Help with Proto2K SW8 bulbs

Discussion in 'FAQs' started by Topo, Aug 22, 2002.

  1. Topo

    Topo Member

    Hello, friends. Can someone help me with this?

    Just I have purchased one P2K SW8. This loco is a twin of the SW9/1200 released by P2K in 1995/96. That model was a real pain to convert to DCC with an standalone -no plug&play- decoder (no NMRA plug, no space, very tight cabin...) After almost eight years, I thinked that Life&Like have had this model upgraded. I would have know better...

    "Easy adaptable to DCC control. See complete instructions inside".
    Uh, Oh! "Easy"?? No "DCC ready"?? @#*!! :mad:
    The "complete instructions" are, well, nonexistent. (more @#*!!) :mad: :mad:

    The facts are: after too much cutting&soldering&fidling, I have been able to install an Lenz 1024 decoder, and I have replaced the original fore bulb with a 14v Miniatronics one, BUT I don't find way to replace the one in the cabin without cutting the small plastic handrails. Do you know any way to dismantle the cabin without cutting/unsoldering this handrails?

    Another way is soldering a resistor in serie with the original bulb, but I don't know the bulb specifications (voltage, amperage) for calculate the dropping resistor (WHY Life&Like DON'T INCLUDE THIS IN THEIR "COMPLETE INSTRUCTIONS"????).
    I suppose that is 1.5v, but I'm not sure about the amperage, and I already have burned the fore "spare" bulb experimenting... :( :rolleyes: :(

    All advice will be welcome :confused:
  2. IMRL393

    IMRL393 Member

    I would also like the answer to Topo's question. I have the P2K SW9 to convert once my Zephyr gets here!

    The nice thing about the Atlas Master, Stewart and Athearn Genesis locos is DCC compatability (AMs come WITH the decoder). So while one might replace the lights...

    (If you need to! Certain DIGITRAX Plug 'N Play DCC chips, for example the DH163LO for P2K GP7s, provide the correct lamp voltage for the 1.5V lamps, so no lamp modification is needed! I don't think there is one for the SW8/9 locos, alas.)

    ..., at least all the other garbage Toco has had to go thru has been eliminated!

    I doubt that I will ever buy a non-DCC ready (or is that DCC not ready?) loco again!

    (Major Manufacturers take note!)

    P2K should know better!

    - George
  3. Vic

    Vic Active Member

    Topo....I don't know beans about DCC but most 1.5V minature bulbs have a current rating of around 50 ma so if you stay on the high side of that when calculating the value of the dropping resistor you should be safe.
  4. Topo

    Topo Member

    Thanks friends

    After the first experience (when I burned one bulb, rats!), I have already tried for 30mA. (450 Ohm resistor) but it was too much and the buld don't light.

    So I will pass it 'old style': trying resistors for 75mA. 70mA. and 50 mA. I will keep you posted about the results.

    George, I hink that NCS and Tony' TTX have plug&play decoders for this loco, but they don't have the 'Back-EMF' feature that the Lenz has.

    Thanks for the help
  5. Topo

    Topo Member

    If someone is interested...

    I tested the bulb specifications.

    After all, these Life&Like bulbs are 1.5 volts, and they sucks 75 milliamperes!!! :eek:

    I have 15 volts on the track, so I need an 180 Ohm resistor: (15 v - 1.5 v)/0.075 Amp = 180 Ohm

    ...and the resistor needs to be 1 watt or over: 13.5 v * 0.075 Amp = 1.01 watt

    These 1 watt resistors are too large to fit easily inside the SW8 hood, and they run HOT. I have considerate to use 3-in-parallel 0.5watt 540 Ohm resistors, but finally I give up all the resistor history and go for opening the cabin and have the bulb replaced with an 16v Miniatronics one.

    IMRL393, the SW8 came with a weight that can be discarded (it is secured by 4 screws) in order to get more room under the hood, but I didn't recommend to do it, because this small switcher needs all weight you can put inside, specially if you plan work it on grades. :(
    If you don't need the 'back-EMF' feature of the Lenz decoders, I conseil you to get a plug&play decoder (NCS or Tony's) for these locomotive and avoid all the hassle.
  6. Gary Pfeil

    Gary Pfeil Active Member

    Topo, The 15 volts at your track will be less at the decoder output because it is rectified. I suggest you measure voltage of light output and recalculate.

  7. Topo

    Topo Member


    You're right. :)
    The diodes used in the decoder take its toll and I would need a minor resistor. I use the track voltage as a rough way to stay in 'safety values' (different brand decoders have slighty different outputs). Besides, I'm a bit lazy, and taking 15 volts as 'the norm' avoid me to repeat measures :eek: :rolleyes:
    But, as you have stated, for exact resistor determination, it's necessary to calculate with the measured decoder output. ;)

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