POWERING LEDS FROM CAR POWER SUPPLY

[makavelly001]

Hi all and thanks in advance for any input and response. My project is to drive between 35-40 SMD RGB  leds in a series, but I want to power the leds  using the  power source from my car. I would like to have 5  rgb leds  in each series and about 7-8 strings.. I understand that leds work more efficiently with constant voltage and current and therefore using the power from the automobile will be inefficient as the voltage and current fluctuate. To overcome this problem I have decided to look into some step up dc/dc converters that will output 30 -35 volts from 12-15 volts  input (car battery) and output a constant current of 10 amps. My  questions for this project are the following:

1. Is this the best way to increase the needed voltage and current to drive the leds from an automobile power supply?

2. If this is the best way to increase the needed power, should I connect  the dc/dc converter  directly to the            battery or fuse box.?

3. Do I need an inline fuse ?

4. Do I need to worry about CCA  blowing the dc/dc converter and the leds as the current can exceed 600 amps during start-up of the car ?

What is CCA ?: http://www.autobatteries.com/basics/selecting.asp
      CCA is critical for good cranking ability. It's the number of amps a battery can support
for 30 seconds at a temperature of 0 degrees F until the battery voltage drops to, unusable levels. A 12V battery with a rating of 600 CCA means the battery will provide 600 amps for 30 seconds at 0 degrees before the voltage falls to 7.20 V (six cells).

5.Should  the dc/dc converter have Short-circuit Protection and what should be the Maximum Input Current:

Below I have pasted the links to several Step Up DC/DC Converters which I believe might be suitable but I am unsure. PLEASE, PLEASE HAVE A LOOK AND SEE IF THEY ARE SUITABLE FOR THE TASK.
The following are from the company site:  http://www.xscyz.com/

http://www.xscyz.com/index.php?main_page=product_info&cPath=67&products_id=190

http://www.xscyz.com/index.php?main_page=product_info&products_id=274

http://www.xscyz.com/index.php?main_page=product_info&cPath=69&products_id=197&zenid=9106c8ca4c116f7ee6a047c88bb43162

http://www.xscyz.com/index.php?main_page=index&cPath=69

http://www.xscyz.com/index.php?main_page=product_info&products_id=189

http://www.xscyz.com/index.php?main_page=product_info&cPath=69&products_id=284

http://www.musclecars.net/parts/Powerful-DC-12V-to-24V-10A-240W-Step-up-DC-DC-Converter-For-Sale_200527576514.html

I have also listed the specs on the leds: in case voltage and current draw becomes a factor.

Forward voltage      min    typical    max    for. current
RED LED                2.0        2.3        2.8        120 ma
GREEN LED          3.0        3.5        4.0        150 ma
BLUE LED              3.0        3.5        4.0        150ma

[Hero999]

Hi all and thanks in advance for any input and response. My project is to drive between 35-40 SMD RGB  leds in a series, but I want to power the leds  using the  power source from my car. I would like to have 5  rgb leds  in each series and about 7-8 strings.. I understand that leds work more efficiently with constant voltage and current and therefore using the power from the automobile will be inefficient as the voltage and current fluctuate. To overcome this problem I have decided to look into some step up dc/dc converters that will output 30 -35 volts from 12-15 volts  input (car battery) and output a constant current of 10 amps. My  questions for this project are the following:

That's not true, LEDs ideally need a constant current source. The inefficiency of powering LEDs from a car battery via a resistor is the power lost in the resistor. The varying voltage just means the brightness won't be constant.

1. Is this the best way to increase the needed voltage and current to drive the leds from an automobile power supply?

The best and most efficient way is to use a switched mode constant current source.

2. If this is the best way to increase the needed power, should I connect  the dc/dc converter  directly to the             battery or fuse box.?

A DC-DC converter doesn't increase the power, it increases or decreases the voltage. If the voltage is increased the output current will be less than the input current and if the voltage is decreased the output current will be greater than the input current.

3. Do I need an inline fuse ?

Yes, if you don't want a fire if a short circuit occurs.

4. Do I need to worry about CCA  blowing the dc/dc converter and the leds as the current can exceed 600 amps during start-up of the car ?

What is CCA ?: http://www.autobatteries.com/basics/selecting.asp
       CCA is critical for good cranking ability. It's the number of amps a battery can support
for 30 seconds at a temperature of 0 degrees F until the battery voltage drops to, unusable levels. A 12V battery with a rating of 600 CCA means the battery will provide 600 amps for 30 seconds at 0 degrees before the voltage falls to 7.20 V (six cells).

Why would that blow the DC-DC converter?

The battery oltage is lower when cranking not higher.

5.Should  the dc/dc converter have Short-circuit Protection and what should be the Maximum Input Current:

Ideally the DC-DC converter should have a constant current output which is usually inherently short circuit proof. The only exception is a boost converter consisting of a single inductor which will short circuit when the output voltage falls below the input voltage.

Below I have pasted the links to several Step Up DC/DC Converters which I believe might be suitable but I am unsure. PLEASE, PLEASE HAVE A LOOK AND SEE IF THEY ARE SUITABLE FOR THE TASK.
The following are from the company site:   http://www.xscyz.com/

http://www.xscyz.com/index.php?main_page=product_info&cPath=67&products_id=190

http://www.xscyz.com/index.php?main_page=product_info&products_id=274

http://www.xscyz.com/index.php?main_page=product_info&cPath=69&products_id=197&zenid=9106c8ca4c116f7ee6a047c88bb43162

http://www.xscyz.com/index.php?main_page=index&cPath=69

http://www.xscyz.com/index.php?main_page=product_info&products_id=189

http://www.xscyz.com/index.php?main_page=product_info&cPath=69&products_id=284

http://www.musclecars.net/parts/Powerful-DC-12V-to-24V-10A-240W-Step-up-DC-DC-Converter-For-Sale_200527576514.html

Only one of those links worked for me and it's not ideal because it's a constant voltage source not a constant current source.
http://www.musclecars.net/parts/Powerful-DC-12V-to-24V-10A-240W-Step-up-DC-DC-Converter-For-Sale_200527576514.html

I have also listed the specs on the leds: in case voltage and current draw becomes a factor.

Forward voltage      min     typical     max     for. current
RED LED                2.0        2.3         2.8         120 ma
GREEN LED           3.0        3.5         4.0         150 ma
BLUE LED              3.0        3.5         4.0         150ma

Well the maximum forward voltage is 4V and you want to connect four in series making the minimum acceptable open circuit voltage should be 32V.

You need three constant current sources, one for each LED and the current should be set to a level which will give white light when all LEDs are fully on. The brightness can be altered by either varying the current or PWM but the latter is preferable as the brightness will be more predictable.

[makavelly001]

Thank you very much for taking the time to answer the questions so directly and properly, this has been a true learning experience for me. Im sorry the links did not work, but based on your insight i have concluded that this converter might be suitable. plese correct me if  needed.
1.
Module Properties: Non-isolated step-down constant current, constant voltage module (CC CV) charging module.
Input Voltage:  DC 5~30 V Output Voltage:  DC 1.25~26 V ( adjustable, O/p Voltage < I/p Voltage by 3V )
Output Voltage < Input Voltage:  3V
Output Current:  rated 2A, the largest 2.6A
Constant Current Range:  0.2~2A (adjustable)
Efficiency:  86%
Output Ripple:  0.05V
Potentiometer adjustment direction:  clockwise (increase), counterclockwise (decrease)
No-load Current:  Typical 10mA
Load Regulation: 

[Hero999]

Those are both constant current sources so would work but they're step down converters, which means the output voltage will always be below the input.

The LEDs will need to be connected in parallel as strings of two. Because LEDs don't current share well you should include current balancing resistors to help share the current, unless you derate them by half.