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Cu wire fusing amps ?

Discussion in 'Electronic Design' started by Phil Allison, Jul 18, 2013.

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  1. Phil Allison

    Phil Allison Guest

    ** Been trying to test common fuse wire for ability to handle inrush surge

    Particularly interested in 0.5mm dia tinned copper wire and current pulses
    of half cycle duration - same conditions as for non repetitive surges in
    power diodes and SCRs.

    I figure it is about 500 amps peak - but are there any tables that cover

    .... Phil
  2. Google for "copper wire i2t". The first hit gives a PDF which contains
    the formula

    ((I/A)^2)t = 0.0297 log ((T2 + 234)/(T1 + 234))

    I = short circuit current (A)
    A = conductor area (circular mils)
    t = duration
    T1 = max op. temp
    T2 = max s/c temp

    Sorry about the non-SI units.

  3. Phil Allison

    Phil Allison Guest

    "Allan Herriman"

    ** That formula breaks down to I being proportional to the sq.rt of 1/t -
    suggesting even the largest fuse will melt in a matter of weeks or months at
    tiny current. But for time intervals of up to a few seconds - it seems
    plausible enough.

    With 10mS and 20 thou diameter, the result is about 600A - for a half sine
    wave, the peak is about double so circa 1000A.

    The interesting conclusion is this: a simple 0.5mm tinned copper wire fuse
    will very likely survive direct connection across a 10A, 240V domestic
    supply for a full half cycle.

    Cos that supply very likely cannot deliver more than about 600 amps peak
    into a short.

    OTOH, a C curve, 16 amp rated, thermal magnetic breaker will trip at 180
    amps in under 2 milliseconds.

    .... Phil
  4. AIUI the concept of I^2.t ignores thermal conduction losses. I^2.R.t is
    the energy you are putting into the wire, it is assumed this all goes
    into raising its temperature I think. Obviously this fails for intervals
    long enough to allow heat to be conducted away.

    Seems to also assume constant resistance for the wire even though it
    gets ~white hot?
  5. Yeah I assume it's for the case when the heat has no time to leave the piece of copper.
    You might try some 'first principle' type calculation.

    So resistance R ~ rho*L/A (rho is resistivity, L is length and A is area)
    (of course rho will change with Temp (T) and that will make it harder.)

    Then energy dumped into the copper I^2*R*t will be heat capacity (HC) * change in temperature (t is the time.)
    HC = constant * volume = C*A*L

    So delta T = E/HC = I^2 * R * t / (C*A*L) = rho/C *t*I^2/A^2

    So as you say, at least the units make sense. To do better you'd have to put in some estimate for how the resistivity changes with Temp. Assuming some linear relation might be OK. (rho ~ T(in kelvin))
    I'd expect the heat capacity to be roughly constant at room temp and above.
    (I'll scribble some more.)

    George H.
  6. Phil Allison

    Phil Allison Guest

    "George Hairoil"
    ** Yeah - and most likely get a:

    " solution that only works for a spherical chicken, in a vacuum "

    .... Phil
  7. Joerg

    Joerg Guest

    Pushing thickfilm far past datasheet limits is risky. They might some
    day cook up another pot of conductive material, it veers a bit towards
    lower specific resistance, trim cuts get deeper ... *PHUT*

    Wirewound may be better here. Ayrton-Perry style if it has to be low

    My first lesson in electro-migration happened around age 16. A loud
    bang, large chunks of a capacitor migrated themselves into the plaster
    of a wall, with gusto. Some metallic parts rained down from there and
    hissed out on the carpet. My parents were not enthused.
  8. Fun!
    A bit off topic, (but then Phil A. doesn't want any spherical cows :^)
    I was wondering last night if I put a piece of heat shrink (or maybe several layers) around a 1/4 watt through hole resistor if I could raise it's maximum DC power.. *NOT* it's pulsed power rating.

    George H.
  9. josephkk

    josephkk Guest

    Bloody cool. You should really publish a paper about your test results.
    Maybe on your company website. That would be a real contribution.

  10. josephkk

    josephkk Guest

  12. Fred Abse

    Fred Abse Guest

    No problem with mplayer:

    mplayer -vf flip=yes Rsense_Flir.MPG

    Flips it, or mirrors it, but won't do both at the same time.
  13. Robert Baer

    Robert Baer Guest

    There may be that kind of info in the Fire Protection Handbook by the
    NFPA; less informative sources is the National Electrical Code (NEC).
  14. Jasen Betts

    Jasen Betts Guest

    Strange it's MPEG level one, nothing fancy.

    OTOH all your players may be relying on the same codec collection.
    do both like this: mplayer -vf mirror=yes,flip=yes Rsense_Flir.MPG

    or fix the recoriding using avconv (ffmpeg):

    avconv -i Rsense_Flir.MPG -vf hflip,vflip Rsense_rightside.mpg

    or mencoder (mplayer):

    mencoder -o Rsense_rightside.mpg -oac copy -ovc copy -vf mirror=yes,flip=yes Rsense_Flir.MPG

    however MPEG1 video is pretty weak, and PCM audio is worse, we can do better.

    mencoder -o compressed.mpg -oac mp3lame -ovc x264 -x264encopts bitrate=360 -vf mirror=yes,flip=yes Rsense_Flir.MPG
  15. Fred Abse

    Fred Abse Guest


    I thought I'd done that, but (instinctively?), I put a space after the

    Without the space (Highlighting your example and middle clicking in an xterm),
    it works fine.

    That's one to remember.

    The man page isn't very clear. I thought it might be my mplayer, it's
    horribly compiler-dependent Every new build with a different compiler
    fixed something and broke something else.
    Mencoder is horribly buggy,here.

  16. Jasen Betts

    Jasen Betts Guest

    shell syntax isn't english (or c) syntax, spaces separate parameters
    comma's don't.
    it's very unclear. there may be some better documentation, but I've
    not looked for it.
    Recently I've just been pulling it and mplayer from deb-multimedia, compiling
    mplayer is no small undertaking.
  17. Fred Abse

    Fred Abse Guest

    Mine I built in 2007. Took about 2 hours to compile, after I found out
    that the code used pi and e, but didn't define their values anywhere. A
    quick couple of #defines fixed that.

    I actually have two versions, one with dvdnav, for those nasty crippled
    Sony DVDs, with apparently bad tracks, which breaks a few unrelated
    things, and one without dvdnav for everything else.

    I have codecs for just about everything.

    There's an HTML guide, that I converted to PDF, that's better than the man
    page. I'll shove it up to a.b.s.e. if you like.

    I now know why the Hungarians invented goulash ;-)
  18. josephkk

    josephkk Guest

    Go for it. I would like a really clean MM player that is reliable as


  19. VLC. For both Windows AND Linux.

    Regular DVDs... Xbox media center (XBMC).

    BD and HD DVDs, not so easy on ANY non-proprietary platform.

    Under Windows, software decoding players usually come with the playback
    device, and it is usually "Power DVD". They are on my list of folks to
    sue for dropping support on hardware they were contracted to support.

    Sad, my original DVD drive for a PC had its own HARDWARE based decoding
    card, back before they had software decoding, and before the speed of the
    PCs they were on could decode them fast enough.

    I wish they would come out with a BD DVD player that had its own
    decoder card. That way they could put the software for the player on the
    card too.

    With the computers being so fast now, the hardware decoder option will
    likely never happen.
  20. JW

    JW Guest

    Great program for the most part, but it lacks a way to set a bookmark so
    you can pick up where you left off watching a video.
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