Hey guys, since I accquired the Athearn P42's, I have been compelled to install ditch lights on the 2 that I own. But I have a problem, when installing them, they don't light up. I am using a Digitrax DH163P decoder, with 6 functions, function 1 and 2 are for the ditch lights. I have 470 Ohm resistors with 1.5 volt miniatronics incandescent bulbs. What am I doing wrong? I instal the resistors, they ditch lights don't light up, if I leave the resistors off, the bulbs light up, but then they burn out. Please HELP!!
Tyler Pirelli -
Modeling the Union Pacific Milwaukee Subdivision in 2005
Check out my pictures of my Flickr account: http://www.flickr.com/photos/52380934@N04/
Do you have 15ma or 30ma bulbs? For the 30ma bulbs you need a smaller resistor, 330 ohms is about right.
--Randy
Modeling the Reading Railroad in the 1950's
Visit my web site at www.readingeastpenn.com for construction updates, DCC Info, and more.
Hmmmm....
They are 40Ma 1.5 volt bulbs, so would 300 or 280 work?
Not much difference between the 2. I'd start with the 280. Might take a smaller one. For instance at .04 amps the drop across the 280 ohm resistor is 11.2 volts.
Springfield PA
So something like 240 and under. I'm new to this so it is taking me a while to understand this all.
Tyler -
I'd suggest getting the 15ma bulbs instead of using 40ma, they won't get as hot and you'll be able to use a 1/4 watt resistor for each, which is smaller. 750 ohm resistor for those.
270 ohm for the 40ma, but those resistors are going to dissipate nearly half a watt each and get warm themselves. Half-watt resistors are physically larger than 1/4 watt.
I'd suggest LEDs but with a Digitrax decoder the effects don't work very well with LEDs.
To calculate these resistor values, take the voltage at the function lead and subtract the voltage of the light bulb. This is how much voltage will be dropped by the resistor. Divide by the current rating of the bulb in amps, 40ma = .040 amps, to get the resistor value in ohms. Except in expensive precision resistors you can't get every value, so pick the next largest closest standard value.
Alrighty, I really appreciate it, looks like I might be going with the 15ma bulbs instead, better to have good lighting instead of melted plastic, right??
Alright, thanks for the responses guys, they are greatly appreciated