How does this work

[doggone]

Apparently the LED comes on if the fuse has blown.
You can also warm your testicles

https://i.postimg.cc/nLjbPkYH/huh.png

[stinkwheel]

I'd imagine straight electrics. Electricity will take the path of least resistance so if the LED/resistor combination is in paralell with the fuse itself, the electricity will simply go down the fuse wire because there is next to no resistance.

If the fuse blows, it'll then go through the LED (and presumably doesn't cook the wiring because the LED is applying load to the circuit).

I use a similar thing for finding shorts where I plug a bulb in in place of the repeatedly blowing fuse. When the bulb goes out, the short is gone.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[WD Forte]

Electrickery will always take the path of least resistance to ground.
If the fuse is intact, the current will flow through that and the resistance
in the led plus its series resistor will effectively be 'ignored'
Also voltages either side of the led which is connected in parallel to the fuse
will be at the same potential.

when the fuse blows (goes open circuit) voltage at the cathode/negative terminal of the led
will be less than at the Anode/positive terminal so current will then flow through the
led but be restricted to say 10-20 mA by the series resistor so unlikely to do any damage
to wiring,components or roast nuts.
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bikers smell of wee

[xX-Alex-Xx]

If it’s wired in parallel, the LED would be on as well as the device at the other end. Electricity doesn’t take ONLY the path of least resistance... eg if you wire 10 lights in parallel, all lights will come on, not just the one with the least overall resistance. They will all have the same voltage across them.

I think the OP has this backwards, the LED is on if the fuse hasn’t blown....
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DILLIGAF

[WD Forte]

A little knowledge is a dangerous thing......
____________________
bikers smell of wee

[Nobby the Bastard]

[Islander]

The resistance of a semiconductor is tricky to calculate as it's non-linear in relationship to the current that's passing through it. However, as the forward voltage of a typical LED is around 1.2v it will require a suitable resistor in series to ensure that the foward current doesn't exceed the maximum value. So if we assume a forward current of around 20mA, it'll need a resistor that will drop 10.8v at that current. This is around 540 ohms - 560 is a good value to use.

A fuse would typically have a resistance of a few millohms - a much lower resistance than the LED and series resistor. The current would flow in proportion to the ratio of the resistances. Let's assume a combined resistance on the LED of 600 ohms and a fuse resistance of 60 milliohms. That would mean that 10,000 times more current would flow through the fuse than the LED. The LED would remain unlit as long as the fuse was intact. If it ruptures, then the led would draw the current that the resistor allowed and would light.

Simple really

[Polarbear]

FFS. Why do you need a frigging LED on a blade fuse?

If you can't tell when it's blown from just looking at it you have no business even approaching an electric circuit.
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Triumph Trophy Launch Edition

[Islander]

[Easy-X]

[stinkwheel]

Anyway.

The smart place for the LED is on the fuse holder, not the fuse itself. You have to throw the LED away every time the fuse blows with an indicator fuse.

And even those are dumb because you can get re-settable circuit breakers that go in the place of a blade fuse these days. They cost about tree fiddy.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.