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Heat sink calculation

Discussion in 'General Electronics Discussion' started by tedstruk, Oct 2, 2018.

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  1. tedstruk

    tedstruk

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    Jan 7, 2012
    I have to rework a 409046 leslie control for a gulbransen/CBS organ into a 409347 because of a lack of a 409347, so it will require a resistor, and maybe a jumper or two. The board has SC146M thyristors on it now, and one is blown. The circuit requires SC141D's which I have ordered. It also requires 3 - 330 ohm resistors of which there are only 2 on the 409096 board. With this extra resistance, the new thyristors will require a heat sink, and they are fitted with a pin for mounting.
    I remember there was a formula for calculating the size of heatsink when they are required, but I can't remember it. I have some scrap heat sink material, but I don't know if it would be a good idea to just cut some pieces so there is lots of dissipation. can anyone help me here? The thyristors are 6a/400 v, the resistors Rtot is 760 ohms, and the caps are .1 uf, reed relay is -12v, diode 1N4148.
     

    Attached Files:

  2. kellys_eye

    kellys_eye

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    Jun 25, 2010
    Schematic? What you described makes no sense whatsoever.
     
    (*steve*) likes this.
  3. tedstruk

    tedstruk

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    Jan 7, 2012
    Sorry!! made perfect sense to me!!!
    I got 2 different builds to use as guides in the repair manual.
    One is a 409347, the other is 870241
    BUT...
    The board I have is a 409046, so I got a Triple threat!!!!
    The board had SC146M transistors on it.

    The diagram for the 409347 calls for SC141D's thyristors which I ordered.

    This diagram has 4 resistors 3 - 330ohm 1 - 100ohm

    The 409046 board I have, has 3 resistors and they are 3 - 100ohm

    The third diagram is for a 870241 controller, and it has 3-100ohm and 1-330ohm

    They are all close to the same thing ...

    I was wondering if maybe the thyristors blew because of not having a heat sink on them...

    I found the formula in You tube
    TempJunction - TempAmbient / PowerDissipated = JuncAmbient

    So where
    Pd(PowerDissipation) = Vdrop x I(Amps)

    JunctionCase + CaseSink + SinkAmbient = device dissipation eg. 25degrees centigrade to see if you need a sink or not.
     

    Attached Files:

  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
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    Jan 21, 2010
    Most of your formulae seem incorrect.

    There is a resource on heatsinking that may help you.
     
  5. kellys_eye

    kellys_eye

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    1,147
    Jun 25, 2010
    meaningless to 99.9% of people - what IS that????
    meaningless to 99.9% of people - what IS that????
    meaningless to 99.9% of people - what IS that????
    what diagram? Show it.....
    If they needed heatsinks they'd have been fitted with them.
    but WHAT'S THE LOAD?

    Without schematics this is all guess work.
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,839
    Jan 21, 2010
    :)

    double :)
     
  7. brevor

    brevor

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    16
    Apr 9, 2013
    I worked on those organs years ago, The triacs dont require heatsinks.
     
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