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Old 04-24-2012, 09:26 PM   #1 (permalink)
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Default LED Headlights & Fitting

I would like to repair the Headlights on my Helene Locomotive as the Globes have blown!, I have and would prefer to fit LED`s instead as I have many here in stock, but after three strokes and about 2 years off the beat I have no ideas which resistors to use!

I have no track Power and use 12 Volt DC Batteries as a Power scause in a Wagon.

Can some one tell me what colour resisters and which end to solder to the LED please!

Thankyou!
John.
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Old 04-24-2012, 09:30 PM   #2 (permalink)
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Default RE: LED Headlights & Fitting

Probably a 1000-ohm resistor will suffice. I use them with my 14.8 volt batteries. As for how to solder them, it doesn't matter which side of the LED the resistor is attached, only which way the current flows through the LED.

Later,

K
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Old 04-24-2012, 09:50 PM   #3 (permalink)
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Default RE: LED Headlights & Fitting

Do a Google search for "LED resistor calculator" and pick any of the sites found. (Try several!) These sites have you enter the circuit parameters and will tell you the resistor size to use. You will need to know the LED forward voltage drop and the current and the supply voltage. You already know the supply (12V) and the other numbers you get from the LED spec sheet. Forward voltage is often 3 to 3.5 volts and the current is often 20mA. (0.020Amp). Most of the sites will also tell you the nearest commercially available resistor value to the calculated value and will also tell you what Wattage resistor to get so it does not overheat.
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Old 04-25-2012, 02:51 AM   #4 (permalink)
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Default RE: LED Headlights & Fitting

Posted By John R on 24 Apr 2012 09:26 PM
I would like to repair the Headlights on my Helene Locomotive as the Globes have blown!, I have and would prefer to fit LED`s instead as I have many here in stock, but after three strokes and about 2 years off the beat I have no ideas which resistors to use!

I have no track Power and use 12 Volt DC Batteries as a Power scause in a Wagon.

Can some one tell me what colour resisters and which end to solder to the LED please!

Thankyou!
John.


John - another alternative is to use a current limiting integrated circuit that will deliver no more than 20 ma to an LED. The device that I use is CL2N3-G - they work very well - I have written up details on their use on my web page - have a look here:

Constant Current IC for LEDs

Please let me know if you have any questions.

dave
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Old 04-25-2012, 06:29 AM   #5 (permalink)
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Default RE: LED Headlights & Fitting

1000 ohms at 20 ma is for 20 volt drop plus 3 for the led.
So, for 12 volts with a 3 volt led, less than 10ma will be flowing for the led with a 1000 ohm resistor.

I would use a 680 ohm resistor for better brightness and still be under 20ma.
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Old 04-25-2012, 07:19 AM   #6 (permalink)
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Default RE: LED Headlights & Fitting

John here is a useful resistor calculator. Resistors are pretty forgiving so if you don't have the exact resistor one close to what is called for will work, as long as you don't go to hog wild. Here is the calculator we use all the time. Regal

LED series parallel array wizard
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Old 04-25-2012, 05:01 PM   #7 (permalink)
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Default RE: LED Headlights & Fitting

Gentlemen, and others,
Thank you all for your answers and input in my problem, I feel sure I will succeed in my Quest from here on in!.This is indeed a real learning curve.;-}


Thank you all sincerely,
John Richards.
Western Australia.
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Old 04-25-2012, 05:11 PM   #8 (permalink)
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Default RE: LED Headlights & Fitting

As an "underscore"... ALWAYS calculate the resistor you need.... also these calculators will tell you the wattage of resistor needed.

I can't tell you how many people I have helped over the years that just thought the resistor was some fixed value irrespective of the voltage and led type.

When you have carefully done a tricky install and got all the wires dressed and hidden and you then burn up the LED, it's frustrating, and it happens ALL the time.

Also, if you don't know the forward voltage drop on your white LED, use 3.6 volts, not 3.4 or 3.0 ... this can indeed cause problems at lower source voltages.

Regards, Greg
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