Using a resistor as a fuse

I may have asked this question a long time ago but I can not find it here on this “new” site.

I have a Uno alone in a wooded field running some sensors and wired to some other Unos a few feet away. Serial communication. All is well. Independent battery power to all sensors groups (common grounds between all).

It has not happened yet but i am concerned about an animal chewing through wires and creating a short. I was wondering is I used a 1/8 watt 1 Ohm resistor off the VCC and / or GND will it blow in the event of a short circuit.

I fabricated a bunch to test out and get inconsistent results (some times a clean blow, some times the resistor will continue to leak about 1/2 voltage, sometimes no blow at all). I assume the cheep resistors I bought online are not made to good tollerances.

Is there a better way to accomplish what I am trying?

Thank you!

I have done similar.

There seems to be little consistency between tests with this application.

Smaller 0803 SMD were the best. Experiment with 2 Ω etc.

You can buy resettable fuses similar to those used on an UNO.

Google PolySwitch Resettable PTCs Fuses

Fuses protect the wiring not the electronics.

Resistors are not made to act like a fuse. Why not use a fuse?

You could use a “polyfuse” like is on many Arduino boards to protect from overcurrent.

All the polyfuses I have seen are for 60V or more. when I google “Arduino Uno Polyfuse” I see things rated way above 5V and 0.5 A. I agree it is probably best to use a fuse rather than a resistor but finding the right fuse seems to be a problem (??) unless I am looking the wrong way (??)

Fuses blow from current flow, not from voltage applied.

I have also use Germanium whisker diodes 1N314 etc.

I thought of that earlier. A 1N34A I think can only take 1VDC (is a envelope detector) so VCC would kill it in an instant. I will google about te 1N314 now. That might be the solution even with a 0.3V (?) penality

Does anyone have a link for the types of re-settable fuses found on an Uno board? I did not see anything directly comparable on line. This will bring me closer to a good solution.

Thank you

Google SMD fuses

Thank you LarryD: I did earlier and there is a lot to search through. Do you have a specific part number : then I can zero in on what will be best.

https://www.digikey.com/en/products/filter/ptc-resettable-fuses/150?s=N4IgTCBcDaIA4BcDGACATgUwM4YQghgEYA2GKAZgK44gC6AvkA

Here is a collection of different values you can get.

Digital Key has lots.

Collection of fuses

PTC Resettable Fuse Kit 0.05 ~ 3A 6 ~ 33VDC Surface Mount 250 Pieces (25 Values - 10 Each)

Thank you everyone! This is a good start for me :slight_smile:

The diode is in SERIES with the load. What is the voltage between the two leads? It is only and ever will be the voltage drop from the junction of the two sides of the diode.
A short circuit will raise the voltage across the junction and destroy the diode, which seems to be what you want.
Paul

The OP seems to be confused about the difference between current and voltage. It’s not the voltage drop across a diode that destroys it, it’s the current. Sure, exceeding its voltage rating can and will damage it as well but we are are discussing the mis-application of diodes as fuses. Don’t do it. Diodes tend to fail shorted, not open.

If you’re trying to protect something from overcurrent, use a fuse. The mentioned polyfuse rating of 60 volts is the maximum allowable voltage. So long as you apply voltage below that rating, only the current matters.

Fuses are thermal rated devices and it is only current that causes them to open.

Resistors are power rated devices. Sure, you can crack a smd fuse open with an overload but it is the volts times the amps that causes the device to fail open, not the current alone.

Personally, if I was trying to protect battery powered wiring, I would absolutely not use a polyfuse. Why? Because it will eventually kill your battery unless the battery has internal protection. Without the battery protecting itself when it reaching its low voltage discharge point, a polyfuse will kill a battery with its open-cool-connect cycling. A picofuse or other clear once mechanical fuse is the best solution for most batteries.

There are “fusible resistors” available that are guaranteed to blow. “Normal” resistors may fail shorted.

I know the current is what blows a fuse. he power supply is 12V so a 60V (max) rated polyfuse will not trip if shorted in 12v (I have not worked with polyfuses so bear with me here).

I am not eager to have a poly fuse that will revert back to open: if there was a short I want to be able to find and fix it. for those reasons I desire a simple type of fuse that will blow throughly and remain blown till I come over and figure out WHY it blew in the first place.

Any reasonable mechanism will suffice.

Fusible resistors might e the best option for me. I will check them out as well, thank you all.

You’re contradicting yourself… and you’ll find fusible resistors are wholly inappropriate for the application. If you need me to explain why, please re-read post #14 or a fusible resistor datasheet, especially the section where they discuss clearing time verses overload.

You could use a common as dirt 3AG type glass cartridge fuse available in any big box home store or even Walmart in the automotive section. You’ll find inline wired fuse holders there as well. Cut, splice, solder, heat shrink, done.

A fuse’s current rating is the current above which it will break the circuit.

A fuse’s voltage rating is the maximum voltage it can break - at higher voltages the current may arc across the gap instead of being stopped. Glass/ceramic fuses usually have separate AC and DC ratings as DC arcs are much harder to extinguish.

For the OP: what is the intended behaviour of the fuse? Should it reset by itself, or simply break the circuit and keep it like that? Disconnect a single branch of the network (the wire that’s under attack), or break it all? How fast should it react? A polyfuse can take a while to react, much slower than a glass fuse.

There are protection circuits for LiPo batteries that protect against a.o. overcurrent. I have a 18650 here that will disconnect when shorted, and only reset itself when placed in a charger. Other types will continue to send a sense current through the circuit (a polyfuse basically behaves like this - when it cools down it resets itself) restoring the current when the short is solved.

wvmarle: The goal is for the fuse to break circuit immediately and cleanly. And to remain that way till I trace it out. If it “resets” It will not d me any good (potential intermittent problem which are often harder to find).

A simple “blown fuse” is all i seek.

Why? They have a bit longer time to blow compared to a fast fuse but they will blow eventually.