Re: wiring marker lights

Vollrath, Don <dvollrath@...>
 

Re - picking resistors.
I'm assuming that there are multiple marker lights, and chances are they will be too bright if run at their rated current or voltage. So a little pre-calc followed by try-&-see is the best way to pick the right resistor value. My assumptions below are that the 'blue wire' output for decoder function outputs is what you will be using for power. This is about 12Vdc.

For LED type there are 2 choices. 1) Wire the LEDs in series and in series with a single resistor to limit current in the string. Start with a 1.0 kohm resistor (~8ma). If it is too bright keep trying with higher value resistors until you get the brightness you like. It could be as high as 10 Kohms. Or 2) wire the LEDs up in parallel, each with its own resistor. Same game as before to select the right resistor value. Just play with one marker and use the same value for both sides. Be careful as the LEDs are polarity sensitive. Don't forget to include the 2 diodes, one to fwd and the other to rev headlamp function outputs to yield non-directional lighting as mentioned below.

For incandescent lamps, it is difficult to say because there are so many varieties, but I would expect that each lamp draws ~15-30 ma at 1.5 V. You can wire them in series with a single resistor, but do not wire them in directly in parallel as the markers + headlight might draw too much current for the function output of the decoder. You could also use a separate resistor in series with each lamp. Similar technique to pick a current limiting resistor. For an all in series connection.. calculate R = e/i, or... (12-2x1.5)/0.015 =600 ohms. I would try a 680 ohm, 1/4 watt resistor. [watts = e^2/R = (12-2x1.5)^2/680 = 0.12W] If it is too bright, go higher in ohms. If it is not bright enough, measure the voltage across each lamp (must not be greater than 1.5V) and try a slightly lower value of resistor ohms. When you think you have the right brightness verify by measurement that the voltage across each lamp is less than 1.5Vdc.

DonV

-----Original Message-----
From: WiringForDCC@... [mailto:WiringForDCC@...] On Behalf Of pbharry2003
Sent: Thursday, November 08, 2012 5:28 PM
To: WiringForDCC@...
Subject: [WiringForDCC] Re: wiring marker lights

Thanks Don
What would be a typical resistance for a led and a 1.5v bulb?

--- In WiringForDCC@..., "Vollrath, Don" <dvollrath@...> wrote:

Do you want to be able to control the marker lights on/off?
If not, wire them directly from the power pick-ups and skip the decoder altogether.

To be able to turn them on/off with the headlights, use 2 steering diodes to couple the marker lights to both front and rear head/rear light outputs. Then the marker lights will be on if either the front or rear lights are on.

Wire both diode anodes to the (-) end of marker lights. Wire the cathodes (the banded end) to the decoder function output channels. Other end of the marker lights are wired to the (+) supply common. Take care as they may be low voltage or LED type and need other additional resistor components.

DonV

-----Original Message-----
From: WiringForDCC@... [mailto:WiringForDCC@...] On Behalf Of pbharry2003
Sent: Thursday, November 08, 2012 3:20 PM
To: WiringForDCC@...
Subject: [WiringForDCC] wiring marker lights

I want to wire marker lights into a digitrax DH163D so that they are always on while the headlight and rear light are directional. What are your thoughts? Thanks.
Paul



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