RMS (Re: Why do primaries get hot?)

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "davep by way of Terry Fritz <twftesla-at-qwest-dot-net>" <davep-at-quik-dot-com>

Tesla list wrote:
 
> Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<jimlux-at-earthlink-dot-net>
 
> Say you've got a 15/30 NST driving your TC.. That's in the area of 400W
> power.  Say 10% of that is dissipated in the primary losses, that's 40W.
> 40W would warm it up noticeably.
 
> The real question would be what is the RMS current (not average) through
> the primary.  Charging up a cap, and then discharging it through the
> primary, gives you fairly high currents.  That current gets squared,
> jacking up the RMS current more than you would think..

> Consider an example..

> 1 Amp continuous

> 10Amps, 10% duty cycle

> Same average current = 1Amp

> RMS of the latter, though, is 3 Amps... Sqrt((10^2) /10 )

	cf below...

> Consider Tesla coiling...

> 30 mA at 15 kV continuous vs

> say, 0.01 uF,253 uH (100 kHz)  pk current is around 100 Amps..
> Assume loaded Q is around 2, so current falls off to 37 Amps in 2 cycles,
> or 20 microseconds.  Assume we do this every 8 milliseconds (each half
> cycle, rounding to make math easier).. The duty cycle is roughly, then,
> 20/8000 or 1/400.

	Concur, sort of.
	I suggest that the use of 'duty cycle' can be iffy EXCEPT in
	pure pulse systems.  With resonant systems (all TC are, more or
	less) the quasi sinusoidal waveforms are EVERY where.

	(A nice, computing scope, capable of doing Real Power on the
	fly, or true RMS reading ammeter & voltmeter & power factor
	set up...)

	best
	dwp