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Rectifier/Regulator circuit for an outboard motor?

Discussion in 'Electronic Repair' started by Sunny, Jun 3, 2004.

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  1. Sunny

    Sunny Guest

    I recently purchased a new work boat with a manual start 30hp 4-stroke
    outboard motor. I need to install running lights, and would like to
    avoid using a battery.

    The outboard has two unused wires leading from a stator coil under the
    flywheel which I'm pretty sure would be used for the battery charging
    circuit on the electric start model. The owner's manual does not include
    a wiring diagram, or other relevant information, but I expect I would
    find crude AC - varying in voltage with engine RPM? - on these two
    wires. I'm hoping I can rectify and regulate the stator output to 12v DC
    to power the running lights.

    My initial idea was to use a bridge rectifier and filter capacitor,
    followed by a fixed voltage regulator. I salvaged an 8A 50V bridge
    rectifier and 10,000uF 50V electrolytic from a dead PC monitor which
    should handle the DC conversion, but the only 12v linear regulators
    available locally are 7812s which are limited to 1.5A - not quite
    enough. An LT1084-12 (5A) would probably be ideal, but is not easily
    available to me.

    I could possibly use a 7812 with a power transistor bypass to increase
    ampacity, but I'm not confident when it comes to selecting a suitable
    transistor and associated resistors given the variable (and unknown)
    input voltage.

    Given the application I would like to keep it minimal and robust.
    Perhaps someone has already encountered this problem and designed a
    simple solution using commonly available parts?


  2. Ken Weitzel

    Ken Weitzel Guest

    Hi Sunny...

    Before you get too deeply into this plan, be aware that
    you must be able to demonstrate the stern light operating

    Take care.

  3. Sunny

    Sunny Guest

    Operating independently of ?
  4. Ken Weitzel

    Ken Weitzel Guest

    Hi Sunny...

    Engine running. DOT's argument is that you could be
    out just before dusk. Engine failure/out of gas, etc.,
    leaving you with no power at all.

    And after dusk you don't need and may not light the bow
    lights if you're standing, but you MUST show the stern

    Beaurocracy! :( But I guess it makes sense.

    Take care.


    PS... I'm in Winnipeg, where are you?
  5. Sunny

    Sunny Guest

    OK, makes sense - but I'll take my chances and plead ignorance in the
    unlikely event law enforcement questions the lighting system. I'm
    required to carry a waterproof flashlight, so white light will always be
    I've owned a few boats over the years and none had separate switches for
    the bow and stern lights. Is this a recent rule, or do the boat
    manufacturers just ignore it?
    Muskoka, Ontario - on a small lake where it's impossible to be more than
    a 15 minute paddle from shore :)

  6. Ken Weitzel

    Ken Weitzel Guest

    Always been the case; bet you'll find that it was a
    three position switch. All of the ones I've owned
    (lots, I'm old) pulled out to the first click and
    that was the stern light. Pulled out all the way
    lit both bow and stern... a dollar to a donut that
    you just never noticed the center position :)

    The idea is if I see other color at the bow and the
    stern I know you're moving and in which direction.

    If I see only the stern I know you're either
    dead in the water, or I'm following you.

    I'm a little more up on it than I would otherwise
    be because my just turned teen grand daughter
    took the course and exam. Being over protective
    and because of her tender years I stayed with
    her while she did :)
    Oh man, what I'd give to trade places with you for a
    summer or two... used to live in TO, (worked for CTV)
    and had a cottage just north of Lindsay. Beautiful
    country!!! :)

    Now for the past 25 years stuck in Winnipeg, with a
    cottage about 15 miles north and east of Lac Du
    Bonnet if you have a map. Good pickerel fishing,
    wonderful neighbors, but it still ain't Ontario :)

    Take care.

  7. WbSearch

    WbSearch Guest

    I think you are referring to an anchor lite not stern lite. Rules state if you
    are not anchored, even with the engines off, you are underway and must show
    running lites. When at anchor, 1 all around white lite, similar or the same as
    a stern lite on a vessel less than 12 meters.
  8. jakdedert

    jakdedert Guest

    In any case, boats out at night often do not even 'have' motors. For those,
    there are available self-contained, battery operated lights for the purpose.
    (I know he didn't want to use a battery supply connected to the motor, but
    we're talking D cells, here.) He doesn't wanna get run down.

  9. Sunny

    Sunny Guest

    Well, that idea failed spectacularly! The capacitor exploded after
    running the boat at 3/4 throttle for less than a minute.

    According to the old analog multimeter I was using (forgot to take the
    DMM to the lake), the motor generates about 15v AC at idle, but up to
    170v at full throttle - it runs the lights via a 12v DC wall-wart at
    half throttle and above! (but they go out below half throttle).

    I'm not sure how to get a constant 12v DC from an AC source that varies
    from 15-150v. Any suggestions?

    Given the feedback I've received on boat lighting regulations, I'm
    resigned to using a battery - but I'd like to keep it small (motorcycle
    type) and have the outboard motor recharge it.


  10. Ken Weitzel

    Ken Weitzel Guest

    Sunny wrote:

    Hi again Sunny...

    But I bet it was fun to watch :)

    Seriously, though, that's exactly what an alternator
    does... the one in your car does, too.

    Can't guess your age but if you're old enough, you'll
    remember when we could buy "AC adaptor kits" from
    Canadian Tire. They were nothing more than a
    fancy box with a switch that disabled the voltage
    regulator. (and a little more) I fell for it,
    bought one, used it to get started on the cottage
    before hydro was in the vicinity. Start the motor,
    rev it up, and use the output to run the power saw,
    drill, etc.

    So, all you're lacking is the voltage regulator.
    OR - you have one in your motor that's faulty.

    Easier question, though. If you're commited to
    using a battery, why not just "buy" one from one
    of your friends or family who are trading it in
    for a new one?

    Out here, we get 5 bucks back from the dealer
    when we return the "dud". Sometimes that dud
    isn't good enough to trust starting in dead of
    winter for our wives/daughters, but would be
    fine for your light use.

    And if you lose it only for rare lighting,
    maybe a couple of amps worth, likely one or
    two dockside charges a year would be ample.

    Just a thought.


    PS. You for sure didn't want an electrolytic
    there anyway :)
  11. Sunny

    Sunny Guest

    I thought so, but number one son and the dog weren't amused :)
    Never seen such a thing - did they at least give you a meter so you
    could adjust the engine RPM to something approximating the correct
    voltage for the tool?
    Nope, just the two wires from the stator. I assume the regulator would
    be connected to those if I'd bought the electric start model.

    I looked at taking the regulator off one of the old outboards I have
    lying around for parts, but they all use a field coil to control the
    alternator so the regulator doesn't have to deal with such wide voltage
    swings. No field coil on the new motor as far as I can tell.
    Believe it or not, that's exactly what I did for the last 20 years in
    the old boat - stop at Canadian Tire on the way to the cottage and ask
    for a traded-in battery. I got odd looks, but they always let me take
    one from the pile out back.

    The problem is there's nowhere in the boat to mount a full-size auto
    battery out of the weather, so it was always parked on the floor in the
    way of loads, and the connections were usually corroded when I needed
    lights. I bought several battery boxes over the years, but they
    inevitably got damaged by freezing or loading and unloading of building

    The boat is mostly a work boat, but we also use it to get back and forth
    to the cottage in early spring and late fall. I'm tired of fiddling with
    battery connections by flashlight with fingers already numb from bailing
    snow and ice on a Friday night!
    Usually the case, but there have been too many occasions when the lights
    didn't work due to bad connections, cold battery etc. I need a better

    I'm not getting any help with the circuit design here, maybe I should
    just order the regulator for my motor and buy a motorcycle battery -
    there's a spot I could put a small battery where it would be fairly
    safe. It'll cost more than I planned, but should work.

  12. Ken Weitzel

    Ken Weitzel Guest

    Sunny wrote:

    They were made by BEL (Beltronics). Still in business,
    but now make radar detectors instead :)

    Nope, no meter. The max output of an alternator is about
    115 volts, so all you had to do in the interest of
    cost effectiveness was get the engine running fast
    enough to do the job. I discovered that 2 popsicle
    sticks stuck under the idle adjustment screw would
    start the table saw - and after starting it, one would
    keep it going provided you didn't try to rip a 2x6
    too aggresively. Funny, the girls always reminded
    me that we'd need popsicle sticks on the way there :)

    Ahhh, the difference between generators and alternators :)
    One of my neighbors owns AVO marine here in Winnipeg.
    OMC and Honda outboards. We're pretty good friends
    for the past 25 or so years, so if you like I'll
    ask him for his suggestions. He may have something.

    Tell me what kind/size of motor you have there.
    Email if you prefer.

    Take care.

  13. George S

    George S Guest

    Have you looked into the small Solar panels used now for keeping a 12 volt
    battery charged? With the day's getting longer it might solve your problem.
  14. Bill Jeffrey

    Bill Jeffrey Guest

    I'm not sure we're reaching the correct conclusions here. You say that
    all you have is the two wires from the stator. But I would expect one
    end of the stator to be grounded, and you would get only one wire - the
    hot one. If that is true, what is the other wire?

    And if the two wires are simply the ends of the stator winding, how
    would the output voltage be regulated - where is the feedback point back
    into the alternator?

    In a car, at least, an alternator has a field coil (which I believe is
    the rotor winding). The voltage regulator (which is usually built into
    the alternator) controls the DC current into the field coil, in order to
    control the AC voltage out of the three-phase stator windings (three
    windings which do the actual power generation). The three-phase AC is
    rectified by three sets of diodes, and the resulting DC is what charges
    the battery and runs the car.

    Since the alternator on an outboard motor has to supply a MUCH smaller
    load than a car's alternator, it is quite possible that your outboard
    motor alternator has only a single power-generation winding (single
    phase of AC output) - but I think that it still must have a field
    winding, so that the field current can be varied in order to regulate
    the AC output voltage.

    I would bet that one of your two wires runs to the field winding (the
    other end of which is connected to ground), and the other wire runs to
    the power-generating winding (the other end of which is connected to
    ground). Can you measure the resistance between each wire and ground?
    If each wire shows a low-resistance connection to ground, then I bet I
    am right. If neither wire shows conduction to ground, but only to the
    other wire, then I am wrong.

    If I am right, then you need a diode pack (to change AC to DC) and a
    voltage regulator (to feed current back into the field coil in order to
    control the voltage being generated). Both should be readily available.
    By the way, you do NOT need a filter capacitor - that was a mistake.
    Both the battery and the lights are perfectly happy with pulsating DC -
    and in fact that battery is a great smoothing device. The alternator in
    a car, for instance, has no filter capacitors.

    Waddya think?

    Bill Jeffrey
  15. Bill Jeffrey

    Bill Jeffrey Guest

    Just a couple follow-up thoughts to my previous post.

    1. If I am right about there being two winding - a rotor and stator -
    then there has to be a brush (or a pair of brushes) somewhere. Can you
    spot one? Probbably at the inner end of one of the wires.

    2. If you look at some of the outboard motor repair parts sites
    you see that external voltage regulators appear to have two connections.
    These would correspond to your two wires. There is actually a third
    electrical connection, which is ground. This makes sense to me - the
    hot end of two windings, plus the ground end of both.

    Bill Jeffrey
  16. Sunny

    Sunny Guest

    Thanks Bill.

    I think you make a great deal of sense, and I must be missing something
    - hardly surprising given my owner's manual doesn't even have a wiring
    diagram, let alone a circuit diagram. The thing that makes least sense
    to me given your theory is that these two wires appear identical, yellow
    with a black stripe, but if one is field and the other is power, they
    should be coded differently - although perhaps the field and power coils
    are interchangeable?

    My understanding is the alternator in an outboard differs from a car in
    that there is no rotor winding. The stator sits under the flywheel,
    which contains permanent magnets to induce current in the stator coils.
    I don't recall the details of the wiring diagram (of a different, much
    older, outboard) I looked at on the weekend, but it definitely had a
    field coil and a power coil, and there were 4 wires emerging from under
    the flywheel connected to the rectifier/regulator.

    I'll probably be forced to buy a service manual to figure this out,
    and/or just order the regulator for my motor (the dealer is looking into
    that for me now). Meanwhile I'll check resistances to ground next
    weekend as you suggested and post the results.

    Thanks again,

  17. Sunny

    Sunny Guest

    Thanks Ken - but it's a Mercury, 2001 30hp 4-stroke, so your friend may
    not be familiar with it.

  18. Sunny

    Sunny Guest

    I did consider a solar panel, but they are somewhat fragile and there's
    really nowhere to mount it on my work boat which would keep it safe from
    damage during loading and unloading of typical loads.

    Thanks for the suggestion.

  19. Bill Jeffrey

    Bill Jeffrey Guest

    Both of your points are good, and I don't have answers. I wouldn't
    expect the two coils to be interchangable.

    A PM-based alternator would certainly work in the sense of producing
    power. I just don't know how a regulator would work. If there is 170
    volts at full throttle, and the alternator can produce, say, 20 amps,
    then a linear regulator that regulates 170 volts down to 14 volts would
    dissipate 156V x 20 amps = 3120 watts! That is clearly ludicrous - but
    I don't know how else it would regulate if you can't reduce the voltage
    via a field coil. Maybe it's like a cycle-counting light dimmer? I'm
    not convinced that would work, either.

    I guess I'm out of my area of expertise, so I will wish you luck and
    fade back into lurking mode.

    Bill Jeffrey
  20. Ken Weitzel

    Ken Weitzel Guest

    Hi Bill...

    I, too, am in way over my head (and it seems my head
    keeps getting lower all the time :)

    The only thing I can throw in that might help to
    put your theory back on track is that your 20
    amp guestimate is way out of line. Outboards
    generate very little electrical power - 2 or
    3 amps tops would be more like it.

    Take care.

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