How to install LED headlight in a Athearn DC diesel to eliminate the bulb


White LEDs are typically 3.3V and 20ma. The 12V LEDs are not really 12V, they just already have a dropping resistor installed.
 
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Smudge617 said:
A 3V LED only needs milliamps to work, that's why you have to have a resistor, and precisely why you use one on a locomotive, I'm not sure how a 12V LED would work, but I would assume exactly like an incandescent bulb which, if correct, defeats the point of switching from incandescent to LED, a 3V LED will give full brightness as long as it has power, even at low speeds.
Click to expand...
The 12 volt LED is only wired with a resistor to work at 12 volts. It is after all a 3 volt LEd so it does consume less.

Using a diode causes a ,7 volt drop which is similar to adding a resistor.

Now the LED uses 20 milliamps at it's top brightness. but will work down to 5 milliamps. Use Ohms law to determine the resistance need with a specific voltage.
 
Dub said:
The 12 volt LED is only wired with a resistor to work at 12 volts. It is after all a 3 volt LEd so it does consume less
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You can get LEDs that work at 12v without resistors, but in this instance won't do the job required.

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Dub said:
Use Ohms law to determine the resistance need with a specific voltage.
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I along with a lot of others, I can't get my head around this law, (it just gives me a headache). I have 6 different resistors and I know which resistor will give me the effect I want, ie, a 1/2W 1.5K resistor on a LED will give me maximum brightness using a power supply regardless of whether I'm using 12v or a lightboard on a loco.
 
some of these answers give me pause led's will light using AC or DC however they should be on DC AC they are pulsing very fast and seem to be lit harder to control
12 volt leds yes but expensive for true ones not for model rr

and yes just a resister with the led will give you directional lighting

resisters control voltage and current yes

what I used is a CL2N3-G led driver can use any dc voltage and only lets 20 ma to the led so constant brightness
if used with a common diode you can get directional lighting

These CL2N3-G are about 49 cents a piece available from numerous places just do a search for CL2N-G led driver
for those in England https://uk.farnell.com/microchip/cl2n3-g/led-driver-temperature-compensated/dp/2448491

if anyone wants further info I can give a link to a site that explains it
 
MikeGTW said:
some of these answers give me pause led's will light using AC or DC however they should be on DC AC they are pulsing very fast and seem to be lit harder to control
12 volt leds yes but expensive for true ones not for model rr

and yes just a resister with the led will give you directional lighting

resisters control voltage and current yes

what I used is a CL2N3-G led driver can use any dc voltage and only lets 20 ma to the led so constant brightness
if used with a common diode you can get directional lighting

These CL2N3-G are about 49 cents a piece available from numerous places just do a search for CL2N-G led driver
for those in England https://uk.farnell.com/microchip/cl2n3-g/led-driver-temperature-compensated/dp/2448491

if anyone wants further info I can give a link to a site that explains it
Click to expand...
Thanks Mike, great info as always.
 
I always used the breadboard. Test out the result and tweek to please.
The math just gives a starting point.
 

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Smudge617 said:
You can get LEDs that work at 12v without resistors, but in this instance won't do the job required.

LED Lamps | Cricklewood Electronics

Visit Cricklewood Electronics for Professional CCTV Systems that give full security to the homeowner. We offer high quality Home Security CCTV Systems.
www.cricklewoodelectronics.com www.cricklewoodelectronics.com


I along with a lot of others, I can't get my head around this law, (it just gives me a headache). I have 6 different resistors and I know which resistor will give me the effect I want, ie, a 1/2W 1.5K resistor on a LED will give me maximum brightness using a power supply regardless of whether I'm using 12v or a lightboard on a loco.
Click to expand...
You gotta find the fine print...
"Internal Resistor inside the LED "
and
" 5mm Diffused Green 12v LED With Integrated Resistor"

And here is a video showing how an LED behaves on a DC layout...
 
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dennis461 said:
You gotta find the fine print...
"Internal Resistor inside the LED "
Click to expand...
Exactly, no such thing as a "12 Volt LED". When the vendors say that they are using common terms to help folks understand the application.

I have never more misunderstanding about anything but LEDs. It is a little more complicated and technical, but the rules of thumb I use are:
1. An LED is not a light bulb do not think about it like it is and everything will be easier.
2. An LED IS a diode. Treat it like a diode when planning circuits and things will work.
3. An diode is a creature of current not voltage. That is a diode does not work not on an operating voltage but rather it has a threshold voltage. Once the threshold voltage is reached (usually between 1.4 and 2.2 volts) it then acts like a short circuit. It will try to pass all available current from the supply. With uncontrolled current it will instantly overheat and burn out. It is never voltage that burns out a diode it is the over abundance of current. This is why a resistor has to be in series with the diode, to limit the current.
4. This is also why ohms law doesn't apply to a diode. Ohms law applies to the resistor in series with the diode. There is a small voltage drop through the diode, but practically it is just along for the ride.
(If anyone cares, the diode formula is exponential and given by I=IS(exp(eVηkBT)−1), for which all the variables can be looked up on the web).
5. Diodes are designed to pass current in only one direction, so if it is put in backwards there will be no current flow.
6. Diodes put into an AC current will pass the current for one polarity and block it for the next. In effect a single diode will convert AC to half wave DC.

Then for LEDs specifically:
1. In an AC circuit the LED will turn on and off (60 times per second in the USA), but your eyes generally will not see this.
2. The more current that passes through the junction the brighter it will be. Playing with the resistor value will vary that current amount and allow one to set the brightness and hence the "mood" so to speak.
 
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Iron Horseman said:
Exactly, no such thing as a "12 Volt LED". When the vendors say that they are using common terms to help folks understand the application.

I have never more misunderstanding about anything but LEDs. It is a little more complicated and technical, but the rules of thumb I use are:
1. An LED is not a light bulb do not think about it like it is and everything will be easier.
2. An LED IS a diode. Treat it like a diode when planning circuits and things will work.
3. An diode is a creature of current not voltage. That is a diode does not work not on an operating voltage but rather it has a threshold voltage. Once the threshold voltage is reached (usually between 1.4 and 2.2 volts) it then acts like a short circuit. It will try to pass all available current from the supply. With uncontrolled current it will instantly overheat and burn out. It is never voltage that burns out a diode it is the over abundance of current. This is why a resistor has to be in series with the diode, to limit the current.
4. This is also why ohms law doesn't apply to a diode. Ohms law applies to the resistor in series with the diode. There is a small voltage drop through the diode, but practically it is just along for the ride.
(If anyone cares, the diode formula is exponential and given by I=IS(exp(eVηkBT)−1), for which all the variables can be looked up on the web).
5. Diodes are designed to pass current in only one direction, so if it is put in backwards there will be no current flow.
6. Diodes put into an AC current will pass the current for one polarity and block it for the next. In effect a single diode will convert AC to half wave DC.

Then for LEDs specifically:
1. In an AC circuit the LED will turn on and off (60 times per second in the USA), but your eyes generally will not see this.
2. The more current that passes through the junction the brighter it will be. Playing with the resistor value will vary that current amount and allow one to set the brightness and hence the "mood" so to speak.
Click to expand...
Think we're going a little off topic now
 
This is great! Just when you think you have a handle on the subject. Something else pops up.
 
So my earlier post about the exact same thing you must have missed plus the link on how they work and how to use them

So maybe I should just delete my post
 
MikeGTW said:
So my earlier post about the exact same thing you must have missed plus the link on how they work and how to use them

So maybe I should just delete my post
Click to expand...
No, it's a good post if someone wants to delve deeper into the mystery of LEDs they can, but it's their choice to do so.
 
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I have fitted lights in the past to my trains. I usually go with a 640R-1K resistor depending on how bright i want it to be, and usually wire a red and white with reversed polarity from each other and sharing a resistor.
Using optical fiber is a good idea too if you don't want to make big holes in the model, you can then have the lighting unit anywhere in the model (wrapped in black tape to hide the light), and then just feed the optic fiber to the lighting points.
 
The LED driver concept takes to me back in the 80's. There was the Lm 3606 (trusting my memory) It became obsolete and never until now, heard of a replacement. I grabbed the data sheets so thank you for that.
It is an alternative to calculating resistance in my small world. For a modest cost it simplifies purchasing the correct resistors or having extras on hand. Also, I do need resistors for other purposes.
SInce 2008, I have been seeking information on LED usage. There certainly has been a few giant leaps for me here. Even if I do not use the technical information, I am now aware of it and better off for it.

The optical fiber is cool too but have not used it, yet.
 
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