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Weird Led Issue, Sometimes It Works, Sometimes It Doesnt

nuffsaid

By nuffsaid,
in General Automotive Discussion

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nuffsaid Veteran

nuffsaid

Posted
Posted

Hi all

I have a 34 GTT and have replaced the bulbs behind the air con LCD display with LEDs. I bought these LEDs from an overseas seller who modified the stock bulb twist lock bases and put in a LED + resistor.

Weird thing is that 1 of the 3 LEDs sometimes works and sometimes doesnt.

3 days ago it didnt work when I started the car up in the morning, when i started it in the afternoon it was fine.

2 days ago, same thing again, didnt work in the morning but in the afternoon after work it worked fine.

Yesterday, didnt work in the morning, worked in the afternoon. Later on during the night it didnt light up again so I pulled it out, all looks to be well. The contacts, LED and resistor look okay (i think) so put it back in, and it works fine. I dont think its a loose connection because how can it work when I park my car at night, then not work when I start it in the morning.

Anyone have any ideas? I would get a new one but they arent cheap and take a while to get over here, just wanted to figure out what the deal is, quite annoying hahah

Thanks

RANDY Veteran

RANDY

Posted
Posted (edited)

Your LED and resistor is getting too hot... I bet.

If you work out which resistor you need (in ohms), you'll probably also notice a "wattage" rating. The bigger, the more amperage it can handle. The more amperage it has to drop for the LED, the more it has to transfer energy into the form of heat.

The heat will make an LED work, not work, flicker... you name it.

For most 14v applications, a 1 watt resistor is MINIMUM, but i've encountered problems even with those! A 2watt would work, but they're HUGE!

Only workaround I can think of is to use two resistors per LED. One to drop the voltage, and one across the LED to drop the amperage. Theoretically, they will both share the load. 2x1watt = 2watt.

Yet to actually TRY this though. =-[

Edited by RANDY
nuffsaid Veteran

nuffsaid

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Thanks Randy

Problem is they were hand made pre purchased items. Strange the other 2 in the exact same design are not having issues.

If heat is making it fail, I would;ve thought it wouldnt work in the morning and not the other way around. Ill swap the 2 working LEDs over to see if its a problem with the bulb or the connection on the circuit itself.

RANDY Veteran

RANDY

Posted
Posted

I think when the LED's get overheated, they are semi-dead. I've had 4 of them do the exact same thing to me, and then I went back to the drawing board and started measuring the temperature of the resistors with my multimeter.

14v down to 3.3v, at 100ma, using a 1/2watt resistor saw the temp go to about 80 degrees celcius within 30 seconds.

I'm using a 1 watt resistor now, and it gets to about 70 degrees. Obviously still too hot, because the globe assembly part has actually deformed from the heat, and those LED's are now stuffed.

My left-hand side doesn't work at all anymore, and the right-side flickers on and off.

nuffsaid Veteran

nuffsaid

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Okay switched around the LED that I thought was broken with one that doesnt give me a problem at all.

Worked well for 2 days...until today.

The one originally with the problem is in a new spot and that is fine.

The one that never had a problem in the problem spot is not fine.

This leads me to think that its the actual connection spot and not the LED itself.

There are 3 spots for bulbs behind the LCD display, why would the first spot from the left sometimes work and sometimes not. e.g. park my car, leave it for 10 hours, come back, and it doesnt work anymore. This is frustrating.

nuffsaid Veteran

nuffsaid

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I've returned the lights behind the LCD back to stock.

No problems yet (apart from the ugly light you get from incandescent bulbs). This morning it was fine.

If it continues to stay fine, what could it be? The circuit not liking the LEDs?

nuffsaid Veteran

nuffsaid

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Stock bulbs still doing okay by the looks of things...what theeee??

LEDs broken? cant be because I switched them around and its always the same spot. Circuit can deal with the board perhaps?

I did see that one of the legs of the resistor for the LED was touching the actual resistor, does this cause a problem?

666DAN Grand Master

666DAN

Posted
Posted

It's the contact being made on the track at the base, it may look OK, but the modified bulbs if treated to too much heat misalign the base giving intermittent contact.

This is why it's good practice to test all bulbs in situ before sending them out, just to check for any invisible defects.

The R34 A/C is prone to needing exact contacts with the rail, that's why I soldered directly to them.

nuffsaid Veteran

nuffsaid

Posted
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So perhaps that one spot is prone to some extra heat, that is why no matter which LED I use (I believe they are all working okay), somehow the LEDs are getting faulted?

Strange why for 3-4 weeks there wasnt an issue at all.

Is there anything wrong with soldering the LEDs directly on? I am worried that I could permanently stuff up something, OR I wont be able to return it back to stock if I wanted to (ie. the copper contacts are ruined?)

666DAN Grand Master

666DAN

Posted
Posted

Sorry, I jsut realised they ones you're talking about. I did the same thing as the guy, soldered them up and wrapped them around the base, as you would with a bulb.

It's the back lights for the buttons I soldered!

Hmm OK I've had no issues with the other ones, they went in extremely snug though, no possibility of them coming out without a screwdriver in the base slot.

nuffsaid Veteran

nuffsaid

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Hahah cool cool. My LEDs which are in a twist lock base for the buttons are working 100%, no dramas there yet (fingers crossed)

But behind the LCD, the guy who gave me the LEDs in the twist lock base, those bases arent a perfect fit, they are actually smaller than the original bases, I think that is where my problem is.

Do you agree DAN? I am inclined to think so seeing as the stock bulbs in the stock bases are doing okay at the momment. Too bad they're almost an orange colour when viewed with the blue buttons.

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