Jim,
You could make a crowbar clamp circuit for it. The only problem is a
straight crowbar will blow a fuse. Lets suppose you pick up a small
voltage across a resistor and place it across a 5-6 volt zener. When the
zener fires, it will put a voltage on an opto-isolator. The opto in turn
will hook to the base of a large transistor. The transistors collector
would go to B+ and the emitter to ground in a clamp to blow a fuse.
However, if it fired a relays coil with the collector going to say a 12-24
Vdc coil and the emitter to ground, I think would work. The wire in the
transformer, I dont think will fuse that quick. The reason being is it
should be wound at least for 750 cir. mils. per ampere for ICAS. For a CCS
transformer, 1000-1200 cir. mils per ampere. A fuse wire is way smaller
than this and way under the conduit rating of a wire. At 500 cir. mils per
ampere, that's about X2 the current rating of a conduit rating. It dont
hurt them for a temporary overload like this. Hardly ever would a shorted
rectifier, capacitor, or even a tube, burn out a winding because the line
fuse opens before any damage. The rectifiers backwards action your talking
about is the same thing, acting like a short.
Will
On Mon, 7 Feb 2005 08:21:57 -0600, Jim Isbell, W5JAI
<jim.isbell@gmail.com> wrote:
Well, my concern is that by the time a relay clicks the secondary is
already gone. Same with a fuse.
On Mon, 07 Feb 2005 08:16:27 -0500, Will Matney <craxd1@ezwv.com> wrote:
On Sun, 6 Feb 2005 16:56:02 -0600, Jim Isbell, W5JAI
<jim.isbell@gmail.com> wrote:
> I am in the final steps of designing and building a linear to
> supplement my station om 160 thru 10 Meters. The chassis is being
> built at this time and I will soon be mounting parts.
>
> It is a single 4-1000A running GG with a plate supply that is
> switchable in steps from 3KV to 6KV. The transformer is a 12KVA
> transformer which will obviously be able to handle 2 amps on the
> secondary winding. I will be using a pair of VT-42A Mercury vapor
> rectifiers.
>
> Yes, I know there are "better" ways of doing it, but none would be
> prettier. This is to be an amp capable of full amateur legal limit
> that will be a JOY TO WATCH. not just an appliance.
>
> OK, the questions.
>
> I have heard from very good authority that the mercury vapor
> rectifiers might short on occasion and that the secondary of my plate
> transformer would probably "fuse" just as fast (or even faster) as a
> FB 1 amp fuse in the plate lead.
>
Wouldn't a current limiting resistor between the transformer and
rectifier
be prudent?
> The first question. If I don't need a fuse any bigger than 1/2 amp
> and the secondary is rated for 2 amps. Will I be safe from blowing
> the transformer?
>
The fuse has the be big enough to carry the max. plate current, what
will
it be?
> The second question. If the above answer is NO, is there any circuit
> I can build that will protect the transformer?
>
Some type of current limiter. A series resistor could be all that's
needed
or sense the voltage across one and when it's high enough, the circuit
would close a relay opening the primary leads.
> I would sure hate to leave off the glow of a pair of VT-42As to light
> the inside of the chassis around my 4-1000A which will be behind a
> window. This is art now, not engineering, and I sure like that purple
> glow.
>
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