Voltage regulator from Radio Shack

Discussion in 'Motorbike Technical Discussion' started by Landser, Aug 9, 2005.

  1. Landser

    Landser Guest

    Radio Shack can be a gold mine when searching for electrical
    components...I replaced the Lucas diode on my 69' Triumph 650 with a
    Radio Shack unit and it worked like a charm. (RS part # 276-1185)

    What I'd like to do now is the following, any help would be greatly
    appreciated. :

    I have a 1977 Honda CT125 that I removed the electrical components
    (lights, signals) from when I was younger...didn't want or need them
    or the battery for that matter as I only used the bike for daylight
    trail riding, and it didn't need a battery to run. I left the
    ignition (key switch) on the bike for obvious reasons.

    To make a long story short, I've recently re-mounted a headlight on
    it. I have found the hot lead from the alternator on the wiring
    harness and have hooked up a headlight that works as it should, from
    the power of the alternator, only when the bike is running. It is
    ground, and has a toggle switch for on/off.

    The problem is (of course) as I accelerate, the light gets brighter
    and will definately blow if I don't wire in a voltage regulator.

    The question:

    Which Radio Shack voltage regulator fits the bill? Can they handle the
    load generated by the alternator at peak output (high speed)? Would
    a heat sink be required?


    I probably still have the original Honda voltage regulator, but would
    prefer a new one if Radio Shack has one that would work (mounting it
    is not a problem).

    Thanks for any help/ideas you may have, it is greatly appreciated...


    I do have the Clymer manual, and the Chilton, and can supply technical
    info about the charging system/alternator if someone needs it to
    answer this question.

    Thanks again.
    Landser, Aug 9, 2005
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  2. The radio shack one is likely not going to work for you unless done right
    and unless it is a remote sensing regulator it won't be right. Use the
    Honda one, and it will last a long long time and your battery will love you
    for it too.

    R. Pierce Butler, Aug 9, 2005
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  3. Landser

    mike Guest

    I have a 75 CB125. Depends on the battery to keep the voltage down.
    Mine has no regulator.
    That works for a few months until the battery resistance goes up.
    Then the headlight blows.
    Fixed the problem with a shunt regulator. Yes, heat sink is required.

    Another option used with dirt bikes is series inductance.
    As the RPM goes up the impedance of the inductor increases to
    compensate for the higher output voltage. They use inductance in the
    magneto, but you could add one externally.
    Without the battery, the lights may not be acceptably bright
    at idle.


    Return address is VALID but some sites block emails
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    mike, Aug 9, 2005
  4. Landser

    David Kelly Guest

    None of those are up to the task. What size fuse is used on your CT125's
    main circuit? 5A to 10A is my guess. Need a regulator capable of at
    least that much. The big RS 3-terminal regulator is only good for 1.5A.

    You would be far better off with something like this:
    David Kelly, Aug 9, 2005
  5. Landser

    bhalicki Guest

    The basic 1.5A 3-terminal regulators (78xx series) are often coupled
    with external parts to increase their ability to handle current, in
    excess of the specified 1.5A rating. I have a circuit I could scan and
    post as an example if required. I am by no means an expert in the
    electrical field, but I assume that most regulators found on bikes
    would use a combination of zener diodes to shunt the excess voltage to
    ground, rather than a 3-terminal regulator. This would effectively
    regulate the overall voltage output.

    I would use the genuine Honda regulator, if you have it. Much easier

    bhalicki, Aug 9, 2005
  6. Landser

    Mark Guest

    reading this thread reminds me of a question i have always had....

    why do motorcycles typically use SHUNT regulators. Seems like a shunt
    regulator would always make the alternator get hot. Maybe thats way
    they fail so much.

    Mark, Aug 21, 2005
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