Re: A Ballast Mystery

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "J. B. Weazle McCreath by way of Terry Fritz <twftesla-at-qwest-dot-net>" <weazle-at-hurontel.on.ca>


At 12:44 PM 05/10/02 -0600, you wrote:

>Original poster: "Gregory Hunter by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <ghunter31014-at-yahoo-dot-com>
>
>OK List Gurus,
>
>This is the common setup with the welder primary and
>pole xfmr LV winding in series.
>
>1) with the welding leads OPEN, the pole xfmer HV
>horns OPEN, and the shunts fully inserted, the 240v
>current was about 0.15 Amp.  No surprise there.
>
>2) with the welding leads OPEN, and the pole xfmr
>horns SHORTED together, the 240v current was about
>5.5 Amps. (???)
>
>3) with the welding leads OPEN, and the pole xfmer
>horns SHORTED out with an ammeter/DMM, the 11.5KV
>current was 0.12 Amp.  Power-wise, 240v at 5.5A is
>pretty darn close to 11.5KV at 120ma. Still though,
>how is the current going up?  Why don't the open 
>welder leads restrict the 240v current to 0.15A?
>
>4) with the welding leads SHORTED, the shunts fully
>inserted, and the pole xfmr horns SHORTED with a DMM,
>I got 460ma from the 11.5KV horns. I'm sure the 240v
>current is too high to safely measure with my 10A max
>DMM.
>
>I'm OK with items 1 & 4.  Items 2 & 3 have me stumped.
>How can adding the inductance of the pole xfmr in
>series with the unloaded welder cause the current to
>go up?  If anything, it should go down!  Thoughtful
>analysis, educated guesses, and half-baked opinions
>are all equally welcome.
>
>Regards,
>
>Gregory R. Hunter
>

Hello Greg,

Items 2 and 3 sound perfectly normal to me.  With the high voltage
terminals of the PDT shorted, it definately will draw more primary
current than when they are open circuit, regardless of whether or
not the welder's secondary is shorted.  If you find that the jump
in current is too great when you do short the welder leads, even
with the shunt at various positions, try putting a high wattage,
low resistance load like a water heater element on the welder's
leads rather than shorting them directly.

73, Weazle, VE3EAR/VE3WZL
G-1#1214

Listening: 147.030+ and 442.075+
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