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[Amps] Crowbars

Subject: [Amps] Crowbars
From: "John Lyles" <>
Date: Thu, 18 Sep 2008 16:43:36 -0600
List-post: <">>
Ya, Jim, we are still using mercury ignitrons. They are good to hold off 46 kV 
DC and they can take a 50,000 amp impulse through them, as long as it is damped 
and doesn't have follow-on power (the primary breaker must open fast). For 
higher voltage (80 kV) klystron power supplies, we use triggered spark gaps, 
sounds like a M80 or worse then they fire. These are 160 kJ capacitor banks 
that are charged. It  takes a pretty stout series resistor to be able to dump 
it across a capacitor bank with a crowbar. 

I am investigating using SCR crowbars up to 30 kV, to replace mercury, as there 
is always a possibility that the device will shatter and blow Hg vapor all over 
the place. Dynex makes some packaged solutions that use optically coupled 
thyristors. I learned about this from the guys at the LHC at CERN. 


> Message: 2
> Date: Wed, 17 Sep 2008 14:38:54 -0400
> From: "Jim Tonne" <>
> Subject: Re: [Amps] 3-500Z glitch resistor
> To: "Roger \(K8RI\)" <>,        <>
> Cc:,
> Message-ID: <005401c918f5$62c19e00$0302a8c0@jim177093b3dd9>
> Content-Type: text/plain; format=flowed; charset="iso-8859-1";
>       reply-type=original
> For very high-power systems (megawatt) I have seen an
> ignitron used.   "Hockey puck" SCRs for moderate power,
> (several kilowatts).  Stud-mounted SCRs for all else.
> - JimT

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