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Re: Ballasting a Pole Pig (Revisited)



Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Colin,

Thats a good data point. I wish I knew more about materials used in cores and what the physics are with respect to magnitization current. I can only speak for my core in regards to its VI curve. It is very linear (constant L) once the excitation voltage is higher than 30Vac. With low exitation voltage, the inductive reactance (associated with the slope of the VI curve) is very high. Certainly one can take the "120mH" reading that prompted this thread and easily realize that it wont allow 30amps at 240Vac.

Gerry R.


Original poster: "colin heath" <colin.heath4@xxxxxxxxxxxxx>

Hi All,
I realise I am vastly simplifying this discussion but here it is. I used a simple LCR meter to check my ballast Inductance on spark gap coils running static, async and sync gaps and although the meter does not have enough power to magnetize core correctly and many other probs I don't understand! It has always yielded close results with regards to what current the coil should have pulled with that inductance. I also used the meter to read values when setting up for the correct primary charging circuit frequency. So why this system worked I don't know, however it did and continues to. I must state I always used air gapped E-I cores (mot cores and others)
Cheers
Colin

----- Original Message ----- From: "Tesla list" <tesla@xxxxxxxxxx>
To: <tesla@xxxxxxxxxx>
Sent: Saturday, January 21, 2006 1:23 PM
Subject: Re: Ballasting a Pole Pig (Revisited)


Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Steve,

I think Dr R said that he measured the inductance with a LC meter and that is probably the source of the high inductance. His physical parameters show an inductance more in the range that one would expect for the job. My program shows 20 amps with 240 volts applied across the ballast (PIG and TC removed from the equation). The slope of the ballast VI curve is very shallow when excited at the low levels of a meter and I can believe the erroneously high measurements.

You are right about the RSG affecting the current draw, especially with a SRSG. The inductive kick of the ballast can allow for higher voltages on the Cp (LTR) then what is obtainable with steadystate draw when firing after peak.

I also believe taking taking the XC into account when determining the ballast XL will get you closer to the real answer. My spice has shown that one can draw upto maybe 2X+ what the ballast is suppose to limit at not considering the XC. Taking just the XC and XL into account should give you the steady state current with no SG.

Gerry R


Original poster: Steve Conner <steve@xxxxxxxxxxxx>

I don't think it's as simple as "Reflected Xc" vs "No reflected Xc". Anyone who has played with a sync rotary knows that the line current, power factor, and spark output can be varied over a huge range by altering the gap phasing, so it's obvious that whatever method you use to size the ballast must take the spark gap behaviour into account, not just the primary capacitor.

If you want to accurately predict how much power/current a given coil will draw through a given ballast, you need to work through pages of differential equations that include the discontinuities at spark gap firing times, or just simulate the whole coil system using PSpice. Richie Burnett shows how to do that on his site.

With an async rotary running at high break rate, it may be somewhat easier, and you could probably take half the line voltage divided by the ballast impedance as a reasonable assumption for the current.

FWIW, I don't believe the 120mH figure either :-P I'd guess that Dr. R's ballast is saturating. As a rule of thumb, if a ballast has fewer turns than a transformer of the same core area and a winding voltage equal to the line voltage you are running off, it is liable to saturate. (but not guaranteed to)

Steve Conner
http://www.scopeboy.com/

Tesla list <tesla@xxxxxxxxxx> wrote:
Original poster: "Jim Mora"

Gerry,

Thanks for figuring out the "reflected XC" issue. Do others concur with this
reasoning? Must this XC on the transformer output always be taken into
account when adding an inductive ballast in the primary of a disruptive
coil? I was baffled by the XL=120mh and 30 amps as well.