What resistor values are needed for wiring LED taillights with a SPDT relay?

[RamSST]

Hi. New here. I'm not necessarily a newb at wiring I've used solder before and have wired up other simple wiring diagrams. I'm hoping someone can help me with a task I'm looking at doing. I'd like to wire up a set of LED taillights. 48 red led's in the brake circuit and about 24 in the turn signal circuit. The brake light will require a SPDT relay to switch from being illuminated and braking. I have a diagram but have no idea what kind of resistor values I will need. It's a 12V system. Any help is much appreciated
These are the specs on the red LED's I have:
Specifications:

Material: InGaN
Emitting Colour: Red
Lens Type: Water clear
Reverse Voltage: 5.0 V
DC Forward Voltage: Typical: 1.9 V Max: 2.3 V
Wave Length: 625-635nm
Luminous Intensity: Typ: 15,000 mcd
DC Forward Current: 20mA
Viewing Angle: 20±5degree
Lead Soldering Temp: 260oC for 5 seconds
Intensely Bright

This is the wiring diagram I intend to use:

 

[Emicro]

The problem that you are going to have with someone responding to your request, is that you are messing with a safety system on a vehicle. There is not only a liability issues, but also a moral issues. If you want to do the math yourself it is very straight forward. What you are trying to do is all covered in ohms law. You can use the resistors as current limiting devices, so you only have to worry about the voltage drop across the resistors you are going to be designing with. Also another thing to consider is the safety where your circuit will be located. Will it get wet? Will it get dirty? Will it be able to withstand the physical jarring of normal vehicle travel?

 

[oswaler]

First of all, welcome to the community! I can provide some guidance on the wiring and resistor values for your LED taillights.

Based on the specifications provided for the LED's, we can calculate the resistor values needed for your circuit. The first step would be to determine the current needed for each LED. From the specifications, we can see that the DC Forward Voltage is 1.9 V and the DC Forward Current is 20 mA. Using Ohm's Law (V=IR), we can calculate the resistor value needed for each LED by subtracting the forward voltage from the power supply voltage (12V) and dividing it by the forward current (12V-1.9V/0.02A = 505 ohms).

For the brake circuit, where you will be using 48 LED's, you will need to use a series and parallel combination of resistors to distribute the current evenly among the LEDs. This can be achieved by connecting 6 sets of 8 LED's in series, and then connecting these sets in parallel. Each set will require a resistor of 505 ohms, so the total resistance for each set in parallel will be 84.2 ohms (505/6).

Similarly, for the turn signal circuit with 24 LED's, you can use 3 sets of 8 LED's in series, and then connect these sets in parallel. The total resistance for each set will be 168.3 ohms (505/3).

In summary, for the brake circuit, you will need 6 resistors of 84.2 ohms each, and for the turn signal circuit, you will need 3 resistors of 168.3 ohms each.

It is important to note that these resistor values are calculated based on the specifications provided and may need to be adjusted if there are any variations in the LED's you are using. I would also recommend using a resistor with a higher wattage rating, such as 1/4 or 1/2 watt, to ensure they can handle the power without overheating.

I hope this helps with your wiring project. Good luck!