Low voltage reading ? Charging issue

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Kenflo

Kenflo

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I have a question about the charging system. Since I rewired the car I have always had a fairly low voltage reading (at least I think it’s low) on the volt gauge in the dash. When at idle 900RPM the gauge is reading 12 volts, when cruising around town 11.8-12 volts. Battery is about 3 years old and I think is ok tests at 12.6 prior to starting. I should mention when the car is between uses battery is always hooked up to a smart charger/maintainer. Alternator is the power master 7018 75 amp. Used EZ wire kit to wire the entire car.
Is this voltage too low? I am concerned that the battery is not charging
 
At idle 12v is not unusual

At above idle only measuring 11.8 to 12 is a problem.

Many possibilities.

No particular order.
  1. Voltage drops in your wiring due to bad connections
  2. Bad voltage regulator
  3. Bad alternator
  4. Bad battery
Many of the items above can be tested on the car but it is more complicated.

The battery would be the easiest to test if you have a parts store near you. Fully charge it then bring it to the store and see what they say.


Alternator next easiest to test. Pull it and take to parts store and have them test it.

The VR can be tested on car assuming the alt and battery are good. By bypassing some wires and seeing what happens. The procedure is different depending on your VR / Alternator

Voltage drops are tested in place with a load on the various points you are testing.
 
If the battery is not "defective" and is not dead or way down, and so, charge it and test it
Then measure battery voltage AT THE battery with a known good meter. With the battery "up and warm" and the engine warm (VR's are temp compensated and temp sensitive) measure batt voltage at an RPM simulating "low to medium cruise." Anything above 1000 RPM should be fine

The system running voltage should be nominal 13.8--14.2

It may be something wrong with charging system, wiring, or the voltmeter in the car. Even the key switch wiring and the switch itself can cause "voltage drop" problems
 
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So I did some testing and there is a voltage drop of 82 MV testing leads placed at alternator post and positive battery post, this seems like a significant voltage drop. Also tested voltage at battery + and - while car is idling and getting 11.8 volts. Tested alternator post and ground while idling and getting same 11.8 volts.
 
Well then it is not charging

You have to follow what I am saying, just "measuring" can lead you down a "road." Voltage drop in the path from alternator output to battery is very non critical with an external VR. Only a "one wire" needs a huge charging wire for no drop, because the one wire IS the sense lead

The drop you may be experiencing is in the ignition harness, whatever feeds the voltmeter

What is the powermaster, is this internal / 3 wire, or internal 1 wire or external VR or what?
 
67Dart273 said:
Well then it is not charging

You have to follow what I am saying, just "measuring" can lead you down a "road." Voltage drop in the path from alternator output to battery is very non critical with an external VR. Only a "one wire" needs a huge charging wire for no drop, because the one wire IS the sense lead

The drop you may be experiencing is in the ignition harness, whatever feeds the voltmeter

What is the powermaster, is this internal / 3 wire, or internal 1 wire or external VR or what?
Click to expand...
The power master alternator is a 2 field wire hook up with an external triangle plug voltage regulator, I have an alternator bypass wire as per EZ wire instructions to the starter solenoid as well
 
I think if you ground the field lead that goes to the electronic VR Your alt will go full power and quickly see what it gets to the battery, should be like 19v. Iirc the electronic VRs varied the ground resistance to that field brush to chassis ground.
 
Kenflo said:
The power master alternator is a 2 field wire hook up with an external triangle plug voltage regulator, I have an alternator bypass wire as per EZ wire instructions to the starter solenoid as well
Click to expand...
Thanks. To determine if the alternator is at fault, remove the green field wire and ground that alternator field terminal. Turn the key to "run" measure the blue wire. It should be close to "same as battery" Start, run, slowly bring up RPM while monitoring battery voltage. Voltage should climb up. Don't or try not to allow it above 15.5--16 by applying throttle

If that works, now determine if rest of harness is OK. So reconnect green, at alternator remove the blue field wire and ground that alternator terminal.

Disconnect VR and devise a way (such as smalls crews) to jumper across the VR connector. This does same thing as earlier, just wired different. Again it should charge. IF so, check and make ABSOLUTELY certain VR is grounded. If that doesn't fix it replace VR
 
pishta said:
I think if you ground the field lead that goes to the electronic VR Your alt will go full power and quickly see what it gets to the battery, should be like 19v. Iirc the electronic VRs varied the ground resistance to that field brush to chassis ground
Click to expand...
Agree that that test can be performed but a safer way is to remove both field wires from the alt. Use jumper leads from batt plus to one field TERMINAL.
Use another jumper lead from the other field TERMINAL to ground.

With engine running you should see very high voltage at the battery.

DO NOT DO THIS TEST FOR VERY LONG.

The reason I recommend this method is you eliminate the possibility of shorting to ground the power feed to the alternator field wire

All this does is show the alternator CAN charge.

It does not show why it is not charging.
 
67Dart273 said:
Thanks. To determine if the alternator is at fault, remove the green field wire and ground that alternator field terminal. Turn the key to "run" measure the blue wire. It should be close to "same as battery" Start, run, slowly bring up RPM while monitoring battery voltage. Voltage should climb up. Don't or try not to allow it above 15.5--16 by applying throttle

If that works, now determine if rest of harness is OK. So reconnect green, at alternator remove the blue field wire and ground that alternator terminal.

Disconnect VR and devise a way (such as smalls crews) to jumper across the VR connector. This does same thing as earlier, just wired different. Again it should charge. IF so, check and make ABSOLUTELY certain VR is grounded. If that doesn't fix it replace VR
Click to expand...
Just want to confirm these are 3 seperate tests right?
1.remove green field wire and ground the alternator field terminal, start, run and check battery voltage, reconnect green field wire
2. Remove blue field wire wire and ground the alternator field terminal, start, run and check battery voltage, reconnect blue field wire
3. Disconnect and jumper VR terminals, start, run and check battery voltage
 
82 Mv is ok. Putting that into perspective, there is a 0.082v voltage drop along the cable that connects the alt terminal to the bat + terminal & is not part of your problem.
 
Kenflo said:
Just want to confirm these are 3 seperate tests right?
1.remove green field wire and ground the alternator field terminal, start, run and check battery voltage, reconnect green field wire
2. Remove blue field wire wire and ground the alternator field terminal, start, run and check battery voltage, reconnect blue field wire
3. Disconnect and jumper VR terminals, start, run and check battery voltage
Click to expand...

This is a test for alternator output. Use an incandescent test light, not LED type. [It looks like an ice pick with a 3' wire and an alligator clip.] Clip it to the alternator case. Probe the output stud. It should light. Unplug blue and green wires. Probe both prongs on alt. It should NOT light. Turn ign. key to run. Probe blue wire. It should light. Key off. Install jumper wire from green [other] prong of the alt to ground. Put a voltmeter on the battery so it is visible from the drivers seat. It should read ~12.6 volts. Plug blue wire back into alt. Start car. It should read more than 13.2 volts at idle. Put headlights on and fan on high. It should maintain the voltage. Turn the Key, lights and fan off......... ...If OK; regulator, regulator ground, or wiring must be checked.
 
Kenflo said:
Just want to confirm these are 3 seperate tests right?
1.remove green field wire and ground the alternator field terminal, start, run and check battery voltage, reconnect green field wire
2. Remove blue field wire wire and ground the alternator field terminal, start, run and check battery voltage, reconnect blue field wire
3. Disconnect and jumper VR terminals, start, run and check battery voltage
Click to expand...
2 and 3 go together, what you are doing:

Normally, the field is supplied battery from the key at the blue wire. The VR "controls the ground" to the other field wire via the green.

By powering the field through the blue, grounding the "was" green alternator terminal you are checking that the blue circuit works, along with the alternator

By reversing this, grounding the "was blue" alternator terminal AND BY jumpering the VR connector, you are now feeding battery to the green and through the field.

This is just a quick rough test that the harness is intact and doing what it should.
 
Would it matter if the blue wire going into the VR was switched? Meaning it’s hooked up directly to the alternator field terminal and green wire feeding from fuse box as alternator exciter wire
See attached pic, I just noticed this and not sure if this matters?

image.jpg
 
NO. the two field terminals simply connect to the brushes, and the field is a simple electromagnet. Only "matters" is the "restoration correct" for looks

But something is wrong. Why is there a splice in the green from the VR plug? That wire should go one place only--from the VR green terminal to one of the field terminals, no other branches or wires

Blue should come off the ballast "ignition run" feed" and feed the blue wire on the VR and the blue wire to one field terminal
Green goes from VR to field

Also as short as that harness looks, are you able to mount the VR away from header heat? The VR MUST be grounded.
 
67Dart273 said:
But something is wrong. Why is there a splice in the green from the VR plug? That wire should go one place only--from the VR green terminal to one of the field terminals, no other branches or wires

Blue should come off the ballast "ignition run" feed" and feed the blue wire on the VR and the blue wire to one field terminal
Green goes from VR to field
Click to expand...

That is probably where you trouble lies. swap the Green and Blue and if you did not fry the VR you should be good to go.

upload_2022-6-4_12-6-14.png


This (assuming the white in the black sheathing is the 12V feed from the ignition)
upload_2022-6-4_12-16-55.png


AND WATCH THE VIDEO!!!!!
 
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Also I don't know if that is hooked up backwards like that will damage the VR or not but "it might"
 
Well after watching that video and reading these posts I am definitely going to hook it as per Chrysler diagrams, I will report back, hopefully it’s a simple fix. I may try to move it away from headers as well although I am using heat shield tape on my harness in this area and wires currently show no sign of melting
 
Dana67Dart said:
That is probably where you trouble lies. swap the Green and Blue and if you did not fry the VR you should be good to go.

View attachment 1715937254

This (assuming the white in the black sheathing is the 12V feed from the ignition)
View attachment 1715937257

AND WATCH THE VIDEO!!!!!
Click to expand...
Yes indeed the white wire from the EZ wire kit was labeled alternator exciter wire, I am wiring as per your diagram
 
"Exciter wire" is a stupid term and comes largely from GM. The Delco internal regulator setups used an idiot lamp in parallel with a resistor for "an exciter." On (at least the older) Delcos, you did NOT want to eliminate the resistor/ lamp, except you could use an inline diode. This prevented high current draw in that circuit that would "cook" what is called the diode trio. Anyhow, it's a gm thing.
 
So made the change, switched the wiring and fired up the car, just getting 12.0-12.1 volts at volt gauge in dash, reading 12.3 volts at battery + and - terminals as well as 12.3 at alternator post to -
I think I will purchace a new voltage regulator as I may have fried the current one
 
Or... Your battery is fully charged!

Turn on headlights, press the brake pedal, turn in the heater fan and check the voltage then. Also be sure you do this at idle AND at 1000 to 2000 rpm.

( My reference to 12 volts is the nominal voltage, maybe it's 12.8 or 12.4 or the like)


At idle the voltage should be under or just at 12

At higher rpm it should be 12 or higher
 
Ok, with car at idle 900-1000 rpm head lights, heater, brakes, turn signal voltage reading 11.5 @ volt meter, increasing rpm does not make voltage increase
 
Dana67Dart said:
Or... Your battery is fully charged!

Turn on headlights, press the brake pedal, turn in the heater fan and check the voltage then. Also be sure you do this at idle AND at 1000 to 2000 rpm.

( My reference to 12 volts is the nominal voltage, maybe it's 12.8 or 12.4 or the like)


At idle the voltage should be under or just at 12

At higher rpm it should be 12 or higher
Click to expand...

No, no no. Sorry, no. If the alternator is running fast enough to charge and overcome the load, and if the battery is healthy and "up" it should run nominal 14. "You can't say" what it should be at idle for several reasons.........don't know what the load is, the battery state of charge, how much that alternator can put out "at idle," or even "what" the idle RPM is.

If the battery is dead enough, output can read somewhat low, but under "low-med cruise" RPM it will almost always come up 13V+ depending on the output rating of the alternator and battery state.
 
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