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Re: Rotary Sparkgap


>Re: Current limited transformers
>	The current which is limited is the short-circuit
>current.  For example, a 12 kV, 60 ma transformer (if it
>really limited to 60 ma) would have an equivalent internal
>reactance of (12000/0.06) = 200,000 ohms.  The
>equivalent inductance would be about 530 henries (assuming
>no saturation effects), and for a resistive load the current
>would decrease with output voltage, reaching zero at infinite
>load resistance.  I started to write that the current would
>decrease linearly, but that is, of course, not true.
>	Anyhow, a capacitive load on the transformer changes
>matters dramatically.  For example, the 530 henry inductance
>calculated above would series resonate with an 0.0135 ufd
>capacitor, the output current could in principle greatly
>exceed 60 ma, the output voltage could (and indeed would) be
>much greater than 12 kV with no other load than the capacitor,
>and the transformer would probably short out.
>	More at some time when I can figure out some real
>numbers.
>Ed Phillips
>
Ed,
        I just ran a SPICE (Simulation Program with Integrated Circuit
Emphasis) analysis on a 7.5KV peak 60Hz sine wave generator, a 20K series
resistor, a 995H inductor and a 1 or 1000 ohm load resistor. I was trying to
simulate my 7.5KV 20ma xformer which measures 19K dcR. I got a current of
about 19.45xx ma no matter what load resistor I used. When I actually
measured the current, I got 0uA thru my multimeter! When I switched over to
using a load resistor and using my miltimeter as a voltmeter, I measured
20ma. I must conclude that 1: my understanding of my multimeter is wrong. 2:
my understanding of a shunt limited xformer is bad. 3: my understanding of
electronics/physics is bad. 4: all of the above ;)

                                jim