Glue to fix a thermal fuse on a ceramic resistor - Page 1
Forum section: electronics / repair

author: Swake
author_rank: Frequent Contributor
timestamp: September 16, 2023, 01:11:36 pm
content: Hi all,To repair a Voltex power supply in a HP 4155A I need to fix a thermal fuse (133°C) to a 10W (or more can't remember) ceramic resistor above it.What glue should I use? Is UV solder mask glue good enough up to that temperature?

author: fmashockie
author_rank: Frequent Contributor
timestamp: September 16, 2023, 04:05:10 pm
content: Why not use some RTV silicone? That stuff will hold well above that temp. And its easier to remove if you need to repair something.

author: Swake
author_rank: Frequent Contributor
timestamp: September 16, 2023, 04:22:27 pm
content: Silicone is more of a thermal insulator than conductor.The idea here is that the thermal fuse should 'monitor' the temperature of the resistance.

author: coppercone2
author_rank: Super Contributor
timestamp: September 16, 2023, 04:24:14 pm
content: get a few and experiment with it.they don't have magic, the resistor can probobly go alot higher then the fuse that was put on it. they account for the glueand honestly if the fuse goes, you probobly want to replace the resistor. if they expect anything different, the power supply is built stupid. Its not a feature for regulation, its a feature for gross failure

author: fmashockie
author_rank: Frequent Contributor
timestamp: September 16, 2023, 04:34:00 pm
content: Quote from: Swake on September 16, 2023, 04:22:27 pmMmm true. this stuff works really well. It's very strong. I use it to secure peltiers to thermal block. But it is expensive.https://www.digikey.com/en/products/detail/mg-chemicals/8329TFF-25ML/9608260

author: inse
author_rank: Super Contributor
timestamp: September 16, 2023, 05:34:21 pm
content: Fix it with wire?

author: Ian.M
author_rank: Super Contributor
timestamp: September 16, 2023, 05:37:50 pm
content: What about a dab of heatsink compound for the thermal contact then wrap it with Kapton tape?

author: wraper
author_rank: Unknown
timestamp: September 16, 2023, 05:51:34 pm
content: Quote from: Swake on September 16, 2023, 04:22:27 pmNonsense, from datasheets where it's mentioned I've seen RTV silicones generally to have about half of thermal conductivity of a cheap white thermal paste, about 0.3-0.4W/m·K

author: Swake
author_rank: Frequent Contributor
timestamp: September 16, 2023, 05:53:15 pm
content: I like that idea with the Kapton tape. Easy and reversable.

author: Swake
author_rank: Frequent Contributor
timestamp: September 16, 2023, 05:59:52 pm
content: Quote from: wraper on September 16, 2023, 05:51:34 pmIf it has 0.4W/mK it is not thermal paste, whatever the label on it says. Cheap thermal paste is an order of magnitude better. Expensive paste 2 orders of magnitude.

author: wraper
author_rank: Unknown
timestamp: September 16, 2023, 06:09:35 pm
content: Quote from: Swake on September 16, 2023, 05:59:52 pmFigure for silicones, not thermal paste. Order of magnitude better is not a cheap thermal paste but quite expensive. Unless you take BS performance claims for granted. EDIT: and two orders of magnitude is non existent.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: September 16, 2023, 06:10:17 pm
content: I used some Plumber's Epoxy. It worked well as a thermal conductor and electrical insulator.But it is VERY strong and Hard.Epoxy Plumber's putty available ar hardware, also known as "Pig Putty" which I believe is the same stuff sold for other purposes.

author: wraper
author_rank: Unknown
timestamp: September 16, 2023, 06:18:26 pm
content: Here you gohttps://mgchemicals.com/category/grease-for-electronics/thermal-paste/Starting from 0.7 W/(m∙K)

author: Swake
author_rank: Frequent Contributor
timestamp: September 16, 2023, 06:27:28 pm
content: That is already twice as good as you claimed. Here is the explanation on why it is like that:https://en.wikipedia.org/wiki/Thermal_pasteTom got some other examples:https://www.tomshardware.com/best-picks/best-thermal-pasteMany are over 40 W/mK in this list.

author: wraper
author_rank: Unknown
timestamp: September 16, 2023, 06:41:25 pm
content: Quote from: Swake on September 16, 2023, 06:27:28 pmDo you confuse thermal paste with liquid metal?

author: wraper
author_rank: Unknown
timestamp: September 16, 2023, 06:53:45 pm
content: Quote from: Swake on September 16, 2023, 06:27:28 pmI say it again, I wrote a figure for RTV silicone, not thermal paste which start about twice better than that. But you don't need performance even of cheap thermal paste either because you don't have much power to transfer into heatsink. And the best you could do is use inexpensive but long lasting thermal paste and a springy metal clamp to keep resistor and fuse together.

author: fmashockie
author_rank: Frequent Contributor
timestamp: September 17, 2023, 01:06:55 am
content: Yea what I had in mind originally was ensuring the resistor and fuse were making contact physically, (maybe using some thermal paste in between). and then add the RTV silicone over it to keep it in place. Just like the kapton tape suggestion.And not all RTV silicones are made equally. Here's an example of a thermal conductive RTV silicone.https://docs.rs-online.com/d8cf/0900766b80f8df6e.pdfMost thermal pastes are silicone-based as well.