Re: [TCML] High Voltage design questions and considerations

[Frosty <frosty90@xxxxxxxxx>]

Hi,


> All pleasantness aside I started to have some concerns. First off, the
> reactance at 60Hz produced a resistance of approx 140KOhms. At 10KV the
> capacitor would draw 71mA. Well above the rating of 23mA of the transformer.
> This also explained the loud hum and 4 Amps of current being drawn by the
> transformer’s primary. Can the standard oil ignition transformer take this
> sort of punishment for very long?


I've not ever used any ignition transformers before, but from what I've seen
they are usually internally current limited by adding 'shunts' to the core
to give a large leakage inductance. Its possible that if you are pulling
more power than usual from the mains that your capacitor is resonating with
the leakage.



> Next I started to wonder where this 71mA was going. Was this purely
> reactance?
>

Yep, if you connect an ac source to an ideal capacitor, the capacitor draws
current, then when the signal changes polarity, discharges and then charges
in the other direction, no actual power is dissipated, just stored in the
capacitor. If the cap is resonant with the transformer, then the energy is
just 'shloshing' about between the transformers leakage inductance and the
capacitor.


>
> I am aware of the dual purpose of the capacitor in a Tesla coil. It needs
> to be able to not draw more current then the power supply can handle at 60Hz
> yet be of a decent value to properly tune the coil's primary to resonate
> with the secondary. BUT, does the 71mA in anyway go to charging the primary
> of the coil? Or is it merely burned off in reactance? This also got me to
> thinking. If indeed the 71mA is just the "Angel’s share" and has nothing to
> do with charging the Tesla Coil's primary, do we then need to insure that
> the power supply can deal with the reactance of the capacitor, the reactance
> of the primary, and only then use the rest of the power to transfer to the
> secondary of the Tesla Coil?
>

The primary coil has little effect on the mains frequency, its purpose is to
form a resonant circuit with the capacitor at a frequency equal to the
secondary's resonant frequency. But these oscilations only occur when the
spark-gap fires, and are caused by the energy stored in the charged
capacitor, the mains frequency from the transformer doesn't really come into
it, it merely charges up the capacitor for every 'bang'. Ideally this occurs
when the cap is fully charged, at this instant the current drawn from the
transformer would have fallen to 0. (With a static gap though, the firings
can be erratic , but the 50/60hz in the primary has little bearing on the
operation of the coil).


Cheers,
Jesse
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