Power Transistor substitutions

Discussion in 'General Electronics Chat' started by Gdrumm, Apr 16, 2010.

  1. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    I accidently knocked over my Car battery charger while charging a 6v battery. The two clamps touched, and I instantly smelled electrical burn.

    I'm pretty sure the power transistor got fried, the board around it's pin is brown, and I see a white spot near the middle post.

    The numbers on it are S 6055K, and 6D123.

    Can I substitute something of the same size?

    I have several, some with a D prefix, like D718, D1397, or D1092.
    I also have some green ones, that say B688.

    Thanks,
    Garry
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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    Those may be house numbers. Are you sure it's a transistor? Most chargers use an SCR as the output device.
     
  3. retched

    AAC Fanatic!

    Dec 5, 2009
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    I guess there is really no way to tell once its toast. Is there another on the board marked the same that survived?
     
  4. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    The board simply says P1, so I'm guessing it means "Power".

    I checked at Radio Shack, they don't sell them.
    I tried to find it on Alldatasheet.com, but the closest thing they showed was an LSCR6?

    I'll contact Harbor Freight (the place I bought it) and see if they have a schematic and parts list.

    Thanks,
    Gary
     
  5. studiot

    AAC Fanatic!

    Nov 9, 2007
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    Well a 2N6055 is an NPN TO3 darlingon rated a t 8A and 100 watts so it would be a good candidate for such a task.

    I can't find a 2SK6055, which might be a jap equivalent.
     
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    more can be done by posting pictures
     
  7. JoeJester

    AAC Fanatic!

    Apr 26, 2005
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    The 6055K may be a discontinued version of the SCR ....

    Like r!f@@ said, post some pictures.
     
  8. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    The TO-218 SCR in Joe Jesters post looks like it.

    I have a phone number for Harbor Freight Tech Support, and will call them tomorrow to confirm parts availability, diagnosis, etc.

    Thanks,
    Gary
     
  9. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    Here is a picture of the component, beside a penny, for size comparison.
    Harbor Freight is unable to help me.
    I went to Fry's, and they have some smaller components (about 1/2 this size), but nothing with matching numbers.

    I'm wanting to know what I might be able to use as a substitute.
    I've also looked on Newark's site and found nothing that looks exactly the same.

    Thanks,
    Gary
     
  10. SgtWookie

    Expert

    Jul 17, 2007
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  11. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    Sgt.,
    Thanks for the links.
    Mouser is a lot cheaper, but I ordered one from Digi-Key.

    I've saved both links as Favorites.
    I'm sure I'll use them again.

    Great stuff,
    Thanks again,
    Gary
     
  12. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    The SCR arrived today, and though it was physically smaller, it had the same first series of numbers, so I spread the prongs out a little bit, and soldered it in place.

    I put the battery charger back together, hooked it up to a battery I knew to be run down, and it's working.

    Thanks you,
    Gary Drumm
     
  13. SgtWookie

    Expert

    Jul 17, 2007
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    Glad you got it working again, Gary - good job. :)

    Did you use heat sink compound on the SCR before attaching it to the heat sink/case? That's important.
    If you didn't, go down to Radio Shack and get a little tube of it. It's a buck or two. It will improve the heat transfer from the SCR to the heat sink/case.

    Keep those batteries charged, but not overcharged. It's good to charge them a bit high every few days to get the electrolyte stirred up, which also helps a great deal to remove plate sulphation.

    Plate sulphation begins at around 12.5v depending on battery chemistry and internal temperature; but that's about right for a typical automotive-type lead-acid battery. At 77°F, you want the battery voltage to be at least 12.5v; you can float-charge them up to around 13.5v to 13.7v indefinitely - again, depending on internal temperature.

    Lead-acid batteries have a negative temperature coefficient of about -3mV per cell per 1°C; for a 6v cell that's about -18mV/1°C.
     
  14. Gdrumm

    Thread Starter Distinguished Member

    Aug 29, 2008
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    Sgt.
    I went to RS, got a small tube, and applied just enough to coat the back of the SCR.

    I'm sure that tube will last me for a long time.

    Thanks again for all your help.
    Gary
     
  15. SgtWookie

    Expert

    Jul 17, 2007
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    OK, good.

    Keep in mind that the physical connection of the SCR to the heat sink is important; it should be quite snug. The heat sink compound helps to improve the thermal connection, but the basic connection must be good to begin with.

    Some manufacturers use/used aluminum "pop rivets" to secure SCR's, transistors, etc. to heat sinks. The aluminum will oxidize over time, and make the connection weak. I prefer to use a screw/nut/lockwasher and a dab of Loctite (like Threadlocker Blue) to keep it from vibrating loose.
     
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