Alternator question

[JerryIkemire]

I have a "79 Thompson w/OMC 350. I've had problems with it shutting down after awhile of running. It's not an overheating problem. Checked all that. I have electronic ignition and just today got to thinking about lack of electricity to fire the ignition. I started the engine and disconnected a battery cable. It immediately died. In all my years I understood that to mean alternator problem. I'm looking at the back of the alternator and see a small rectangular component mounted to the back of it with a couple wires from it running off somewhere. I'm wondering if that is a component to the electronic ignition and is it failing? The alternator is a reman with a date of '05 on it. I've never worked on an engine with elec. ign. before. What should my next step be?

[steele m.a.]

Don't build a short circuit into your boat .
Any electrical system that uses an alternator , be it electronic ignition
or points , relies on a battery - to - alternator connection all of the time .
If you take the battery out of this equation , you take the alternator's
ability to charge out as well .
It sounds like your alternator isn't the problem . If it was , your boat's
electrical system would consistently run itself down .
If your engine is cutting out - suspect the ignition circuit .
Often - You mentioned that this is a 1979 , small ground wires that run
from coil to distributor become loose , or wear through .
This will cause the symtoms you describe.
markalfredsteele@yahoo.ca

[JerryIkemire]

But if the alternator is good, wouldn't it still supply electricity to the rest of the system? I know that it can't charge the battery once a cable is disconnected. I thought the battery just started the engine and the alternator supplied the electricity while the engine was running, also charging the battery at the same time.

[steele m.a.]

No - alternators only develop EMF ( voltage ) when their field windings
and stator windings spin by each other , when a charge is present in
the field windings .
No electricity - no joy .
Mark

[JerryIkemire]

Ok, I understand now. Having that knowledge I just put a meter on the battery, 12.73 volts. I started the engine and put the meter back on the battery, 12.72 volts. If the alternator is good shouldn't that reading be somewhere in the neighborhood of 13+?

[PAR]

Yep, you should be reading 13.8 or more, depending on the alternator and if the engine is spinning it fast enough.

These types of things are fairly easy for a skilled mechanic to track down. You'll probably drive yourself nuts or blow out diodes, rectifiers and regulators in your efforts. There's a sequence of "usual suspects" that I'd look for and some simple tests to track them down.

Take it to someone familiar with these systems.

[CDK]

Originally Posted by JerryIkemire

Ok, I understand now. Having that knowledge I just put a meter on the battery, 12.73 volts. I started the engine and put the meter back on the battery, 12.72 volts. If the alternator is good shouldn't that reading be somewhere in the neighborhood of 13+?

Your alternator is dead. It may also be not connected to the battery or not properly grounded. These two may have been the cause of death, but that isn't important.

[FAST FRED]

These two may have been the cause of death, but that isn't important.
Reply With Quote

Dissconecting an OPERATING ALTERNATOR WILL USUALLY KILL THE OUTPUT DIODES .

FF

[pistnbroke]

LOOK FOR SOMEONE FAMAILIER WITH THESE SYTEMS ..THATS ME

only just picked this up ..loads of crap from previous contributors ...when its running and the load is below 10A the battery voltalge should rise to 14.4-14.7v if it does not then battery life will be seriously reduced .. to as little as 6 months

check alternator WL out at night ..if not fully out diodes faulty.
Warning light on with igniton off //// main output diode failure
battery volts rising to below 14.4v ..regulator faulty to name but a few....

Let me know the problem and I will sort it for you ....

Note for steele Ma ...alternators do not have field winding ...its a rotor !!!! but fast fred is right ....