DIY 12V LED Taillights: Resistor & LED Setup

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Discussion Overview

The discussion revolves around the setup and optimization of DIY 12V LED taillights, focusing on resistor selection, LED specifications, and circuit design. Participants explore various aspects of LED performance, including brightness control and power requirements.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant seeks guidance on selecting the appropriate resistor for maximizing LED brightness without damaging them.
  • Another participant suggests determining the maximum current specification of the LED and using Ohm's law to calculate resistance.
  • Specifications for a 5mm LED are provided, including forward voltage and current ratings.
  • Discussion includes the use of Pulse Width Modulation (PWM) for controlling brightness in LED taillights.
  • A suggestion is made to use four LEDs in series with a 270-ohm resistor for optimal brightness.
  • A link to an online resistor and power calculator for LED panels is shared.
  • A participant inquires about the minimum power required for LEDs, expressing uncertainty about the lowest operational thresholds.
  • Another participant states that the minimum power is zero and suggests a low power setting of about 5mA.
  • Concerns are raised about measuring low voltage outputs from an LED circuit, with requests for alternative measurement methods.
  • Participants discuss potential issues with driver circuits that may lead to low brightness in LEDs, including high resistance and possible faults in the circuit.

Areas of Agreement / Disagreement

Participants express varying opinions on the minimum power and voltage requirements for LEDs, with no consensus reached on the best approach to measuring low voltage outputs or resolving issues with LED brightness.

Contextual Notes

Some participants mention specific LED characteristics and circuit configurations, but there are unresolved questions regarding the effectiveness of driver circuits and the implications of high resistance in those circuits.

riviknights
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I work on cars, and love the led look in the taillgiht of a car or vehicle. I want to learn how to make them, I know how to solder. I have made one just playing around, but am not sure if it is set up right. The first questiong I have is how do figure what type of resistor to use with how many leds to get the max light out of the leds without burning them out? Thanks for you time.
 
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You need to know the maximum current spec of the LED you wish to use. Considering it's for a car, you will most likely use 12vdc. Once you find the rated current, you can find the resistance using the following equation: V = IR where V is voltage, I is current (in amps) and R is resistance (in ohms).
 
Thanks for your time...

Size: 5mm

Lens Color : Water Clear

Forward Voltage (V) : 2.0~2.4

Forward Current (mA):20

View Angle: About 25 degree.
Static Sense:Yes

Luminous Intensity: 15000mcd
Life Rating : 100,000 Hours
 
LED Taillights use Pulse Width Modulation (PWM) to change brightness for taillight to brake.

There are a few solder together PWM demonstration kits to get started.
 
riviknights, if you want a simple circuit to get you started then try using 4 of those LED's (in series with each other) in series with one 270 ohm resistor. That is all five componets in one series circuit. That will get you somewhere near maximum brightness reasonably safely.
 
Here is a neat resistor and power calculator for a panel of LEDs

http://led.linear1.org/led.wiz
 
Thanks for all the help and advice, I greatly appeaciate it. I'm going to make some trial and test lights, I think I have enough information now, but just one more ? What is the lowest amount of power that can be put to these leds? I mean is there a minimum? Thanks agian for all the help. I will be back to show my result once I get them done.
 
The minimum power is zero.


If you want a low power setting then try about 5mA (which will reduce the voltage on each LED to about 1.7 volts) giving about 8 to 10 mW per LED
 
bipolar said:
LED Taillights use Pulse Width Modulation (PWM) to change brightness for taillight to brake.

There are a few solder together PWM demonstration kits to get started.

This page on my site shows a PWM circuit used to save battery power with LED lights.
It was found that the human eye could not detect the difference if duty cycle was 1:3.
Link here:-
http://www.geocities.com/sirkituk/sirkit_electronics_night_light.htm"
 
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  • #10
hi, I have made a circuit connected to an led . It produces very low voltage,which could not be measured by multimeter.so ,if anyone have better idea to measure that ,please reply.
And I also want to know about the minimum power ,voltage and current required for lighting the LED.thanks
 
  • #11
sulabh.dudex said:
hi, I have made a circuit connected to an led . It produces very low voltage,which could not be measured by multimeter.so ,if anyone have better idea to measure that ,please reply.
And I also want to know about the minimum power ,voltage and current required for lighting the LED.thanks

Is the LED lit when you measure this very low Voltage?
I assume not. So
1. your driver circuit is not working. or
2. your LED is faulty and causing a short circuit.

A standard red LED will need about 2Volts and will draw about 10mA for normal brightness.
Power = VI =2X0.01 = 0.02Watts = 2mW.
Hope this helps.
 
Last edited by a moderator:
  • #12
sirkituk said:
Is the LED lit when you measure this very low Voltage?
I assume not. So
1. your driver circuit is not working. or
2. your LED is faulty and causing a short circuit.

A standard red LED will need about 2Volts and will draw about 10mA for normal brightness.
Power = VI =2X0.01 = 0.02Watts = 2mW.
Hope this helps.

SIR, the LED lit (that's what the main problem is)with a very low brightness.I have tested the LED in other circuit and it doesn't have any fault,so the problem still remain as it was.
 
Last edited by a moderator:
  • #13
sulabh.dudex said:
SIR, the LED lit (that's what the main problem is)with a very low brightness.I have tested the LED in other circuit and it doesn't have any fault,so the problem still remain as it was.

It sounds as if your driver circuit has a very high resistance, which would cause a large volt drop when a current is taken from it.
It would help to know what that circuit is.
 
Last edited by a moderator:

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