3G Alternator Mod with DB Alternator Issues

[Machspeed]

I recently did the 3G alternator mod with the recommended DB alternator. I don't think I have more than an hour on this alternator, as I've been doing other things to the truck and it has been sitting. Yesterday, I noted that my voltmeter was low. Pulled out my diagnostic voltmeter and measured voltage at the battery and was only getting 12 Volts, not the 14 I was previously getting. Wondering now if this DB alternator is taking a dive on me. I did change out the regulator to one that has a delay. Is it possible that the regulator is the problem and not the alternator? If so, is there a way to rule out the defective part?    

[Gary Lewis]

John - I think there is something written on the back of the regulator that tells how to test the alternator by grounding a spot on the regulator.  You said you replaced the regulator, so if you can find the original regulator see what it says.

If it has the directions then follow them, which should put the alternator into full boost.  So with your voltmeter on the battery you should see 15 or more volts, which you don't want to do for very long.  If that is the case I'd say the alternator is good and the regulator is bad.

In which case I'd swap the original regulator back in and see what happens.

And if yours doesn't have the directions I'll check after church to see if I can find them.

[ArdWrknTrk]

"Ground here to test" is on the right side of the regulator as viewed from the plugs perspective.

Is your Y/W  'sense' wire getting a good connection to the output stud?

[Gary Lewis]

Perfect, Jim.  That terminology let me find this pic, which makes it pretty obvious.  I'd ground that screw and watch the voltage at the battery.  If the alternator is good, and if the "sense" wire is hot, the output should head for 15 or more volts.

[ArdWrknTrk]

F is 'field', so we have the term "going full field"
By grounding the field -instead of letting the regulator regulate resistance- you should reach full output.
I'm fairly sure the old mechanical type regulators would just pulse on and off, similar to a ICVR.

But don't do it for long. The winding insulation and diode board heatsink can't keep up with that.

I think you will see closer to 18-20V, but this depends on how much charge the battery can sink.

[Gary Lewis]

Yep.  And how fast you spin it.

[ArdWrknTrk]

You've already plotted the various pulley ratios these trucks came with, Gary.

[Machspeed]

To be clear, I'll run a wire lead off that screw head to ground while truck is running and take voltage measurements at the battery?

[ArdWrknTrk]

Hook a meter across the + & - battery terminals.
Use something as simple as a paper clip to ground the screw to the alternator case.

[Machspeed]

That's what I was looking for. Thanks, Jim!

[ArdWrknTrk]

Use a pair of pliers if you're going to hold it there longer than just see the voltage rise.  (which you probably shouldn't)

I imagine that bit of nickle plated steel is more resistive than the copper field winding.