fuses, etc.

To: tesla-at-poodle.pupman-dot-com
Subject: fuses, etc.
From: Tesla List <tesla-at-stic-dot-net>
Date: Tue, 20 May 1997 23:53:58 -0500
Approved: tesla-at-stic-dot-net
Subject:  fuses, etc.
  Date:   Tue, 20 May 97 11:39:39 EDT
  From:   pierson-at-ggone.ENET.dec-dot-com
    To:   tesla-at-pupman-dot-com        
    CC:   pierson-at-ggone.ENET.dec-dot-com


[i'm hand rewrapping these...]

>   But today I burned out half of a very nice TransCo unit, and I'm not
>certain how.  I had it directly connected to a rotary spark gap, running
>flat out to check if any of the electrodes were missing.
        .....

>   Deepening the mystery, however, is this (and I'm sure this is an easy
>question, given the experience on the list.)  A 15,000 V:120 V
>transformer which puts out 30 mA should ideally require 3.75 A input, but
>because obviously no transformer is ideal, the TransCo is rated 4.12 A
>input.

>Doesn't this mean that it requires 4.12 A input to output 30 mA?  I ask
>this because I put a 4 Amp fuse
        Fuses are wonderful things.  Like anything else, they have
        characteristics.  A typical 4A fuse will carry 4 amp
        indefinitely.  How long it will take to blow at what current
        is (when fully defined) a graph that takes a page, and has
        footnotes.  And a SEPARATE graph for normal blow, slow blow,
        fast blow, etc, etc...
        [There used to be a standing joke in power transistor work
        that a power transitor was an expensive device (and they were,
        too) that WOULD blow EVERY time, just to protect the 10 cent
        fuse.  8)>>]

        It JUST so happens i have a fuse catalog here: 3ag, normal blow,
        will carry 4.5A indefinitely, 4.7 A for 10 seconds, etc....

>in the input line, thinking to limit the output at something less than
>30 mA.  I thought that this was smart, but either there is some other
>method of burning out other than exceeding the current limit,
        Lots of ways to take down a transformer.  Overcurrent
        for short time, over current for long time, over voltage.
        (And i'm likely missing some...).

>the RSG allows very large intermittent currents too short in duration
>to blow the fuse, or I need to think about this much harder.
        The 4A i mentioned (may not be wot U had) is rated at 80A
        for 0.01S....

        My GUESS is that there was an overvoltage that killed it, from
        switching the secondary 'fast'.  Was the safety gap in place?
        Any other protective gear?

>As an aside, the burned side can still generate a really small spark
>when grounded to the case.  Is it truly burned out, or is this maybe
>a case of the carbon arcing I've read about (that can be fixed by
>baking in the oven)?
        If it makes any output, its still alive, at least somewhot.
        Could be blown open connection, which is leaking current to
        the terminal, could be carbon track inside which is limiting
        the output.  Others here can speak MUCH better to the repair
        odds than i....

        regards
        dwp