[Amps] Fuses

[Jim Thomson]

Date: Sat, 8 Jan 2011 19:36:03 -0500
From: "Carl" <km1h at jeremy.mv.com>
Subject: Re: [Amps] Fuses
To: "James R Carr" <n7fcf at hctc.com>, "Roger \(K8RI\)"
<sub1 at rogerhalstead.com>, <amps at contesting.com>
Message-ID: <01b501cbaf95$341b1890$6401a8c0 at DAVES>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
reply-type=original

Can you two get back to earth and keep it somewhat relative to ham amps in 
the under 20KW range (-;

Carl
KM1H

King carl

##  the basic concepts are still the same.. 'slightly'  larger scale.     Same problems too....
huge back EMF, when opening off a fully loaded plate xfmr..esp if on rtty/fm. 

##  Now Rich Measures, and other's will say the HV fuse in the B+ line is not required..and
that the 'follow on'  current can easily be shut down with the fuses/breaker  in the 240 vac line,
[or some kind of current sense lead scheme that open's off the main contactor].  

##  If a HV fuse is used in the B+ line..just prior to the 50 ohm glitch R...  and a B+  to chassis 
arc occurs  [or anode to a  chassis grnded grid]  the 50 ohm glitch R ...LIMITS the fault current
to a safe value.   The HV fuse  INTERRUPTS  the fault current..a split second later.  The 240 vac
breaker/ fuses in the primary of the plate xfmr will never open.   Ok, now you don't have the back
EMF problem any more.    I also use a 2nd HV  fuse in one leg of the plate xfmr sec..[ either leg].
Same deal, if the HV-AC fuse blows open,  no back emf on the 240 vac primary side of plate xfmr,
FWB is still protected, and so is the plate xfmr.   I  still use big, fused mov's directly across the pri 
of  the plate xfmr.. and also from each side of the plate xfmr hot leg to neutral...also fused.  And
more movs  directly across all contacts  on the contactor.   

later... Jim  VE7RF