Sunday, September 16, 2018

Basic blocking and tackling, electric fences

Sixteen seconds.  Testing an electric fence with a weed cutter.

One of the best electricians I ever worked with is named Javier.

We had a spot weld gun that had a top-end of 15.5 thousand amps.  Since the weld schedule started at 13 thousand amps and we added one amp for every weld to account for cap wear, the gun ran into problems after two or three thousand welds.

The issue is that the transformer ran into saturation problems.  That means that when the controller modified the input to ask for one more amp, the output was less than the "requested" additional amp.

In point of fact, any weld engineer who has a system where the "degrade" mode is to run on the stepper is never comfortable unless the "top end" is 2X the base amperage.

Since these guns were asked to make 12-to-15 welds per job and we made over five hundred jobs per shift, you can see we had a problem.

One way to squeeze more capability out of your weld gun is to "double jumper" it.  That is, where the design calls for one jumper (a REALLY thick wire) you install two.  Jumpers are cheap.  That is what we decided to try.

Javier and his crew worked third shift.  They had just enough time to do the work.  They checked their work and the current meter told them they had bumped the gun from 15.5 thousand amps to 32 thousand amps for a 100% shot.  They high-fived and started production at 5:30 in the morning.

Two hours later the weld checker wandered over and checked his first job of the day and there were no welds!  What happened?

If you think of a weld gun in the simplest possible terms, it is your thumb and index finger pinching together.  In their haste, Javier and his crew had run both sides of the transformer to the same finger.  There was NO current passing through the metal that was to be welded.  The current went up through the double jumpers on one side and down through the double jumpers on the other.

The electricians had checked their work but they made the mistake of putting the current meter around the jumpers and not the arm of the weld gun.

Electric fences
I installed the lightning choke and air-gap device.

I replaced the main feed to the fence.  The original feed was 17 gauge (0.95 sq-mm) steel with two splices.  I replaced it with a single run of 14 gauge (2.0 sq-mm).

Coat-hanger wrap connections were replaced with double cable clamp connections.

The final check was to turn on the fence and go to the nethermost reaches.  There, I took my Canadian Thistle weeder and I shorted across the hot wire and the woven wire fence behind it.

It made a satisfying "Snap!"


  1. I gotta say that for all the weld schedules I have programmed, I never once took into consideration any of the factors you mentioned.
    Please don't take that wrong.
    It just goes to show how lucky I was.
    It seems these days with tip dressers, nobody wants to use steppers.

    1. Hi Ed:

      Thanks for reading and thanks for commenting.

      Tip dressers are a superior technology.

      I wonder how long it will be before the cost of cutters comes down to a Lee Precision shell holder

      I don't see that common cutters are any more complex or are of superior material to a Lee Precision shell holder. Don't know why they run 10X-to-20X the price.



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