In late 90s, I found a schematic of a resetteable fuse made with an thyristor. That was not automatically resetteable but instead when triggered, you had to push a button to rearm it. I built that circuit (and I remember using a potentiometer to make it adjustable) and used it as the fuse at the ouput of my homemade bench variable power supply. However, I remember it being not reliable at low voltages.
I just watched a video on this very subject yesterday. This guy does a really great explanation of a "crowbar circuit", which uses a zener diode, to trigger a thyristor, which blows a glass fuse. The beauty of this circuit is that it 'immediately' squashes an over-voltage/current before 'slowly' burning the fuse. It's also simple and cheap to implement, though I'm inclined to substitute a resettable fuse for the glass one he used. Search youtube for: "All You Need To KNOW About CROWBAR Circuits To FIX Stuff! How crowbar circuit works tutorial"
@@greatscottlab Yes, something like that. It was in a book like the old "Elektor 300 schematics". It was a nice addition to my power supply. Maybe I dig it out and if I find it, I will add a link.
@@greatscottlab So, I will describe the circuit, as I can not upload a image and I did not find it online. Between the positive of the power supply and the load is an 2N3055, collector to PSU, emitter to the load. Between the collector and the base is connected the tyristor (anode to base) and between the base and emitter a resistor of 0.2-1Ohm (it sets the fuse current). The tyristor gate is connected trough a push-button and a 47k resistor to its cathode and transistor collector. To power the load, have to push the button to latch the tyristor; when the overcurrent, the transistor opens, shorting the tyristor, making it to shutdown and powers off the load. Hope it is clear enough to be replicate and analyzed.
@@sebastian19745 I mostly get it, but it doesn't seem like the thyristor would ever be completely shorted. As the voltage drop across the resistor gets above about half a volt due to excess current, it's going to start turning on the transistor, but I only see it turning the transistor on enough to keep the voltage across the resistor (and the current through the thyristor) from rising even more. It relies on the current passing through the thyristor to stay on.
I've seen many PCB's with surface mount fuses. But I never thought that they were the resettable ones. So thank you for letting me know that and this video topic is awesome 👌.
A story on resettable fuses that an aerospace engineer once told me: GPS satelites have some of them. Now for ground testing, they use non-resetting fuses, which get swapped out for resettable ones prior to final assembly. After launch, the new satelites go through a series of tests to verify they are working correctly. One of these tests involved deliberately triggering the overcurrent protection. When they ran the test on one of two newly launched satelites, they suddenly lost contact with it. After a round of testing, debugging and analysis, they arrived at the conclusion that the fuses never had been swapped out, and the two satelites were launched with the test fuses still in place. Immagine the bone-chilling realization that there was another satelite in orbit with the same flaw, and ground control was about to begin the test sequence! A frantic phone call from the testing facility to ground control managed to get the test called off by mere seconds. So the second satelite had escaped doom by the skin of its metaphorical teeth. Bottom line is, one dead GPS satelite is orbiting earth, and another one has a damocles sword hanging over it, which is a very strange metaphor in microgravity. Oh and probably some GPS flight engineers and testers, when they have managed to entangle themselves in their bedsheets on a hot summer night, dream of that fuse getting hotter and hotter...
@@paulcohen1555 It sounded to me like the guy knew what he was talking about, and it wasn't "a friend of an uncle" but himself who had been on the team. But then, on the internet you never know if the 18yo japanese girl isn't really a fat, bearded guy in a midwest trailer park.
Reminds me of when I did competitive robotics. We were limited to 12 rather underpowered motors that had these kind of fuses (we called them PTCs but I guess technically they were PPTCs). Between matches we would turn canned air upside down to spray the motors with the refrigerant or the PPTCs would trip in the next match. There were actually a few teams that got caught bypassing the PPTCs, which was a big no no.
You ment cooling down the electric motors so the pptc wont trip? I sure dont see how that would help a pptc not to trip unless you used a wrong trip current..
@@ClosestNearUtopia I think their issue was that the PPTC was "undersized" for what they were trying to accomplish. Active cooling the PPTC within the power limit would spend less energy than the fuse would be dissipating, so if the fuse can never reach its temperature, it can never trip.
If the resettabel fuse is in a hot place, one should take set temperature into account. The datasheets usually state trip-current vs ambient temperature, in a chart...
This was a very well presented introduction to these fuses. I never knew they were that complicated, or available in so many different ratings. Thanks, as always ;-))
Hahaha, I've been buying from Mouser since the early 80's, when they had one of their outlets here in San Diego (actually a nearby suburb). You could place an order in the morning and pick it up in the afternoon. Now with modern conveniences like the internet, you can get parts only three or four times as slowly!
Hi scott! I just have to say that yours and Electroboom's videos are the videos that made me interested in electronics as a kid, and made me choose a Electrician major in HS. And videos like these make me love electronics even more. So, Thank you!
My favorite technique is to use a resettable fuse followed by a transient-absorbing Zener such as a 1N6373 in parallel with the load. This not only protects from overvoltage but also protects against reverse voltage since the Zener would then be forward-biased instead of reverse-biased. I ran my own set of tests and melted the insulation on my power supply wires because the resettable fuse - transient Zener could handle more power than my power supply leads could. (The combo did get very hot though - space them away from your PWB!)
totally. ive seen this often done in industrial electronics. but i think it would work better if you glue the PTC fuse to the zener with silicone. that way heat can transfer from zener to the PTC fuse and help it activate. the combo might run cooler than both things separately. what temperature are the PTC fuses anyway? i havent done any tests. maybe you do them. a big flat surface mount zener and PTC fuse of similar size glued together might work best.
Fuse + crowbar in the reverse voltage situation. Makes sense to force the trigger in some situations like this instead of having constantly a voltage drop with a series diode.
@@echelonrank3927 Interesting idea, but I do wonder now about how the zener would behave, given semiconductors aren't really happy above 100ºc often enough. Might be interesting to check it out on the datasheets.
You should have mentioned that these components do degrade with each trip, and also degrade if held in a tripped state for long periods (degradation=untripped resistance increase). They are not suitable for applications that are likely to be regularly tripped.
I watch your videos every Sunday you publish it on TH-cam and I really like the fact that you in every video came up with a new idea to solve many problems and also explaining the basics
Polyfuses are great, and I agree they are an underappreciated and underused component. They're quite useful, simple and easy to integrate into designs, and very affordable. You do have to watch out for their quirks as noted in this video ("soft" trip, temperature dependence, don't quite reset to the same point after they've been tripped once) but any time you need overcurrent protection, they're worth considering as an option. In most cases, I leave regular fuses for more "industrial" applications at higher currents especially where the chance of tripping them is very low unless somebody has done something seriously wrong. In the "electronics" space, if I have very tight thresholds for when to trip I'll use an e-fuse but otherwise the PPTC is my go-to for low current stuff. Another related useful technique is the "crowbar" circuit. Basically, you use some mechanism to detect a fault condition in your circuit and then you deliberately short across the power rails to purposefully trip the fusing element. This can really expand your options for exactly what trips your fuse and can give you more precise control over the trip point while using a soft/simple trip element like a polyfuse, while still retaining the easy "unplug it for a bit to reset it" behaviour.
Great video as always and a big +1 for Mouser!!! Two things to be aware of with PTCs vs a normal fuse or breaker though. The max interrupt rating and how fast it interrupts. PTCs are fine for low power electronics, but if there is a device with a high current source feeding it the PTC can destroy itself or not stop the inrush of fault current. Since, as like in your example, they can be rated as low as a 60 Amp interrupt rating. Fine for devices with small power supplies. But if you are powering something with a large power supply that can deliver 100's of amps (batteries, mains powered power supplies) and the device has a solid short the PTC may not be able to absorb the current spike. Whereas fuses have interrupt ratings from 5k up to 200k amps. Why some fuse holders are reject style holders, they will only fit a certain interrupt rated fuse and you physically can't install a lower rated fuse in the holder. Then there is the speed. Sure, tripping a 1A fuse or PTC with 2A will take a while, but how fast will a 1A PTC interrupt a fault with 20A of fault current vs a fuse that will instantaneously blow. Sure most of the viewers projects would be fine with a PTC, but to avoid possible damage with higher powered devises a fuse or breaker is still needed. It can be in series with the PTC and at a higher trip level, yet will still provide protection in high current fault situations. PTC will take care of overloads and lower amperage faults and the fuse will take care of interrupting higher current faults that may have destroyed the PTC and NOT have interrupted the current flow.
I haven't watched your video yet, but your thumbnail gave me an idea that solves a problem I've been having all week! And I think it'll work and makes my solution 1000x easier, cheaper and more reliable!
I enjoy you videos and find the informative. I was disappointed to see this video was sponsored by Mouser. I have had unhappy times dealing with them last year. Mouser started canceling item from my orders saying "The following item(s) have been cancelled from your order due to either the manufacturers’ distributor sales restrictions or Mousers’ distributor sales restrictions", via a phone conversation with customer service they told me I must be a distributor because I buy to many parts to be a hobbyist. Their web sales policy states they can refuse to sell to anyone for any reason, so I just gave up and started using other sellers. I liked using Mouser because they have a wide variety of items in stuck at a good price and they do ship quickly. I now have to use four different sellers (DigiKey, Newark, TME and Arrow) to get what I used to be able to buy from Mouser. I hope you followers have better luck with Mouser then I did..
These capacitor shreds are an absolute horror to clean up, respect that you still did it, I once accidentally exploded a large capacitor, I had the whole wall full of the stuff😆
I love your content. I am a mechanical engineering student and I don't know much about electronics.Even so, your channel is has been an easy and great way to get close to this world. Thanks a lot 😁
Interesting! I thought those are capacitors just from the thumbnail. Gave me the idea of making this fuse to trigger something like a relay to fully cut-off the current after the trip.
I've seen these on circuit boards of equipment I've worked on or disassembled. I had no idea what the long tubular thing with what looks like heat sink blades was. Now I know. Thanks for the tip !
We recently had a Fender amp with a PPTC inside. They reported it started play less loud over time and the unit eventually turned off. When we tried to troubleshoot it we found one of those PPTC inside which had tripped. Thanks for the great video!
That is very interesting. I have a Bose system that behaves the same way. I couldn't find the cause when I opened it up. I don't recall seeing a PTTC. Will take another look. thanks,
For example, if you have your normal current for your IC of about 500mA, in case of a short circuit you will have maybe 10A (if your power source can supply). So it means that typically, current consumption will increase not twice, but much-much more. And in this case, this kind of fuse will (must) react immediately.
The glass/ceramic fuses are similar to those used to protect your house installation as they will trigger at 10x their rated current within 10ms(FF Superflink) to 3s(TT Superträge) depending on the class/characteristic of the fuse. Die Schmelzsicherungen für Geräte sind ähnlich, zu denen, die in der Hausinstallation verwendet werden, da sie auch erst beim 10x ihres Nennstromes sofort 10ms bzw. innerhalb von 3s abhängig von ihrer Charakteristik auslösen.
never knew about resettable fuses before this! It's amazing how technology is evolving to make our gadgets safer and more durable. Can't wait to see this in action in more devices.
i often use fuses, but they usually don't blow until after damage has been done, that's why i always incorporate a crowbar circuit in my designs because they are faster, and can protect delicate IC's
Hey Scott! Just want to mention that 3D printers used PPTC's in the old ages of the RepRap project. If you take a look at the design of the RAMPS1.4 Shield you can see that they used PPTCs to protect against overcurrent/shortcurcuit, but sadly this method didn't work that well so it was scrapped and got replaced with blade fuses.
A very effective way to protect a circuit is just a light bulb. When small intensity is consume it has a low internal resistance, in case of a short circuit it will limit the current to the rated lamp current. Of course a little more difficult to select but has the huge plus to emit light if "activated", 100% safe. Very useful in case of fugitive faults...
Great video! I occasionally restore old transistor radios which may or may not have shorts in any part of the circuit so connecting to a battery might be "terminal". I built 3 volt, 6 volt, 9 volt and 12 volt battery supplies with a tiny "pea" sized 100mA light bulb (for each voltage) in series. At 10-20mA (correct) current the light is off and the radio might work. If there is a short, the bulb lights up very quickly and limits the current, AND tells me that there is a fault. It uses less wires and needs less hands to work. In some ways it is like a PPTC but I have not done your accurate work in measuring the rate of heating and current limitation. Dave D. Australia
@@misterbonzoid5623 Yep. I have done this for valve/tube amps and radios. A 20 watt lamp has a higher resistance giving a lower voltage and current to allow the capacitors to reform slowly. When there is noise from the speaker and no smoke, swap to the 60 watt lamp and then full power. Dave D. Australia
I use automotive fuses. I take a U.S. outlet plug apart and align the contacts to the fuse blades then mount it all by the edge of the enclosure so the fuse sticks-out enough to pull if need be from the outside. Its not small though comparatively. But I trust it. Can handle 20a easily with the proper fuse. The hepa filter beside me pulls 1.9a on start then settles to 1.1, I put a 2a on it and its never popped.
FWIW: In my designs I use a PTC & a TVS diode for overvoltage and reverse voltage protect. I put the TVS diode behind the PTC so if there is a overvoltage condition the PTC fuse will trip protecting the TVS diode. A unidirectional TVS diode can also protect against reverse polarity from the power source. TVS diodes (basically a Zener diode) will have a forward voltage drop of a bout 0.7V so it will limit reverse polarity to -0.7V. So with just two low cost components you get current protection, overvoltage protection, & reverse polarity protection.
The problem with companies such as Mouser is that they tend to have very high delivery costs when only ordering a few parts. The advantage is that the components you receive are clearly marked and packaged in a proper way.
SUPER useful as always! I knew about PPTCs, but not their details, and didn’t know about e-fuses at all: gonna go watch that video of yours right now 😁
One problem I have found with these as a result of the small power leakage is some devices like CVCC regulators can "crash" and when the fault clears are no longer regulating. Tried to do this with a battery charger and when there was an overload cleared it then would appear to work but the CVCC no longer limited and would have blown up the battery. The total cutoff of a fuse eliminates the "funky control failure" of chips due to the brownout the PTC causes in a fault state.
Seen it in a homebuilt led lamp for plants. It was used to prevent thermal runaway in a 2s3p build. The goal was to achieve protection if one series broke and the other 2 got a higher current flow. When one was disconnected to simulate a brakeage it made the lamp dim because it limited the current. Interesting enough the other fuses actually restored themselves very slowly(almost simultaneously) until they tripped again. It will therefor slowly "blink" which can hint that something has happened. A perfect way to save the LEDs which can be pretty expensive in comparison to one of the PPTCs. Also the plants therefor never completely lost their lights.
Long ago, when thinking about my prototype EV builds. I thought about just replacing all fuses with Circuit-breakers, to not only save money on blowing fuses during experiments, but also keep me from being stranded. Breaker trips, just readjust something, reset breaker, and continue testing or riding around doing my delivery job. But the only circuit-breakers I knew about at the time were too big for a bike. I'm going to revisit that idea. But thank you for teaching me about this option.
I highly recommend mouser. Many times shopped there. Just once there was missing items, but after i raised it to support, they send me them without shipping fees (That would definitely not happen with some random "Chinese" sellers).
Very nice! As always it comes down to the right tool for the job. Within micro-electronics, that's usually never the fuse. When working with mains, it very likely is a fuse.
i don't think these are considered micro electronics...i mean there's fuses less than one amp and it's not unusual for a circuit to draw near one amp I'm pretty sure micro electronics is more like what's inside of an IC package or even smaller than that... just saying. but i think you still made a good point.
I found out about resettable fuses as a kid when I accidentally covered my laptop PSU with a blanket. Thought it broke, only to find out it healed after a couple of hours. That blew my mind back then
Mouser is awesome. I've been getting hard to find parts from them for years. They have the largest selection of parts that I've ever seen. And their prices are reasonable. The shipping costs are very high however.
i blew up my UPS because it didn't have any reverse current protection, I'm still mad. It was just a small tap of the wrong cable for less than a second, the reverse current dropped directly at the junction of the mosfet, I was like, WTF no reverse current diode ? I'm never buying from this brand anymore
Wow what a good video about fuses. I learned very much and finally understood why the fuse in my selfmade motor driver circuit never tripped... To be honest, after you blew up the capacitor I had to zoom in to check if you started growing an unibrow ;)
i think the conclusion here is - whatever protection device thats appropriate to your specific circuit is whats best. have you seen 3 terminal surface mount fuses with built in resistor heaters designed to melt fuse element? part number ITV4030
THAT'S WHAT THOSE ARE!!!!!? I always though these were some kind of weird capacitor and never paid them any attention, and the SMD ones on my Arduino Due's USB ports really confused me - despite how pretty they look. But the timing of your video couldn't have been better, as I've been bringing myself up to speed on electrical engineering to design/simulate my first complete circuit for a prototype and I've been planning on adding a fuse to it for protecting itself and my Arduino... But now I might rethink that. PS: Just checked for these in the PC Power Supply I use for a bench power supply and found them, which explains why it cuts out when I accidently short it, but has never blown up or popped it's soldered-in-place fuse. So cool!
There are also bi-metallic thermal fuses of course which are standard for thermal cut-outs. I guess you could fix one to a low value resistor to make it trigger based on current (as the resistor heats) and it would be automatically resetting and have no 'trickle' current.
There's a version of thermal cutout made specifically for overcurrent protection. Instead of using a resistor they run the current through the bimetallic strip and the self-heating makes it trip. Or now that I think about it, this trip mechanism is exactly how regular circuit breakers work. Look for "auto reset circuit breaker" online.
These old fashioned glass fuses come in different versions, like the FF (Fast Fuse) and the SF (Slow Fuse). The fast ones react, as the name implies... quite fast. Even a small peak current, like when a device is powered up, can be enough to trigger them. Which type did you use in your test to do the comparison?
If resettable fuses were good for really sensitive applications they'd be used there but - to date - glass fuses or ceramic fuses are still in use in both protection of digital multimeters (and other measurement devices) as well as power semiconductors. Obviously that's not the case. Actually fuses come with more categories than just slow blow and fast acting. On the other hand there really are quite slow when just slight overload is induced. And that is also intentional.
I wanted point this because my multimeter in the manual say use fast fuse 350mA and they are really fast, I just did touch the circuit and was fused even when I realized instantanly was in current mode instead voltage, :,D at least I have spare because that happen too like 4 years ago and was impossible to me find those values in my city, I had to imported them and wait because also UPS didn't have a normal service to my location. Slow fuses are useful on high capacitive loads like power supply or motors, even on USB devices they are intentionally slow to alow charge a big condenser before trigger.
@6:35 The 1A at the glass fuse is the hold current. So you should use a 500mA glass fuse. An the time it needs to get triggered depends on the characteristic. You did not mention it. But it looks like you use a slow one. A fast triggering glass fuse should trigger with double current in about 30ms.
Great video! There was one very important fuse at the start of this video that you may or may not have covered previously? - The Multimeter fuse these are super interesting fast blow HRC fuses that stop people creating accidental arc-flash events.... also a good reason to never use a cheap meter on anything above SELV. May be a good topic for a video?
These would come in quite handy in some of our ceiling air con units, which do blow their glass fuses (F3.15A and M3.15A) quite regularly after power cycling. I need to look into that further...
If you are in a country with regular power fluctuations you should have motor starters in your aircon, refrigerator etc with a delay that prevents fuses tripping after short brownouts.
@@mrfrenzy. I didn't mean the main fuse of a compressor unit. It's more like the internal air handler unit which is mounted on a ceiling, that works with a cold water heat exchanger. I'm talking about industrial sized cooling here, not domestic. You just need to supply power, cold water supply run, warm water return run and a drain line to it and you're good to go (as long as you have some machine, that cools the water circuit down). These only have to run the fan, the solenoid valve for the water circuit and the internal drain pump on occasion. It's always the little fuse on the control board which blows, but that power line is supplying power to the whole thing.
@wiedapp the airhandler probably has a soft start circuit for the fan motor. If power is cut and reapplied before the soft start "cools down" it will "hard start" the fan with full current which blows the fuse. You can add a small 1 minute time relay which solves the problem.
@@mrfrenzy. Unfortunately these ones don't. It's just on or off, but on in 3 power modes (low, medium, high). They don't really draw that much current, but if the power company has to do some switching to keep the grid stable, you sometimes get spikes in both positive and negative value. And these do blow the fuses sometimes. I tried to exchange the fast fuses for some medium slow fuses already, but the super slow ones I want to avoid.
Very good... I never used glass fuses in my projects, I think they take up too much space. I've always used resettable fuses mainly because of their size and the advantage of not having to change them all the time.
Glass fuses can be useful if you want to force the device to be serviced by a professional before applying any power to it again. In some circuits, fuses blow for a good reason, and you don't want any power to be applied again before the faulty components are replaced. Also be careful about possible failure modes, safety first!
There are glass fuses are are labeled 'fast blow' are those still slower than a PPTC The 1 project i have a glass fuse in is my pico smart light, i put a 1A fuse on the AC side of my SSR rated at 2A
Common practice for some circuits could be to select a fuse that is rated to reset at a lower Amperage than you initially want. That would help speed up the time required for a trip. eg. instead of selecting a 1Amp trip select a 800mA trip
I've seen PTCs in transistor radios from the 60's in the load side (I believe) of BJT's, as the old germanium transistors were prone to thermal runaway.
I had resettable fuses on my first 3d printer in 2015. I did not know what they were so I counteracted their current limitations with fans. in my use case they were not sized correctly and a glass fuse would have been better.
My favorite protection is a lamp instead of a fuse. Its so ridiculously simple and it will light up indicating a short 😁. Must be the right lamp for voltage and current. 😁🍻
We called these inrush current limiters when designing power supplies with high front end capacitance. Great for limiting short and expected inrush transients
Polyswitch fuses were a revelation to me when I encountered them. BUT they are not as fast as fuses, since they need to physically heat up to increase their resistance and break the circuit. They are great for some applications - like inside a phone which is powered by a battery. But for higher performance power sources they might not protect circuits quickly enough to prevent damage.
A PTC is commonly used in self regulating heaters, as the temperature increases the resistance increases and hence the power draw goes down, when the power draw has decreased to the amount of heat loss then it has reached its stable temperature. This way the heater cannot go above its rated temperature even if it fails on and you can get them designed with lots of different max temperatures. Edit: Another example is the smoke stoppers used with drones for testing, they are just a lightbulb but they are effectively a PTC and limit the current flow.
I could understand this type of fuses to use with any type of controller that detects the trip and use as alarm (for example, in lithium batteries to detect shorts and disconnect the output with an additional power transistor). Or with sensible electronics, to limit the current in case of critical failure. But not for use with big loads that requires instant disconnect and non reset without supervision.
I tried to repair my Xiaomi robot vacuum. I saw this piece but didn't understand what it was. Thanks so much for this video. now it's like you gifted me a robot vacuum :D
In late 90s, I found a schematic of a resetteable fuse made with an thyristor. That was not automatically resetteable but instead when triggered, you had to push a button to rearm it. I built that circuit (and I remember using a potentiometer to make it adjustable) and used it as the fuse at the ouput of my homemade bench variable power supply. However, I remember it being not reliable at low voltages.
Sounds similar to an eFuse. Just with older technology.
I just watched a video on this very subject yesterday. This guy does a really great explanation of a "crowbar circuit", which uses a zener diode, to trigger a thyristor, which blows a glass fuse. The beauty of this circuit is that it 'immediately' squashes an over-voltage/current before 'slowly' burning the fuse. It's also simple and cheap to implement, though I'm inclined to substitute a resettable fuse for the glass one he used.
Search youtube for:
"All You Need To KNOW About CROWBAR Circuits To FIX Stuff! How crowbar circuit works tutorial"
@@greatscottlab Yes, something like that. It was in a book like the old "Elektor 300 schematics". It was a nice addition to my power supply. Maybe I dig it out and if I find it, I will add a link.
@@greatscottlab So, I will describe the circuit, as I can not upload a image and I did not find it online.
Between the positive of the power supply and the load is an 2N3055, collector to PSU, emitter to the load. Between the collector and the base is connected the tyristor (anode to base) and between the base and emitter a resistor of 0.2-1Ohm (it sets the fuse current). The tyristor gate is connected trough a push-button and a 47k resistor to its cathode and transistor collector.
To power the load, have to push the button to latch the tyristor; when the overcurrent, the transistor opens, shorting the tyristor, making it to shutdown and powers off the load.
Hope it is clear enough to be replicate and analyzed.
@@sebastian19745 I mostly get it, but it doesn't seem like the thyristor would ever be completely shorted. As the voltage drop across the resistor gets above about half a volt due to excess current, it's going to start turning on the transistor, but I only see it turning the transistor on enough to keep the voltage across the resistor (and the current through the thyristor) from rising even more. It relies on the current passing through the thyristor to stay on.
I've seen many PCB's with surface mount fuses. But I never thought that they were the resettable ones. So thank you for letting me know that and this video topic is awesome 👌.
Glad to help
Replacing SMC fuses is very tricky.
A story on resettable fuses that an aerospace engineer once told me: GPS satelites have some of them. Now for ground testing, they use non-resetting fuses, which get swapped out for resettable ones prior to final assembly. After launch, the new satelites go through a series of tests to verify they are working correctly. One of these tests involved deliberately triggering the overcurrent protection.
When they ran the test on one of two newly launched satelites, they suddenly lost contact with it. After a round of testing, debugging and analysis, they arrived at the conclusion that the fuses never had been swapped out, and the two satelites were launched with the test fuses still in place.
Immagine the bone-chilling realization that there was another satelite in orbit with the same flaw, and ground control was about to begin the test sequence! A frantic phone call from the testing facility to ground control managed to get the test called off by mere seconds.
So the second satelite had escaped doom by the skin of its metaphorical teeth. Bottom line is, one dead GPS satelite is orbiting earth, and another one has a damocles sword hanging over it, which is a very strange metaphor in microgravity. Oh and probably some GPS flight engineers and testers, when they have managed to entangle themselves in their bedsheets on a hot summer night, dream of that fuse getting hotter and hotter...
Really or just an "Urban legend"?
(Smells like one)
@@paulcohen1555 good story either way 🙂
It's a nice story, but it doesn't match my experience.
@@paulcohen1555 It sounded to me like the guy knew what he was talking about, and it wasn't "a friend of an uncle" but himself who had been on the team. But then, on the internet you never know if the 18yo japanese girl isn't really a fat, bearded guy in a midwest trailer park.
Electronics creepypasta😄
Reminds me of when I did competitive robotics. We were limited to 12 rather underpowered motors that had these kind of fuses (we called them PTCs but I guess technically they were PPTCs). Between matches we would turn canned air upside down to spray the motors with the refrigerant or the PPTCs would trip in the next match. There were actually a few teams that got caught bypassing the PPTCs, which was a big no no.
was fuse active cooling an option? :D
@@dv5809 Using one of the motors to run an AC compressor for cooling the fuses😏
You ment cooling down the electric motors so the pptc wont trip? I sure dont see how that would help a pptc not to trip unless you used a wrong trip current..
@@ClosestNearUtopia I think their issue was that the PPTC was "undersized" for what they were trying to accomplish. Active cooling the PPTC within the power limit would spend less energy than the fuse would be dissipating, so if the fuse can never reach its temperature, it can never trip.
If the resettabel fuse is in a hot place, one should take set temperature into account.
The datasheets usually state trip-current vs ambient temperature, in a chart...
This was a very well presented introduction to these fuses. I never knew they were that complicated, or available in so many different ratings. Thanks, as always ;-))
You are welcome :-) And thanks for the feedback
Congratulations on getting Mouser as a new sponsor. I have been buying from them since about 2007 and have always been very satisfied.
Hahaha, I've been buying from Mouser since the early 80's, when they had one of their outlets here in San Diego (actually a nearby suburb). You could place an order in the morning and pick it up in the afternoon. Now with modern conveniences like the internet, you can get parts only three or four times as slowly!
Yep they always have pertinent datasheets for nearly all of the components they offer..
Hellova sponsor
Hi scott! I just have to say that yours and Electroboom's videos are the videos that made me interested in electronics as a kid, and made me choose a Electrician major in HS. And videos like these make me love electronics even more. So, Thank you!
My favorite technique is to use a resettable fuse followed by a transient-absorbing Zener such as a 1N6373 in parallel with the load. This not only protects from overvoltage but also protects against reverse voltage since the Zener would then be forward-biased instead of reverse-biased. I ran my own set of tests and melted the insulation on my power supply wires because the resettable fuse - transient Zener could handle more power than my power supply leads could. (The combo did get very hot though - space them away from your PWB!)
totally. ive seen this often done in industrial electronics. but i think it would work better if you glue the PTC fuse to the zener with silicone. that way heat can transfer from zener to the PTC fuse and help it activate. the combo might run cooler than both things separately. what temperature are the PTC fuses anyway? i havent done any tests. maybe you do them.
a big flat surface mount zener and PTC fuse of similar size glued together might work best.
Fuse + crowbar in the reverse voltage situation. Makes sense to force the trigger in some situations like this instead of having constantly a voltage drop with a series diode.
@@echelonrank3927 Interesting idea, but I do wonder now about how the zener would behave, given semiconductors aren't really happy above 100ºc often enough. Might be interesting to check it out on the datasheets.
I haven't seen it myself, but I have read that Zeners always fail shorted.
@@hardlygamaliel455 i've always wanted to know how TVS diodes degrade and fail. the type report that requires effort.
You should have mentioned that these components do degrade with each trip, and also degrade if held in a tripped state for long periods (degradation=untripped resistance increase). They are not suitable for applications that are likely to be regularly tripped.
I watch your videos every Sunday you publish it on TH-cam and I really like the fact that you in every video came up with a new idea to solve many problems and also explaining the basics
You're welcome :-)
we use those resettable fuses at work, I never knew these existed so it was really cool to find out about these
Yep. I wasn't aware of them for a long time as well.
Polyfuses are great, and I agree they are an underappreciated and underused component. They're quite useful, simple and easy to integrate into designs, and very affordable. You do have to watch out for their quirks as noted in this video ("soft" trip, temperature dependence, don't quite reset to the same point after they've been tripped once) but any time you need overcurrent protection, they're worth considering as an option.
In most cases, I leave regular fuses for more "industrial" applications at higher currents especially where the chance of tripping them is very low unless somebody has done something seriously wrong. In the "electronics" space, if I have very tight thresholds for when to trip I'll use an e-fuse but otherwise the PPTC is my go-to for low current stuff.
Another related useful technique is the "crowbar" circuit. Basically, you use some mechanism to detect a fault condition in your circuit and then you deliberately short across the power rails to purposefully trip the fusing element. This can really expand your options for exactly what trips your fuse and can give you more precise control over the trip point while using a soft/simple trip element like a polyfuse, while still retaining the easy "unplug it for a bit to reset it" behaviour.
I really love what ur doing since I followed u 4 years ago. Your brilliant Sir!
Great video as always and a big +1 for Mouser!!! Two things to be aware of with PTCs vs a normal fuse or breaker though. The max interrupt rating and how fast it interrupts. PTCs are fine for low power electronics, but if there is a device with a high current source feeding it the PTC can destroy itself or not stop the inrush of fault current. Since, as like in your example, they can be rated as low as a 60 Amp interrupt rating. Fine for devices with small power supplies. But if you are powering something with a large power supply that can deliver 100's of amps (batteries, mains powered power supplies) and the device has a solid short the PTC may not be able to absorb the current spike. Whereas fuses have interrupt ratings from 5k up to 200k amps. Why some fuse holders are reject style holders, they will only fit a certain interrupt rated fuse and you physically can't install a lower rated fuse in the holder.
Then there is the speed. Sure, tripping a 1A fuse or PTC with 2A will take a while, but how fast will a 1A PTC interrupt a fault with 20A of fault current vs a fuse that will instantaneously blow.
Sure most of the viewers projects would be fine with a PTC, but to avoid possible damage with higher powered devises a fuse or breaker is still needed. It can be in series with the PTC and at a higher trip level, yet will still provide protection in high current fault situations. PTC will take care of overloads and lower amperage faults and the fuse will take care of interrupting higher current faults that may have destroyed the PTC and NOT have interrupted the current flow.
I haven't watched your video yet, but your thumbnail gave me an idea that solves a problem I've been having all week! And I think it'll work and makes my solution 1000x easier, cheaper and more reliable!
I used PTCs years ago in industrial control circuits. They work a treat if you design a trip indicator into your circuit.
I've also have looked for resettable fuses. Ty for sharing!!!!
I enjoy you videos and find the informative. I was disappointed to see this video was sponsored by Mouser. I have had unhappy times dealing with them last year. Mouser started canceling item from my orders saying "The following item(s) have been cancelled from your order due to either the manufacturers’ distributor sales restrictions or Mousers’ distributor sales restrictions", via a phone conversation with customer service they told me I must be a distributor because I buy to many parts to be a hobbyist. Their web sales policy states they can refuse to sell to anyone for any reason, so I just gave up and started using other sellers. I liked using Mouser because they have a wide variety of items in stuck at a good price and they do ship quickly. I now have to use four different sellers (DigiKey, Newark, TME and Arrow) to get what I used to be able to buy from Mouser. I hope you followers have better luck with Mouser then I did..
These capacitor shreds are an absolute horror to clean up, respect that you still did it, I once accidentally exploded a large capacitor, I had the whole wall full of the stuff😆
I love your content. I am a mechanical engineering student and I don't know much about electronics.Even so, your channel is has been an easy and great way to get close to this world. Thanks a lot 😁
Interesting! I thought those are capacitors just from the thumbnail. Gave me the idea of making this fuse to trigger something like a relay to fully cut-off the current after the trip.
I've seen these on circuit boards of equipment I've worked on or disassembled. I had no idea what the long tubular thing with what looks like heat sink blades was. Now I know. Thanks for the tip !
We recently had a Fender amp with a PPTC inside. They reported it started play less loud over time and the unit eventually turned off. When we tried to troubleshoot it we found one of those PPTC inside which had tripped. Thanks for the great video!
That is very interesting. I have a Bose system that behaves the same way. I couldn't find the cause when I opened it up. I don't recall seeing a PTTC. Will take another look. thanks,
For example, if you have your normal current for your IC of about 500mA, in case of a short circuit you will have maybe 10A (if your power source can supply). So it means that typically, current consumption will increase not twice, but much-much more. And in this case, this kind of fuse will (must) react immediately.
I just used this! So wonderful to have. Got a whole box for 250Vac. Thank you for the introduction and explanation.
The glass/ceramic fuses are similar to those used to protect your house installation as they will trigger at 10x their rated current within 10ms(FF Superflink) to 3s(TT Superträge) depending on the class/characteristic of the fuse.
Die Schmelzsicherungen für Geräte sind ähnlich, zu denen, die in der Hausinstallation verwendet werden, da sie auch erst beim 10x ihres Nennstromes sofort 10ms bzw. innerhalb von 3s abhängig von ihrer Charakteristik auslösen.
never knew about resettable fuses before this! It's amazing how technology is evolving to make our gadgets safer and more durable. Can't wait to see this in action in more devices.
Excellent video, thanks :) I was incorporating resettable fuses into my projects but was never sure how exactly they behave.
i often use fuses, but they usually don't blow until after damage has been done, that's why i always incorporate a crowbar circuit in my designs because they are faster, and can protect delicate IC's
Hey Scott! Just want to mention that 3D printers used PPTC's in the old ages of the RepRap project. If you take a look at the design of the RAMPS1.4 Shield you can see that they used PPTCs to protect against overcurrent/shortcurcuit, but sadly this method didn't work that well so it was scrapped and got replaced with blade fuses.
A very effective way to protect a circuit is just a light bulb. When small intensity is consume it has a low internal resistance, in case of a short circuit it will limit the current to the rated lamp current. Of course a little more difficult to select but has the huge plus to emit light if "activated", 100% safe. Very useful in case of fugitive faults...
Great video!
I occasionally restore old transistor radios which may or may not have shorts in any part of the circuit so connecting to a battery might be "terminal".
I built 3 volt, 6 volt, 9 volt and 12 volt battery supplies with a tiny "pea" sized 100mA light bulb (for each voltage) in series. At 10-20mA (correct) current the light is off and the radio might work. If there is a short, the bulb lights up very quickly and limits the current, AND tells me that there is a fault. It uses less wires and needs less hands to work.
In some ways it is like a PPTC but I have not done your accurate work in measuring the rate of heating and current limitation.
Dave D. Australia
This is a standard test-jig in audio amplifier repair, where the lamp is a 60W mains lamp in series with the live mains wire.
@@misterbonzoid5623 Yep. I have done this for valve/tube amps and radios. A 20 watt lamp has a higher resistance giving a lower voltage and current to allow the capacitors to reform slowly. When there is noise from the speaker and no smoke, swap to the 60 watt lamp and then full power.
Dave D. Australia
I use automotive fuses. I take a U.S. outlet plug apart and align the contacts to the fuse blades then mount it all by the edge of the enclosure so the fuse sticks-out enough to pull if need be from the outside. Its not small though comparatively. But I trust it. Can handle 20a easily with the proper fuse. The hepa filter beside me pulls 1.9a on start then settles to 1.1, I put a 2a on it and its never popped.
FWIW: In my designs I use a PTC & a TVS diode for overvoltage and reverse voltage protect. I put the TVS diode behind the PTC so if there is a overvoltage condition the PTC fuse will trip protecting the TVS diode. A unidirectional TVS diode can also protect against reverse polarity from the power source. TVS diodes (basically a Zener diode) will have a forward voltage drop of a bout 0.7V so it will limit reverse polarity to -0.7V. So with just two low cost components you get current protection, overvoltage protection, & reverse polarity protection.
The problem with companies such as Mouser is that they tend to have very high delivery costs when only ordering a few parts. The advantage is that the components you receive are clearly marked and packaged in a proper way.
SUPER useful as always! I knew about PPTCs, but not their details, and didn’t know about e-fuses at all: gonna go watch that video of yours right now 😁
One problem I have found with these as a result of the small power leakage is some devices like CVCC regulators can "crash" and when the fault clears are no longer regulating. Tried to do this with a battery charger and when there was an overload cleared it then would appear to work but the CVCC no longer limited and would have blown up the battery. The total cutoff of a fuse eliminates the "funky control failure" of chips due to the brownout the PTC causes in a fault state.
Thanks. I just realised I had to replace my PPTCs with the correct ratings. cheers mate.
One day, when my mind grows up, I want to be just like you. Great video and thanks.
I learned about thermistors a loooong time ago.
Seen it in a homebuilt led lamp for plants. It was used to prevent thermal runaway in a 2s3p build. The goal was to achieve protection if one series broke and the other 2 got a higher current flow. When one was disconnected to simulate a brakeage it made the lamp dim because it limited the current. Interesting enough the other fuses actually restored themselves very slowly(almost simultaneously) until they tripped again. It will therefor slowly "blink" which can hint that something has happened. A perfect way to save the LEDs which can be pretty expensive in comparison to one of the PPTCs. Also the plants therefor never completely lost their lights.
one of the most informative videos I've witnessed in this channel, thank you for your service!
First time I ever saw one of these was in the battery holder for my SnapCircuits kit. Had a lot of fun with that kit as a kid, would recommend
Long ago, when thinking about my prototype EV builds. I thought about just replacing all fuses with Circuit-breakers, to not only save money on blowing fuses during experiments, but also keep me from being stranded. Breaker trips, just readjust something, reset breaker, and continue testing or riding around doing my delivery job. But the only circuit-breakers I knew about at the time were too big for a bike. I'm going to revisit that idea. But thank you for teaching me about this option.
And thank you for exposing me to Mouser.
I highly recommend mouser. Many times shopped there.
Just once there was missing items, but after i raised it to support, they send me them without shipping fees (That would definitely not happen with some random "Chinese" sellers).
You wouldn't expect it from their shiny glossy catalog but Jameco competes well in that space too.
The "Stay creative, I will see you next time" always does it for me!😅
Great content!
I took an electronics class in high school and remember having a Mouser catalog for ordering components by phone or by mail.
Very nice! As always it comes down to the right tool for the job. Within micro-electronics, that's usually never the fuse. When working with mains, it very likely is a fuse.
i don't think these are considered micro electronics...i mean there's fuses less than one amp and it's not unusual for a circuit to draw near one amp I'm pretty sure micro electronics is more like what's inside of an IC package or even smaller than that... just saying. but i think you still made a good point.
Excellent vid, really clear, much less of the annoying over-writing of the felt pens (a pet hate but I realise it is your thing so just ignore me)
I found out about resettable fuses as a kid when I accidentally covered my laptop PSU with a blanket. Thought it broke, only to find out it healed after a couple of hours. That blew my mind back then
Mouser is awesome. I've been getting hard to find parts from them for years. They have the largest selection of parts that I've ever seen.
And their prices are reasonable. The shipping costs are very high however.
Interesting stuff. Reminds me of the Frantone crowbar circuit with a PTC resistor and a Zener diode.
You can get resetable car fuses that moves a leaver when blown an a led comes on to show you it's blown,then you just pull the leaver back to reset it
Great(scott) video 2x👍
reverse current diodes are also very helpful keeping the components safe.
i blew up my UPS because it didn't have any reverse current protection, I'm still mad. It was just a small tap of the wrong cable for less than a second, the reverse current dropped directly at the junction of the mosfet, I was like, WTF no reverse current diode ?
I'm never buying from this brand anymore
Definitely
@@monad_tcp I has more than one or two things let the magic smoke out. 💣⚡
There are also NTCs, that act as in rush current protection! It means that they have a decent resistance that decreases over time while it heats up.
True. You can find out about them in my soft starter video ;-)
Thermistors
7:15 the way the wire just went around the Component
Wow what a good video about fuses. I learned very much and finally understood why the fuse in my selfmade motor driver circuit never tripped... To be honest, after you blew up the capacitor I had to zoom in to check if you started growing an unibrow ;)
Darn fine write-up here. I will sometimes use a circuit breaker for small electronics, but this is a better idea.
Glad you did this video and agree totally on Mouser. Have used them for many years.
Great walk-through of the different overcurrent protection
Thanks for sharing your experiences with all of us 🙂
MOV's
transients . i'm too tired
i think the conclusion here is - whatever protection device thats appropriate to your specific circuit is whats best.
have you seen 3 terminal surface mount fuses with built in resistor heaters designed to melt fuse element?
part number ITV4030
Oh... Really interesting indeed, dude! Thanks!!! 😃
I'm going to try to use them in my next projects!
Stay safe there with your family! 🖖😊
THAT'S WHAT THOSE ARE!!!!!?
I always though these were some kind of weird capacitor and never paid them any attention, and the SMD ones on my Arduino Due's USB ports really confused me - despite how pretty they look. But the timing of your video couldn't have been better, as I've been bringing myself up to speed on electrical engineering to design/simulate my first complete circuit for a prototype and I've been planning on adding a fuse to it for protecting itself and my Arduino... But now I might rethink that.
PS: Just checked for these in the PC Power Supply I use for a bench power supply and found them, which explains why it cuts out when I accidently short it, but has never blown up or popped it's soldered-in-place fuse. So cool!
There are also bi-metallic thermal fuses of course which are standard for thermal cut-outs. I guess you could fix one to a low value resistor to make it trigger based on current (as the resistor heats) and it would be automatically resetting and have no 'trickle' current.
There's a version of thermal cutout made specifically for overcurrent protection. Instead of using a resistor they run the current through the bimetallic strip and the self-heating makes it trip. Or now that I think about it, this trip mechanism is exactly how regular circuit breakers work. Look for "auto reset circuit breaker" online.
Mouser is great! I have been ordering components from them for 20 years. Mouser my first preference when I order components 👍
This video is definitely made for me. I keep blowing up almost everything I touch. And no, I am not a ghost yet
Glad I could help :-)
I’ve recovered a load of various sizes of these but never bothered to learn what they do. Now that I know I might reuse some of them.
Old fashioned fuses do trip faster than any of the alternatives in the cases of severe overloads, which can be a factor in some situations as well.
These old fashioned glass fuses come in different versions, like the FF (Fast Fuse) and the SF (Slow Fuse). The fast ones react, as the name implies... quite fast. Even a small peak current, like when a device is powered up, can be enough to trigger them. Which type did you use in your test to do the comparison?
If resettable fuses were good for really sensitive applications they'd be used there but - to date - glass fuses or ceramic fuses are still in use in both protection of digital multimeters (and other measurement devices) as well as power semiconductors. Obviously that's not the case. Actually fuses come with more categories than just slow blow and fast acting. On the other hand there really are quite slow when just slight overload is induced. And that is also intentional.
I wanted point this because my multimeter in the manual say use fast fuse 350mA and they are really fast, I just did touch the circuit and was fused even when I realized instantanly was in current mode instead voltage, :,D at least I have spare because that happen too like 4 years ago and was impossible to me find those values in my city, I had to imported them and wait because also UPS didn't have a normal service to my location.
Slow fuses are useful on high capacitive loads like power supply or motors, even on USB devices they are intentionally slow to alow charge a big condenser before trigger.
@6:35 The 1A at the glass fuse is the hold current. So you should use a 500mA glass fuse. An the time it needs to get triggered depends on the characteristic. You did not mention it. But it looks like you use a slow one. A fast triggering glass fuse should trigger with double current in about 30ms.
Great video! There was one very important fuse at the start of this video that you may or may not have covered previously? - The Multimeter fuse these are super interesting fast blow HRC fuses that stop people creating accidental arc-flash events.... also a good reason to never use a cheap meter on anything above SELV. May be a good topic for a video?
These would come in quite handy in some of our ceiling air con units, which do blow their glass fuses (F3.15A and M3.15A) quite regularly after power cycling. I need to look into that further...
If you are in a country with regular power fluctuations you should have motor starters in your aircon, refrigerator etc with a delay that prevents fuses tripping after short brownouts.
@@mrfrenzy. I didn't mean the main fuse of a compressor unit. It's more like the internal air handler unit which is mounted on a ceiling, that works with a cold water heat exchanger. I'm talking about industrial sized cooling here, not domestic.
You just need to supply power, cold water supply run, warm water return run and a drain line to it and you're good to go (as long as you have some machine, that cools the water circuit down).
These only have to run the fan, the solenoid valve for the water circuit and the internal drain pump on occasion.
It's always the little fuse on the control board which blows, but that power line is supplying power to the whole thing.
@wiedapp the airhandler probably has a soft start circuit for the fan motor. If power is cut and reapplied before the soft start "cools down" it will "hard start" the fan with full current which blows the fuse. You can add a small 1 minute time relay which solves the problem.
@@mrfrenzy. Unfortunately these ones don't. It's just on or off, but on in 3 power modes (low, medium, high). They don't really draw that much current, but if the power company has to do some switching to keep the grid stable, you sometimes get spikes in both positive and negative value. And these do blow the fuses sometimes. I tried to exchange the fast fuses for some medium slow fuses already, but the super slow ones I want to avoid.
Very good... I never used glass fuses in my projects, I think they take up too much space. I've always used resettable fuses mainly because of their size and the advantage of not having to change them all the time.
Those little yellow claw connectors are really cool.
Glass fuses can be useful if you want to force the device to be serviced by a professional before applying any power to it again. In some circuits, fuses blow for a good reason, and you don't want any power to be applied again before the faulty components are replaced. Also be careful about possible failure modes, safety first!
This is one of the best starts to a video I've ever seen 😂😂
There are glass fuses are are labeled 'fast blow' are those still slower than a PPTC
The 1 project i have a glass fuse in is my pico smart light, i put a 1A fuse on the AC side of my SSR rated at 2A
You have such a thick accent but you enunciate so well.
Metal bending from heat, old fashioned thermostat. Cuts power, job done.
I always put this on passive crossover, PPTC is so handy
Some multimeters have PTC fuses. If you work with (school) students, I highly recommend to get those, because reasons ...
Common practice for some circuits could be to select a fuse that is rated to reset at a lower Amperage than you initially want. That would help speed up the time required for a trip. eg. instead of selecting a 1Amp trip select a 800mA trip
I popped one in my multimeter. Been going strong ever since.
A VERY big plus on resetable fuses is many models also act as a heat protection device, disconnecting at a certain temperature.
I've seen PTCs in transistor radios from the 60's in the load side (I believe) of BJT's, as the old germanium transistors were prone to thermal runaway.
I am not sure about that.
I remember them coming on to the market in the 1990s.
0:14 lol never had a component desolder itself due to human error... amazing!
I had resettable fuses on my first 3d printer in 2015. I did not know what they were so I counteracted their current limitations with fans. in my use case they were not sized correctly and a glass fuse would have been better.
Haha. Yes, cooling them down with a fan destroys their functionality. It happens though ;-)
I was studing pptc in this days.. the right video in the right time. thank you very much. i was asking me about theys slowness too..
Glad it was helpful!
Surprised you had trouble finding them - search PTC fuse or polyfuse will find plenty at any distributor
New subscriber here, also a big fan of mouser, they legit have just about anything your looking for
My favorite protection is a lamp instead of a fuse. Its so ridiculously simple and it will light up indicating a short 😁. Must be the right lamp for voltage and current. 😁🍻
These resettable fuses often have a recovery time associated, and a much higher delay than a simple fuse. Read the specsheets!
We called these inrush current limiters when designing power supplies with high front end capacitance. Great for limiting short and expected inrush transients
Almost the same but exactly the opposite. ICLs are NTC.
I use a 10A circuit breaker for my WLED setup, it's all 12V based and the breaker fits in an automotive blade fuse holder.
Polyswitch fuses were a revelation to me when I encountered them. BUT they are not as fast as fuses, since they need to physically heat up to increase their resistance and break the circuit.
They are great for some applications - like inside a phone which is powered by a battery. But for higher performance power sources they might not protect circuits quickly enough to prevent damage.
A PTC is commonly used in self regulating heaters, as the temperature increases the resistance increases and hence the power draw goes down, when the power draw has decreased to the amount of heat loss then it has reached its stable temperature. This way the heater cannot go above its rated temperature even if it fails on and you can get them designed with lots of different max temperatures.
Edit: Another example is the smoke stoppers used with drones for testing, they are just a lightbulb but they are effectively a PTC and limit the current flow.
A fuse rating is the curent that it can hold without tripping. The tripping current/time is however on datasheet and is usually significantly higher.
Wow man! These fuses are quite trippy. 👀✌
I could understand this type of fuses to use with any type of controller that detects the trip and use as alarm (for example, in lithium batteries to detect shorts and disconnect the output with an additional power transistor). Or with sensible electronics, to limit the current in case of critical failure.
But not for use with big loads that requires instant disconnect and non reset without supervision.
I tried to repair my Xiaomi robot vacuum. I saw this piece but didn't understand what it was. Thanks so much for this video. now it's like you gifted me a robot vacuum :D