Re: Outboard Motor Charging System.


"Jerry Martes" <j.jmartes@xxxxxxxxxxx> wrote in message
news:AKgIe.40809$MW5.37928@xxxxxxxxxxx
>
> "Mike Fields" <spam_me_not_mr.gadget2@xxxxxxxxxxx> wrote in message
> news:AtudncfaIaYI62zfRVn-jA@xxxxxxxxxxxxxx
> >
> > "Jerry Martes" <j.jmartes@xxxxxxxxxxx> wrote in message
> > news:5_3Ie.12525$Bx5.838@xxxxxxxxxxx
> >>
> >> "Derek" <joe@xxxxxxxxxxx> wrote in message
> >> news:8h31f1tp5as2oi072sfr2jmoibgevih5hv@xxxxxxxxxx
> >> > Sorry for the O.T. post but I love the knowledge database here.
> >> >
> >> > I have an old Chrysler outboard motor, 45 HP circa 1967 and it runs
> >> > great. I recently installed a Volt Meter and was alarmed to see it
> >> > charging my very expensive deep cycle battery at around 17 Volts at
> >> > high r.p.m.s.
> >> > There is no regulator, it just seems to go through a bridge rectifier
> >> > and to the battery. As a quick fix, I'm thinking of putting a toggle
> >> > switch on the Positive (purple wire) so that I can shut down the
> >> > charging system periodically to save the battery.
> >> > Could I blow the diodes this way?
> >> >
> >> > Apart from the starter and the ignition, there is no other draw in
the
> >> > battery. The battery Voltage would be monitored using the meter and
> >> > flipped on as required. I also carry a smaller spare battery.
> >> >
> >> > Any suggestions appreciated.
> >> >
> >> > Thanks.
> >>
> >> Derek
> >>
> >> Since the terminal voltage of a good lead acid 12 volt battery doesnt
> >> go
> >> to 17 volts without extremely high charging currents, there is
something
> >> missing in the description of the voltage. That is, the generator
> >> voltage
> >> terminal voltage might go as high as 17 volts while the battery
terminal
> >> voltage rises to only 14 volts, with the remaining 3 volts dropped in
the
> >> wiring between the generator and the battery.
> >>
> >> The information you posted here indicates that the charging system is
> >> an
> >> AC generator with no output voltage controller. If thats correct, you
> > might
> >> want to consider installing a 14 volt zener diode across the battery
> >> terminals and enough resistance in series from it to the generator to
> >> drop
> >> the excess voltage.
> >>
> >> The switch concept might have a flaw. Open circuiting the output of
a
> >> charging alternator can produce excessively high circuit voltages that
> >> can
> >> destroy rectifires.
> >>
> >> Jerry
> >>
> >
> > No, you don't want a zener -- if the battery is at a full charge and
> > not taking any current and the alternator can put out 5 amps, then
> > the zener is going to be dumping 5 amps at 14 volts = 70 watts.
> > On alternators that have a field winding, the regulator switches the
> > field on and off to maintain the desired voltage (keeping the switching
> > transistor in the saturated or off mode to minimize dissipation), with
> > the permanent magnet alternators I have seen, they short the output
> > of the alternator with an SCR as needed to keep the voltage down.
> > You definitely do not want a regulator running in the linear mode
> > unless you have water running past it to keep it cool ;-)
> >
> > mikey
>
> Mikey
>
> Zeners work for this aplication. There are lots of vehicles that use
> them in high production quantities.
> There is something else wrong with the data suplied. I submit that the
> battery voltage isnt actually 17 volts. But the original poster hasnt yet
> commented on where the 17 volt measurement was made. I read the post to
> state that the charging system was designed to have no regulator, ever.
> That would imply that the original design of the charging system has
> accounted for some current limiting.
>
>
> Jerry
>

My comment is still valid -- if you are trying to shunt 5 amps at even 14
volts to ground, you have 70 watts to get rid of -- and I am not aware of
any zeners in the 100 watt range that you could pick up for a reasonable
price. 5 amps would not be an unreasonable output from a simple
alternator with the permanent magnets and you certainly want to limit
the battery to less than about 14.5 volts. You are correct in the fact
that we don't know exactly how or where the 17 was measured but
overcharging a battery is one of the better ways to kill it (although one
of the guys I work with tried putting his wife's saline contact solution
in the battery to top it off thinking that "saline" was somehow the same
as distilled. That will kill a battery too (watch for the chlorine gas when
salt water gets in a battery).

mikey


.

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