Charge / ignition light problem

[Cobber]

I have just put the dash in the cobra and I have used LED warning lights.

The problem is the charge / ignition led does not go out when the engine starts it just glows at about half intensity.

If I change it to a normal filament bulb it goes out straight away.

I'm thinking it's a load thing?

Is there anything I can do so I can use the led or do I have to swap it out to a filament bulb?

 

[madmont]

It should have a filament bulb. It is only a warning light and the alternator will work without it. If you use the filament light and find that the motor still runs when you turn off the ignition (the light will illuminate) put a diode in the circuit as the 12v from the regulator feeds back through the light to the ignition circuit.

 

[Cobber]

alternator is charging fine and all things are working as they should. I would just like to keep all the warning lights the same led's if I could.

I want to understand why the led stays lit up and why it won't go out but a filament bulb will.

If things beat me I still have to understand why

 

[madmont]

You must still have a difference in voltage there which is just enough to light the led which does not need much current. Possibly a resistor across the terminals of the led to eliminate that voltage when running but not when not running

 

[Cobber]

Thanks Mont,

In series or parralel?

I guess I could use a variable resistor adjust it until the led works as it should and then buy a resistor to that value?

 

[Cobber]

Well I couldn't find a variable resistor so I put a test light in parallel with the LED and it goes out now as it should.

The resistance of the test light is 40 ohms so I will buy a resistor of that value and try it.

 

[devojet]

I would try a larger resistor first. Maybe start with something like 1000ohms. A 40ohm resistor with potentialy 12V accross it migh get a bit hot. Just buy a few different sizes, 1/2 watt resistors are cheap.

 

[Cobber]

Thanks makes sense, I'll get a few different sizes.

 

[sideshow]

just hide anothr globe in parallel under the dash
i fking hate led globes into dashes

ive done 8 cobras and half of them run the leds

they fail trice as much tooo

ive seen really good lights leds for dashes
but most guys wont spend the money

 

[devojet]

If set up correctly LED's should last almost forever. They should only fail if used outside of there ratings.

 

[Cobber]

I first put a 510 ohm 1/2 watt resistor in parallel with the led and that worked fine and the LED went out when the engine was started.

After talking to a friend about the problem he suggested the same as sideshow to put a filament bulb behind the dash but to point the light down into the foot well.

I have changed it now to a courtesy light that shines down near the pedals so that when you get in and switch the ignition on the foot well lights up so you can see the pedals at night, as soon as you start the car the light goes out.

The cobra has very small foot wells and the pedals are somewhat offset so being able to see at night works out well.

The LED's are Narva 12v units and have a nice chrome surround that match the rest of the instruments and were cheap at $4 each so even if they do blow it won't break the bank.