Is there an easy way to get a LED switch to work properly (i.e. ALWAYS like this ... fan on light on ... fan off light off)

 

What kind of resistor would I need ? I've seen posts involving three 10K ones parallelled and also seen one involving a 680 ohm one

 

680ohms gives you about 15mA through the LED
3 10k in parallel = 3333ohms
3333ohms gives you about 3mA through the LED

LEDS usually want 5-20mA depending on what type, and how bright you want it.

typically for normal leds, on a car, 1k is what your after. that gives you 10mA.

Si.

 

The switches with the LED built in should also have the resistor built right in so there is no need for an external resistor. And the answer to you question is depends on the switch, but most of them, that just how they work, as long as you switching B+, not ground. But anything can be done.

 

I haven't installed mine yet but I was under the impression that in most cases this is what happens when one uses a LED fan switch:

1) Sometimes it works sometimes not
2) When it does work, light is on when fan is off, light is off when fan is on

 

Thanks for that usefull info Iroc-si. I was kinda in the blue about that until now.

One problem with the way i hooked mine up Vorgath is that when the fan is off, its dark outside, and im doing 45-50+mph the wind coming through the radiator causes my fan to start spinning in return slowly brighten ups my LED on my fan switch. You could prolly use a diode to take care of that.

 

hmm I may just wire the fan using a regular switch and add the LED separately, space it some more, besides not 100 percent happy with the LED switch anyway (looks that is).


Resistor, anything between 1K and say 4.5K ? And it has to be a 1/4W resistor ?


Switch should be hmmm 15 Amp, 20 Amp or higher ?

(knew I shouldn't have forgotten the electronics classes I took back in college grrrrr)

 

If you are wiring the switch in place of the temp switch in the block then that is wired into a relay. Therefore you do not need a high Amperage switch. probably 1A is fine.

As for the rating of the resistors, P=IIR. So for example, I=10mA, R=1k. Therefore Power= 0.01*0.01*1000 = 0.1W. 1/4W resistors are the ones your most likely to find, and they do just fine.

91GTABird, how have you wired the led? I would wire the switch to short the temp switch wire (dark green) to ground. Then wire a led via a resistor from a 12V source, to the switch. This setup should not cause the led to light unless turned on. Also this uses the standard relay, so the switch doesn't need to be that powerful.

Si.

ps. Just for the record the led current sums are as follows :

Current through a led is calculated :
Iled=(Vbat-Vdrop)/Resistor.

Where Vdrop is the voltage drop across the resistor. This is usually about 1.8v, but depends on the led.

 

OK, I went to Radioshack, looked around, their selection of blue LED's is not as big as red or green.

Which brightness should I get ? And what voltage ? Their LEDs are rated for like 4.5 Volt.

 

Here's one, that's rated 2600 MCD intensity, I think the lowest intensity was hmmm around 800 or 900 something like that. Max voltage is 4.5 Volt.

http://www.radioshack.com/product/in...&tab=techSpecs


Now the second one is lower intensity and is rated for max 6 Volt.

http://www.radioshack.com/product/in...&tab=techSpecs



How do I use any of them in a 12 Volt system ?

 

LED Museum_Anything you need to Know about LED's

Iroc_si, my car doesnt contain the factory relays for the fans or the original fans. I now have a single 16" that i have wired indirectly to a switch.

 

The voltage rating of those leds is the Vdrop in the equation I quoted. So for the low intenisty one you'd want something like 20mA with Vdrop of 5.0. Thus :

Resistor = (12V-5V)/20mA = 350ohms. usually best to round the resistor value up to the nearest common value.

Si.

 

Most LED's are capable of handing 20 mA with no problem. Red, Orange, and Yellow LED's want no more than 2.0 -2.2 volts; Green, Blue, and White can take 3.4-3.8 volts. That would mean a 680-ohm, 1/4 watt resistor will be perfect, but you can always go larger - within reason.

Don't overlook the fact that the charging system puts out about 14.7 volts when charging; you'll be blowing up a lot of LED's with a 350-ohm resistor.

I'm using a small rocker switch to operate a relay to power the fan; much safer than trying to run 25-30 Amps through a switch alone.

To be used as an indicator, you don't want (or need) a bright one. I use a red tinted one for mine, and it works the same way as that of 91GTABird as it's wired directly to the power wire of the fan. This way, I know for certain when the fan is spinning, and not just when the relay is engaged.

And Radio Shack is highly overpriced; I can ship you 2 6000 mcd 5mm Blue LED's with 750-ohm resistors for about $3.50. They are overkill for use as an indicator - you don't want to look into them when lit up...

 

Ditto

 

willie's total fan control

this thread deals with what you are talking about. willie mentions 12volt LEDs. then there ar eno resistors to worry about.