Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>Good point Dr. R. The current ballast inductance is what Gerry was referring to (Zballast should include all current limiting inductance from source to tranny), so are you specifically referring to the variable voltage inductance which is in front of the current ballast on pigs (in other words, take that inductance into consideration?). Just trying to clarify the point since variacs can be used as both voltage and current control on pigs.
Take care, Bart Tesla list wrote:
Original poster: "resonance" <resonance@xxxxxxxxxxxx>When using a pri ballast on a pole xmfr, keep in mind the variac itself also acts as a partial ballast. It's inductance needs to be taken into consideration when designing your pri current limiting reactor.Dr. ResonanceHi Scott,Your ballast (on the primary is assumed) needs to be such as to limit the line current to whatever you chose. For example, if you are using 120V line, the ballast impedance needs to be 120V/Ip_rms. For 10amps (rms), the impedance would be 12 ohms. The corresponding inductance is:Lballast = Zballast / (2*pi*line_frequency)So for 12 ohms and 60Hz, Lballast would need to be 32 mH. Since the inductance is often hard to calculate for many geometries, it is often determined emperically. That is, put 120Vac across the inductor (ramped up slowly with a variac) and measure the AC current draw. This is the bottom line anyway, to get an inductance that will limit the current to a previously chosen limit. Be on the watch for saturation (current is no longer a linear function of voltage, but starts to go up faster than voltage).Gerry R.Original poster: "Scott Bogard" <teslas-intern@xxxxxxxxxxx> Hello all,I have a quandary, I am using a shorted MOT as ballast for my 6 and 4 MOT stacks, for my TC. I don't think I am getting the performance I should, and I think the ballast is the culpret. What other options do I have, and If I make a ballast, how do I determine the "optimum" inductance (I am limited on tools, so I don't have a tool to measure inductance). I don't have a variac, so It will need to withstand full power (120V 15-25A).Thanks a lot. Scott Bogard. _________________________________________________________________Get a FREE Web site, company branded e-mail and more from Microsoft Office Live! http://clk.atdmt.com/MRT/go/mcrssaub0050001411mrt/direct/01/