Who tried to replace the bulbs of the arrows of the machine with LED ones?
Were there any problems?
We all know the answer: yes! Do arrows flash too quickly (new cars) or too slowly (vintage cars)? Are errors displayed?
In this article I will explain how to avoid the car's error of the car when installing LED bulbs instead of incandescent ones. I will also explain how to make the direction indicators flash correctly.
Why the car's error happens
When you replace, with LED bulbs, position lights, direction indicators, reversing bulbs or stops, where previously incandescent bulbs were installed, problems can occur and even an error of the car's control unit.
On vintage cars, where there is no electronic control unit, the replacement is quite easy and the new bulbs, if of good quality, will work without problems. Eventually it is possible that the arrows (direction indicators) flash too quickly or too slowly.
On the most modern cars it is much more likely to find a control unit of the control unit (which some call canbms errors). The error is shown on the car monitor (Evic - Electronic Vehicle Information Center), has been equipped with it, or are stored on the control unit. Arrows (direction indicators) can flash too quickly.
These problems happen because LED bulbs are much more efficient than their incandescent sisters. At equal brightness, they absorb only 5-15% of the current of a traditional light bulb.
It is no wonder, therefore, if the control unit that controls the lights of the car is amazed that, where before there was a high absorption, now there is practically no more current absorption. In such a situation, an error is generated. The same situation happens for arrows (direction indicators): if the incandescent bulb absorbed 1.75a (the 12v 21w bulb), a LED bulb can only absorb a few dozen or hundreds of but.
LED arrows on vintage cars
If, after the installation of LED bulbs on the arrows of a vintage car, these flash too quickly or slowly, before trying what is indicated in the next paragraph, that is, to connect a resistor of value appropriate in parallel to the LED bulbs, I would suggest replacing the flashing light (Blinker, Flasher, intermittent relay) which is located in the car plant, with one suitable for LED bulbs.
There are several types for sale online. From 2 poles, 3 poles and also with adjustable flashing frequency. I recommend putting back the original relay and use the resistor (as I explain in the next paragraph), only after unsuccessfully trying to replace the flasher.
Solve the control error
To resolve the error of the control unit (or canbus error, as some say), or to restore the correct frequency of freshery flashing, it may be necessary to install a resistor in parallel with the LED bulb. I do not hide how much this solution is really not very elegant: light bulbs are installed and then a resistor is mounted that dissipates a mountain of energy in heat. It would be better to be able to reprogram the vehicle control unit, in order to activate the alarm only for lower absorption. It seems that this situation is not very practicable, as several control units do not allow you to enter the programming thus deep.
Many recommend using a resistor (R) of resistance equal to the one that had the incandescent bulb replaced. For example, replacing a 12V 5W bulb, the resistance would have a value of 27ohm and at least 10W of power. Replacing a 12V 21W bulb, the resistance would have a value of 6-6.8ohm and at least 50W of power.
I partially agree with the values suggested by the most and above. Obviously they are values that allow you to eliminate the control unit error, without damaging the system.
Value of the resistor to eliminate the control unit error
I suggest dedicating a little more time to experimentation and installing resistors (R) of higher ohmic value, in order to reduce current absorption and thermal dissipation.
For example, to simulate the load of a 12v 5W bulb, you could start with a 100Ohm 10W resistor (which would absorb only 1.5W instead of 5W) and check that the control unit no longer gives a mistake. If there was still a mistake, one could move on to an 82ohm 10W resistor, and so on until you reach the value recommended by most, hoping obviously to stop first to make the system more efficient.
With regard to the 12V 21W bulb, it cannot be excluded that the control unit is scheduled to report the error, for example, to 250ma in place that at 1.75a. In this case it could start with a resistance (R) of 47ohm 10W (as the actual absorption would be about 3W) and then get closer to the value of 6Ohm (consequently also increasing the power of the resistor (for example 22ohm 10W or 10ohm 25W).
Having to dissipate a lot of heat, I suggest installing the resistors on a metal part of the car, screwing them with screws and using the thermal and termination pasta on the surface of the resistor in contact with the bodywork of the bodywork. It is also necessary to pay attention to isolating electrical cables well.
Non-standard absorptions
Standard bulbs should not always be replaced. Sometimes you understand that they have to make changes to American cars to make them compatible with European regulations, for example. Or you want to replace LED optical groups with others more pleasant or performing. Furthermore, it is possible that the new light already consumes a lot of energy, but not enough to turn off the error of the control unit. In this case it is not possible to use predefined resistors (r), but you have to put your hand to the calculator.
By feeding the old and the new headlight separately, via a 12V bench power supply or battery, you will have to use a current tester to measure the two absorptions.
Suppose we measure the two currents:
- Vecchio light absorption IV = 200ma (about 2.4W)
- absorption of the new light in = 50ma (about 0.6w)
Through Resistor (R) in parallel to the new light, we will have to increase the absorption of about 150mA (= 0.15a, difference between IV and in).
We can calculate the value of the resistance by Ohm's first law: R = V / I = 12V / 0.15A = 80ohm.
We will never find on the market an 80ohm resistance, the closest value is 82ohm. We must now calculate the power dissipated by the resistor. W = V * V / R = 12V * 12V / 82ohm = 1.75W. We will have to choose a resistor of greater power, say from 5W for safety.
As explained above, to optimize the thermal dissipation, we can start from a higher value, and then reduce it up to 82ohm. We can start, for example, from a resistor from 180ohm (which would dissip less than 1W), to get closer to the final value.
Reduce the brightness of the LED bulbs
I dedicate this small paragraph to those who would like to reduce the brightness of some LED bulbs that are used as position lights. It often happens, in fact, to buy light bulbs that are too dim as reversing lights, but too bright as position lights!
We are obviously talking about bulbs that absorb little current (a few tens of mA) and that have an internal resistance current regulator. For other types of light bulbs, the following does not apply.
Solution 1: If you do not want to open the LED bulb, but you prefer to cut the wires of the car's electrical system, you can install a resistor (in the scheme indicated as King) in series on the thread that leads the positive power supply to the light bulb. Without being too many sizes and too many accounts, you could try resistors from 47OHM 5W or from 100ohm 3W. The higher the resistance value, the less bright the bulb will be.
Solution 2: If, on the other hand, you want to work inside the light bulb, safeguarding the car system, you can disassemble the light bulb and replace the internal resistors (in the scheme, indicated with RI) with others of higher value. It is possible to increase these values by 30%, to almost double them if you want to reduce the brightness a lot.
In the event of an error to the control unit (due to the reduction of the fulfillment of the light bulb), a resistor must be installed in parallel to the power supply, before the resistor Re.
Finally, for those interested, I wrote a article in which I explain why several LED bulbs that you buy online are damaged quickly.