Re: Rectifier/Regulator circuit for an outboard motor?

From: Sunny (sunny_at_nospam.net)
Date: 06/08/04 

Date: Mon, 07 Jun 2004 22:48:27 -0400

Ken Weitzel wrote:
>
>
> Sunny wrote:
>
> <snip>
>
>> 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.
>
>
> Hi again Sunny...
>
> But I bet it was fun to watch :)

I thought so, but number one son and the dog weren't amused :-)

> 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.

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?

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

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.

> 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.

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
materials.

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!

> 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.

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
solution.

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.

Sunny

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