Thermal Fuse question - Page 1
Forum section: electronics / repair

author: Excavatoree
author_rank: Frequent Contributor
timestamp: January 07, 2015, 12:08:00 am
content: I know in many cases, the leads of a thermal fuse are crimped to the wires, because the heat may melt the solder, or because improper soldering could trip the thermal fuse.I am working on my aunt's portable cooker. The fuse is rated at 142 degrees C, far too low to be worried about solder melting. If I use proper heatsinking and solder it, would it be acceptable? Am I overlooking something?The thermal fuse and all wiring leading to it are covered in a fiberglass like covering, with a metal clamp around the fuse itself (encased in the tube) screwed to a bracket.

author: Mr.B
author_rank: Unknown
timestamp: January 07, 2015, 01:15:57 am
content: You might have trouble keeping the fuse below 142 degrees C while soldering with your iron at 330 degrees C.Assuming it is a non-resetable thermal fuse.IMO crimping is better in this case...

author: wraper
author_rank: Unknown
timestamp: January 07, 2015, 01:16:39 am
content: Should be OK, however you should test your heatshrink with soldering iron at say 170-200oC as some types don't hold high temperatures well. If you are concerned about solder melting temperature, then use Lead free solder, 217oC for Sn/~4Ag/~0.5C and 227oC for Sn/~0.7Cu common types.

author: wraper
author_rank: Unknown
timestamp: January 07, 2015, 01:19:38 am
content: Quote from: Mr.B on January 07, 2015, 01:15:57 amI guess it is square 2A fuse with thin leads, so no problems there. Could use tweezers holding wire as heatsink between soldering point and fuse itself too.

author: Mr.B
author_rank: Unknown
timestamp: January 07, 2015, 01:22:45 am
content: Quote from: wraper on January 07, 2015, 01:19:38 amYip... Could work.If it doesn't Excavatoree will just have to buy a new fuse and use a different method...

author: Excavatoree
author_rank: Frequent Contributor
timestamp: January 07, 2015, 03:16:53 am
content: It's one of these. (not exact fuse, pictured are fuses of differing ratings)I am concerned that I'll either:1. not have enough iron to heat the lead with a protective heat sink.2. not have adequate heat removal and blow the fuse.I'm not confident of my crimping ability, but I've got to weigh that against my ability to solder.Well, they are cheap, so a bit of trial and error seems to be in order.

author: Mr.B
author_rank: Unknown
timestamp: January 07, 2015, 03:31:28 am
content: That is exactly what I had pictured in my mind that you were talking about.The method wraper suggested of heatsinking close to the body should work.You may need something with a bit more heatsink capability than a pair of tweezers.I have some little spring loaded clamps made out of alloy that are perfect for such things. Cannot remember where I got them from.

author: Leadfootin
author_rank: Contributor
timestamp: January 11, 2015, 01:49:24 pm
content: You may get lucky soldering it in IF the leads are well heat sinked. Use pliers or similar as light weight clips will not limit the heat sufficiently. Thermal fuses are far more heat sensitive than most semiconductors.

author: Excavatoree
author_rank: Frequent Contributor
timestamp: January 11, 2015, 02:23:09 pm
content: I used two pair of hemostats as heatsinks, and soldered to the very end of the leads as carefully as I could and got away with it.I was, however, prepared to buy another if I got this one too hot.