# tesla tc plans

Posted on Feb 4, 2014

A PFC capacitor on the mains side can act as `current limiting` to some extent. Otherwise, use resistive or additional inductive ballast (a MOT in series with shorted secondary winding). Power factor correction (PFC) shifts the VA rating of the transformer closer to actual input and/or output watts, and reduces input current needed. Reduced current is a benefit as all your switches, relais`, fuse

boxes and so on can be smaller - without PFC they would have to stand twice or more the current. Additionally, I2*R losses in the wire resistances would be at least four times as high. For example a 400VA cos(phi)=0. 55 transformer takes in about 0. 55*400VA ~= 200W with and without a PFC, but without a PFC it will draw about 2A from a 200VAC line. With an exactly matching PFC the input current is just ~ 1A. The capacitors are non polar capacitors, and it seems like they are mostly oil filled wax-paper capacitors used with mains voltage motors. Method: First calculate transformer input impedance according to the values written on the transformer. For example 2. 2A @ 220V gives Z = 220V/2. 2A = 100 Ohm. Then calculate the PFC with C = 1/(wZ). At 50Hz, this would be 1/(2*pi* 50 Hz * 100 Ohm) = 1/(pi*10) * 10-3 F ~= 31 uF. You could also ask neon sign manufacturers if they have PFC caps for your particular transformer. Note: A fellow coiler pointed out that the above calculated 100% PFC may generally not give the optimum value for spark-gap coils, as the gap break rate and other things change the power factor. For a nice match it might be easier to try out different capacitances, or calculate by simulation. The only things that should/must be grounded to the mains grounding is the stuff on the mains side that you are going to touch (switches, dials, variac and so on). The HV secondary side of the transformer must not be...

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