesity need to be through RS or such.

Thank you
Garry

 

If it used aluminum wiring normal solder won't work, you'll need to find some low melting point aluminum brazing rod or better yet come up with some sort of mechanical connection method such as a sawing off two "holes" of an electrical circuit breaker box neutral bus bar. Remember - tons of current in a welder's secondary wiring.

If it is the secondary circuit it's probably no more than 36 or 48V so common polyurethane varnish would serve well as an insulator, even that "liquid tape" you occasionally see would work if the winding doesn't get too hot. That "molds to itself" rubber tape might be a good option too.

http://www.suns-usa.com/show/g.jpg

3M™ Temflex™ Rubber Splicing Tape 2155

 

I was thinking of bolting the two together with possible a U shapped copper clamp or even using a couple of pop rivets after folding the two windings over each other, but I am reluctant to do so in case it was not sufficient, it is a 150A welder and I am unsure as too how much heat that winding etc would put out. I did toy with the idea of using some hi-bond polyimide adhesive tape rated at up too 250 degrees C and 4.8kv from RS just to cover over the windings, but would that be overkill.

I just want to be able to use the thing without too much hassle or cost but without compromising safety for the user.

Garry

 

I second your idea of a mechanical coupling. Aluminum soldering is not that easy, even with a proper solder. The solders are usually high in zinc and poor electrical conductors.

As for a mechanical coupling, how about a regular crimp union?

John

 

I would but they are flat windings not round cable.

 

A crimp fitting can be squished to form an oval before inserting the Al flat wire. The purpose of the flat wire is for winding efficiency. Since this coupling is external, maintaining that geometry is probably unimportant. The crimp simply gives you a work hardened copper coupling that doesn't need a clamp. Your clamp idea should work too, but I would not put pop rives through the Al wire, if that is what you were planning to do.

John

 

Why not John ?, does it change the current carrying capabilities or such. Could I put a Brass bolt or two through the copper clamp and the windings once clamped together, I really want to ensure it is secure.

 

Why not John ?, does it change the current carrying capabilities or such. Could I put a Brass bolt or two through the copper clamp and the windings once clamped together, I really want to ensure it is secure.

A pop rivet is likely to distort the connection and concentrate the contact area around it. Since the cross-section of the wire would be reduced by a hole in it, it might unnecessarily add resistance compared to a simple crimp.

Pop rivets are very nice fasteners and specialized pop rivets are used in airframe construction and other demanding applications. I assumed, perhaps mistakenly, that you were referring to a typical consumer pop rivet.

John

 

No john you were right in your assumption of my using a conventional rivet , I will try for the clamp first, hopefully there will be no contraction or expansion due to heat and or any electrolysis (if this is in fact a problem ) that would cause the nuts to undo.

I will see.

 

I'd go with a clamp or that bus bar I posted as it would likely be more compact, a rivet will only cause problems as will any sort of crimp connector.

 

Don't forget the anti-oxidant paste. Think of why we don't use aluminum house wiring any more.

 

I never did quite understand the whole aluminum wiring thing anyway, probably had something to do with the need for copper during wartime since, at the time, I think aluminum was more expensive.

 

The whole aluminum wiring thing was that too many houses burned to the ground due to oxidized splices in the wiring. Oxidized splices with wire nuts got hot with normal currents and ended up causing fires. The Anti-oxidizing past is supposed to eliminate the problem.

 

The oxidation factor was amplified by the contact of dissimilar metals setting up electrolysis as there was usually a mix of aluminum to copper contact in the equation at the circuit breakers and outlets. There are now replacement outlets and breakers that are marked as safe for Cu/Al, mainly because it's usually impractical to rewire an entire old house. I remember my grandparent's house actually having tube and knob wiring, it was obvious being exposed in the basement and was also probably used in the walls.

I keep a copy of the current NEC on my office bookshelf at all times and consult it regularly before I take anything on, I hold a lot of responsibility dealing with a huge commercial building occupied by almost 200 people during the day and, due to my status as not holding a full Journeyman's Commercial License, I'm far more subject to a spot inspection than most. For what I do, per the State law I'm legal, however under the City municipal code which supercedes it I'm not but over the years the head City inspector and I have never pressed the matter as he's seen my work many times and knows I'm quite capable of reading, understanding and following the NEC to the letter.

 

sounds as though your secondary conductors, having to carry 150 amps are fairly large.

I would hope you have access to a product called "Alumalloy" ........Magnificent, marvelous, priceless / pricey stuff @ $50 usd per pound. [ when I bought some several years ago ] Source available............gimmee a yell.

As long as you brush your aluminum clean, [ except cheap grades of die-cast ] and heat it with any applicable source of 728° F. either a soldering iron or gas microtorch, Alumalloy will give you an absolutely rock solid connection. A good grade of heat-shrink will serve for insulation.

It will even allow you to splice a necessary piece into your winding, in case circumstance has left it too short to splice otherwise.
In any case, be certain to place heatsinks on both sides of the repair, or otherwise protect undamaged parts.

 

They sell that exact product in sticks at welding shops here, even Harbor Freight carries it. Can't recall where I picked mine up, think it was on closeout at Home Depot.

At that melting temperature it's really just a solder that will stick to aluminum. In any case I'd use MAPP gas instead of common propane to apply it, and be darn sure the pieces you're bonding are very clean as in going over them with #400 sandpaper.

The thing is I don't trust solder on high amperage circuits, sometimes the difference between the solder alloy and the material to be bonded is enough for it to create hot spots.

 

If you are heating aluminum buss bar (your winding seems to be more like that than wire), you will need to provide some means of heat sinking on either side of your connection area during the soldering process. Aluminum conducts heat very well. Don't want that heat to travel to places it isn't wanted.

 

If you go with a mechanical type of connector, don't forget to retighten it after using it for a while. You'll be surprised how much it'll loosen, if the aluminum gets hot.

 

Well I used a 20mm earth clamp in the end, it worked and the welder is now up and running. So a good result all round and I am happy to have resurrected an old welder.

Thanks to all those who helped and suggested ways and means to bring the alien beast back to life. It is truly appreciated.