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Thread: How to fix flickering courtesy LED's?

  1. #1
    Senior Member HID Rookie Akshay's Avatar
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    How to fix flickering courtesy LED's?

    For some reason when you replace the interior courtesy light on the TT they flicker when the engine is running but fine when off. It seems that any LED replacement causes this effect so is there any way using resistors or other components. It seems that there is some strange circuitry in the unit that causes an LED bulb to flicker when turned on whilst the engine is running.

    Is this a common problem and is there a reliable fix?

  2. #2
    Senior Member HID KING need4speed's Avatar
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    mine does that too from time to time - not TT. what i have managed to identify is this usually happens when the battery voltage is low. like in a cold morning start or the battery has been drained from blasting the stereo. so the ripple waveform coming out of the alternator does not get filtered out by the battery as effectively and you see it in the flickering LED since LEDs respond to smaller voltage / current fluctuations compared to incandescent bulbs.

    only thing i can think of is to use a cap ahead of the LED array. what size? i dunno....... :-k

  3. #3
    Senior Member HID KING sy272004's Avatar
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    using voltage regulator might help
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    Senior Member HID KING apkarian100's Avatar
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    You could also install a Sharp PQ12RD21 12v regulator into the system and then make sure you install a 0.33uf capacitor between pins 1 and 3. This will serve 2 purposes, it will save the life of your LEDs and the capacitor will stop the flicker issue.

  5. #5
    Senior Member HID KING need4speed's Avatar
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    but what will the v reg do to the theatre dimming function? :-k

    right now for mine, i'm just using a shunt regulator becuz it only caps how much voltage gets fed to the array but not regulate it. so the theatre dimming function still works.

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    Senior Member HID MASTER azdave's Avatar
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    Quote Originally Posted by apkarian101
    You could also install a Sharp PQ12RD21 12v regulator into the system and then make sure you install a 0.33uf capacitor between pins 1 and 3. This will serve 2 purposes, it will save the life of your LEDs and the capacitor will stop the flicker issue.
    A capacitor of the correct size is the simplest choice assuming that the flicker is from "ripples" on the power system when the car is on and not from too much voltage or low quality LEDs.

    What size capacitor is determined by how much current the LEDs pull. If the cap is too small then the flicker will still be noticed. If the cap is too big the flicker should be gone but any PWM-controlled theatre dimming may not look as nice as before. I don't know the LED load you have but maybe try a 100uF cap to start with (wired across the leads in parallel and watch the polarity when you install it).

    A regulator might hide the problem but is more work to install and also could completely hide any theatre dimming feature.

    The Sharp regulator suggested would probably have the same issues of defeating the theatre dimming and the .33uF cap mentioned on the input would not be enough in this case to be of any help. The purpose of the .33uF cap on the input of the Sharp regulator is to deal with ocillations created within the Sharp regulator when you are using a high frequency PWM signal to trigger the on/off lead (pin #4).

  7. #7
    Senior Member HID KING apkarian100's Avatar
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    Sorry about the wrong info.
    Quote Originally Posted by azdave
    The Sharp regulator suggested would probably have the same issues of defeating the theatre dimming and the .33uF cap mentioned on the input would not be enough in this case to be of any help. The purpose of the .33uF cap on the input of the Sharp regulator is to deal with ocillations created within the Sharp regulator when you are using a high frequency PWM signal to trigger the on/off lead (pin #4).

  8. #8
    Senior Member HID Rookie Akshay's Avatar
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    I tried the resistor route previously but it didn't work so I gave up at that point. So a 100uF across the -ve and +ve ends of the LED is a good start then?

  9. #9
    Senior Member HID MASTER azdave's Avatar
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    Quote Originally Posted by Akshay
    I tried the resistor route previously but it didn't work so I gave up at that point. So a 100uF across the -ve and +ve ends of the LED is a good start then?
    I don't know since I have no idea what LEDs you have in your dome light. I'm just suggesting a starting point. If you have some high-current LEDs in there then 100uF might not even be close to enough. If you have just a few 20mA LEDs then 100uF might do it. Radio Shack usually has an assorted package of caps you could sample. You can also hook more caps in parallel as a test to gain more capacity.

    Yes, hook them in parallel across the LED power leads. You are basically placing a tiny, rechargable battery across the LEDs to help absorb short power spikes and also provide power when voltage drops out.

  10. #10
    Senior Member HID Rookie Akshay's Avatar
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    Thanks Dave I will try that route and see how I go.

    I was using flexible LED strips cut to size as I had some off-cuts left over so not high power.

    One other thing I find very annoying is that my lead free solder refuses to stick to the metal surface of the courtesy light holder no matter how much i file it down. Is there a better way?

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