Got a LED wired up to my manual fan switch, yes you've heard me talk about it before, but hey now I had it working, for a few days.


The LED's keep burning out, due to something in my wiring or selection of components.


1) 12V source, here I used the power to the radio.

2) Resistor, have used 2.2K and up to 10K. They've all been the 1/4 Watt resistors.

I believe both LED and switch are rated for 20 or 30 A.


I'm going to use a different power source, since when I was working on it tonight I managed to short out the radio twice (blew the fuse twice, and had only one spare fuse). The LED acted up a bit before it blew, when I turned the key to accessory (i.e. radio on, ignition off) the LED came on anyway, without me flipping the switch.


Resistors, should I use the 1/2 Watt versions ? That shouldn't matter that much though should it ?

 

No way that LED is going to sink 20A. With the 10K (make certin that it is a 10K and not something eals) you should see a max of around 1.5mA. That shouln't be a problem. You've got something funning going on with your wiring job I think. The LED was in with the switch off? How do you have this thing wired?

 

Is this the blue LED in your other post? What's the max current and current at rated output?

BTW, just adding resistors to an LED is not the best way to control brightness. To obtain better dimming results you should be looking at things from a controlled current approach. LEDs tend to have vary linear light output Vs drive current. But not so linear if going at things from a controlled linear voltage approach.

 

A bit rough but ...

 

You have 2 options:
1. You have the wrong resistance on the resistor (measure it)
2. You wired it wrong.
3. Your LED isn't rated at the same voltage as the most others you see out there.

I'd double check the specs of the resistors and LEDs before you go any further wasting time with wiring issues.

 

How would I have the wrong resistance on the resistor ?

The LED I'm using this time is, I believe, rated for 3.7 V and 4.5 V max.

 

One: You don't just need to know the forward voltage of the LED, you also NEED to know the rated current of the LED. Though, even with the 2.2K resistor you should be OK.
And I think he means to measure the resistor, in case you got one in the wrong package.

Now on to what is happening with the LED working for a little while then dyeing. Do you have the LED wire to the switch side of the relay or the coil side of the relay. If it's on the coil side move it to the switch side. It is possible, but not likely, that back EMF from the coil field collapsing is causing them to poop.

 

Yeah good call. Maybe he should put a diode across the coil to tame that.


Maybe you should try wiring the LED and resistor straight to the battery just to see if they still pop. That rules out wiring and relay EMF.

 

put a diode on the relay

 

How do I put a diode on the relay, and where to do I put it, and what kind of diode ?


The wire running from the fan relay, to the fan switch, it's a wire that's spliced int othe green/white wire on the fan relay.


Could this problem be caused by my choice of 12V source ? Would it be any different if I ran the power from the fuse box instead ?

 

If I would take the wire from the fan relay, route in to the compartment, run through a resistor, to the LED and then to the switch.


Would that work ? Or would the result be the somewhat common Light On Fan Off error ?

 

They got an Auto Swap Meet this weekend at Qualcom. Going there tomorrow right after we got off at work.

 

You have two choices.
One, run a wire for the LED out under the hood and connect it to the switch side of the relay.
Or out under the hood at the relay see if it has a diode wired in with the coil right at the relay harness. If not get a diode (a 1N4001 or equivalent for the 1N400x series. Though if you can get a fast/ultra fast acting diode that would be best, but the 1N400x series is commonly used) and put it on the relay coil REVERSE BIASED. To do that, take your DMM and use it to check the voltage polarity at the coil. (The green wire should be the - and the 'other' wire should be the +) Look at the diode, one side has a stripe. Put the diode in paralle with the relay coil with the striped side of the diode to the + side of the coil and the 'non-striped' side of the doide to the - side of the coil. A 27pF cap is often used to help quench any relay chatter as well.

 

As dumb as it may sound, how do I know which side is which on the relay, since you guys are talking about "switch" vs "coil" side ?

 

Some should be able to help out with wire colors, but it should be the two thinner gage wires.
And a 1N914 would be a nive diode it use as well.

 

My signature has a link to all 3rd gen wiring diagrams.

Like needaz said, its the two thin gauge wires- should be a noticeable size difference.

 

<CENTER><B>When I add switches to my cars I use illuminated
ones with the led built in, and to isolate
it from power surges I go from ground to a 12 volt main
terminal on the fuse block.
Therefore this way I have a separate
and clean source of 12 V to the LEDS.
No burnout’s so far!.</B>
<P>
<TABLE BORDER=9 CELLPADDING=18
<TD BGCOLOR=black WIDTH=60><B><H3><CENTER>REFUSE
.TO
.LOSE</TABLE></CENTER>

 

I just looked at your schematic. Get a DPDT switch, do it right, and call it a day.

 

OK, what's a DPDT switch ?

How is it different ?

Is it wired different ?


Do they come in stainless and chrome versions ? I'm trying to combine function with looks

 

I'm going to reccomend googling DPDT switches and basic electronics and wiring. I could tell you but there is so much to cover. Basically, DPDT means Double Pole, Double Throw. So its just two switches build into package (still has the single lever though). Comes in all shapes and sizes.

One half of the switch would ground the relay, the other half of the switch would ground the negative LED leg.

 

Used to know more about electronics, just haven't touched it in years. DPDT switches is something I never used.

But .... ok... that does make sense though... I tried one of my old LED's, not sure whether I had used it in this particular fan switch setup or not, but the LED worked.

So a DPDT switch, so I would need wo different sources of 12V coming in ? And a ground for the fan switch and one for the LED.