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

 

It.looks like a thermal.fuse of.some sort..

 

I'm with Dr.killjoy. Thermal fuse like these?

 

I'm with Dr.killjoy. Thermal fuse like these?

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

 

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??

 

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

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

 

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.

 

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

I do think that should be my first step. We'll see what happens from there.

Chuck

 

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

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.

 

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

 

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.

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

 

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

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.....

 

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.

 

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.

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

 

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.

 

Hello,

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

Bertus