**Understanding Resettable Fuses: A Deep Dive**

In this video, we explore the world of resettable fuses, also known as PPTCs (Polymeric Positive Temperature Coefficient Devices). These devices are designed to protect electronic circuits from overheating and can be used in a variety of applications, including LED strips.

**The Basics of Resettable Fuses**

To begin with, let's discuss the basics of resettable fuses. Unlike traditional glass fuses, which burn out when they reach their maximum current rating, PPTCs are designed to trip at a specific current level and then recover once the current drops below that threshold. This makes them ideal for applications where the current draw is constantly changing.

**Comparing Resettable Fuses to Traditional Fuses**

Next, we compare the performance of resettable fuses to traditional glass fuses. While traditional fuses are faster at tripping than PPTCs, they also tend to take longer to recover once they have tripped. In contrast, PPTCs can quickly become conductive again after they have tripped.

**Adding a Power Resistor as a Load**

To truly understand how resettable fuses work, we added a big power resistor as a load that normally draws around 1.2A. This allowed us to see how the fuse would react when the current draw was high, and the results were interesting. Even though the fuse tripped at a relatively low current level, it still managed to limit the current flow to just over 100mA.

**Power Losses in Resettable Fuses**

We also measured the power losses in resettable fuses and found that they are quite significant, with around 1.2W being lost when the fuse is in its high resistance state. This is a higher power loss than what is claimed on the datasheet.

**Higher-Rated Resettable Fuses**

Next, we tried out a PPTC with slightly higher ratings, which held at 0.9A and tripped at 1.8A. The results were similar to those of the lower-rated fuse, but with less power loss during normal operation.

**The Area Between Hold and Trip Currents**

Finally, we looked at the area between the hold and trip currents and found that the resettable fuse can trigger but does not have to. At 700mA, the voltage drop and temperature increase slowly, meaning the fuse might eventually trip if the ambient temperature is high. However, at 900mA, the voltage and temperature increase much faster, causing the fuse to trip in our case after around 1 minute and 42 seconds.

**Conclusion**

In conclusion, we have learned a lot about resettable fuses and how they work. While they are slower than traditional glass fuses, they offer several advantages, including being resettable and having lower power losses. Each type of fuse has its own strengths and weaknesses, and the choice of which one to use will depend on the specific application. We hope that this video has been informative and helpful in understanding how resettable fuses work.

**Recommendation**

If you are working with LED strips or other electronic circuits, we recommend using resettable fuses as a protection device. They offer excellent protection against overheating and can be easily integrated into your design.

**Support the Channel**

If you have found this video informative and helpful, please consider supporting our channel through Patreon. Your support will help us continue to create high-quality content for you. Thank you!

WEBVTTKind: captionsLanguage: enSometimes when building circuits mistakescan happen which can be a reverse voltage,a voltage applied to the wrong pin, componentsfailing due to their age or wrong usage oryou simply accidentally short something.No matter the cause, the now appearing overcurrentis the root of all evil that needs to getstopped so that nothing explodes or burnsdown completely.To do that I think everyone is familiar withsuch small glass fuses, that you just putin series to your circuit and as soon as toomuch current is flowing the thin metal insideof it melts and thus interrupts the currentflow.Only problem is that replacing such fusescan be cumbersome, it can get expensive ifyou are testing stuff and constantly destroythem and in case of enclosed electronics likeyour smartphone, there is simply no way toreplace such a fuse.The solution to all these problems thoughare Resettable Fuses like these ones whichI often feel like not many people know about.So in this video I will show you exactly howyou can use them and with what limitationsthey come with because even though they areresettable and thus reusable, they are certainlynot perfect.Let's get started!This video is sponsored by Mouser Electronics.Now truth be told I have been searching forfitting resettable fuses for a while on theinternet and Mouser was the only seller thatnot only came with a big selection of them,but most of them were also in stock, I couldeasily filter for preferences and best ofall they sell to private people like you andme and not just companies.I have been ordering my components from themsince 2018 and I can tell you for sure thatthey have all the components you could everneed and you usually receive them within 3or sometimes even only 2 days.So feel free to check out Mouser Electronicsif I piqued your interest.Now first off; If you want to use resettablefuses then you always have the choice betweenthe through hole ones; that I feel like areeasier to use; and small SMD ones, which youprobably already have seen on devices likethe Raspberry Pi.Sometimes resettable fuses are also knownas a Multifuse, Polyfuse or Polyswitch butif we want to be technically correct thenthey are actually called PPTC which standsfor polymeric positive temperature coefficientdevice and............wait a minute PTCs areactually quite popular.What they do and what their name basicallyimplies is that they increase their resistancewhen they get hotter.You can actually find their relative, theNTC aka negative temperature coefficient,on lots of 3D printers because they decreasetheir resistance when their temperature risesand thus they both can be used to measuretemperature.But back to the resettable fuse which doesin fact increase its resistance when temperaturerises but it still features lots of differencesto normal PTCs or NTCs.So as a practical example let's say I gota circuit that normally draws around 500mAat 12V like this RGB LED strip right hereand I want to protect it from shorts so thatthe fitting power supply does not get damaged.Now to choose a suitable resettable fuse weonly have to worry about 4 crucial propertiesand those are the maximum voltage and currentas well as the hold current and trip current.And I think the maximum voltage and currentis pretty self explanatory, meaning that ifyou exceed them you basically risk damagingyour fuse.The hold and trip current is a tiny bit morecomplicated, but still pretty easy to understand.The hold current basically stands for thecurrent that can flow continuously withouthaving to worry about that the fuse will evertrip.And the trip current of course is the currentthat needs to flow so that the fuse will activateand thus interrupt the overcurrent, prettysimple.So with these 4 rough values in mind for mycircuit, I went onto a search on Mouser Electronicsand decided on this PPTC that can do 60V and40A max and comes with a hold current of 0.5Aand a trip current of 1A.And if you are asking yourself right now:“Why not use a fuse with slightly higherratings for a bit of wiggle room?”then just wait a few more minutes for a littlerevelation.Because first off; it was time for a smallexperiment in which I simulated my “to beprotected” circuit with a constant loadto which I of course added my resettable fusein series and powered it all with 12V.Now while slowly increasing the current flowthrough my fuse, I also directly measuredand wrote down the voltage drop across itbecause those electrical values give us insightabout the power the fuse wastes which directlydetermines its temperature and also what resistanceit currently possess.So first big stop was the hold current of500mA at which point only a small voltagedrop across the fuse occurred that at somepoint also did not increase anymore meaningthe temperature of the fuse was stable andthus it would never trip at this point.Next was the trip current of 1A and here thevoltage drop did in fact increase over timeuntil the fuse ultimately reached it highresistance state in which my constant loadcould no longer draw 1A and thus turned off.Now you might be thinking that these 26s ittook for the fuse to activate are way toolong but as a comparison let's see how a 1Arated glass fuse would react to 1A of current.And yes we could sit here forever becausethe glass fuse would never trip and even at2A it still took way longer to activate onceagain in direct comparison to the resettablefuse.So yeah PPTCs are a bit slow; but traditionalfuses are even slower.But getting back to topic because next; totruly investigate the trip occurrence I addeda big power resistor as a load that wouldnormally draw around 1.2A.And by the way these three components I addedin parallel to the fuse are just a trip indicatorwhich lights up as soon as the fuse entersits high resistance state.OK; so now with the resettable fuse in placethe big current the resistor normally drawsgot quickly limited to only around 103mA.But wait a minute?Shouldn't a fuse cut down the flowing currentto nothing like a normal glass fuse woulddo?Well; such PPTCs can not do that because theyare basically just resistors whose resistanceincreases drastically at the trip currentbecause of the rising temperature.That does not mean they are useless thoughbecause such a drastic current reduction candefinitely prevent exploding capacitors, smokingtransistors or even save battery packs whenthings go accidentally wrong.And speaking of battery packs; PPTCs alsooften gets used with them since they tripwhen they get too hot and battery packs definitelylove to get hot when they are not handledcorrectly.But getting back to the trip event at whichpoint a so called leakage current keeps flowingthat basically keeps the fuse hot enough sothat it stays in its high resistance state.I also did some additional measurements inthis state to find out that no matter whatinput voltage gets applied, the resettablefuse basically creates a power loss of around1.2W which is quite a bit more than what thedatasheet claims.And speaking of datasheet; this is a goodtime to try out a PPTC with slightly higherratings like this one that holds at 0.9A andtriggers at 1.8A.I pretty much did the same tests and measurementsas before and the differences are that the“bigger” fuse features less power lossesduring normal operation but waste more powerwhen it got tripped.So the choice is up to you what is more importantfor you.Now the last thing we have to take a lookat is the area between the hold and trip currentand here the resettable fuse can trigger butdoes not have to.For example at 700mA the voltage drop andthus temperature only increases very slowlymeaning eventually this fuse might trip ifthe ambient temperature is also high.But at 900mA the voltage and temperature increasesway faster and thus the fuse tripped in mycase after around 1 minute and 42 seconds.This typical time to trip diagram given bythe datasheet can also help you out a lotregarding those questions.And by the way the PPTC also becomes ratherquickly conductive again as soon as the currentdecreases; but after tripping once its resistancewill take quite a long time until it willreach its initial value once again.And with that being said you should now befamiliar with most of the basics when it comesto resettable fuses and yes; they are definitelya good fit for the LED strip example we startedwith and they are also a standard when itcomes to many other protection tasks.Of course traditional fuses are a bit moreefficient meaning they produce less powerlosses.But then again eFuses, which I presented youin a previous video, pretty much come withthe same low power losses as traditional fuses.And even better, they do trip in a way moreprecise and fast way since they do not relyon a rising temperature that burns a metalor increases a resistance.But then again such an eFuse is a bit morecomplicated to set up, it is more expensiveand also not resettable by itself.They can also only be used for a limited voltageand current range, while the resettable fusescan handle quite a bit more and traditionalfuses are beasts in that regard.What I am trying to say here is that eachone of these fuse types is tailored to a specificapplication and I feel like with this videocoming to an end you should now have a verygood idea when to use which one.I hope you enjoyed it and learned somethingnew.If so consider supporting me through Patreonto keep the show going.As always don't forget to like, share, subscribeand hit the notification bell.Stay creative and I will see you next time.