does hbnx30 hub dynamo have a diode?

Discussion in 'Technical Chat' started by TerryJ, Nov 14, 2010.

  1. TerryJ

    TerryJ Guest

    son's front light BandM oval) snapped off by a moron.
    If i send him a cheap replacement I would expect him to blow the bulb
    in it unless the hub dynamo already has voltage protection. I think it
    might because the rear is a cheap vacuum bulb and has not blown in a
    long time, but perhaps the oval light was protecting it.
    does anyone know if the shimano hbnx30 hub dynamo has a diode to limit
    the voltage and protect the light bulbs?
    TerryJ, Nov 14, 2010
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  2. TerryJ

    Clive George Guest

    It won't.

    (which is fortunate because eg the Cyo deliberately runs it over voltage
    to get more light)
    Clive George, Nov 14, 2010
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  3. TerryJ

    Tosspot Guest

    I pretty certain it doesn't based on experience of spinning a hub and
    touching the contacts, and the B+M definitely does. I'd send him a B+M
    rear while you're there. You must be able to buy one for a tenner and
    the standlight is always appreciated.
    Tosspot, Nov 15, 2010
  4. TerryJ

    TerryJ Guest

    the way I connected it the rear takes power from the contacts on the
    (broken)band m light
    if a diode protected rear light is used in a similar way will that
    protect the front?
    I am not keen to provide the scallies with a regular supply of
    expensive lights when I have a couple of old cheap ones.
    TerryJ, Nov 15, 2010
  5. TerryJ

    David Nutter Guest

    I don't think so. There may be protection circuitry in the Shimano
    switch and sensor that bolts to the fork crown as these are intended
    for use with cheap lights lacking switches (and presumably other
    fripperies like overvoltage protection). Unfortunately those switches
    are a work of Stan and best avoided. That said, if you want one of
    mine just let me know. They've been cluttering up the bits box for


    David Nutter, Nov 15, 2010
  6. TerryJ

    TerryJ Guest

    That is a good idea, and might be worth trying.I fitted that device
    originally and have never had any trouble with it.
    TerryJ, Nov 15, 2010
  7. TerryJ

    paul george Guest

    Yes it will.
    The lights are connected in parallel to the dynamo output so it
    doesn't matter where the diodes are.
    Note it is diodes plural not singular. If you use only one diode
    you will be virtually short circuiting the generator on one half
    of the AC cycle.
    paul george, Nov 16, 2010
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