[C320-list] alternator question

[Jeff Hare]

The stock alternators with internal regulation (on the 320) don't deliver
much charge current for very long before the increased diode temps cause the
current to drop off.  A 50A alternator will be hard pressed to deliver even
close to 50A for more than a minute, and then may settle in well below
10-20A depending on the alternator temp.

The stock alternators are connected to the Starter Solenoid's Positive post
(which then feeds back to the battery usually through the A/B/Both switch),
and the Starter Ground post (again which feeds back to the battery.

So, if there is a loose or bad connection in this short run, you'll likely
blow the diodes due to the vibration of this short wire.  It doesn't need to
be a particularly fat wire, 10awg or 12awg or so is probably enough, but run
the numbers.

You can protect the diodes by using a reverse biased zener diode in line
with a small fuse between the positive and negative terminals of the
alternator.  This will allow the magnetic field to safely discharge/collapse
if the connection to the battery is interrupted.

If you're blowing the diodes in an internally regulated alternator, this is
most likely the cause.

There is no problem whatsoever with having your shore power charger running
while the engine alternator is running.  Depending on the shore power
charger, the result might be reduced recharge time, but I wouldn't count on
it since most shore power chargers will base their charging stage off of
what they observe is the state of the battery.  The alternator running will
likely confuse it into thinking that the battery is fully charged and then
just sit in float mode.  But it's a little more complicated than that in
reality.

My $.02
-Jeff Hare



-----Original Message-----
From: C320-list [mailto:c320-list-bounces at lists.catalina320.com] On Behalf
Of Graeme Clark
Sent: Thursday, July 14, 2016 8:25 AM
To: C320-List at Catalina320.com
Subject: Re: [C320-list] alternator question

Ive never looked at the wiring in detail but why would an alternator be
connected to a starter motor? Its output should be a heavier gauge cable
that goes to the battery - possibly via a split charger depending on what's
fitted to your boat?

Not sure if that helps or confuses. 

Graeme



Sent from mobile: please excuse typos etc.!


> On 14 Jul 2016, at 13:13, <dmcnamara3 at woh.rr.com> <dmcnamara3 at woh.rr.com>
wrote:
> 
> Hi
> Thanks for the information.  So if I am thinking correctly, the only way
to blow the diodes is to momentarily break the B+ wire from the Altermator
to the post on the starter? the B- is ran thru a fuse and grounded, and the
other two wires go to the tach and charge light/gage.  I still think I am
missing the smoking gun.
> 
>