Diodes, and the many uses.

[Adam N.D.J.]

Ohkay, I've got a few dash lights out in all my vehicles. I was thinking, what about putting some LED's in there in place of a standard bulb. LED's use less power for the amount of light they put out, and they aren't that much in bulk. I was thinking that I could replace all the dash lights in all my rigs with them. And whot's the life of an LED?, the life of the car? I've never had one go out in any other the applications that I have them in. And I have an LED flashlight that I've had for years now. I was also thinking of putting them in place of other things like the map and dome lights and stuff. Whot do ya'll think? Has anyone else done this before? Or am I going to be the guinea pig?

[GLCraig]

Just remember that sufficiently bright LEDs do cost a fair amount still depending on the color. Also you just can't replace the bulb with an LED you will need to add resistor in parallel or is it series.

[Adam N.D.J.]

When I was building hot rods back in high school, we used LED's on several different cars for all kindsa lighting, to include dash lights. If you use a low voltage LED then you will need a resistor, but the ones that we used were 16 LED's, so they could be used in the automotive application without any resistors to bring down the voltage. If you used say a 6 volt LED on 12 volts, it will produce about twice as much light, but the life of it will be reduced by to 1/4 of normal. I've worked with LED's in all kindsa other applications, and have taken some college classes in electrical engineering, so I've gotten down what it takes to put em in. Guess I'll just go with the idea, then let everyone know how it turns out.

[bbbs53]

LED at correct voltage, up to 100,000 hours of UN-INTERUPTED use. Turning them on and off shortens there life somewhat, but they will far out last bulbs with those pesky filaments. There are 12 volt and 13 volt leds in a variety of colors. They do not produce the light of a bulb and are directional. Go for it, they will look cool. Your dimmer may not work, but who uses it anyway?

[frag]

Good! I think i found the experts i was looking for, you guys!

I want to use leds in a variety of circuits to inform me if voltage is getting to them or not. Example: on led in the fuel pump circuit. If the engine stops and fuel pressure gauge is at 0, looking at the led will tell me if voltage is getting to the pump or not. EtC.

What kind of led do i need and how do I wire them? The most important thing being I dont want them to take up too much current. Just act as sorts of extra idiot lights.

Do I just splice one lead of the led in the hot wire and the other one to ground. That simple?

Thanks in advance!

[Adam N.D.J.]

You can run a wire from your hot wire at the fuel pump to an LED in the dash, then the other lead on the LED to ground, when power is being supplied to the wire on the pump, then the LED will be lit. Just remember that the long wire on the LED is positive, and if wired backwards won't work.

As far as the dimmer goes, LED production of light varies with the amount of voltage supplied to them, so a 12v LED will produce less light at 6volts then at 12volts. Since the dimmer works by varying the amount of voltage to the dash lights, they should still work just fine.

[oddcomp]

go here for some high brightness low cost l.e.d's

i have not ordered from them myself yet

but a few of the peoplewho also do car computer installs like mine have used them

 

http://lsdiodes.home.comcast.net/

[NorseKode]

You can get much cheaper bright LEDs on ebay:

 

http://search.ebay.com/search/search.dll?cgiurl=http%3A%2F%2Fcgi.ebay.com%2Fws%2F&krd=1&from=R8&MfcISAPICommand=GetResult&ht=1&SortProperty=MetaEndSort&query=led+bright+mcd

 

 

Just add a resistor in series with each to limit current. Figure a max voltage drop across the LED at 3.6V with a max operating vehicle voltage of 15V gives 11.4V across the limiting resistor. So, for lights that operate when the engine is running, shoot for 20 - 50 mA across some resistance. Ohm's law states that resistance is equal to voltage over current, so 11.4V/50mA, 20mA = a resistance between 228 and 570 ohms. A 470 ohm resistor dropping 11.4V at 50mA would dissipate a little over half a watt of power, so. . . . a 1 Watt, 470 ohm resistor in series with your LED should work pretty well for warning and idiot lights. Since you want to have nominal brightness in the rear compartment when the engine is off, figure that at 12.8V - 3.6V = 9.2V. 9.2V / ~40mA =~ 230 ohms. Call it 220. This gives about three eighths of a watt dissipation. Just use a 1 watt resistor for simplicity and piece of mind.

 

Of course, if you are willing to add a zener diode into these arrangments, the input voltage will be more stable, and your calculations more precise.

 

Actually, now I think on it, putting three 3.6V leds in series with a 1/4 or 1/8 wat resistor makes a lot more sense. Ummm.... 3.6 times 3 is 10.8, which leaves 1.2V across some resistance to get ~40 mA. 1.2/.04= 30 ohms. Err... try it the other way for common resistor values..... 1.2V/22ohm = 55mA (pretty much the max current for a long useful life in these things.) 1.2V/47ohm = 25mA. This would yield a useful life of something like 10,000 hours of illumination from these leds.

 

Anyway, if you find this less than clear (and who could blame you) feel free to pm me, and I'll try a more structured explanation.

 

 

HTH.

Kalo