Stopping dim leds

[al50991]

Hi i am doing an electronics course at college so should know this but i cant for the life of me remeber.

Anyway, what i would like to do is put some led strips in my car just in the boot so i can see a bit clearer. This i can do. The problem is that im pretty sure that once i switch the LED's off they will still stay on dimly. The power supply is a little under 13V so a 12v supply. However when the switch is turned of there is still 11.8V or so supply. This is fine for the normal filament bulb but im thinking not so much for the LED strips.

Im sure there is a circuit that can stop the supply once it gets below a set 12V trigger.

Thanks in advance for the help.

Alex

 

[audioguru]

Your switch is wired wrong if there is still 11.8V when it is turned off. A normal 12V filament bulb and 12V LEDs light perfectly with 11.8V.

You say your supply is "triggered"? How and why is it triggered?

 

[al50991]

Your switch is wired wrong if there is still 11.8V when it is turned off. A normal 12V filament bulb and 12V LEDs light perfectly with 11.8V.

You say your supply is "triggered"? How and why is it triggered?

This is exacturally what i thought. Ill go have another check as i must be wrong.

Ye its my boot light so it is triggered by the switch when the boot is closed.

Thanks

 

[al50991]

ok just checked again and it does go to 0V when its turned off with a load. It doesnt when there is no load. Surely this isnt right?

And will it still cause any LED's to stay on dimly

Thanks

 

[Reloadron]

OK, this points to the sensor and it can be normal. Now forgive me if this sounds stupid but the boot I think is what we call the trunk and the bonnet I think is the hood? Matters not but I keep trying to remember that.

Anyway, it depends on the sensor used to determine if the boot is open or closed. It may not be a simple switch. Many sensors need a load out there or leakage will show a voltage. If the sensor was chosen and designed to see an incandescent load the LEDs may not provide enough load. The trick becomes to shunt the LED circuit with a resistor.

Just a guess...
Ron

 

[audioguru]

the boot I think is what we call the trunk and the bonnet I think is the hood?

He is not talking about a "lorry" (truck) because only a woman has a boot and a bonnet. Maybe he is talking about a car?

 

[lilimike]

Ron is talking about a trunk, uncle $crooge is talking about a truck...
I have never heard the term boot light but in my car the dome light (that's the french term and I figure it is also the English name for it) turns off very slowly when I close the doors like if there was a really large capacitor. Being that the dome uses an incandescent light bulb perhaps using LEDs it would takes much longer for this capacitor to discharge?

Mike

 

[unclejed613]

i've seen the same problem with other LED lighting devices. you're getting a few microamps leakage current through the switch. or, if it only happens with the engine running, you're picking up alternator whine capacitively coupled from other wiring. a 1uf/50V cap across the LED strip should take care of a whine induced problem, a 4.7k resistor across the LED strip should shunt any leakage current.

 

[al50991]

i've seen the same problem with other LED lighting devices. you're getting a few microamps leakage current through the switch. or, if it only happens with the engine running, you're picking up alternator whine capacitively coupled from other wiring. a 1uf/50V cap across the LED strip should take care of a whine induced problem, a 4.7k resistor across the LED strip should shunt any leakage current.

Cheers mate that sounds like the thing i will need.

And its a car and in my car the boot (trunk) light doesnt slowly dim to off as i know some do so should be ok with unclejed suggestion.

Thanks alot guys.

Alex