Re: Power protection toriods
Subject: Re: Power protection toriods
Date: Thu, 20 Jul 95 16:47:03 +0000
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Quoting Richard Quick:
> First, the choke is not designed to prevent "the high frequency
> capacitive discharge from getting back into the transformer", nor
> is it intended to attenuate kickback. The RF choke is simply the
> first line of defense to reduce the level of RF "hash" or "line
> noise" in what we wish to be a clean 60 cycle line. The effect-
> iveness of the RF choke in this function can be measured with a
> remote lead running to a resonate pickup coil placed outside of
> the inductive field of the coil system. The goal of the choke(s)
> is that RF line noise on the transformer side of the choke be
> somewhat lower than the line noise on the coil side.
> Second, no mention is made in the quoted passage of bypass
> capacitors used in combination with RF chokes. Bypass caps
> provide the second line of defense, and aid to further reduce the
> levels of RF noise in the 60 cycle lines connecting the trans-
> former to the oscillator tank circuit. Bypass capacitors should
> be placed across the line on the transformer side of the choke.
> Nothing but a properly set safety gap is going to attenuate
> kickback. Kickbacks can neatly pass thru RF chokes and over
> bypass caps as if they were nonexistent; they might help some,
> but not enough that I have ever noticed a drastic reduction in
> the force of a kickback. Leave the kickback to the safety gap.
I tried to say pretty much the same thing in a message yesterday
but my mail was bounced back.
Anyways, I'd like to dig a little deeper here. Can you describe
the construction of these chokes to me? It's my understanding
that these chokes are a single wire winding in series with each
of the high voltage line feeds. I can understand how a bifilar
choke or a monofilar choke parallel to the lines work because
there will be a phase angle difference between the conductors.
The RF energy builds a flux in the toroid that can pass energy
between the conductors that won't be canceled out because of the
difference in phase angle.
It's my impression that these chokes as we are using them do very
little filtering themselves but are a necessary part of the filter
system to shift the phase angle 90 deg and keep the bypass
capacitors (which ARE doing the filtering across the line) from
looking into the tank circuit caps and acting in parallel with them.
By the way, how does one calculate the inductance needed for a
choke like this in a given circuit?