# DCC Voltage/current specs for head/rear light and blue (common V+)



## Gigasaurus (Aug 22, 2013)

I am working with a friend on our own DCC decoder of sorts, and I'm trying to understand the voltage and current requirements for accessories - like front/rear lights and the blue wire (common V+ on the DCC harness).

I'm targeting having this board work for an Athearn or Bachmann HO DCC-ready train.

Is there someone with some technical knowledge in this field who could help me understand what voltage and current I should be supplying to the white (headlight), yellow (rear light) and blue (common V+) wires?

Much appreciated.


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## Brakeman Jake (Mar 8, 2009)

Normally,decoders supply 12VDC(+) through the blue wire,then the white and yellow are used to supply individual negative to regular 12V bulbs.If you want to use LED's,then you need resistors to each W and Y wires.

You will have to check what's in the loco for lighting because you can find either.Since you seem to be designing your own decoder,you may want to incorporate the resistors to it.


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## Gigasaurus (Aug 22, 2013)

Bravo. That's what I was looking for. Thanks very much Brakeman!


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## Mark R. (Jan 26, 2013)

Actually, the function output voltage will vary based on the DCC track voltage. Different DCC systems use different voltages at track level. The function output voltage will be 1.4 volts less that what is on the rails due to rectification within the decoder.

While knowing this really isn't all that important when using LEDs, it's very critical when using 1.5 volt bulbs. A 1 volt swing in either direction could make the difference between a bulb being too dim, or destroying itself.


Mark.


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## DonR (Oct 18, 2012)

For the reasons Mark and Jake have described it would
seem that converting the head lights to LED would be
the most desirable way to go. They'll stay burning thru
thick and thin.

I love those 1.5 v grain of wheat or rice bulbs and use them
a lot but in scenery where they can easily be replaced. Not so
easy in a loco.

Don


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