Voltage Drop

[DoubleYOOHZ]

Hey SteveJ, are you referring to just removing the F connector or 
removing A and connecting it to F? 

[SteveJ]

The fusible links. For the factory testing methods, I would have to read them. It's been a while.

[Zed Head]

16 hours ago, DoubleYOOHZ said:

Trial #1 
12.6v - Engine Off
13.6v - Engine Idling
11.88v - Engine Idling w/ headlights on
11.90v - Engine Idling w/ headlights on and max fan
12.90v - Engine Idling w/ lights and fans turned off 

Trial #2 
12.42v - Engine Off
13.34v - Engine Idling
12.06v - Engine Idling w/ headlights on
12.01v - Engine Idling w/ headlights on and max fan
13.36v - Engine Idling w/ lights and fans turned off 

I do have to bring up that about a year ago when I was working on my car, when I tried to start my car the fusible link caught fire. Weirdly enough, it was the alternator and Relay fusible link. 

Seems like some facts are being convoluted.  The alternator charged, at least for a short while, according to the above.  And the fusible link fried a year ago.

But now the alternator doesn't charge.  Post # 6 - " I just had tested the car when at 2000 RPM and it read 12.07v."

Just saying there's odd things going on.  Maybe a loose Lamp wire?  No Lamp, no charge.

[Dave WM]

good point Zed, seems it was that last post about 2000 rpm and 12.07 that made  me think there is an issue but as you noted the  red results, that is pretty much normal, and inconsistent with the 2000/12.07v.

OP you need to nail that down better exactly which is it.

Edited July 13, 2016 by Dave WM

[Dave WM]

OP, Don't bother with the F to Batt stuff until you get back to us on what's going on with voltage readings at idle.

As far as the process, you unplug the plastic plug on the back of the alt, its the F/N plug with the F/N noted right on the alternator.

BTW the N lead is used to energize the charging light circuit, it  tells the car the alter is turning.

next you rig up a jumper, I used an alligator clip on the F term from the back of the alternator to the Bat terminal of the alternator. Exercise some care here so you don't short the clips to the any part of the alternator as this would ground the Battery and vaporize you jumper, quite possibly giving you a nasty burn for your trouble. use insulate clips. and make sure of what you are clipping to.

This fully energizes the Field winding (no voltage regulation) and if you alternator is good it will output as much as it can. Again there is NO regulation so you don't want to rev the engine, just get a reading at the Bat term of the alt and at the Battery post (+).

 

Edited July 13, 2016 by Dave WM

[DoubleYOOHZ]

@Zed Head & @Dave WM - The quote " I just had tested the car when at 2000 RPM and it read 12.07v " occurred when I started the car and had a second person rev the car to 2000 rpm to which gave me a reading of 12.07v. Car was not in idle. When car is in idle and idling at 1100 rpm, the readings from the battery gave out 13.6 and 13.34v.  Im sorry about the confusion. 

thanks for the detailed explanation Dave. I really appreciate this. Unfortunately, I do not have alligator clips and I will pick some up tomorrow to test this out. 

[Zed Head]

That's odd.  Others might know a component level reason for it (I don't), but what you're saying is that either the VR or the alternator stops working at higher RPM or higher current/voltage.  You really need find a way to attach your leads to the battery terminals and work the throttle by hand while watching the meter to get some more information.  If you get charging at idle but it kicks off  at higher RPM, then the F to Bat test might tell you if it's the alternator or the VR.

I would connect the meter to the battery, start the car, and confirm that charging kicks out at higher RPM.  Then connect F to Bat and do the same.  If it keeps charging at higher RPM (don't rev too high) then you most likely have a VR problem.  If it's a solid-state VR it could just be that the circuitry can't handle the heat.  If it still stops charging at higher RPM with F to Bat, then it's the alternator.

[siteunseen]

Yeah, you should twist the throttle rod and not have to get in the car.  What about the shade tree ways of testing the alternator?  Unhook the negative battery cable and see if it keeps running.  See if a screwdriver sticks to the back of the alternator like a magnet.  I guess that works on all alternators and I've done that a bunch of times on older cars, probably not a good idea on a newer one with a computer though.  Or what about stopping by an auto parts store and they'll roll out that cart that checks to see if it's the battery or the alternator?

[Zed Head]

He's a couple of simple steps away.  He has the meter, the engine runs, he's taken measurements.  He just needs to take a few more measurements, with the right conditions.

He knows the alternator will charge.  He just doesn't know why it stops doing it.

[Dave WM]

That is indeed odd, less voltage at higher RPM. I agree with Zed Head, make sure you have a good test setup and confirm this is indeed what is happening.

A couple more things to consider

The car come equipped with a voltmeter and a charge light, do these work? If they do then it should be pretty obvious if there is an issue that would preclude driving until corrected.

So Does the voltmeter show more voltage after the engine starts If so then you are pretty much good to go, does it show this odd drop in voltage as RPM increase? Unplugging the F/N plug should make the charge light come on (or go off, not sure how it works) and the voltage should drop. You should hear the difference the F/N plug on and off as the alt should sound different as it loads with the plug in.

My 75 has an amp meter which I prefer but the voltmeter can give you the same info as long as you remember the starting voltage before the car engine is running.

So with a working voltmeter you can pretty much diagnose with out even using any outside equipment. If its not working then that should be the very 1st thing to address. I would never drive my car if any of the gauges were not functioning properly. I just recently spent some time going thru the fuel sending unit to make sure it was calibrated so I would know how much gas I have.

Edited July 14, 2016 by Dave WM

[Zed Head]

That's a good idea about the Charge light.  On the internally regulated alternators, the Charge light would not light if the L wire was disconnected, and charging would stop.  But with externally regulated systems L runs to the VR.  Looks like F comes straight through from Ignition and the charge light just indicates the balnce between A and the battery.  So, it should light if charging stops, I'd think.

So, good question - what is the Charge light doing?

 

[DoubleYOOHZ]

@Zed Head - Terminals are all clean. Simply, you stated it outright. It isnt charging at higher rpms. 

@siteunseen - The car is running but it is not registered. No insurance or paper work done yet because it is still in its revival period. I was going to take it to autozone or oriellys but I did not want to risk getting the car impounded. I want to make sure the car runs great before I purchase insurance and all of the above. 

@Dave WM - From the tachometer, the lights do turn red before I crank the car. The voltmeter does show higher voltage after the car has started. Then there is a drop in voltage when lights are turned on. Also, voltage seems to drop when car increases its RPM. 

So today, I did the F alligator to A (Bat) to test the alternator and measured the voltage. I got 16.47v. Seems like the alternator is doing its job at making as much voltage as possible. We can assume the culprit is the voltmeter?