Soundtraxx and LEDs

Discussion in 'DCC & Electronics' started by Woodie, Jan 10, 2007.

  1. Woodie

    Woodie Active Member

    Hi Guys,

    Soundtraxx DSD-101LC decoder.

    It says on the packet, LED use(for lights) is not recommended, as they "may glow faintly when the function is turned off".

    (using a dropping resistor of course, as if it were for a 1.5V lamp, as the light functions are 12 - 16V).

    Anyone know if the use of LEDs actually damages these decoders, or it's just not recommeneded due to the above "glowing faintly", and the aesthetics of, maybe, a "faintly glowing" rear headlight, when going forward.

    As I "bash" my locos with decoders etc, I also put in LEDs and fibre optics for the lights etc, so I'd prefer LEDs if possible.

    Thanks guys.
  2. cidchase

    cidchase Active Member

    Hi Woodie,
    It must just be the decreased load of the LED that would cause the glow effect. If you do
    get this glow, and it is objectionable, add a resistor directly across the decoder output;
    about 1K 1/2watt. It should load the decoder output enough (about 15mA additional) to stop the glow.

    As many LED's as are used in locos, you would think that they would have this covered.
  3. Woodie

    Woodie Active Member

    Thanks Cid. What I might do, is hook up some LEDs temporarily (i.e. with the loco case off, etc) and see what sort of "faint glow" they are refering too. I suppose if doing this would damage the decoder, they would actually say so on the packet..... You hope they would, anyway.
  4. nhguy

    nhguy Member

    LEDs with a resistor and a diode are fine to use. The problem is that the voltage leaks through the functions as LEDs ar sensitive bulbs don't pick this voltage up. The LED will also 'blink' with speed steps. Bulbs will not. The diode with the resistor blocks the voltage from getting to the LED until it is turned on. It will NOT damage the decoder. It is a voltage leak problem. This has been discussed on the Atlas Forum and a few Yahoo groups. I believe the circuit for it is posted on either the Soundtraxx Yahoo group or the Soundtraxx sit or Tony's trains site.
  5. Woodie

    Woodie Active Member

  6. nhguy

    nhguy Member

    That's it Woodie!!
  7. rperego

    rperego New Member

    If you don't want dimming, if all else fails use a relay. For loads that exceed the decoder I use an NTE R57-10. Coil only draws 10 MA, output contacts good for 5 amps at 12V. 14 pin chip, very small. As noted in various decoder manuals, use a diode so the coil colapsing doesn't feed back to the decoder.

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