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

author: 2X
author_rank: Frequent Contributor
timestamp: January 24, 2025, 07:04:47 pm
content: Hello,I have a thermal fuse resistor (at the below images) but I can't find it anywhere or some other similar. I removed the external ceramic material and inside the resistor is fine but the fuse is open. Also, I found the same thermal fuse. As I understand this fuse open independent of the current that passes inside it; if the temperature at the casing of the thermal resistor goes above 128Celcius it will blow up. How can I make something like the ceramic body? I found the below adhesive where is Thermally Conductive. I thought to put the resistor and the thermal fuse inside a heatshrink and fill it with this "8329TFS-25ML" adhesive or with some RTV silicone. Has anyone done something like this... do you believe is good idea or there is available a ceramic material for sale so I will make it as original was? Any suggestions are welcomed.Cement resistor/10N40/10W40ohm/Vertical/1pchttps://www.11st.co.kr/products/1690272509SDF DF128Shttps://www.digikey.gr/en/products/detail/cantherm/SDF-DF128S/10147628329TFS-25MLhttps://gr.mouser.com/ProductDetail/590-8329TFS-25MLRTV162-85MLhttps://www.mouser.dk/ProductDetail/MG-Chemicals/RTV162-85ML?qs=sbrGYOVz3HeDc3Zk7MUnMg%3D%3D

author: Audiorepair
author_rank: Frequent Contributor
timestamp: January 24, 2025, 07:22:12 pm
content: What equipment is this from?I have seen this before, so I am guessing it is in an audio Power Amp, my memory can't get further than that.Point being is the thermal fuse really necessary?

author: 2X
author_rank: Frequent Contributor
timestamp: January 24, 2025, 07:33:36 pm
content: Quote from: Audiorepair on January 24, 2025, 07:22:12 pmQuoteIt is from the power supply of an old MMA/Stick Welder.QuoteJust I want to make it like the original was and it is interesting to find a way to make it like the original. I use and a simple 40ohm/10W resistor and works fine... but for safety reason I beleive the designeer add the thermal fuse.

author: Gyro
author_rank: Super Contributor
timestamp: January 24, 2025, 07:33:52 pm
content: Quote from: Audiorepair on January 24, 2025, 07:22:12 pmIf the equipment manufacturer designates it a safety component, yes absolutely.

author: Audiorepair
author_rank: Frequent Contributor
timestamp: January 24, 2025, 08:53:47 pm
content: Quote from: Gyro on January 24, 2025, 07:33:52 pmIt is not unknown for manufacturers to make stupid decisions.In the case of an audio Power Amp there is little that can harm the user.A welder is a whole different kettle of fish I don't fry, so I would go for safety.

author: Gyro
author_rank: Super Contributor
timestamp: January 24, 2025, 09:05:08 pm
content: Quote from: Audiorepair on January 24, 2025, 08:53:47 pm(Slightly gobsmacked!)It is not unknown for manufacturers to always know better than you regarding safety, especially after they have been through reviews and qualification. A 'casual' repairer introducing a fire risk can certainly harm the user!If, as your username suggests, you repair audio equipment for other people, you should be following manufacturers' service information to the letter. If you are not doing this, you'd better have a bloody understanding public liability insurance provider, because worst case, theywillthrow you to the wolves.

author: Haenk
author_rank: Super Contributor
timestamp: January 25, 2025, 02:15:04 pm
content: https://www.mouser.com/datasheet/2/219/WF-10358.pdfMaybe suitable? EOL though.Well, seems impossible to find. Found 68R though.Maybe go with a cement one and attach a temperature fuse to it; I don't think potting one yourself is possible.

author: 2X
author_rank: Frequent Contributor
timestamp: January 28, 2025, 08:33:16 pm
content: After some thoughts and experiments I ended in the below solution that the image shows. I used a thermal pad between the thermal fuse and resistor and tied them with a heatshrink. I also made a short circuit with connected 10ohm resistor after the resistor with the therma fuse that I made and the thermal fuse blow like it should. Also the device itself have glass fuses so I beleive it is a safe solution and closer to what the designer had designed.Thermal Pad Part Number: COH-4065LVC-200-10

author: Haenk
author_rank: Super Contributor
timestamp: January 28, 2025, 09:32:00 pm
content: Yep, that looks like how it should be (as a replacement).I don't think the exact temperature of the fuse is important, just the "about" range should be the same.

author: Whales
author_rank: Super Contributor
timestamp: January 28, 2025, 09:50:20 pm
content: Quote from: Audiorepair on January 24, 2025, 08:53:47 pmFire dude, fire.

author: Simmed
author_rank: Frequent Contributor
timestamp: January 28, 2025, 10:30:54 pm
content: Quote from: 2X on January 28, 2025, 08:33:16 pmi think heat shrink long term exposure to heat = crackingso the heater will decouple from fuse and you get a new failure mode, maybe something else will burn this time ?

author: 2X
author_rank: Frequent Contributor
timestamp: January 30, 2025, 11:58:21 pm
content: This fuse is only for the startup and for the inrush current that the capacitors draw. It is in use for some miliseconds when the power supply is turned ON and then a relay where is in parallel with the resistor activated, so the fuse will be heat only when there will be a problem on power supply (a shortcircuit) and consicouently the thermal fuse will blow out. If the thermal fuse is all the time in use and heated the heatshrink propably will crack (this also it depends and from the temperature that its heatshrink can withstand).

author: Geoff-AU
author_rank: Frequent Contributor
timestamp: January 31, 2025, 03:19:34 am
content: Quote from: 2X on January 30, 2025, 11:58:21 pmTo me, it sounds like the resistor is there for inrush. The fuse is there so thatwhenthe relay fails (electromechanical device, finite switching life) the thermal fuse will detect that the resistor has stayed inline and open the circuit before things get too hot. Resistor wiring will glow white-hot before it fuses, so the outside ceramic surface will be dangerously hot if the overload is a slow one. The thermal fuse is there to protect against fire. Check the health of the relay! And also for inrush duty, the thermal fuse can likely be lower value like 60 degrees. 128C is a perfectly fine value, wouldn't want to go much hotter though.Quote from: Audiorepair on January 24, 2025, 08:53:47 pmCounterpoint: you don't know what you don't know.