Help identifying component

Discussion in 'General Electronics Chat' started by clwhitt, Jul 20, 2013.

  1. clwhitt

    Thread Starter New Member

    Dec 23, 2009
    16
    0
    I'm trying to identify the component in the attached picture. This is on the final output trace of an old RV power converter (converts 110V to 12V, and charges the house battery). It looks like a diode to me. On the end closest to the electrolytic capacitors, I read 13.8 - 14.4 volts DC. On the opposite end, soldered to the trace for the POS output lug, I get a steady 0.39 volts.

    What I can read off of it is:
    TOTEM

    81 (may be B1, or 31)

    AJB 2

    [​IMG]
     
  2. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
    1,190
    156
    It.looks like a thermal.fuse of.some sort..
     
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  3. paulktreg

    Distinguished Member

    Jun 2, 2008
    612
    120
    I'm with Dr.killjoy. Thermal fuse like these?
     
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  4. clwhitt

    Thread Starter New Member

    Dec 23, 2009
    16
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    Thanks to you both. That's actually what I was hoping to hear, that it was some kind of fuse. Possibly, when I desolder it, I'll be able to glean enough information off of it to find a replacement.

    Another thought, could I (should I?) replace it with a standard fuse? I mean, when you really get down to it, aren't all fuses really "thermal" fuses?

    Chuck
     
  5. Metalmann

    Active Member

    Dec 8, 2012
    700
    223
    That looks identical to an old coffee pot fuse I replaced in the 80s. Radio Shack carried them.

    Seems to me, a regular fuse could be inserted in place??
     
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  6. clwhitt

    Thread Starter New Member

    Dec 23, 2009
    16
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    Searching online, I see Radio Shack still carries thermal fuses (and lists them in the same category as ceramic fuses). The problem I see here is that they're rating them by temperature (whereas Mouser rates them in amps). I need to figure out what the correct rating is before replacing or substituting the defective thermal fuse. The power supply here is rated as "55 amps" (I think). Does that mean the fuse on this output circuit should be at or near 55 amps?

    Chuck
     
  7. MrChips

    Moderator

    Oct 2, 2009
    12,449
    3,365
    Thermal fuses open when the temperature exceeds a specific value. Like current rated fuses these are last resort safety mechanisms in the event of catastrophic failure.

    I suggest you remove the fuse and look for proper ID.
     
  8. clwhitt

    Thread Starter New Member

    Dec 23, 2009
    16
    0
    I do think that should be my first step. We'll see what happens from there.

    Chuck
     
  9. ian field

    Distinguished Member

    Oct 27, 2012
    4,415
    784
    Some of the lower temp' thermal fuses open if you try to unsolder them (must put them in with low temp solder!).

    Wouldn't recommend a regular fuse - try to get a thermal, even if its a different case style.
     
  10. Relayer

    New Member

    Jan 1, 2013
    18
    1
    If you decide to replace it with another thermal fuse, then DON'T solder the new one in. It will go open circuit as soon as you hit its thermal temperature with the iron.
    You need to set up a crimp system that will make good contact without the use of a soldering iron.
    Regards,
    Relayer :D:D:D
     
  11. clwhitt

    Thread Starter New Member

    Dec 23, 2009
    16
    0
    I was wondering about this. The one in the picture was definitely soldered in, and was a bugger to get out. I identified the old one as a Microtemp 10A 240V 240°C thermal fuse, and the local Radio Shack had 10A 240V 226°C thermal fuses in stock. I bought two.
    But I begin to think that, man, I am not all that great at soldering, that I'm using a Weller setup at 750°F, and that I'm basically going to screw it up putting it in (that's why I bought two - ;) ). Now, particularly with your message (and Ian's), I think maybe soldering some connectors on the board, then crimping connectors onto the thermal fuse, may be the wiser move. Right?

    Chuck
     
  12. Metalmann

    Active Member

    Dec 8, 2012
    700
    223




    Thanks, I didn't know that.

    Like I said, I replaced only ONE of those, and I did solder it in. That was in the 80s I think. It worked for several years later.....;)
     
  13. Gdrumm

    Distinguished Member

    Aug 29, 2008
    684
    36
    When installing thermal fuses, put an alligator clip on the leads (on either end) as you solder that end onto the board. The alligator clip will carry the heat away from the fuse during soldering. Leave the clip attached for a couple of minutes after soldering, to fully remove the heat. Repeat from the other clip.
    These little cylinders have a wax plug inside, that melts at a certain temperature. Usually shown on the cover, in Celcius. Buy a new one rated at least as high as the original. If unknown temp, buy the highest one you can get of the same size.
     
  14. clwhitt

    Thread Starter New Member

    Dec 23, 2009
    16
    0
    I had bought two replacements from Radio Shack (226° vs the 260° pulled out), and have a couple more coming from a Mouser order (NTE8242 -260°). So I thought, what the heck, at a buck 99, I can afford to give soldering one in a try. I used a set of pliers (lots of metal to soak up the heat) and soldered in each end without any problems. In fact, the pliers did such a good job of capturing the heat, that the body of the thermal fuse barely got warm at all.

    You said they're wax inside. I thought I read that they're lead. It could be that the compound inside is a factor of its thermal rating. That would make sense anyway.

    Thanks to all for their help. Once again, All About Circuits proves to be an awesome community of like minded electronics enthusiasts. If only the world could get along as well as this community does.

    Chuck
     
  15. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    You can solder them fine, with good technique. I solder 1W resistors (about the same size) and the resistor body barely gets to "ouch" temp, it would be far below the trip point of the thermal fuse.
     
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  16. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    You can also hold the leads of the fuse, to distract the heat during the soldering process.

    [​IMG]

    Bertus
     
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