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Ballast Buddy Bill Burns Billions of BTUs...
Guys,
Did some experiments on the pig - maybe this will help decide whether a
resistive or inductive ballast is "better", whatever that is...
Experiment:
Hooked up the pole pig. Jammed two lengths of #4 copper in each terminal,
and placed the ends about 3/4 inch apart or so. Hooked up my variable
ballast and two meters so I could measure the pig primary (low voltage side)
voltage, and current. The current was measured by measuring the voltage
produced across a 5 ft length of #6 copper wire in series with the pig.
Note that I also connected ONLY to one outer and the center pig lug - thus I
was applying 240 V to the 120 V lugs to get more output voltage. (again
this is just the setup - not implying this is a good idea or anything)
Here are the results:
Load Vshunt Vpig
1 0.018 18.4
2 0.037 14.4
3 0.056 12.1
4 0.077 12.0
5 0.096 10.5
6 0.113 10.4
8 0.152 10.6 (not sure why there is a plateau here)
10 0.188 9.5
12 0.226 8.4
14 0.263 9.4 (arc getting unsteady)
16 0.299 9.0 (arc very unsteady - wants to stretch)
The column "Load" indicates the number of cal-rod type stove heaters
connected in parallel. Each heater is approx 57.6 ohms.
I also "calibrated" the Vshunt value (via clamp-on ammeter) such that a
voltage of 0.233 volts was caused by a current of about 60 amps. Thus the
shunt resistance is about 3.88 mOhms.
So we can see that this arc has the typical negative resistance slope we've
all heard of. Here are the cold hard numbers to back it up!
So for example - at data point #14 - the pig has an effective impedance of
Z= v/i = 8.4 / (0.263*60/0.233) = 0.124 ohms. Not a good match for the
impedance of the ballast which is, at that point, something close to 4.1
ohms. This is one reason much energy is lost in the ballast! :)
I haven't measured the impedance of a pig powering a tesla coil, so I'm not
sure what could be said about that. Ideally it would look capacitive, with
a load component I suppose. Real numbers would be nice here.
There's been talk of resistive vs inductive ballasting. My impression is
that if you have a particular budget of, say, 70 amps to deal with, and your
ballast allows you to limit to that value, then it has done it's job. I
can't see a huge difference between a resistive vs inductive if the load
(pig) only gets 70 amps through it either way. Personally I don't mind the
electric meter spinning round and round faster with the resistive ballast.
I could run a 10 KW JL for an hour for something like $1. Thats cheap
entertainment!
Of course the resistive ballast gets hot, in my case it was dumping some
I^2*R = (0.299 * 60/0.233)^2 *(51.6/16) = 19118 watts! :) Yes it makes the
lights dim nicely. Might make winter coiling a bit nicer having all that
heat...
At the same time - while the resistive ballast is busy dumping 19118 watts
into the air - the pig is only converting 9.0* (0.299*60/0.233) = 692 watts
(assuming no phase angle -which is valid for a pig and an arc I think).
Kinda strange, eh?
Sometime soon I'll try the welder technique...
Comments appreciated! :) All I know is what I've done...
-Ballast Bill (the arcstarter)
(who is dying for his spool of #22 to arrive so he can finish his 2nd 6.5
inch secondary...)
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