On 10/27/2013 12:54 AM, Jim Thomson wrote:
Date: Fri, 25 Oct 2013 05:38:56 +0000
From: "Fuqua, Bill L" <wlfuqu00@uky.edu>
To: Jim Garland <4cx250b@miamioh.edu>, "Amps@contesting.com"
<Amps@contesting.com>
Subject: Re: [Amps] HV fuses
This does not sound right. I assume you are saying that they are glass
fuses.
I suspect if you blow one in a HV powe rsupply it will shatter or explode into
pieces if
you have a reasonable value of filter capacitor. Do you have a data sheet on
these
fuses?
High voltage fuses can be glass or ceramic. Even the high voltage fuses
in power substations are often glass. The only ones I've seen were
about 4" in diameter 1/4" to 5/16ths " wall, and they appeared to be
about 16-18 inches long (Might have been 2 feet) . IIRC they had several
parallel elements and were packed with fine sand. The PS HV fuses had a
glass tube around a 1/4 to 5/16ths inch in diameter and were packed with
a very fine, white, quartz sand.
The engineers forgot to remove the shorting cables after we PM'd a sub.
those small, HV wires with about a #16 conductor vaporized so
violently there was not a sign of them left. The entire sub cabinet was
8' high X 12 ft wide X 6' deep were completely coated with a copper
film. The doors were about 3' wide , had an inch and a half formed edge
and were made of 1/8th inch steel. I was looking at the sub when it
blew. The center of those doors arched out between 1 and 2 feet.
It blew the fuses, but they remained in tact.
The cables feeding the subs were larger than 500 MCM, but I don't
remember the actual size.
Sure was loud, expensive, and embarrassing!
73
Roger (K8RI)
73
Bill wa4lav
## why would they explode ? Mine don’t. The 50 ohm glitch R LIMITS the
current..and the
HV fuse INTERRUPTS the fault current. BTW, you always put the HV fuse B4
the glitch R. Reason is, if the glitch was damaged, and dangling down onto
the chassis, you
want the HV fuse INBOARD of any glitch, so the fuse will open.
Yes, you can parallel em for more current..and you can also series em for
more HV.
You can also wire em series-parallel for more current + Voltage.
## another useful place to insert a HV fuse is between EITHER plate xfmr
secondary.....and the
FWB or FWD. Then if any B+ shorts in the filter caps, or any problems
inboard of the B+ fuse,
then you are still protected. Dirt cheap insurance. I have seen the AC HV
fuse blown open twice
and the B+ HV fuse blown several times... while de-bugging a new hb RF deck.
Later.... Jim VE7RF
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