Which blown fuse indicator works best?

[MartOn]

I am building some blown fuse indicator LEDs and have found many solutions. Some very complex and some very simple.
I have ended up with 2 potential solutions:

Solution1:

One question here. What is the purpose of the Cap here? Why will not a pull-down resistor work instead?

solution2:


Which would you choose and why?

I am using it on a 12V system in a boat.. Fuses range from 5 - 30A.

[philba]

The cap in the first one does not have anything to do with the LED. It's a filter cap.

Solution 1 requires that there is at least a 20 mA (or so) load to light the indicator. If you don't have a problem with that, it's the better solution. You could add a load resistor but I think you don't want the circuit to drain your batteries over a long period . Solution 2 will work whether there is a load or not. It has a 20 mA load when it's on which you could cut in half by increasing R1 to 1K. It will drain .25 mA constantly, though.

I'd probably pick solution 2 and see if R2 could be raised to 100K.

[MartOn]

Hello
Thanks for your feedback.. I designed the circuit with 1k and 100k resistors. Seems to work fine.
My Schematic is ready and looks like this. I also had to use a different Transistor, since I did not have the 558. I used the 2N5401.

MarFuse Schematic

MarFuse scematic.png (10.42 KiB) Viewed 988 times

/Frode

[philba]

looks good. Any cheap small signal NPN would work. Do you really need the "power good" LED? That will drain your batteries over time.

At the risk of being overly redundant, you might want to fuse the power to your "fuse blown" circuits just in case a short happens there somehow.

[MartOn]

I want the option to connect the Fuse Good. The reason is that I have a bildgepump level monitor. that will automatically pump water out of the boat. It is important to have a visual notification that the pump has power. I will not connect all the "Good LEDS", but now I have the option to have that indicator on the box. I have quite large batteries in the boat. The largest bank is 2x180Ah, so there is plenty of Amps available. The boat normally charges from shorepower 24h per week, so I will not have problems with power. Also the start battery banks are totally separated from all other consumption.

I sent v1.0 of the PCB to manufactoring on friday. Its my first PCB design in Eagle, so I am excited to see how it turns out :p

I will put a small fuse on the 12V wire. With the 1k resistor, each LED will draw 9-13mA (voltage range from 11.7V-14.8V), so to drive 4 fuse-LEDs , I will put a 100mA fuse or something in that range.

/Frode

[MartOn]

Here is the PCB I designed..
Its my first PCB design ever, so keep that in mind

MarFuse PCB.png (136.97 KiB) Viewed 967 times