A little update on my welder project

Something unpleasant that I discovered with my AC ammeter.

There is a lot more current going from the contactors to the terminals on the rectifier, than is going from the transformer (A1, B1, C1) to the rectifier. 60A per leg at 100 A welding current.

I think that I misunderstood current flows for my configuration. I will have to replace wires going from the rectifier to contactors, with something heavier or will use triple wire.

Everywhere else the currents are quite manageable for 10 gauge, 200C rated military hookup wire. (about 20 or so amps per wire at 100A welding current)

I think that I understand the issue.

Two currents are added, one from lower secondaries (A3, B3, C3) to upper secondaries (A1, B1, C1), plus the current for delta winding A1 to B2, B1 to C2, C1 to A2 -- all are conducted through connections (A1, B1, C1) to contactors.

I replaced the three overloaded 10 gauge wires with quadrupled 10 gauge wires (I have a big spool of military high temp hookup wire). That makes all currents quite manageable.

So, what I have by now is a finely working 200A stick welder.

Also, after looking at my currents coming in through the incoming 60A household garage circuit, it is clear to me that 200 amps is my "hard limit" and that bothering with allowing the welder to go up to 300 amps is not worth it at the time, unless I upgrade the garage circuit to 100A capacity at least. Not practical.

The 6 gauge incoming wires get quite warm under operation, but within their current rating.

If these wires are not bundled up and have some air flowing around them, I wouldn't be uncomfortable running approx 100A thru 10ga wire with 200C insulation - the NEC allows 90A for a single copper conductor with 200C insulation in free air.

Sounds right based on my experience with the input current of old Miller ABP welders. You'd want a 100A circuit for 300A output. Ned Simmons

Well, yes, sure, but there is other stuff next to it and I do not like things getting hot. If you wish, I want a lot of safety margin to compensate for my mistakes (which I do not know what they are). So I am not very comfortable with 200C stuff next to other wires (control and such).

Like I said, I have about 60 lbs of that 10 ga, 200C flexible hookup wire. I suspect that it is actually silver plated. So I could use a few extra feet.

There is a lot of air flowing around those wires indeed, the welder has a 0.11 HP exhaust fan.

Yep. Unless I find some clever way to compensate for low power factor, I am stuck with 200A. Realistically, it is not bad, Don's point about needing 300A for welding 0.25" aluminum notwithstanding.

Hey Iggy,

Best to use what are called "starter panel" contactors. These would be two contactors mounted side-by-side and have both an electrical and a mechanical interlock. Contactors that are multi-pole double throw (for your instance 3PDT) are prone to "welded contact" hangups, unless they use carbon (graphite) fixed contacts. The cost for new is probably pretty prohibitive, but do a google or ebay look. Another source would be an elevator company that is modernizing something from the 1950's or 60's or early 70's. (Make sure they believe what it is you want to use it for.)

Take care.

Brian Laws>I am working on converting an old Hobart CyberTig into a welder/plasma

I looked it up, it is "nickel cored", whatever that means. Maybe it is made of nickel and not copper.

Brian, do you mean that the contactors (of which I have five) that I used for "dynamic rewiring" of the transformer, are not suitable? That would be upsetting, as I paid $10 for each.

Or did I misunderstand you and perhaps you referred to the 4pdt relay that would control coils of these contactors? If so, that relay would carry a very small current, way below its capacity. Maybe 1A in total at most.

Just one more note, they are supposed to be switched WITHOUT load, load is to be applied later.

HMMM if much of that 60 pounds is nickel it could be cost effective to sell it.

Hell even if it's just plated copper it'd be worthwhile to sell. Copper is gangbusters expensive these days.

Tim

-- Deep Fryer: a very philosophical monk. Website:

XXXXXXXXXXXXXXXX Hey again Iggy,

Well, now I'm confused. I took it that these would be "contactors" versus "relays", and as such would be switching and carrying welding lead currents in the 100 plus amp range.

No???

Brian Lawson, Bothwell, Ontario..

The contactors will be switching welding current.

Switching events will happen without any load (with welding voltage turned off).

Note that I have another contactor that switches incoming 3 phase power on, which happens ONLY when I start welding, that's how I can switch these 5 contactors without any load or voltage present during switching.

You see, I redid this welder. It used to always carry 3 phase electricity in its main transformer, even when idle. Which was kind of expensive, as the tramsformer was always warm because of it. It was getting 110v power for controls from one of the legs.

I changed that. Now I have a separate 120V control circuit, powered by a wall outlet. It turns on the 3 phase mains only when needed.

Getting back to the "5 rewiring contactors", the coils of these 5 contactors will be controlled by a double throw relay, so that either one set of coils, or another, but never both, are energized.

Sorry for being so lengthy.

Are you sure it's not nickel *coated* copper? That's pretty common for high temperature wire. Of course neither would help if you're concerned with hot conductors affecting other stuff.

Ned Simmons

I experimentally listed 40 ft of that 10 ga wire on ebay for 0.01 starting price, $5 shipping. I believe that it is made of nickel. I cut a piece with pliers and looked at the cut, there is no red coppery color see on the cut.

See picture of the cut at

(I do not want to give ebay auction details to avoid "commercializing" this thread).

Here's the whole specification:

Technical Characteristics ( ILs ) 6145-01-058-4195 MRC Requirement Reply AAGR CROSS-SECTIONAL SHAPE STYLE 2 TWIST ABJH TEMP RATING 200.0 DEG CELSIUS ADVN CROSS-SECTIONAL HEIGHT 0.316 INCHES NOMINAL ADWH CROSS-SECTIONAL WIDTH 0.316 INCHES NOMINAL AMQN CONDUCTOR QUANTITY 4 AWXS COLOR CODING DOCUMENT ST5M1298-76301 SPECIFICATION BLNZ STRAND QUANTITY PER CONDUCTOR 37 ALL CONDUCTORS CXCW CONDUCTOR FORM STRANDED ALL CONDUCTORS CXDC ROUND CONDUCTOR SIZE 10 AWG ALL CONDUCTORS CXDG STRAND AWG SIZE PER CONDUCTOR 26 ALL CONDUCTORS CXDQ CONDUCTOR ARRANGEMENT AND QUANTITY 1 TWISTED TOGETHER W/NO OUTER COVERING CXFK VOLTAGE RATING 600.0 MAXIMUM ROOT MEAN SQUARE (RMS) OPERATING VOLTAGE ALL CONDUCTORS FEAT SPECIAL FEATURES OPTIONAL IDENTIFICATION METHOD 2 APPLIES HUES COLOR BROWN 1ST POSITION COVER ALL CONDUCTORS

SFTT SURFACE TREATMENT NICKEL CORE CONDUCTOR ALL CONDUCTORS Look here ===> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

SR-1 MANUFACTURERS CODE 81349 SR-1 NON-DEFINITIVE GOVERNMENT SPEC/STD REFERENCE MIL-C-27500 SR-1 MANUFACTURERS CODE 81349 SR-1 DEFINITIVE GOVERNMENT SPEC/STD REFERENCE M27500B10TA4U00 STDC SURFACE TREATMENT DOCUMENT AND CLASSIFICATION ASTM B355 ASSN STD SINGLE TREATMENT RESPONSE CORE CONDUCTOR ALL CONDUCTORS ZZZW DEPARTURE FROM CITED DOCUMENT AS MODIFIED BY BASIC BODY COLOR PER CONDUCTOR _________________________________________________________________

I don't see any mention of copper, so would assume it's solid nickel. That's also not too unusual, though I think more commonly seen with insulation good for temps even higher than 200C.

Ned Simmons

Hmm, seems rather unconductive, no *wonder* it's 200C or more.. LOL

If it is indeed nickel, I may want a pound or two of that if you'd be willing to part with it cheap. Or hell, since you've got so much, make it 5 or 10 pounds, I've got a friend who would love to have some nickeley bits.

Tim

Ian, what would happen if the contactors create an accidental short? Would the circuit breakers simply open? I am not trying to argue, I just want to understand the ramifications.

You have an interlock problem indeed. The following suggestions would probably not be suitable for commercial use or if personal safety was involved.

DONT use a single changeover relay to operate your existing contactors.

Your PLC or control circuit needs to, in sequance, 1. open the main contactor and check for *any* output. Abort with an error light if there is any output. 2. open all the rewiring contactors. 3. close the main contactor and check for *any* output. Abort with an error light if there is any output. 4. open the main contactor. 5. close one set of rewiring contactors. 6. close the main contactor.

Unless you have auxillary contacts on all the contactors that do not operate if the main contacts are welded this would be the best you could do. If you are useing relays to control the contactors, you should use two single pole changeover relays each of which disconnects the feed to other one's coil at the same time as it operates its contactors. This interlocks against PLC crashes of the all outputsd on variety. It would be preferable to have the feed to each set of contacters coils also through all the normally closed auxillary contacts (assuming these dont close if the main contacts are stuck closed) in series of the other set so that if one is stuck the other set cannot be engaged. I doubt it is worth interlocking it so the main contactor has to be open before you can change the seleted rewiring contactors.

You could tell if it is copper or nickel by measuring the voltage drop over a few feet of it, with a known current flowing. You can then calculate the resistivity of the metal from the length and area and the measured resistance. You might also be able to see if there is copper in it by just cutting off the end and looking at it with a magnifier to see if it is copper-coloured.

If it is nickel then it would be much less useful for wiring up welders I think. I doubt it is solid nickel though.

Chris

The exact consequences of a short on the secondary of a transformer can vary considerably. The circuit breakers are sized to protect the supply wiring not the load. In any case when they operate with an inductive load there will be an extremely large transient which *may* damage any control electronics fed from a seperate transformer or a different limb of this one. Many smaller transformers have non-resettable thermal fuses buried in against or under the primary winding. I dont know how common this sort of protection is on larger and/or three phase transformers but in any case there is a risk of the primary going open circuit. If the short is slightly higher resistance, you can easily get enough external heat to cause a fire *WITHOUT* tripping the breaker or blowing any thermal fuse present in the transformer (large thermal mass). Its a welder, it can probably reduce half whats in the case to molten slag before it trips the breaker. Why risk it?

Bruce Bergman has covered the case where the main breakers fail to clear the fault.