Re: [TCML] Terry Filter for OBIT/ Resistor Ratings

[Gary Lau <glau1024@xxxxxxxxx>]

Terry designed the filter to be used in a wide variety of applications.
Indeed, if using a low-powered NST, 100W is overkill.  Note that the figure
you calculated is for the sum of both resistors.

I use a 15/60 NST with two 1600 Ohm  130W ('cause that's what I found)
resistors.  But while it may seem that the power would be .06*.06*1600=5.8W
each, they actually get painfully hot.  I'm sure they're nowhere near 130W
(which would literally be smoking), but you do want some headroom ;-) in the
rating.

Using a 100W resistor will give you room to grow, but if that's unlikely,
you could probably use a lower-power rating.  Just beware that part of the
reason to use a high power rating is that the resistor must be able to
withstand end-to-end voltage spikes on the order of the NST rating, and this
is why metal-cased resistors should not be used.  Physically long ceramic
resistors are better able to stand off high voltages.

Regards, Gary Lau
MA, USA

On Tue, Jul 20, 2010 at 4:11 PM, <vatercox@xxxxxxx> wrote:

> Dear List,
> I have an 8kV, 18 mA OBIT for which a Terry Filter is to be constructed.
> Most if not all coilers suggest two 100 watt, 1K resistors for the pass
> resistors in the filter.
>
> Noting that 0.018 Amps x 0.018 Amps x 2000 Ohms = 0.648 Watts, would it be
> feasible to reduce the resistor power rating to say, 10 watts when using a
> transformer as small as this?
>
> Why is the suggested resistor power rating so high?
>
> Jolyon Francis Vater Cox
>
>
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