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Trip computer LED install gone haywire. 

 

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 Post subject: Trip computer LED install gone haywire.
Posted: Tue Oct 18, 2005 11:02 pm 
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My tripcomp blue LED install has gone haywire on me, the backlight is intermittant (still have power to tripcomp only backlight goes off)

Ive checked the following:

Still have + 12v to the LED's (from the tripcomp lamp circuit)
LED's still work when powered externally.

my thoughts are:

voltage from tripcomp is too low for LED's (they get 3.0v each from my measurements)

voltage reg for dimming circuit has gone loopy, and is supplying 12v but at 0 amps.

my wiring loom thats been added to the car is still A OK,
LED's are fine,
tripcomp is fine

and every time i remove the tripcomp from the bloody dash it seems to start working again!

 

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Posted: Wed Oct 19, 2005 12:35 am 
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You say you remove it.. you mean when you power it externally? Or something else starts working when you remove it?

Ill put my bets on either a short, or a bad ground


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Posted: Wed Oct 19, 2005 12:59 am 
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did u uses teh correct resistors?

 

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Posted: Wed Oct 19, 2005 1:17 am 
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by "removing" i mean if i remove it from the surround and leave it plugged in, then the backlight starts working,

didnt use any resistors, i wired the 4 LED's in series so they each get 3.0 volts, (yes i know - dodgy) but they would have died Instantly or died then never came back.

im starting to think it may be a short as justfordima suggested (cant be bad ground cos i still have 12v going to the LEDs) or my inital idea of a stuffed voltage reg, tommorow i havent got school so im going to get to the bottom of this.

(and ive got a s**t of LED's and resistors on the way so i could do it properly)

 

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Posted: Wed Oct 19, 2005 1:26 am 
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well, just visually inspect it.. check the voltage at the feed line, and then compare it at the first LED.

Just remember, 4 LEDs in series doesn't mean they all get 3V... 12V goes, first LED gets 12V, then the LED resistance isn't that great, but reduces the 12V, and goes to the next LED, and so forth. This may be creating a bad circuit.. almost like a fuse breaker.

Do the resistors, and that should fix it.

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Posted: Wed Oct 19, 2005 2:07 am 
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JOSE wrote:
by "removing" i mean if i remove it from the surround and leave it plugged in, then the backlight starts working
Could be an intermittent connection at the plug - I know a lot of people push the wires in and glue them, but for best long term reliability 2nd hand pins from another clock plug should be used.
JOSE wrote:
didnt use any resistors, i wired the 4 LED's in series so they each get 3.0 volts, (yes i know - dodgy) but they would have died Instantly or died then never came back.

justfordima wrote:
Just remember, 4 LEDs in series doesn't mean they all get 3V... 12V goes, first LED gets 12V, then the LED resistance isn't that great, but reduces the 12V, and goes to the next LED, and so forth. This may be creating a bad circuit.. almost like a fuse breaker.
Putting 4 LEDS in series is okay to do - I use 2 lots of 4 in series as domelights in my cars, and they work fine, the only disadvantage is if any of the individual LED's are dodgy, it will stop all 4 from working correctly. So as mentioned, individual fits with a resistor each may be the better setup. A good calculator: http://www.hebeiltd.com.cn/?p=zz.led.re ... calculator
JOSE wrote:
im starting to think it may be a short as justfordima suggested (cant be bad ground cos i still have 12v going to the LEDs) or my inital idea of a stuffed voltage reg, tommorow i havent got school so im going to get to the bottom of this.)
Probably the easiest way to test things is to fit a normal lamp and holder and see if the problem remains.
JOSE wrote:
(and ive got a s**t of LED's and resistors on the way so i could do it properly)
I take it you're using LED's from that Ebay 'Wiseleader' dude - I use them too, but have found on average in every batch of 20, 2 or 3 will fail prematurely, giving signs such as intermittent lighting, flickering, etc - still, replace the faulty ones, for the price they are pretty cheap.

 

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Posted: Wed Oct 19, 2005 2:47 pm 
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i actually soldered the wires from the LED's to the metal contacts of the globe holder.

It wasnt working again today (still hanging out of the dash) checked the supply to the LED's 12v then the volt drop across the induvidual LED's, was all over the place, so id say as they have aged their resistances (however tiny) have begun to wander, one had 5v across it, another had .2v across it.

Just tried a verified working globe in the tripcomp and it works, so it looks like it was my dodgy series LED's (was a good idea at the time)

 

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Posted: Wed Oct 19, 2005 10:40 pm 
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well, stick resistors on each one, and use some new LEDs, as those won't last long if you said they had voltage drops and spikes... Let us know how it goes.


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 Post subject: Try this
Posted: Thu Oct 20, 2005 4:19 pm 
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Putting 12v across 4 leds and no resistors is not a good idea unless the leds are specificly 3v leds. Normal leds are 1.2v and need a current limiting resistor of around 1800 ohms.Leds are a current device not a voltage device. Too much voltage causes them to draw excess current and they die. Depending on the quality of the leds used some will go open circuit or short circut.
Also even using 3v leds you may need a resistor to limit current for when your voltage goes up to 14 or so volts. u need to know what current the leds draw and work it out from there. The place u purchased them from should b able to tell u the current.

 

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