BLOWN FUSE INDICATOR 220VAC

Thread Starter

Craps1956

Joined Aug 21, 2015
35
Hi all

I came across this blown fuse indicator circuit (Fig 1) on the net which I want to use in my projects.
1607986740664.png
Fig 1

So I put it together and tested it (without the bulb Fig 2) and it works fine.
Green led on, red led off with a good fuse in place.
Red led on, green led off when the fuse is removed.
1607986815648.png
Fig 2

But now here is the problem. When connected to one of my projects, (Fig 3) upon turn on the green led dies and the red led pops when the fused is removed. The connected project still works perfectly when the fuse is put back.
1607986868999.png
Fig 3

I tried again with a new led and this time increased R1 to 1M Ohm. Once again green and red led pops.

Any ideas what is wrong and how it may be fixed?
Any help will be much appreciated
 
The circuit is a failed design, the green LED has no protection against reverse voltage from the -ve portion of the mains sine-wave and will die. Oh well, it was good intentions. I'll think of a way to fix it.
 

MisterBill2

Joined Jan 23, 2018
11,583
Hi all

I came across this blown fuse indicator circuit (Fig 1) on the net which I want to use in my projects.
View attachment 224896
Fig 1

So I put it together and tested it (without the bulb Fig 2) and it works fine.
Green led on, red led off with a good fuse in place.
Red led on, green led off when the fuse is removed.
View attachment 224897
Fig 2

But now here is the problem. When connected to one of my projects, (Fig 3) upon turn on the green led dies and the red led pops when the fused is removed. The connected project still works perfectly when the fuse is put back.
View attachment 224898
Fig 3

I tried again with a new led and this time increased R1 to 1M Ohm. Once again green and red led pops.

Any ideas what is wrong and how it may be fixed?
Any help will be much appreciated
One thing will be to adda protection diode in series with the green LED to protect it from the reverse voltage. That diode will point in the same way as the green LED diode points. Also, make sure that the wiring is actually correct.
 

dendad

Joined Feb 20, 2016
4,110
Adding a diode in series with LED2 is a must, and you may have to also add an extraone in line with LED1 to prevent it turning on when the green LED2 is on.
It just depends on the forward voltage drop of the LEDs.
 

Thread Starter

Craps1956

Joined Aug 21, 2015
35
Thank all for for your input, I will use some of your ideas and continue to experiment and will report back here if I ever get it to work well. Thanks guys
 

Ian0

Joined Aug 7, 2020
4,845
The neon bulb and resistor combination is far less complicated and far more robust. And you can easily have a second neon indicator for power available. And a 1000 volt spike will not do any damage at all.
LEDs are fine for low voltage DC fuse-fail indicators. Nothing beats the neon for mains. Assuming that something nasty happened to make the fuse blow, it is likely to have killed the LED as well.
 

AlbertHall

Joined Jun 4, 2014
11,953
Hi all. Sorry I forget to report back on this one. I did get it to work. It benn working well for many months now. Thanks to all your comments and to Dendaf post #6.
That circuit will feed only half wave rectified voltage to the load. The bulb will be considerably dimmer than it otherwise would be.
It might work OK with an LED bulb but for a lamp having a 'fuse blown' indicator is a bit pointless.
 

MaxHeadRoom

Joined Jul 18, 2013
24,992
Here is the industrial fuse method I mentioned in #5, I took one of the ones I had apart.
It just has two half megohm resistors and a neon in series, . good for up to 600vAC.
Lit when the fuse is blown.
 

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