Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx> Hi Chip, Tesla list wrote:
Original poster: "Chip Ford" <chipford@xxxxxxxxxxxx>Now, can we talk about the ballast for a minute. The function of this and how to wire it in is a little fuzzy. I am thinking it will be wired in series with the with the primary curcuit. I have spent most of my "Tesla Time" working with NST. I have never used a "Ballast" with one. I am trying to understand what is going on with it. What I am getting so far is that this "Load" somehow keeps from over-volting things. I don't know how to figure what to use? I know where to get several different sizes of "Larger transformers" reasonabley priced, I just don't know what to look for yet nor what it's function is in a TC. I know that in an old automotive breaker point system, the ballast was a resistor used to keep from over-heating/over-volting the coil. I think that the "Ballast" in a fluoresent light is a Step-up transformer used to make the plasma in the bulb. I know that "Ballast" can also be wieght added to a ship or a race car for example. I'm sure someone out there will straighten me out on this stuff.
The addition of a ballast to our coils is the art of limiting current. The ballast can be resistive, inductive, capacitive, or a combination of these. The ballast can be hooked inline with the transformers LV winding or even be installed on the HV side. As mentioned, a resistor (big for a pig) can be used, but the voltage drop across the resistor is a linear function of the current through the resistor and the heat created by this current is a big loss. Inductive or capacitive ballasting is preferred and usually inductive ballasting is the choice because there are devices that work great for this purpose. The most common inductive ballasting is the use of a Welder, a large variac, and even homebrew inductors. The Welder is usually the best choice (as opposed to a variac) because you'll get smoother operation and better control over the entire range of current, where a variac is a little erratic (both will work, but the variac will see more damage over time to the brushes, especially at high powers).
As far as why a pig needs a ballast in the first place: Well, pigs can draw massive currents under short circuit conditions. Distribution transformers will have a percent impedance value. This value will determine how much current could be drawn from your mains during a short circuit event. My pig indicates a value of 1.9% impedance, so 1/1.9% = capable of drawing 53 times it's rated current or 2200A during a short circuit. That kind of draw would likely take out your house electrical panel, cause a fire, or even do the same to other houses in your area. Yes, a coil could run without the ballast, but it's a "very" bad idea. Limit the current and protect everything before the transformer and be sure to install a dedicated breaker for the line to the pig.
Take care, Bart