Uh oh.. what do I do..

[tim_l_012]

Hi All,

As some of you may know, I am into making things for my car.
I thought I'd be smart, and have a flashing LED, so it looks like I have a car alarm. Now, I ran a wire from the car battery, to my central locking. I split this wire, so that I could get a direct 12v from the battery, even with the ignition off.

Now that worked ok for a while, until I needed to turn the light off, so I put in a switch. This also worked for a while, until I thought about controlling the LED from the ignition.

I went out and got a relay from the electronics store, 5 pins, which was supposed to turn off the circuit when current passed into the coil.

This is the relay I used:
**broken link removed**

Now, I had the positive wire coming from radio power wire, into pin 85. Pin 86 went straight to ground. The wire from the battery went into pin 30.
I connected the LED negative to the car ground, and put the positive onto pin 87.

I left 87a disconnected.

With the car off, the LED was fine.. at this stage I was happy.. I then clicked over the ignition.. the LED went off, the radio came on, I was very happy. My friend then said to me, Tim, there is smoke coming from your car.. I thought he was joking so I laughed a bit, then my other friend said very seriously, TIM THERE IS SMOKE COMING FROM YOUR CAR.

I got soo worried, and the wire coming from the battery had melted. The wire inside was just particles of metal, and I have no idea why..

If Anyone knows how to fix this, please drop me a reply, asap.

Thanks in advance,

Tim.

 

[some1_234]

Maaaaah

 

[karenthestudent]

you can buy very cheap flashing LED's connected to a simple battery,then you will not need to tamper with your car electronics, which sounds likely to go wrong from the start.
just an easy suggestion...

 

[ChrisP]

The relay that you used is a SPDT type of automotive relay. I am curious about a few things:

• 1. how it was working as described if you left terminal 87a open -- 87a is the NC terminal, meaning that the circuit is complete through terminals 30-87a when the relay is de-energized, and through terminals 30-87 when power is applied to the coil;
  
  2. what you used for LED current limiting -- you don't indicate that anything was used;
  
  3. how you achieved the "flashing" of the LED -- again, you don't say how this was done;
  
  4. why there was (apparently) no overload protection (read: FUSE) on the battery feed to terminal 30;
  
  5. and finally, was the relay really wired as described?

The fact that a wire burned indicates that excessive current was present in that wire. This could be as a result of an improper circuit design, but it could also result from a failed component or an inadvertant shot to ground.

From what information I could find, the relay appears to be a 12V 30A SPDT type, so load current should not be a problem with this circuit if properly designed and constructed.

 

[tim_l_012]

Hmm I probably should have mentioned the LED.. It's a 3v-15v Flashing LED, from Dick Smith Electronics. Cost me about 3 times as much as a normal LED, but has its own flashing circuit.

My friend suggested its because when the circuit was switched, that power was going straight to ground, basically causing a short circuit.

What would I have to put in my circuit to stop it doing this again. Thanks in advance,

Tim.