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Old 4th September 2014, 12:27   #16
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Re: DIY: LED Tail lights on my Fiat Linea T-Jet

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Originally Posted by adrena View Post
Very neat job @Zblue!

I got here looking for LED replacement bulbs for my TJet when one has blown and found this treasure.

Really want to see the diagram. I am certain I will be able to do this without much hassle. I've done a fair amount of this in the past.
Well the electronics bit here is quite simple. What is more involving is fitting the LED boards so that the LED's are at the proper angle , sealing the lights so that they are watertight etc. Also , it is imperative that one has the tail light lenses available separately in order to do this DIY.

The original lights have the following bulbs :
  • Park - 5W
  • Brake/Fog/Turn/Reverse - 21W
The power draw for these are :
  • Park - 5W/12V ~ 400mA
  • Brake/Fog/Turn/Reverse - 21W/12V ~ 1750mA
Now what I have found is that the CANBUS is satisfied as long as the power draws/resistances are around a certain range about the above figures. For example , for the park lights , you do not get an error as long as they draw around 150mA to 600mA. Anything less than this and you would get the error message in the MID but the lights would still work. But if your park lights draw around 1A for example , then the BCM would cut power to the park lights completely (after sampling for about 3 seconds) and you would again get the error message.

Basically , your LED's would need to draw current as mentioned above (either just the LED's themselves , or through a combination of LED's and load resistors) in order to be error-free.

The LED's that I have used are these :

DIY: LED Tail lights on my Fiat Linea T-Jet-369821193_830.jpg

These are called "superflux" LED's and are a popular choice among DIY'ers. I used Phillips red-orange ones for park/brake/fog and Cree amber ones for turn. These are rated for a max current of 70mA , but are usually run at 50mA to increase longevity , and also because visually there is very little difference between the brightness at 70mA and 50mA. They have a forward voltage of around 2.4V and I ran them in series of 4.

Just to take the brake lights as an example , if each series of 4 LED's is run at 50mA , I would need a total of 1750/50 = 35 strings. This comes to 35*4 = 140 LED's.

if I regulate the input voltage to 12V , then by Ohm's Law the resistor is calculated as :

Voltage through the resistor = 12 - (2.4*4) = 2.4V

V = IR gives R = 2.4/.055 = 43ohms.

Is that helpful ?
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Old 4th September 2014, 13:38   #17
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Re: DIY: LED Tail lights on my Fiat Linea T-Jet

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Is that helpful ?
Extremely helpful.

I suppose I should then fire up Corel Draw to line up these strings in similar concentric circles and wire things up.

Now I only have to find the time.

I also noticed a post that mentioned the VW Jetta tail lamps. I really loved the way they looked. I've always maintained that the VW group really gets lighting and gets it right more often than anyone else.

Let me try a combination of stuff I see here and report back on how this goes.
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Old 4th September 2014, 13:55   #18
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Re: DIY: LED Tail lights on my Fiat Linea T-Jet

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Originally Posted by adrena View Post
Extremely helpful.

I suppose I should then fire up Corel Draw to line up these strings in similar concentric circles and wire things up.

Now I only have to find the time.

I also noticed a post that mentioned the VW Jetta tail lamps. I really loved the way they looked. I've always maintained that the VW group really gets lighting and gets it right more often than anyone else.

Let me try a combination of stuff I see here and report back on how this goes.
While I'm sure Corel would work , I used a software called Diptrace myself - quite user-friendly and it's meant specifically for designing PCB's. Just to give you a sneak peek , this is what the Diptrace circuit for the turn signals looks like :

DIY: LED Tail lights on my Fiat Linea T-Jet-screenshot-20140904-135135.jpg
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Old 28th April 2015, 20:06   #19
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Re: DIY: LED Tail lights on my Fiat Linea T-Jet

That's an exellent job.
I think the amount of patience & work hours spent would have been tremendous.
Should rate more than 6.5/10 just for that.
I also want to replace my bulbs with LEDs but am procrastinating. Probably will go for some ready to install replacements. But impossible to get the result that you get from a custom DIY job.
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Old 30th April 2015, 15:01   #20
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Re: DIY: LED Tail lights on my Fiat Linea T-Jet

That is one really impressive DIY ZBlue. The final result is fantastic, the rear look of the Linea looks really transformed now. The turn indicators are simple ingenius.
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Old 22nd September 2018, 15:50   #21
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Re: DIY: LED Tail lights on my Fiat Linea T-Jet

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[*]Park - 5W/12V ~ 400mA[*]Brake/Fog/Turn/Reverse - 21W/12V ~ 1750mA[/list]Now what I have found is that the CANBUS is satisfied as long as the power draws/resistances are around a certain range about the above figures. For example , for the park lights , you do not get an error as long as they draw around 150mA to 600mA. Anything less than this and you would get the error message in the MID but the lights would still work. But if your park lights draw around 1A for example , then the BCM would cut power to the park lights completely (after sampling for about 3 seconds) and you would again get the error message.
Well done, Zblue. A bit late to see this thread. What was the error-free lower current limit for the 21W lamps ? Was it 1750/2 or 1750 - 200 ? IF former, can I assume that the monitoring system has 50% leeway in either direction for the value of current that its concerned about ? Reason for asking is, what if we add simple aliexpress LEDs, note the current draw after the replacement, and just add as high a parallel resistor as possible (value dictated by your answer) inorder to just be within the current draw zone expected by the monitoring system. Hoping that heat can be dissipated safely, since the total heat from LED & added resistor would be lesser (theoretically).
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Old 5th November 2018, 19:11   #22
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Re: DIY: LED Tail lights on my Fiat Linea T-Jet

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Well done, Zblue. A bit late to see this thread. What was the error-free lower current limit for the 21W lamps ? Was it 1750/2 or 1750 - 200 ? IF former, can I assume that the monitoring system has 50% leeway in either direction for the value of current that its concerned about ? Reason for asking is, what if we add simple aliexpress LEDs, note the current draw after the replacement, and just add as high a parallel resistor as possible (value dictated by your answer) inorder to just be within the current draw zone expected by the monitoring system. Hoping that heat can be dissipated safely, since the total heat from LED & added resistor would be lesser (theoretically).

Sorry , it's been so long that I do not remember the exact values. But I would think that each of the 21W bulbs is monitored individually. You can always use a resistor which gives you close to 1750 mA current (together with the LED's).
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Old 5th November 2018, 19:39   #23
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Re: DIY: LED Tail lights on my Fiat Linea T-Jet

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Sorry , it's been so long that I do not remember the exact values. But I would think that each of the 21W bulbs is monitored individually. You can always use a resistor which gives you close to 1750 mA current (together with the LED's).
of course, the full 1750 would be the sureshot way to get rid of the error, but it would result in lots of heat.

My Q was more on the lines of "how much less than the 1750 can we afford to be, to quiten the error" . I asked this because I saw your comment that in place of the OEM parking bulb drawing 400mA , error is not shown if the draw ranges anywhere from 150mA to 600mA.

Lets say we make the parking bulb draw 200mA (instead of the OEM 400mA), how can this workaround be extended to the 21W lamps whose OEM draw is 1750mA ? What should I assume as margin - 50% reduction or 200mA reduction ?
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Old 6th November 2018, 17:30   #24
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Re: DIY: LED Tail lights on my Fiat Linea T-Jet

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of course, the full 1750 would be the sureshot way to get rid of the error, but it would result in lots of heat.

My Q was more on the lines of "how much less than the 1750 can we afford to be, to quiten the error" . I asked this because I saw your comment that in place of the OEM parking bulb drawing 400mA , error is not shown if the draw ranges anywhere from 150mA to 600mA.

Lets say we make the parking bulb draw 200mA (instead of the OEM 400mA), how can this workaround be extended to the 21W lamps whose OEM draw is 1750mA ? What should I assume as margin - 50% reduction or 200mA reduction ?

Sorry I never measured the minimum power draw required for the 21W bulbs.. because my LED's consume around the same amount of power
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