Electronics - Generic - Adjustable Voltage ?

no idea but any pics??

DonMaximo said:

I'm modifying an existing headlamp assy to include "Audi-like" LEDs within the 2 units.

After installing and testing, these lamps are little too bright for my liking.

I've read about installing simple voltage regulators that will allow me to drop voltage on the LED's. I don't know exactly how much voltage I would like to send to the LED's... and I thought about the mini-pot that is used in my Delta Controls FK55 Fan controller unit to set temperature.

Is there a means or a product that will allow me to use an "adjustable" voltage regulator on these LED's ???
...

Click to expand...

1. The brightness of LED's is determined by how much current is allowed to flow through them, up to some maximum value.
2. You could put a power resistor in series with the light, not efficient, but would allow you to measure the voltage the LED's will need to get the lumens you want.
3. You will have to do some Ohm's Law calculations to size the resistor for voltage drop & power dissipation.

Blown88GT said:

1. The brightness of LED's is determined by how much current is allowed to flow through them, up to some maximum value.
2. You could put a power resistor in series with the light, not efficient, but would allow you to measure the voltage the LED's will need to get the lumens you want.
3. You will have to do some Ohm's Law calculations to size the resistor for voltage drop & power dissipation.

Click to expand...

You won't find the resistor at Radio Shack either... you are looking a a resistor rated at 5-10 watts or more and probably less than .25 ohms. Automotive low voltage circuits are very sensitive to resistance due to the amount of current they pass.

Stock headlights = GE Part # 9004 headlight 45/65 watts each (low beam)

I=W/E
I= 45/14
I= 3.2 amps each stock headlight on low beam

I=W/E
I= 65/14
I= 4.6 amps each stock headlight on high beam

R=E/I
R= 14/4.6
R= 3.04 Ohms stock headlight resistance

E=IR
E= 4.6 amps x .25 Ohm
E= 1.15 Volt drop across .25 Ohm
now your 14 volt supply has dropped down to 12.85 volts, further reducing the light output. The resistor consumes 5.25 watts of power (W=EI)

The 12.85 volts on 3.29 Ohms reduces the current to 3.9amps

So you see that this mathematical puzzle just keeps going round and round: Increase the resistance, reduce the current, reduce the wattage.

jrichker said:

You won't find the resistor at Radio Shack either... you are looking a a resistor rated at 5-10 watts or more and probably less than .25 ohms...

Click to expand...

0.1 Ohm 5W Power Resistor-MPJA, Inc.

A 3-terminal regulator would do a better job, but most are limited to 1-1.5A.
National Semiconductor is the primary maker of these.
LM-317 +2 TO 35V TO-220ADJ.REG-MPJA, Inc.

DonMaximo:
1. You need to find out how much current the LED headlamps draw.
2. The mini-pot that is used in the Delta Controls FK55 Fan controller unit to set temperature are rated 1/4W. BTW, I know Brian.

Blown88GT said:

0.1 Ohm 5W Power Resistor-MPJA, Inc.

A 3-terminal regulator would do a better job, but most are limited to 1-1.5A.
National Semiconductor is the primary maker of these.
LM-317 +2 TO 35V TO-220ADJ.REG-MPJA, Inc.

DonMaximo:
1. You need to find out how much current the LED headlamps draw.
2. The mini-pot that is used in the Delta Controls FK55 Fan controller unit to set temperature are rated 1/4W. BTW, I know Brian.

Click to expand...

The LM 317 is rated at 1.5 amps.
The LM 350 is rated at 3 amps.

The gotcha for both regulators is there is a minimum of 2 -3 volts difference between input voltage and output voltage. If you input 14 volts the max you can get out is 11-12 volts. Look at the math from my previous post and you'll find that it probably too much voltage drop to accomplish what you want to do.

The next step is a Pulse Width Modulation regulator like the Delta control unit uses. PWM circuitry is much more complicated than a simple 3 terminal regulator. See http://www.ee.teihal.gr/labs/electronics/web/downloads/What_is_PWM_and_why_is_it_useful.pdf for more information
OR
http://fab.cba.mit.edu/classes/MIT/961.04/topics/pwm.pdf
OR
Pulse-width modulation - Wikipedia, the free encyclopedia