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Resistor Value Calculation for 5x 5050 SMD LED Car Bulb Replacement

jas2010 58659 29
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How do I choose a resistor for a 12V car LED bulb with 5 5050 SMD LEDs so the CANBUS system does not switch it off?

Do not add a series resistor to the 5 LEDs; the bulb itself is already a 12V automotive LED module, and the real problem is that the car computer sees too little load and turns it off [#14604119][#14604261] The practical fix is to add a load resistor in parallel with the bulb to mimic an incandescent lamp, not to calculate one resistor per LED [#14604392] One reply recommends about 75 Ω with at least 3 W, preferably 5 W, because you need to dissipate about 2–3 W and the resistor will get warm [#14604392][#14604653] Another reply suggests starting with 100–150 Ω in parallel for testing, using a low-power resistor first, then sizing the power with P = U²/R at 14 V [#14604782] A weak 560 Ω / 0.25 W resistor may be too small to fool CANBUS; if needed, more than one resistor in parallel may be required [#14604698]
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  • #1 14601464
    jas2010
    Level 8  
    I replace the bulbs in the car with LEDs and some of them, unfortunately, do not have a resistor, which causes them to go out immediately. Such a bulb has 5 5050 SMD LEDs.

    I count well? The resistor for one should be: 420 ?? and times 5 now?
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  • #2 14601487
    Grzegorzm2121
    Level 15  
    You gave no tension or efficiency to the source but by reading the tea leaves I can tell you did it wrong! (kidding). First, state the voltage of the source, maybe the current efficiency and the type of bulb.
  • #4 14601591
    Grzegorzm2121
    Level 15  
    It looks like these bulbs are specially made for cars so you don't need resistors unless you have a 24V battery.
    It is strange that they are going out, maybe you have a wiring diagram in the car?
  • #5 14601624
    jas2010
    Level 8  
    In the car, the canbus system checks the bulbs and it seems they do not fit. I will look for a diagram in a moment, skoda octavia estate 2, 2007.

    Added after 3 [minutes]:

    Diagram:
    Resistor Value Calculation for 5x 5050 SMD LED Car Bulb Replacement
    This is how we put attachments on the forum!
    [_P_]
  • #6 14601655
    Grzegorzm2121
    Level 15  
    These bulbs are where do you want to install?
  • #7 14601692
    jas2010
    Level 8  
    I want to set up as positional.
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  • #8 14603532
    Grzegorzm2121
    Level 15  
    I found a problem! These bulbs you install have 3W and the car bulbs should be 5W so they probably burn out. See in the drawing a circle with a cross near the word "parking".
  • #9 14603549
    Molejnic

    Level 21  
    What do I have the power to burn out a light bulb? 3 or 5 watts is a question of power consumption. I would bet more on the problem of polarity or the fact that they have too little power and the car's computer turns them off because it treats them as burned. You would have to make sure if they were burnt or just not lit.
    Company Account:
    Elektroautomatyka Marcin Olejniczak
    Spacerowa 77, Leszno, 64-100
  • #10 14603573
    Grzegorzm2121
    Level 15  
    Can you check how many volts there are in the socket? Also check the current (only in series!) With a 10k resistor, we'll see if the voltage is constant.
    Also check the fuses.
    And if the car has a computer, it's bad because it is not known how it will react to these bulbs. Can you see them on some other power source, do they work?
  • #11 14603733
    jas2010
    Level 8  
    They are not burned, they go out because the computer disconnects them. On the back of the car I have 4 positional LEDs and the LEDs work in a combination of 2 LEDs +2 standard T10

    Added after 43 [seconds]:

    The bulb according to the manufacturer is 4.2 W
  • #12 14603738
    Grzegorzm2121
    Level 15  
    Maybe it is due to the resistance of these bulbs (too big or too small) you can get around the computer but it's difficult and risky. Maybe you need to give some resistor to confuse the computer.
  • #13 14604029
    jas2010
    Level 8  
    exactly, from the beginning, I am asking you to calculate the resistor, the formula gives me strange values :(
  • #14 14604043
    Grzegorzm2121
    Level 15  
    How do you count it? Because I too had problems with complicated layouts.
    You have to count every single resistance in the circuit so it will be difficult.
    And you also have to take into account everything that the bulb has inside, so it's a bit almost a miracle.
  • #15 14604064
    jas2010
    Level 8  
    In the calculator, for 1 white diode it comes out:
    The resistor should be: 420?
    Resistor power required: 168mW

    and for 5 diodes I have a message:
    This will not work - the supply voltage does not exceed the forward voltage of the diode (s)!

    Added after 1 [minutes]:

    http://kalkulor.pl/rezystor-do-led
  • #16 14604119
    vodiczka
    Level 43  
    jas2010 wrote:
    exactly, from the beginning, I am asking you to calculate the resistor, the formula gives me strange values

    If these are 12V LEDs, they have a built-in resistor or current limiter. What other resistor do you want to choose?
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  • #17 14604261
    jas2010
    Level 8  
    And they don't have little resistance and the computer (Canbus) sees them as blown and then cuts off the electricity?
    I see it that way. I will summarize what I know about the light bulb:
    4.2W power
    Voltage 12V
    Max forward current 60mA
    white color - about 3.6 V per diode (there are five)
  • #18 14604392
    Anonymous
    Anonymous  
  • #19 14604406
    mendozek666
    Pupil  
    Hello
    It seems to me that the problem with these leds is caused by one integrated circuit that is located in the comfort module or the BSI module.
    I did this recently in my car.
    After inserting all the LED bulbs inside the car and in the trunk, after closing the car with the remote control, the bulbs glow a little. The voltage measurement in this case is around 6-7V. I replaced one bulb with an old tube one and it's ok. Now all goes out to zero.
    I will add that in my module it is the U4791B chip and it is probably called a car lamp failure monitor or something like that.
    The system checks the set current consumption threshold, and after replacing ordinary lamps with LEDs, it is probably smaller, so problems with possible errors or turning off lamps with LED bulbs.
    Regards
  • #20 14604556
    jas2010
    Level 8  
    WoZaj wrote:
    According to the link provided by you, this LED bulb draws a power of 3W.
    You should have a 5W load for CAN.
    So you do this:
    You connect this LED bulb (YOU WILL NOT CHANGE NOTHING IN IT) in place of the old bulb.
    From the side of the plug you connect an additional resistor PARALLEL.
    Since you have to lose 2W on it, this resistor should be at least 3W (preferably 5W) and should be 75 Ohm.
    The resistor will be warm.
    And that's all.


    it makes sense :-) the same bulb has more on this page
    http://www.ledlumen.pl/produkt-1693-samochodowe.html

    for 12V there is no 0.25W resistor? I read something somewhere, but I might be wrong

    Added after 3 [minutes]:

    mendozek666 wrote:
    Hello
    It seems to me that the problem with these leds is caused by one integrated circuit that is located in the comfort module or the BSI module.
    I did this recently in my car.
    After inserting all the LED bulbs inside the car and in the trunk, after closing the car with the remote control, the bulbs glow a little. The voltage measurement in this case is around 6-7V. I replaced one bulb with an old tube one and it's ok. Now all goes out to zero.
    I will add that in my module it is the U4791B chip and it is probably called a car lamp failure monitor or something like that.
    The system checks the set current consumption threshold, and after replacing ordinary lamps with LEDs, it is probably smaller, so problems with possible errors or turning off lamps with LED bulbs.
    Regards



    maybe that would be enough
    http://www.sklepledowy.pl/pl_PL/p/Rezystor-0,25W-560ohm-dla-Zarowek-Led/525
  • Helpful post
    #21 14604653
    Grzegorzm2121
    Level 15  
    Since the resistor is to lose 3W power, using a resistor with a lower power will burn it.
  • Helpful post
    #22 14604698
    Anonymous
    Anonymous  
  • #23 14604748
    jas2010
    Level 8  
    You did not understand, it was supposed to be for my friend mendozek666

    what should I check? 1W and How Many Ohms?
    I care about the safe work of the light bulbs, Canabusa will finish cheating with Vag (the indicator of the burnt bulb)

    Added after 4 [minutes]:

    filter price PLN 20 :(
  • Helpful post
    #24 14604782
    Anonymous
    Anonymous  
  • #25 14605380
    vodiczka
    Level 43  
    Friends. What is the point of replacing an ordinary light bulb with an LED and then inserting a resistor (deceiving computer) that uses the battery energy uselessly?
    It is like replacing light bulbs in an apartment with energy-saving ones and turning on a small heater constantly :)
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  • #26 14605562
    jas2010
    Level 8  
    I replaced the low beam with a decent 50W kit. CREE and there is too much contrast between them.
    I admit that there is much greater visibility on Ledy.
    All glare on the road, signs. Overall a more enjoyable drive :-)
  • #27 14607822
    vodiczka
    Level 43  
    The topic is about parking, not passing.
  • #28 14608129
    jas2010
    Level 8  
    vodiczka wrote:
    The topic is about parking, not passing.


    Lists the reason for the positional swap.
  • #29 16057008
    jackins
    Level 10  
    Hello,
    I connected the LEDs without the module - 3 cables from lamps + and - and + control room.
    + control connected to the parking lamp
    - connected to the akku.
    + after the ignition switch to the ignition module in the cabin under the glove box.

    Unfortunately, they don't work properly.
    After turning the key, the LED lights are ok. After starting the engine, it is also ok. Unfortunately, after turning on the lights, the LEDs do not go out but they dim and blink or light up: /

    Parking light bulbs are not LEDs ... well, maybe LEDs are behind if it has meaning.

    Where is the devil sitting?

    Link to (probably exactly like mine):
    Link removed / trimmer01
    Moderated By trymer01:

    Regulations, point 3.1.19. Do not send messages on archival topics if this is another question, in particular other than the questioning person. Out of respect for the questioner, create your own topic. You can only add a solution to the problem.
    3.1.13. Take care of linguistic correctness and follow the rules of netiquette. Do not post messages that make it difficult to deduce what their author wanted to convey.
    3.1.18. Do not send links that will cease to be active after some time. This will make the discussion meaningless.
    3.1.11. Don't post messages that add nothing to the discussion.

  • #30 16057087
    Zdzisław1980
    Level 26  
    jackins wrote:
    Hello,
    I connected the LEDs without the module - 3 cables from lamps + and - and + control room.
    + control connected to the parking lamp
    - connected to the akku.
    + after the ignition switch to the ignition module in the cabin under the glove box.

    ...


    Shouldn't this control be connected to the + dipped headlamps?
    I am ignoring the fact that it has nothing to do with this topic.
    We write about something else here.
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Topic summary

✨ The discussion revolves around the challenges of replacing car bulbs with LED alternatives, specifically addressing the need for resistors to prevent the bulbs from burning out due to the car's CAN bus system. The user initially inquired about the appropriate resistor value for a 5-LED bulb setup, which operates at 4.2W and 12V. Responses highlighted that the bulbs might not require resistors if they are designed for automotive use, but issues arise when the car's computer detects insufficient load, interpreting it as a burnt-out bulb. Suggestions included using a parallel resistor to simulate the required load, with recommended values ranging from 75 Ohms to 150 Ohms, and ensuring the resistor can handle the power dissipation. The conversation also touched on the implications of using LED bulbs in vehicles with sophisticated monitoring systems, emphasizing the need for careful calculations and testing to avoid electrical issues.
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FAQ

TL;DR: Switching from a 5 W W5W bulb to a 3 W LED cuts current by about 40 %, triggering Skoda CAN-bus errors; “The resistor will be warm” [Elektroda, Anonymous, post #14604392] A 75 Ω / 5 W shunt restores the expected 350 mA load.

Why it matters: The right resistor stops flicker, dash warnings, and premature LED shutdown.

Quick Facts

• OEM W5W (T10) parking bulb: 5 W @ 12.8 V, 0.39 A [Osram W5W Datasheet]. • 5×5050 LED replacement: 3 – 4.2 W draw [Elektroda, jas2010, post #14603733] • Recommended shunt: 75 Ω, ≥5 W; dissipates ≈2.6 W at 14 V [Elektroda, Anonymous, post #14604392] • White 5050 LED Vf: 3.0 – 3.4 V @ 60 mA [Cree Spec Sheet; Elektroda, jas2010, #14604261]. • Power check formula: P = U² / R; e.g., 14 V² / 75 Ω ≈ 2.6 W [Ohm’s Law].

Why do my new 5050 LED parking bulbs shut off after a few seconds?

The Skoda Octavia’s CAN-bus monitors load current. Your LEDs draw only 3–4 W instead of the expected 5 W, so the controller thinks the bulb is blown and cuts power [Elektroda, jas2010, #14603733; Elektroda, Anonymous, #14604392].

Do 12 V car-LED bulbs need an external series resistor?

No. Quality 12 V LED bulbs have internal current-limit resistors or drivers. Adding another in series will dim them and can cause instability [Elektroda, vodiczka, post #14604119]

Which resistor value tricks the CAN-bus without harming the LED?

Add a 75 Ω resistor in parallel with the LED. At 14 V it sinks ≈185 mA and supplies the missing 2 W, restoring the 5 W total load [Elektroda, Anonymous, post #14604392]

What power rating should that resistor have?

Use a ≥5 W resistor. It must tolerate 2.6 W continuous dissipation plus heat from the engine bay. Aluminium-cased wirewounds handle this well [Elektroda, Grzegorzm2121, post #14604653]

What happens if I try a tiny 0.25 W or 1 W resistor?

It will overheat and fail within minutes because it must dump ten times its rating. Worst-case, it scorches nearby wiring—a documented edge failure [Elektroda, Anonymous, post #14604698]

How do I calculate a different shunt value for another bulb?

  1. Find required lamp power (Preq). 2. Measure LED power (Pled). 3. Compute Pr = Preq – Pled. Then choose R = U² / Pr using 14 V for U. Select the nearest standard value and a power rating ≥2×Pr for safety.

Is there a ready-made plug-and-play module?

Yes. ‘Warning Canceller’ harnesses with 50 Ω / 15 W resistors are sold for W5W sockets; they dissipate 3–4 W and simply plug inline [Elektroda, Anonymous, post #14604698]

Can software coding solve the Skoda bulb-check instead of resistors?

Many VAG models let you lower the lamp-out threshold with VCDS/Vag-Com. Owners report clearing the error without hardware changes [VW Self-Study Program SSP, 2019].

Will adding a shunt waste the energy I saved with LEDs?

Yes. The resistor burns 2–3 W as heat, so total power equals the original 5 W bulb. Energy saving is lost, as noted: “It is like turning on a small heater constantly” [Elektroda, vodiczka, post #14605380]

What surface temperature should I expect from a 5 W resistor?

A 5 W aluminium resistor running at 2.6 W typically reaches 80 – 95 °C in still air—hot enough to melt plastics if not mounted on metal [Arcol HS25 Datasheet].

How do I wire the resistor safely?

  1. Solder or crimp the 75 Ω resistor across the bulb’s + and – leads.
  2. Bolt the resistor to a metal chassis point for heat sinking.
  3. Insulate joints with heat-shrink and test; no dash warning should appear.

What if my vehicle uses a 24 V electrical system?

At 24 V the same 75 Ω resistor dissipates 7.7 W, exceeding its rating. Use a 220 Ω / 15 W resistor instead to mimic a 5 W lamp without overheating [Ohm’s Law; Truck Electrical Guide].
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