blown fuse indicator

[stingray_65]

While I was building a new control panel for my CNC I found a few fuse holders in my box-o-stuff that had an LED blown fuse indicator on them.

I got to playing around and wound up with this little circuit.

Uses 2 1n4007 diodes, a bi-color 3 lead red green LED and a 50k 1W current limiting resistor (100k for 220VAC)

the whole thing solders on to the leads of the LED and I used shrink tube on each leg and again around the whole thing.

Remember Main voltages are present here even if the fuse is blown use shrink tubing judiciously.

It lights green when the fuse is good, and red when the fuse blows. my first try I only used 1 1n4007 and the Red would shine a bit giving the whole thing a yellowish glow, the second diode seemed to be enough to block (lower) the current flow thru the red LED and only let the green light up.

when the fuse is blown, no current flows through the green and then the red glows nicely.

I wire my mains fuse before my mains switch, so this glows as long as it is plugged in, but if the fuse were wired after the mains switch it would only come on after the switch is thrown,

This little circuit can be retrofitted very easily most anywhere and may have many applications in other projects besides amps.

The LED's I used are 3mm, so all I need to do is drill a 5 mm hole for the 3mm LED holder and solder the 3 pigtails in.

[jay15511]

does this work?
i am a student and i get my final project similiar with this.

[stingray_65]

works well

[jay15511]

can i know how much is ur fuse and source?

[stingray_65]

You can use any fuse.

if this is for demonstration purposes, you could use a switch instead of a fuse.Opening the switch is the same as when the fuse blows.

the circuit does not need to be under load for this to work.

If you do not have a bi-colored LED, you can used 2 LEDs and solder the cathodes together

[jay15511]

Thx for the helping.but i got another question.when the fuse blown out,i have to use an optocoupler to trigger a siren.for sure,the red led have to glows like previous. please help as i not familiar with optocoupler connection

[HotBluePlates]

While I was building a new control panel for my CNC I found a few fuse holders in my box-o-stuff that had an LED blown fuse indicator on them.

I had a power supply that had a simpler method, but required a special cap for the fuseholder.

The cap itself housed a small neon bulb. When the fuse was good, it shorted the bulb. When blown, the 120vac line was across the neon bulb, which caused it to light.

You only needed it because there were multiple fuses (like 4-5). I imagine the bulb was rated for some of the additional higher voltages present, but I should probably check the schematic... the extra fuses might have been across the primaries of the multiple HV and filament transformers.

[FranciscoPerez]

Thanks for the contribution stingray.

I find this really useful in amps whose mains fuse is inside the chassis and not mounted in a fuse holder, and there's no easy way to check if fuse is blown.

[Shrapnel]

Another use: blown fuse or not, it could tell you if you forgot to plugin/unplug your amp, (or in the case of known to be plugged in, if you got power to the amp at all.)

Of course you'd have to make a habit of looking at it.