I'm adding an operational headlight to a steamer. I have on hand 1.5v microbulbs, 30 milliamps. For the moment I'm using an NCE D13SJR decoder. Can anyone recomend a resistor for an appropriate steam era light brightness?
Jay
C-415 Build: https://imageshack.com/a/tShC/1
Other builds: https://imageshack.com/my/albums
It looks like around 360 ohms. Here is a link to a lamp/LED primer. Save this guys stuff to your Favorites folder.
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.
I'd use a much higher value resistor than what Ohms law calls for to dim the bulb; something in the range of 560 to 1K. Steam engines had incandescent bulbs for headlights and were nowhere near as bright as today's halogen bulbs in diesel engines.
Using the resistor values in the link I posted, make a little resistor substitution box with a rotary switch using different resistor values for 1.5v lamps. You can then easily determine a suitable value resistor that pleases "you". Lamps change brightness quite a lot for small resistance value changes compared to LEDs. Hope this helps.
One of the handiest gadgets I've ever built for determing a resistor value is called a Decade Pot Box. The schematic and construction details appeared in the April 1999 issue of Nuts & Volts Magazine.
The basic principle is to use a series of potentiometers that can be switched into the circuit with each having a value 10 times higher than the last; i.e., 100, 1K, 10K, 100K, and 1Meg Ohm.
You start with the highest value, and work your way down until the bulb is the desired brightness, then measure the resistance with a VOM and use that value of fixed resistor.
I don't know if Nuts & Volts is still published or who published it.
Here is a link to a double decade box. Only one switch would be needed with a selection of resistors.
http://www.flickr.com/photos/moonbear3325/256488526/in/set-72157594305988969/