I just finished installing an NCE decoder and LED lighting in a new Athearn loco. I used the 470 ohm resistor that came with the Miniatronics LED's in the (-) side of the lighting circuit. Works fine. Each light, front and rear, consists of two 3V LED's wired in series.
Only problem is the Miniatronics LEDs are super bright. I would like to dim them. A friend suggested upgrading to 1000 Ohm resistor. That doesn't seem to dim the LED much if any.
Does anyone have experience with the miniatronics LEDs that can offer insight as to what resistance would cut the stadium glow of these LEDs? I was thinking of leaving the 470 Ohm resistor in the (-) and install a 1000 Ohm in the blue (+) feed from the decoder. My thinking is that would then get me a combined 1470 Ohms of resistance, or 3x what I have now. But if 1000 didn't dim them LEDs, I'm not sure if 1470 will be any better.
Any ideas and thoughts appreciated.
LED's are current driven devices. The higher the current the brighter they are. By adding a resistor you are lowering the amount of current that passes thru the LED. Most Decoders Function outputs run at whatever track voltage is (~14 volts for my Digitrax DCC system). Most LED's are rating somewhere between 20 and 30 Milliamps (Based on the resistor that was included, yours are probably 30 milliamp). Ohms Law (Voltage= Current*Resistance). Your LED is probably running around 14 milliamps with a 1000 ohm resistor. the 1000 ohm will put it at half brightness.
i would try two 1000 ohm resistors in series for a total of 2000 ohms. This should dim it quite a bit as that is 1/3 of the current rating.
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shay,
I found that Miniatronics LEDs with 1K resistors was sufficiently bright enough for headlights. I also place a piece of 1/8" OD heat shrink around the bulb to reduce light leakage.
Tom
https://tstage9.wixsite.com/nyc-modeling
Time...It marches on...without ever turning around to see if anyone is even keeping in step.
Most LED's I have come in contact with are 20 max. Usually, 1k allows about 9ma from all the ones I have worked with. LED brightness does not change as much with resistance change.
Some who use the super bright LED's just increase the resistance. Realize, installing LED's is not plug and play. You have to have some knowledge on how LED's operate.
Below is link for more info.
http://www.members.optusnet.com.au/nswmn1/Lights_in_DCC.htm
Rich
If you ever fall over in public, pick yourself up and say “sorry it’s been a while since I inhabited a body.” And just walk away.
In your post you state that you wired each pair of LEDs in series, you need to rewire them as singles, then add a 1k ohm to each LED, that should cut down the brightness quite a bit.
Jay
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modelmaker51 In your post you state that you wired each pair of LEDs in series, you need to rewire them as singles, then add a 1k ohm to each LED, that should cut down the brightness quite a bit.
Actually, that will make them brighter.
An example using 12 volt function outputs, 3 volt LEDs and 1000 ohm resistors: For two LEDs in series yo get (12 v - 3v - 3v) / 1000 = 0.006 amps or 6 ma. for each LED. When wired in parallel each leg gives you (12 - 3) / 1000 = 0.009 amps or 9 ma. for each LED.
here's some info on led's http://www.abctronics.com/media/abcT_The_LED_History.pdf
The only locos I've had to use other than a 1K resisotr are some Stewarts, the clear palstic used for the headlight lens is SO clear, it was way too bright. If you swapped the bulbs for LEDs on an AThearn I'm guessign the LEDs are directly visible, ie, there is no 'lens' in the headlight, just like it is with their stock bulbs. Instead of exposing the LEDs you might want to consider putting soem MV lenses in the openings and putting the LEDs behind them. This will serve to dim and diffuse the light from the LEDs more.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
CSX Robert modelmaker51: In your post you state that you wired each pair of LEDs in series, you need to rewire them as singles, then add a 1k ohm to each LED, that should cut down the brightness quite a bit. Actually, that will make them brighter. An example using 12 volt function outputs, 3 volt LEDs and 1000 ohm resistors: For two LEDs in series yo get (12 v - 3v - 3v) / 1000 = 0.006 amps or 6 ma. for each LED. When wired in parallel each leg gives you (12 - 3) / 1000 = 0.009 amps or 9 ma. for each LED.
modelmaker51: In your post you state that you wired each pair of LEDs in series, you need to rewire them as singles, then add a 1k ohm to each LED, that should cut down the brightness quite a bit.
Oops!