Solved: charging system puzzle

Hello everyone,

I have been lurking for the last 8 months(first Tacoma) and have enjoyed the the forum for its vast amount to inspiration and information. I find myself at a point where the search has yielded some help but not the key answer I need.

my rig is a 2009 DCLB v6 sr5(200 000 km) and I have been recently chasing the wine noise in the front. This led me to throw the volt meter on the battery to see what the alternator was producing...well.

• 19 volts truck running at battery.
• 19 volts at the alternator connection(connection under grey cover next to green connector, 10mm nut)
  
• test battery (truck off 15v..probably high because of over charging?)
  
• So off to the parts store, replaced the alternator...Same readings.
• switched battery...same readings
• if i pull the green connector on the alternator (3 wires) the reading drop to 12.5v(truck running)
• checked the fuses(blindly looking for an obvious blown fuse. nothing obvious to me)

Does anyone know what i should look for? I'm stumped.
I suspect that the systems is telling the alternator to send power to the battery...but 19v? i would have expected 14v ish at most and with 15v reading on the battery the system should not be looking for more. Is there a test for the Green connector(is that the regulator?)both n the alternator or the wire harness connection?

Thanks for any leads
Brad

 

I would try another meter

 

And meters with weak batteries will give skewed readings as well.

 

Measure the voltage between the battery negative post and the generator body with the engine running. It should in theory be 0.0 V, though in practice it may be 0.25 to even 0.5 V. If it is more than 0.5 V there is a bad connection between the negative post and the generator body. If that is the case check the ground connections at the body and engine--especially at the engine.

The voltage regulator maintains the generator output at 13.2 to 14.8 V above what it believes to be "ground" (0.0 V), If the ground connections between the battery post and the generator body are bad there will be a voltage drop across those bad connections and the voltage regulator will be tricked into believing "ground" is really what ever that drop is--and make the generator output whatever the ground drop is + 13.2 to 14.8 V. To get to the 19 V your are observing would require a 5+ V drop in the ground connection, which is quite a lot but not unheard of.

Verify your meter's accuracy of course before continuing.

 

I really can't add anything to diagnosis that wasn't said in the above ^.

However, after replacing the alternator, did the whine go away?

 

Hello Gentlemen,

Thank you for the post and the reminder that a sharp knife cuts better, this was indeed a case of not seeing the forest for the trees.
The meter was at fault(me mostly) and double checking with a second meter showed my error.

Well, i have a new alternator and leaned from the wisdom of the forum.

Maticuno, yes still the wine is still there and is most likely the bearings in one of the pulleys. I guess to make lemonade out of the situation, I can use the core charge to buy the new bearings/pulley.

Thanks go out to all of you for your time and expertise.

Brad