Alternator / Voltage Regulator

[strictlypersonl]

Originally Posted by Large Arbor

Hey Patrick and others,

New battery, new VR, and New Alternator and the battery is not staying charged. It was tested last week and had 800 plus cranking amps. I ran the car for 20 minutes and the battery is now reading about 9 volts with a charger on it. I took a voltage reading from the alternator when running and it read 18 V.

The only thing known drawing current is the fan. How do I diagnose this problem? Could I still have a bad VR?

Phil

You should see a maximum of about 14.7V when charging a fully-charged battery. More than that and there's a problem in the voltage regulator, its circuit connections and/or its ground.

[patrickt]

Originally Posted by davids2toys

AYIYIYI
So what is the purpose for the ohms function on the multi-meter if it is useless. I did a quick Google search on voltage drop test and in what I do understand, it makes sense!

Well, completely useless may be an overstatement. The only times I actually measure ohms in an automotive troubleshooting situation, as opposed to just using my ohm meter as a glorified test light, are: 1) When I have the manufacturer's troubleshooting instructions that specify what the resistance must be on a particular piece of hardware (common); 2) I am comparing two pieces of hardware to see if there is an obvious and big difference (rarely); 3) I am performing the "jiggle" test (common).

If I'm tracking down a bad connection, I use the voltage drop test. I think that's the number one electrical test that shade tree mechanics, working on "old school" type of cars, should be familiar with. You're right, there are lots of videos showing how to use the Voltage Drop Test -- it's pretty easy to learn.

[Large Arbor]

Picked up another VR and installed. Will charge the battery overnight and doublecheck wiring in the morning. Hopefully this will solve the problem.

Phil

[Large Arbor]

Still does not appear to be charging. Any chance I could have a bad disconnect switch? I am all out of ideas here on what to do next.

Phil

[Grubby]

Large -

Take a step back and test a few things instead of just replacing parts.

1. At the VR you can jumper terminals A and F. This should cause the alternator to go to full output (about 16V).
2. If 1 doesn't work then check continuity for the F (Field) and the A (Bat). Unplug the VR plug and disconnect the Alternator wires to make this check. Check for continuity from the black F wire at the VR to the black FLD at the alternator. Then do the same with the red (Bat) wire.

The tests will verify good/bad for the VR and good/bad for the alternator. It also verifies good/bad wiring from the VR to the alternator.

Page 11 of the ERA wiring diagram will show you diagrams of what I am talking about.

Let us know the results.

John

[Large Arbor]

I did just that and had a brother who is very sharp help. We traced the problem to this and is now solved and fixed.

[Grubby]

Large,

Give us more detail on the picture. What is it and where was it found?

John

[Large Arbor]

It was in the alternator feed to the battery. It was a splice and looked to be a type of fusible link. It gave up its location when we only measure 5V going to the alternator with the key off. Pulled the tape back and viola. Now I am on to starter issues in which it seems to be binding. The bolt holes for the Dynaforce were larger than the 5/16th (i.e. 1/2" head). I cut some 3/8th copper and made the bolts fit tighter in the holes and its a little better, but I will have to try shims. Dynaforce has no lateral movement so shims will only do in / out. I will have to try that later in the week. I think the starter was moving around because the bolts were smaller than the starter case holes. Something is not quite right, but I will get to the bottom of it. It may be its not pulling away enough from the flywheel or engaging too much. Thanks again for sagely advice.

Phil