Voltmeter reads 12 volts until I throttle up

[pontooner]

I have a 1998 3.0L 4cyl mercruiser with an alpha 1 outdrive. Sometimes when I am just putting around my voltmeter shows its charging the battery at around 12 Volts. When this happens it will discharge the battery. If I throttle up the voltmeter jumps to just over 14 volts (where it should be). The battery will then charge. After I have throttled up, I can return to idle and the voltmeter will remain at 14 volts.

Now that I know this I can avoid draining the battery (simple enough), but still don't believe this is normal. Is my alternator going bad?

Thanks

 

[THE BEEF]

Re: Voltmeter reads 12 volts until I throttle up

Check the belt for tightness. Sounds like its slipping.
Beef

 

[Haut Medoc]

Re: Voltmeter reads 12 volts until I throttle up

I'd like to see the answer to this one....
My engine does the same as yours, but is not the 3.0.....
The belt does not slip.....
It has been like that since I bought the boat five years ago.....
As long as I rev it initially after starting it charges normally.....
So, that's what I do.......​

 

[tommays]

Re: Voltmeter reads 12 volts until I throttle up

I think a 3 wire ALT needs some RPM to decide to charge

As long as it is charging all the time after that



Tommays

 

[Windykid]

Re: Voltmeter reads 12 volts until I throttle up

 

[skeat]

Re: Voltmeter reads 12 volts until I throttle up

As long as I rev it initially after starting it charges normally.....
So, that's what I do.......​

I do the same thing. I just always attributed that to the initial discharge of the battery due to starting the engine... just needed a good boost to restore the charge I guess..never thought about it much

 

[krisnowicki]

Re: Voltmeter reads 12 volts until I throttle up

mine operates at 12.3 or 12.4 the whole time is this bad?

 

[slia67]

Re: Voltmeter reads 12 volts until I throttle up

It's a normal condition. The charging curcuits in the alternator need to be "excited" by the voltage regulator. That usually happens when the alternator reaches a set RPM (usually higher than idle speed), but once it has been "excited" it will continue to charge even at lower RPMs.

Doug

 

[Haut Medoc]

Re: Voltmeter reads 12 volts until I throttle up

mine operates at 12.3 or 12.4 the whole time is this bad?

It should be higher....

 

[slia67]

Re: Voltmeter reads 12 volts until I throttle up

mine operates at 12.3 or 12.4 the whole time is this bad?

Double check that your gauge is reading true voltage. Your gauge may be off. Normal output should be between 13.8 - 14.5 volts.

Doug

 

[peejcj8]

Re: Voltmeter reads 12 volts until I throttle up

Mine does the same thing. 1 wire volvo penta 5.7.

When I first crank it, it will read 12 volts until I get the motor above 1200 RPM's, then I read 13-14V

I do not see it as much of a problem. When I back down the rpms the voltmeter usually stays at 13-14. In the back of my mind I think if I cleaned all the connectors from the alt to the battery the "problem" might go away.

 

[ziggy]

Re: Voltmeter reads 12 volts until I throttle up

fwiw. i'll throw in that mine acts the same way. only after starting though. i probably idle at 500-600. usually have to idle up to around 800-900 to get it to start chargeing. couldn't tell ya what it charges at though. i got a ammeter.......shows discharge till i get the rpms up. goes to chargeing then drops to just above 0 no matter what rpms........guess i figured it just needed a little rpm to get excited too....

 

[TilliamWe]

Re: Voltmeter reads 12 volts until I throttle up

It's a normal condition. The charging curcuits in the alternator need to be "excited" by the voltage regulator. That usually happens when the alternator reaches a set RPM (usually higher than idle speed), but once it has been "excited" it will continue to charge even at lower RPMs.

Doug

This is my exact understanding also.

 

[wire2]

Re: Voltmeter reads 12 volts until I throttle up

It's a normal condition. The charging curcuits in the alternator need to be "excited" by the voltage regulator. That usually happens when the alternator reaches a set RPM (usually higher than idle speed), but once it has been "excited" it will continue to charge even at lower RPMs.

Doug

That's very close.

The iron plates laminated together holding the stator windings exhibit a characteristic called hysteresis. It's the delay of iron to magnetically align to a field induced by AC current in the windings.

After a start, the regulator feeds full voltage to the field through the brushes/slip rings, usually ~12v. The iron laminations hold back some current and therefore limit efficiency. At higher rpm, more voltage and current is generated which more forcibly aligns the magnetism of the iron.

Once the threshold is overcome, it will continue to generate at elevated current and voltage.

 

[peejcj8]

Re: Voltmeter reads 12 volts until I throttle up

Now your bringing up memories from My Naval Avionics school.

 

[Bondo]

Re: Voltmeter reads 12 volts until I throttle up

Ayuh,.......... All Perfectly Normal...............

 

[THE BEEF]

Re: Voltmeter reads 12 volts until I throttle up

WIRE2
Is that a neat way to say the laminated plates on the stator winding housing
cancel out the eddy currents?
Beef

 

[wire2]

Re: Voltmeter reads 12 volts until I throttle up

WIRE2
Is that a neat way to say the laminated plates on the stator winding housing
cancel out the eddy currents?
Beef

They won't cancel them but the laminations do minimize the losses.

Eddy current will be induced in any conductive material present in a magnetic field. If the stator was made of a single piece of steel, losses would be very high due to heat generated by induced current. (transformer action).
Using thin laminated plates divides it into many very small currents.

Very old motors and generators used less efficient laminations and were physically larger for a given HP.

There is a material called ferrite that exhibits no hysteresis, and very little loss. It's typically used for high frequency circuits and *could* be used to make a hi-efficiency alternator except for the cost.

 

[THE BEEF]

Re: Voltmeter reads 12 volts until I throttle up

Thanks
You helped me understand them better.
Beef