fuses with leds

Post by **ttocs** » Thu Jul 29, 2010 9:58 pm

the different fuses with leds that light up when the fuse pops has made me start thinking today. Why can't we just add that led to the fuse holder so that it lights up when the fuse pops. Would it be as easy as putting a 12v led inbetween the two terminals? The current would follow the path of least resistance which would be the fuse, till it pops and then it would light up the led right?

I got two pf1f1414kf fuse holders and was noticing how much space there was under the fuse to do something like this with out too much touble.

Post by **joerg** » Thu Jul 29, 2010 10:27 pm

You will find the explanation why just a simple led only won´t work!

http://www.wisc-online.com/objects/View ... ID=DCE5203

Post by **ttocs** » Fri Jul 30, 2010 5:22 am

there has to be a way to make it work, what would be needed other then math homework?

eulogious · Post by **eulogious** » Fri Jul 30, 2010 5:33 am

If you were to do that, it would pull the full load through the LED, causing it to pop as well. You are correct that it would take the path of least resistance, and then it would light the LED up for about 2 seconds, and then it would pop the LED, since the LED isn't capable of handling 20+ amps running through it.

You would have to come up with a circuit that would still kill all power to the amp (the whole point of a fuse) but still light up a LED, hence why they came up with the niffy $100 fuse blocks. If you just wired in a LED, you would still be providing voltage to the amps as well, and you might not want that, again that's the whole point of a fuse is to remove power from the circuit.

So yes I am sure you can do it, but it is not as easy as it seems...

Post by **ttocs** » Fri Jul 30, 2010 6:38 am

so how do they do it in the fuses?

I know how to build a circuit with relays to do it as I did it in my mustang but.......

str3atwarrior · Post by **str3atwarrior** » Fri Jul 30, 2010 7:00 am

Just a guess, but they probably just hook it with a diode to stop current going to the equipment when the fuse blows

eulogious · Post by **eulogious** » Fri Jul 30, 2010 7:03 am

Well that's a good question. The only thing that I can think of is that when the green LED is lit up on the fuse block it's getting it's power from the "output" of the fuse block, ie the side actually going to your amps. The red is powered by the "input" side of the block. Once you lose power to the "outside", it switches power to the other one. Like you said, you could do it with micro relays or something like that, but other than that, IDK... Just thinking out loud here...

str3atwarrior · Post by **str3atwarrior** » Fri Jul 30, 2010 7:16 am

I'm supposed to see my ex boss this weekend, i'll ask him to draw me a schematic on how it should be done, and i'll post it here. If someone know, he should be that someone :p

Post by **ttocs** » Sun Aug 01, 2010 8:00 pm

It has to be something pretty simple, as they can fit it all in a fuse. Is there a way I could reverse engineer it and cut it apart and figure out its voltage rating, polarity ect?

The Golden One · Post by **The Golden One** » Sun Aug 01, 2010 8:11 pm

you could put one leg of the led to the + side of the fuse and then run a small wire to the other leg and then run it to frame ground the led will only receive enough current to light up but not to much to blow. (':-s') man i think your gona have to have a way to cut the power to the led i think either a mini transistor or maybe an opamp can be used as a relay or maybe they make mini relays i dont know. im sure someone on here is mega genius enough to know for sure and can expend some info on this.

Post by **Jacampb2** » Mon Aug 02, 2010 4:10 pm

Ttocs,

the fuses work exactly like you are envisioning. The led is parallel w/ the fuse element, when the fuse blows. the led lights. The only thing you are leaving out is a current limiting resistor in series with he LED. The resistor will limit the current through the parallel LED side of the circuit, when the fuse is in tact, electrically the parallel stuff makes so little impact that is is virtually non existent. When the fuse blows, the only path left is the LED path, the resistor then limits the current to the entire circuit, not just the LED, the load at the end of the line will never come on because your current limiting resistor is limiting current to 10-20 mA for your LED.

I've built fuse indicators with exactly this method, it does work.

Good luck,
Jason

Post by **ttocs** » Mon Aug 02, 2010 4:46 pm

I fugured there is something simple and stupid like that. Any idea what value of resistor to use?

Post by **Jacampb2** » Mon Aug 02, 2010 6:10 pm

ttocs wrote:I fugured there is something simple and stupid like that. Any idea what value of resistor to use?

It depends on the forward voltage of the LED and the operating current, size the resistor for at or bellow the LEDs operating current to determine how bright it will be. You can fine tune your brightness with just a 12V supply and testing with a few different resistors.

There are some online calculators to figure out the resistance needed, I'll see if I can find one real quick... here you go: http://led.linear1.org/1led.wiz

Later,
Jason

Post by **ttocs** » Tue Aug 03, 2010 9:37 pm

I am guessing that a 4v led would be better off for this correct? How low do you think I need to keep the current to keep the amps from working? I would like to add the leds(and the resistor) to some pg fuse holders I just got. There is enoug space below the fuse to do this and I think it would be a cool mod to do so that when the fuse blows the holder will light up blue.

eulogious · Post by **eulogious** » Tue Aug 03, 2010 11:18 pm

I think I got 4 of the same fuse holder that you are talking about, and I agree it would be sweet to do this. I am going to be installing one of them into my wife's car here soon, so this would be really cool to do.

I will look into this tonight if I have time and see if I can come up with something. It should be be easy to figure it out...

As for the current the amps need to turn it, then should take a minimum to turn on, does it say in any of the manuals? Like a voltage range? A min amp draw maybe? I will look here shortly when I gots more time...

Post by **ttocs** » Wed Aug 04, 2010 4:43 am

it occured to me that 4 ft behind my laptop I had my meter, power source, leds and resistors that I could try this out for real. With a 4.2 ohm blue led and an 820 ohm resistor I was able to light the led plenty bright with only 16 mA of current draw. Do you think that would be low enough?

eulogious · Post by **eulogious** » Wed Aug 04, 2010 4:50 am

A relay uses like 200mA I believe, so that's plenty low I would think. Maybe try using your remote turn on and wire the LED up and see if the LED lights up and the amp does not turn on, that would be the answer I would think...

Post by **ttocs** » Wed Aug 04, 2010 5:25 am

and with a 1.2k ohm resistor it only pulls 2.3 mA, I can gurantee that isn't enough. With about 15 mins, some solder, one led and one resister(maybe $1 worth of parts) I was able to put it together and test it out. It lights up bright enough to be easily viewable in a bright room as it lights up the smoked case pretty bright. I just unscrewed the teminals on the bottom, looped the wire under it and then tightened it up. I can get pics up later if you want.

Post by **ttocs** » Wed Aug 04, 2010 5:47 am

here ya go, easy and cheap mod to do.

http://www.cardomain.com/ride/2395420/9

easier to put the link then to cut and paste everything.

dwnrodeo · Post by **dwnrodeo** » Wed Aug 04, 2010 5:54 am

Looks good!

eulogious · Post by **eulogious** » Wed Aug 04, 2010 6:00 am

Nice man! Thanks for the pics. I will have to do this when I install my wifes stuff!

str3atwarrior · Post by **str3atwarrior** » Wed Aug 04, 2010 6:01 am

Looking good!

Post by **ttocs** » Wed Aug 04, 2010 6:07 am

the 2nd one I did I actually took the time to center the led but I don't think it matters really. But yea it really only took the time to make one solder connection and loosen a few screws. With black heat shrink you would see almost nothing until it blows.

I see this happening to alot of holders on here, I want my cut of the profits!

Enjoy it fellas!

dwnrodeo · Post by **dwnrodeo** » Wed Aug 04, 2010 7:21 am

I see this happening to alot of holders on here, I want my cut of the profits!

You'd have to pay Jacampb2 then for engineering it.

str3atwarrior · Post by **str3atwarrior** » Wed Aug 04, 2010 7:39 am

Yep i have to agree that some black heatshrink would makes it even better!