Non-resettable thermal fuse disassembly | Hacker Day

2021-11-26 09:40:55 By : Ms. Samantha Zhong

This component is a disposable thermal fuse. When the body rises above the specified temperature, the two leads cease to conduct electricity. They are useful in applications such as motors, where you want to ensure that the power to overheated hardware is cut off before permanent damage occurs. They are very simple, but thanks to [Fatkuh's] video, we still like to watch them.

The metal shell is lined with a ceramic insulator, and you can see that one end of it is tapered out. It surrounds a spring that is connected to the two leads and is under a little tension. The alloy used for the connection has a low melting point-in this case about 70 degrees Celsius-and will melt, causing the spring to pull apart and disconnect the connection. In the clip after the interruption [Fatkuh] uses his soldering iron to heat the case above the melting point, thereby tripping the fuse. Then he broke the ceramic cone to reveal the contents.

The only problem with using such a fuse is that if it trips, you need to solder a new component. For applications that require a fuse to prevent overcurrent (rather than overheating), multiple resettable fuses are the best choice.

It is also used in espresso/coffee machines, so that they will not overheat if there is no water for a long time (my uncle can hardly find this).

I did the same, and last month for this exact reason, I had to reorder (and remove it for fun) this exact part.

A warning! You can't just solder those. Their rated temperature is 240 degrees, which is within the melting range of the solder. You don't want it to desolder on its own and touch other things. They were spot welded and crimped on the machine I took apart. I used some 18ga steel wire to make a spring-like tube to re-press them.

Soldering these things is common and easy. There are several methods, all of which use cooling to keep the fuse cool while soldering.

If the temperature is above 100 degrees but far below 180 degrees (the melting point of ordinary lead solder), such as the overheat protection of ordinary water heaters (usually around 120 degrees), you can use a piece of wet paper or cloth to cool it while soldering.

If the temperature is below 100 degrees, you can use some kind of alcohol or even ice cubes to cool the fuse.

If the temperature is close to or above the melting point of the solder, they obviously need to be crimped.

Bleh, forgot to mention that the second method is a cooling clamp, which is basically a special metal clamp that is clamped on the component wire and cooled during soldering.

It is called a heat sink...or "heat sink clip", suitable for people who want to frighten when using a "heat sink" in a computer processor or IC environment.

Bulky repairs are common, easy, and wrong. I have seen the awkward repair of the electric kettle cause it to burn a hole in the kitchen workbench, and then eventually pop up the main switchboard protection device and barely avoid a major house fire. Good luck is more than good practice.

Storage water heaters have multiple levels of over-temperature and over-pressure protection, but there have also been cases where the water heaters boil and blow up houses. The Rumorbusters made a presentation.

These thermal fuses are used in various electrical appliances, especially those that are heated, as secondary or tertiary fire protection after the low-temperature bimetal self-resetting circuit breaker fails, and is a very common cause of failure of the entire electrical appliance. If one of them fails, the thermostat/main protection device is suspicious and should be checked for normal operation.

They have a variety of temperatures to choose from to suit the application, such as 77°C, 133°C, 157°C, 192°C, 216°C, 228°C, etc., printed on the side. Like traditional fuses, they should always be replaced with *same* temperature values, and they should be *always* soldered in place and *curled* (this is standard practice for all connections in heating equipment).

A good reason for this is that the melting point of electronic solder is 183°C, which is in the middle of this range. If the thermal fuse is used at a lower temperature, it may be damaged by welding. If the temperature is high, the lead wire may be unsoldered by itself, and the idle lead is easy to cause a dangerous situation, especially it may bridge the blown thermal fuse .

The second reason is that heating equipment usually uses alloy wires that do not absorb solder well.

These are your last line of fire-always replace them, but please don't mess up their value and always replace them correctly by crimping.

Thank you, AussieTech for the insight. If anyone hasn’t watched the episode of Rumorbusters, check it out: it’s impressive and frightening. After that, I have more respect for stressful things.

So please explain, if you should never solder these thermal fuses, why lower temperatures (120 degrees and below) are almost always soldering...

If the conventional solder melts at a temperature much higher than the fuse value, soldering can be performed because the component will never reach the level of conventional solder melting.

"I used some 18ga steel wire to make a spring-like tube, which I used to crimp them again." Cool for you!

These are merely planned scraps, which are intended to expire after a predetermined time. Just jump it out of the circuit.

Don't be pedantic, but polyfuse also operates based on heat. Yes, they are very different in operation and intended use, but if you heat a multi-fuse from an external source (that is, not the current passing through it), it will still become high impedance...

You often see this in the shredder. The fuse is stuck to the motor, which is why the shredder seems to stop working when you use it for too long and overheat. Then they magically worked again after 10 minutes.

These types of fuses are usually crimped because they are cheap and easy.

There are also thermal circuit breakers, which use bistable springs to cut off at a given temperature and then reset when the system cools down.

Wow! Until now, I thought there was a calf of a magnetic flux capacitor inside. When enough current flows and the temperature is right, the internal components move in time, breaking the circuit! Who would know? ? ?

Those resettable contact microwave guns found in microwave ovens will shut down if they are too hot?

These are also in older lithium-ion battery packs, such as laptop computer packs (and possibly new) and portable power tool battery packs. I have seen them in small ceramic heaters.

I replaced the one in the laminator with the high-temperature version (they are cheap on eBay), and then connected a 50K resistor in series with the temperature-controlled thermistor.

Operating the laminator at a temperature higher than normal is good for toner transfer.

To others who might read this article: If you don’t know *exact* what you are doing, please don’t do it!

The manufacturer designates a thermal fuse as the last line of defense (usually using thermal switches, multiple fuses, etc. as the main protective element), the temperature is usually reasonably higher than the normal operating temperature but lower than the temperature at which other internal components may catch fire due to overheating; Inserting a higher-rated thermal fuse may cause the heating components (housing, wiring, electronic equipment, etc.) to exceed the safe temperature relative to their proximity to the heating element, especially when the main component fails; in the coffee machine This is usually a thermal switch that adjusts the temperature of the heating plate... The laminator may have a similar mechanism that you have effectively defeated.

I use one of them to fix the fan speed resistor group in our car's AC system (the fan only works at 0 or 100%, which is annoying when you have to defog the windows). The dealer quoted $40. The repair is an 80-cent part. The original was spot welded, but I managed to get it with solder.

I actually soldered a lot. Even for medical applications. :-) Just use metal clamps and not too long welding time. It sounds crazy because most manufacturers will only crimp them, but it does work.

"When the body rises above the specified temperature, the two leads stop conducting electricity."

Isn't it the body that stops conduction? The lead should still be conducting.

The final "ceramic" usually (always?) follow the color code of the rating.

The "Slo-Blo" fuse works on the same principle. If it is in a glass capsule, you can see the tension spring near one end and the metal alloy fuse at the other end.

Once, I put one of them on my George Forman grill... Just got rid of it and repaired it together :)

There is a pair of broken ones in the coffee machine... Throw them away together, please refer to the picture for the Chinese parts;)

What looks like a solder joint may be pulse welding.

The most important thing is that the melting point of the joint must be higher than the melting point of the thermal fuse. The melting point of SN05Pb95 is 301-314C, and the melting point of Sn10Pb88Ag02 is 268-299C (data from Kester).

When crimping tubes are not available, a compromise is to wrap the exposed overlapping joints with a tight spiral of solid copper wire and use Sn40Pb60 solder.

This is a new turning point in this problem.

I want to know if I can bypass the thermal fuse on my small vacuum because I only use it intermittently for a period of time at a time?

The ceramic thermal fuse is blown on my old Dirt Devil Breeze Canister Vacuum that is more than 10 years old. We only use it for about half an hour a week to clean a one-bedroom apartment. (The fuse is a white ceramic cylinder with a metal cap, approximately 1 1/4 inches, with solder leads). The motor smells very good, and I temporarily bypassed the fuse to test it. It works fine. (FYI, I did buy a new dust filter recently, so maybe the air intake has a big impact on the motor, but according to Amazon, it is the right filter to replace and it is very suitable... .?)

Anyway... one end of the fuse is burnt. But hell, it has a history of 10 years, with soldered contacts.

So...Since I only used the vacuum cleaner for a while **when I was using it** to clean the apartment, if I don't care about damaging the motor, is it safe to bypass the thermal fuse?

Is there another fuse (or anything else) inside the motor that can send it to heaven when the time is right?

FWIW, I am indeed looking for an alternative thermal cutout, but it is difficult to figure out which b/c I need. It seems to say "LF.25/250VP" on one end and 324 and a diamond PSE with letters on the other end. , And a backward italic UR). (My understanding is that the vacuum is 12A, not 1/4A???) Anyway, there are crimped wires on the welding cap of the dead fuse, and it is contained in a transparent plastic insulating tube, so I need an enclosure to install the new fuse .

I understand how these things happen. The guy in the repair shop said, "We don’t fix the dirt demon. Pick it up and replace it with a new one." But I didn’t grow up like that. I hate throwing away one that has served me for so many years. The perfect engine. We spent a lot of time together, I just bought her a new filter and so on! Oops, she is like an old friend, in my opinion, it is wrong to treat her as rubbish.

By the way, her name is Norma.

I may be late, but never bypass the thermal fuse, and do not replace the fuse with a higher rating. Even if you bring it with you, it may be too late when you smell something, and the contents may already be on fire.

Either find its exact specifications (try searching for the vacuum model and the phrase "thermal fuse" or "thermal fuse"), or do what the maintenance person says, and then throw it away. I know this is bad, but unfortunately, some manufacturers deliberately use obscure parts to force planned obsolescence-if you just replace the thermal fuse, Dirt Devil won't make more money from you, does it now? Now, if you buy a new Dirt Devil (because you like it so much!), it's even better-for them!

PS: There are several possibilities... 1. It may be low current; some tricky things may happen, for example, the thermal fuse will directly cut off the power supply of the controller or other things instead of the motor, but I find this is a little unlikely. 2. 324 may be the reference value of Fahrenheit — 324˚F = 162˚C. 3. LF = Littelfuse; they do have a 324 series ceramic box fuse-could this be a real electric fuse instead of a thermal fuse? If it is a metal can with a colored tapered drill on one end, it is a thermal fuse. If it is a white cylinder with two metal covers, it is a ceramic box fuse.

If your only choice, if it was me. I will choose to continue so that you can say goodbye to her like a real champion, because we don't need water to make motha#!:la burn. Don't just pull the rope, pour your wine on her if necessary. But I will look at other obsolete equipment to find the thermal fuse.

I bypassed the thermal fuse and rescued 3 appliances from the trash can. My experience and opinion is that they have only one purpose... for you to buy new appliances. They all collapse over time, and they are all hidden from ordinary consumers. Why not use a resettable thermal overload switch? The answer is simple, they are more expensive, and manufacturers want us to consume more things. 5 years ago, I saved an expensive battery charger by bypassing the thermal fuse, and it was used every day without any problems. It is also a vacuum cleaner from 2 years ago and a convection heater from 16 months ago. None of these appliances actually malfunctioned or overheated. They are just a few years old. Thermal fuses will eventually be damaged and become O/C, because they are hidden, most people think it is time to buy new shiny things. No matter what you say, I believe in their true purpose. Experience and observation are always better than theory.

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