On Friday, September 1, 2000 7:05:15 PM UTC-7, macleanpd wrote:
I'll make this simple-There is usually a small wire going to the
alt./regulator that is energized when the ignition is turned on-this is what
tells the reg. to start charging-sometimes there is a bulb in this circuit -
either way pull off the small wire from the alt. and check for 12V with a
METER with the key on--DO NOT START THE MOTOR. If you don't get 12V then the
wiring is bad or the bulb is burnt out( if so equipped ). I suspect that
this is where your problem lies - Some alternators will self energize after
they have run awhile and when they do they work normally until you shut
down. The noise you hear is the normal whine when high output charging
begins-this high output tapers down rather quickly. Some alternators are one
wire systems,but I doubt that yours is one of them.

Doug

wrote in message ...
I have a 1990 Merc Alpha 1 4.3 L that has exhibited what I consider to
be a strange charging trait. The boat has a dual battery setup with
isolater switch although I use only one regular marine battery as its
trailered. It starts normally but the OEM Volt Meter shows only 11
volts for some time under way. After 5- 20 minutes it will increase
rapidly over a space of 2-30 seconds to the normal 13.5 volts. This is
sometimes by a subtle high pitched whirring noise coming from the
engine area, ( presumably alternator). After a few minutes the noise
subsides. Everything seems fine otherwise yet the period between
startup and some indicated charging activity seems to be getting
longer.
On the bench the battery seems to charge right up although I haven't
checked the specific gravity. Its age is 3 or 4 years but it never
has given a hint of starting problem. Aside from buying another
battery to check it any ideas. I am not that cheap but just replaced
5 or 6 other batteries due to a lousey Century Battery charger I bought
last year that ruined every battery I own but the boat battery. Any
suggestions concerning this problem would be appreciated.


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Before you buy.

If it is a Dlco ssystem. I agree. There will be two wires on a slide connector to the alternators internal volt regulator. Under the normal circumstances the alternator will have an "F1" and "R2" designation on the back of the housing. If so equipped, the "R2" will read full battery voltage or 'hot all the time' because it's a direct connection to the pos. of the battery and is intended to be so regardless of if the key is on or off.This is a dedicated 'voltage sense terminal' which helps the volt regulator maintain a 13.8-14-2 volt rate. Thee "f1" is your field terminal which should be live when the key is on only. This turnes thee alternator on. So thee standard delco 10si alt. will have battery 'hot' on thee back output terminal, battery hot on the "R2" and switchable hot on the F1. Even if the "F1 isn't coming on, (via bad plug/wiring) at a high throttle it should turn itself on due to the residual magnetism of the rotor activating the internal circuits of the volt. reg. Which could be the reason for the delay in the alternators activation.

But back to your original complaint. I see you are using a battrey isolation switch. That could be the source of a problem as well. maybe the contacts inside are not connecting well, and actually causing you to lose battery voltage on the alternators output bolt.

I'd suggest using a dedicated battery isolater.

http://bluewatermarinesvc.com/html/bat_isolator.html


They are simple to install (in most applications) and are very reasonably priced.

http://bluewatermarinesvc.com/images...olator_dia.gif

This way your engine and 'house' battery will be simultaneously maintained. Even if you run your secondary (house) battery flat, your engine battery will be unaffected and be fully charged. Once starting the engine, the house battery will recharge itself at a normal rate.

Remembering to flip the charge switch can be a pain. A great advantage to this is that the isolator doesn't have to know what to do.

What I'd recommend is that if you have a 55a alternator, I'd go with an isolator capable of at least a 70a. load. A 70a. alt- 100a. load etc. . Always go at least a step higher amp isolator than what your alternator is rated for.

I have a 120a. alternator on my '77 Marquis, and I use a 150a. isolator.