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Re: [TCML] Terry filters

On Dec 31, 2007, at 7:56 PM, Lau, Gary wrote:

Hi Bill:

There are two components to the power dissipated in the resistors of a Terry filter. The actual power dissipated in the resistors is the sum of two things.

First is the P=I*I*R from the NST current through the resistors. Note that the actual RMS NST secondary current can actually be MUCH higher than the faceplate current rating!

I've never measured that, but I suppose it must be possible if there is significant resonant voltage rise on the NST output.

A less obvious component has to do with the fact that each time the gap discharges the main cap through the primary, it also discharges the caps in the Terry filter through the resistors in the Terry filter. Unlike the energy in the main cap, the energy in the TF caps is just wasted as heat in the resistors, and is BPS-dependant.

But those caps are also being charged from the same source - the NST secondary. So ultimately, it still comes down to how much RMS current is being delivered from the NST. You can't dissipate more power in those resistors than the NST is delivering. I ought to put a mechanical milliammeter in series with an NST secondary some time, I've never bothered.

It's this that sets an upper limit on how large a cap we want to use in the TF.

Regards, Gary Lau

-----Original Message-----
From: tesla-bounces@xxxxxxxxxx [mailto:tesla-bounces@xxxxxxxxxx] On
Behalf Of Bill Lemieux
Sent: Monday, December 31, 2007 7:31 PM
To: Tesla Coil Mailing List
Subject: Re: [TCML] Terry filters

On Dec 30, 2007, at 8:53 PM, bartb wrote:

A Terry Filter can dissipate about 100 to 200 watts easily.

Each gap conduction must be added. For a Terry Filter or similar,
consider the following:

P = 2 x 0.5 x C x V^2 x BPS

Now do the math.

You'll find it is still be low comparatively, but not quite as low
as you are thinking.

I must be missing something.  How can the current be any higher than
feeding a dead short?
At 120mA continuous, I'm assuming not just intermittent gap
conductions, but actually more
as if the gap were shorting the transformer 100% duty cycle.

(unless you're running a resonant cap, something I'll never do, as I
don't care to risk
my hard-to-replace 120mA NST)

Take care,
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