Author Topic: How to pick the correct rated Fuse to protect my Arduino project  (Read 2525 times)

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Offline pete1111

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just wanted to ask for some help please  :)

i have an arduino project that i have painstakingly made a PCB  design in Eagle and i was wondering i should probably protect it with a fuse.

my project consists of an arduino pro micro (SparkFun Version) running on 5v (from a pc ATX power supply)
it is connected to a 20x4 LCD (Backlit) and it simply displays 4 temperature readings from 4, TMP36 sensors.
there is a 3mm blue led also connected to the arduino.

i was thinking on using this Fuse ?
resettable 1812 msmd050-15v  500ma 15v auto recovery fuse pptc a6

I have a crappy M-830B multimeter


Offline danadak

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Re: How to pick the correct rated Fuse to protect my Arduino project
« Reply #1 on: June 04, 2016, 01:43:51 am »
Whats the sum total of all worst case component current ?

Regards, Dana.
Love Cypress PSOC, ATTiny, Bit Slice, OpAmps, Oscilloscopes, and Analog Gurus like Pease, Miller, Widlar, Dobkin, obsessed with being an engineer

Offline evb149

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Re: How to pick the correct rated Fuse to protect my Arduino project
« Reply #2 on: June 04, 2016, 03:06:38 am »
Sorry if it is bad news, but fuses whether they're of the normal blow once variety or PTC resettable fuses often can't protect the function of the circuit components.  Generally they're used to prevent safety hazards like fire and to protect the wiring itself (wires, maybe the PCB traces though that is of less concern since PCBs are typically not hazardous when burned).  ICs can be damaged with milliamps (sometimes less) of current going to the wrong place in the circuit, so a badly designed circuit or one exposed to miswiring or bad external inputs will often be damaged well before a fuse will blow.  But the fuse should protect the wires and PCB tracks in the circuit directly connected to the fuse so at least "all" you should have to do is replace damaged components.

If you want to protect the components themselves
{1} be careful and don't make wiring / circuit design mistakes.
{2} add ESD protection wherever possible (TVS devices, shunt capacitances in the 22pF to 1nF range)
{3} add series impedances (small enough to be harmless to the circuit's normal function) like resistors, ferrite beads, that sort of thing to signal and power lines to limit the current due to ESD or short circuits or crossed circuits so help protect the circuits from forseeable misconnections and transients.  Resistors 50 ohms or less might be harmless to lots of circuits but the particular details vary.
{4} Use robust buffers and couplers between the sensitive parts of your circuit and the "outside world" where more risks of misconnections and shorts and transients occur.  A 74HCT541 or whatever is much harder to blow up than a fancy MCU and is cheaper / easier to replace if it is damaged in many cases.  Optoisolators, et. al. can of course also help.

PTC resettable fuses aren't a bad way to add some protection to power lines, though, particularly in the lowest "hold current" ratings that will work for your power line needs, e.g. 500mA or more or less depending on your needs.  Just don't expect them to trip in microseconds or even a few milliseconds unless the fault current through them is considerably higher than their "hold" current rating.  So a power transistor or power FET or DCDC regulator or LDO or such might be protected by them, but not so much a MCU GPIO port.

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