New 3g alternator--High voltage and then low voltage, bad regulator?

[DirtyWood]

Installed the new alternator and double checked the new wiring before starting the engine. First start the voltage slowly climbed up to about 17.5 volts so I turned off the engine and rechecked my electrical connections--everything tight and looking good. Start the engine again and get the same results. Triple check my wiring and verify that I made the connections correctly. Start the engine again but now the voltage only reaches 12.28 and doesn't change with an increase in engine speed. With engine running I wiggled the new wires to see if there was a change in the voltage but nothing happened. I turned on the lights and defrost and voltage dropped to about 12.02 and held steady regardless of RPM.

Is it somewhat safe to assume the voltage regulator must be defective? I've never dealt with a bad voltage regulator but I can't see anything else being the culprit here. The yellow/white sense wire is connected to the output lug on the back of the alternator, and I've installed one other 3g alt this way and it has about 70k on it with no issues charging at 14.2v or so.

This is so irritating but at least I did not remove the 1g wiring yet so I can put things back the way they were and still get to work.

 

[IDIBRONCO]

From your description, I'd say that it sounds likely. Take it somewhere and have it tested.

 

[BeastMaster]

You have the battery in there. It should hard clamp the voltage above 15 volts. The current should go through the roof! ( Hundreds of amps, then burnout ). The battery would be hot and "boiling" , venting electrolysis gas: hydrogen, oxygen. Explosive!

But the regulator catches it and tries to avoid this condition, hence the voltage doesn't go through the roof.

The alternator is not seeing the battery.

And the regulator is not seeing it either.

And calling for more and more voltage to drive more current into the battery. But to no result.

You have a wiring issue somewhere. What you have posted so far is exactly what a voltage regulator, not seeing the battery, as well as the alternator, making voltage but not finding anything to absorb the current, is apt to do. It's going to increase armature drive and try to charge the battery.

It's not seeing the battery.

Look for opens on both your alternator output and voltage sense lines. The regulator is going to try to hold the terminal voltage around 14.5 volts or so. Anything less, it will increase armature current to call for more stator current. The battery feeds from the stator windings.

Three Phase AC internally -> three phase rectifier -> Battery.

 

[DirtyWood]

You have the battery in there. It should hard clamp the voltage above 15 volts. The current should go through the roof! ( Hundreds of amps, then burnout ). The battery would be hot and "boiling" , venting electrolysis gas: hydrogen, oxygen. Explosive!

But the regulator catches it and tries to avoid this condition, hence the voltage doesn't go through the roof.

The alternator is not seeing the battery.

And the regulator is not seeing it either.

And calling for more and more voltage to drive more current into the battery. But to no result.

You have a wiring issue somewhere. What you have posted so far is exactly what a voltage regulator, not seeing the battery, as well as the alternator, making voltage but not finding anything to absorb the current, is apt to do. It's going to increase armature drive and try to charge the battery.

It's not seeing the battery.

Look for opens on both your alternator output and voltage sense lines. The regulator is going to try to hold the terminal voltage around 14.5 volts or so. Anything less, it will increase armature current to call for more stator current. The battery feeds from the stator windings.

Three Phase AC internally -> three phase rectifier -> Battery.

Wiring is solid. No open circuits. There's not much to check with these 3g alts. I double checked the 3g connector and it's good. Mega fuse is good. Alt passes basic diode test. I doubt it's an issue with the wiring.

 

[ihc1470]

What about the ground side of the circuit?

 

[DirtyWood]

What about the ground side of the circuit?

The alternator should ground through the brackets. I've done the 3g conversion on another truck and did not need a separate ground wire. I'll have to double check but I'm not sure this alt even has a post for a ground wire.

Edit: Could you just run a ground wire from one of the mounting ears?

 

[Nero]

You could, would only help if one of the ground straps at the block are poor.
If I remember right the 3g needs ignition source to energize, if the ign source is poor it'll cause the regulator to be all over the place. From recent experience... Make sure none of the pins are pushed into the connector, and none are expanded.

 

[ihc1470]

That was the reason I asked about grounds as many assume that the ground system is good when often it is not. Easy enough to run some voltage drop test to determind what may or may not be an issue.

 

[DirtyWood]

How is the 1g alt grounded? The 1g setup works very well at the moment and the E4OD doesn't complain so I think the wiring is in decent shape. New battery cables and grounds are on the list.

 

[Nero]

Through the case

 

[DirtyWood]

UPDATE: Installed a new voltage regulator and now the new alternator seems to be working normally. 14.4v charge at idle.