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Subject: Re: Spot Welder
Date: Jun 06, 8:41 am
Poster: Richard Hull

On Jun 06, 8:41 am, Richard Hull wrote:

>Care to tell us what capacitance/voltage/energy values are used for spot welding Rich? Know what kind of electrodes to use? Probably a good topic for rec.crafts.metalworking.

Scott's questions will be answered below, but first............

I finally tore into the spot welder last night and found that it was robbed of the three key tubes. the large mercury thyratron NL760 and the two smaller ones 5557's. I had one 5557 on hand and an FG-17 which is supposedly a good sub. So that is solved, but I had to use a larger FG5545 to sub for the 760. It will work, I am sure, but the case won't close over it. So, I have a nice want list for the next hamfest and its multiple vacuum tube vendors. The welder also had a blown 50k ohm 40 watt resistor which I replaced with a 50K 50W job I had in my stash at the lab.

I know, I know, SCRs are the way to go, but there is something about that blue, humming glow of those thyratrons sweating beads of mercury into their hollow state device bodies that is pleasing to the eye and soul. Plus, they are far more robust than any SCR can ever hope to be.

This thing was really built the the proverbial brick ---- -----! Bulky, heavy, lots O' breathing room. A typical example of a 1950's overkill and over engineered marvel. It is as robust today as when built back then. Unlike modern gear, this unit had the typical large, clear, schematic pasted neatly into the back cover. Without it, I am sure all would have been lost.

The 2 discharge capacitors inside are 28uf units rated at 440 volts. The front knob which selects the discharge range will select 14, 28 or 56ufd.(using the normal in series, one only and parallel arrangements. As the one is used, for 28ufd, I assume this thing probably uses about 400 volts on the caps to discharge into the large output pulse transformer. The welder is a 60 amp unit. The input to the pulse xfrmer primary is selectable to parallel connection or series. The output of this transformer is center tapped and you can hook the handpiece to use half the secondary or the whole thing, as needed. What a tank!

I will have to hand craft the hand piece and I think about 4 feet of soft and flexible #4 welding cable would be fine for its connection to the welder.

The contacts for welding, as I have posted before on this list, are a special copper, beryllium, chrome bronze alloy and can be picked up in a number of forms and shapes from most good, big city welding supply houses.

I'll keep you posted on the results of the first tests.

Richard Hull