Humming Alternator

[ftpiercecracker1]

Just tonight I noticed a humming or buzzing sound coming from the alternator, engine off and key out.  Unplugging the alt makes the noise go away. I have done some preliminary research and have heard something about an 'exciter' wire, what ever that is. Or something has been left on in the cab, which there isnt.

 

ftpiercecracker

[jimoshel]

Isolator diode going bad letting current leak thru to the exciter winding.

[ftpiercecracker1]

Isolator diode going bad letting current leak thru to the exciter winding.

 

Exactly, just as i thought. . . . now, what the heck is that thing again? 

[Geonovast]

Not sure exactly what an exciter winding is, but a diode is basically a one way valve for electrical current.  If it's shorted, it'll let power flow the wrong way when the alternator isn't turning.  Could easily be the source of the humming sound.

[ftpiercecracker1]

To revive this topic, does this mean my alternator is bus, can it be repaired? I have tested it with my multimeter and its still putting out plenty of juice. Soo  :dunno:

[Geonovast]

It'll probably still function as usual, but could drain the battery if it's leaking current when the truck's off.

[ftpiercecracker1]

It'll probably still function as usual, but could drain the battery if it's leaking current when the truck's off.

 

With the truck running the battery reads a steady 14 or so volts, but that darn humming is going to drive me insane. :fs1:

[Geonovast]

I would replace it.  If it's simply a matter of that diode being shorted, you'll charge fine, but it'll hum and drain the battery when it's off.  But if that failed component becomes open, you're screwed.

 

I have no idea if the diode itself can be replaced or not, but to be safe, I would replace the entire unit.

[ftpiercecracker1]

I would replace it.  If it's simply a matter of that diode being shorted, you'll charge fine, but it'll hum and drain the battery when it's off.  But if that failed component becomes open, you're screwed.

 

I have no idea if the diode itself can be replaced or not, but to be safe, I would replace the entire unit.

 

 

I am assuming that when that particular component does become open the alternator will no longer charge at all?

[Geonovast]

Yup, there would no longer be a connection between the alt and the battery.