Low charge to no charge issue pulling hair out

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J.B.

J.B.

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I cant figure it out everything I can test checks out. The alternator battery post when running at 14.04 tells me its making charge and everything in between has tested great. New voltage regulator and old one i had on car everything act the same. Hope someone can shed some light

✅KEY OFF Alternator BATTERY terminal matches battery

✅KEY ON Alternator 1 point drop normal loss

✅KEY ON-Alternator field terminal blue 12.58

✅RUNNING Alternator BATTERY terminal 14.03

❌RUNNING battery at 12.4 not charging at 13.5-14. If I remove voltage regulator connection charge drops even more to 11.9.

✅Alternator charges with lower charge field wire jump test (simulating green wire terminal)





KEY OFF WIRE HEALTH TESTING AT 200 ohms

✅Green field wire from voltage regulator side connector head to alternator side field terminal connector 00.8 ohms resistance

✅Blue field wire from connector head to field terminal connector 00.8 ohms resistance

✅Alternator battery charge wire (black) to bulk head (firewall side)00.6 ohms

✅Bulk head charge wire (firewall side)to starter relay (red)1.4 ohms resistance

✅Alternator ground terminal post wire to cylinder head 00.9 ohms

✅Green field wire with key on sparked when connecting jumper to either the voltage regulator connector side or alternator field connector side.



Interior bulk head side

✅Black charge wire to ammeter from ammeter terminal to bulk head connection 00.7ohms

✅Red charge wire to ammeter from ammeter terminal to bulk head connection 00.8ohms

✅Key on - Both sides red and black wires going into ammeter had 1 point volt drop. Matches the battery terminal on the alternator.
 
J.B. said:
RUNNING battery at 12.4 not charging at 13.5-14. If I remove voltage regulator connection charge drops even more to 11.9
Click to expand...
It is charging but it does not need much so the alternator is putting out a maintain charge.

A battery with higher internal resistance might cause what you are seeing.

Also testing wires with an ohm meter will tell you at least one strand of wire is connected.

To determine wire health you need to check for voltage drop under load.

The smaller wire diameter (gauge) the higher resistance under load = more voltage drop.
 
With the ignition off, put your high beam headlamps on for three minutes. Then switch them off and measure voltage across the battery; what do you see?
 
Just did it, 12.13 to start then after 3 minutes with highbeams on multimeter shows 11.87
 
Battery charge is low.
Whether it is battery itself or lack of recharge, can't say for sure.
However the fact you could start the engine suggests there may be a decent amount of stored energy in the battery and you can probably revive it.
Put it on a current constrolled charger at 2 amps or 5 amps. So a voltage reading after turning the lights on briefly gives a truer indication of energy stored in the battery.
Turning on power briefly removes any surface charge.

J.B. said:
✅RUNNING Alternator BATTERY terminal 14.03

❌RUNNING battery at 12.4 not charging at 13.5-14. If I remove voltage regulator connection charge drops even more to 11.9.
Click to expand...
Removing the connection on the regulator opens the field circuit. The alternator can not produce power without allowing electicity to flow through the field windings.
So that's all normal.

J.B. said:
✅RUNNING Alternator BATTERY terminal 14.03
Click to expand...
The alternator at 14.0 an the battery at 12.4 V indicates resistance to flow.
What did the ammeter show?
This is one of the keys to figuring out where the problem lies.
 
Mattax said:
Battery charge is low.
Whether it is battery itself or lack of recharge, can't say for sure.
However the fact you could start the engine suggests there may be a decent amount of stored energy in the battery and you can probably revive it.
Put it on a current constrolled charger at 2 amps or 5 amps. So a voltage reading after turning the lights on briefly gives a truer indication of energy stored in the battery.
Turning on power briefly removes any surface charge.


Removing the connection on the regulator opens the field circuit. The alternator can not produce power without allowing electicity to flow through the field windings.
So that's all normal.


The alternator at 14.0 an the battery at 12.4 V indicates resistance to flow.
What did the ammeter show?
This is one of the keys to figuring out where the problem lies.
Click to expand...
Ammeter showed second line on charge side
 
The ammeter was pointing at #1 or #2

Screenshot_20241128-142115.png
 
Also just took battery off charger said 100 percent charged and result 12.17
 
J.B. said:
Ammeter showed second line on charge side
Click to expand...
That's about 20 amps charging.
20 amps is about right immediately after starting, but it should drop toward zero within the first minute.

1732829196055.png


I'd say.
A. If it stays at 20 amps charge, especially at slow idle, the battery charge state is low.
B. If it stays at 20 amps or more for a long period of time, connections and other weak spots in the circuit will get warm or even hot.

We don't know the total current flowing from the alternator, but for sure there is more resistance in the circuit than we'ld like.
14 - 12.4 = 1.6 drop in Voltage for 20 amps.
We can do some calculation so you can see why a resistance check using a meter doesn't reveal problems unless they are more extreme. And by then its often too late.
V = I x R
V/I = R
1.6 Volts/ 20 amps = .08 ohms

Back to finding the problems.
One problem is resistance in the circuits.
The ignition and field current on a stock 70-71 will be around 5 amps. More if a newer alternator has been installed. Same if an electric choke installed, etc.

We don't really need to know the exact current, but its useful to keep in mind if you decide to use the voltage drop to hunt for resistance points.
Follow the path the current was taking and look at all the connections along that path. Also look at places wires for those ciruits can get get exposed to chafing or heat or strain.
 
J.B. said:
Was pointing to #1
Click to expand...
That's between 10 and 20 amps, my 67 will go there for a few minutes after a hard start. But it will settle down once the battery is happy.


My battery is 7 years old, garaged in northern Colorado, 1000 to 2000 miles per year.

I do think you have an issue either with the wires and connectors between the alternator post and or the battery.
 
Mattax said:
That's about 20 amps charging.
20 amps is about right immediately after starting, but it should drop toward zero within the first minute.

View attachment 1716333222

I'd say.
A. If it stays at 20 amps charge, especially at slow idle, the battery charge state is low.
B. If it stays at 20 amps or more for a long period of time, connections and other weak spots in the circuit will get warm or even hot.

We don't know the total current flowing from the alternator, but for sure there is more resistance in the circuit than we'ld like.
14 - 12.4 = 1.6 drop in Voltage for 20 amps.
We can do some calculation so you can see why a resistance check using a meter doesn't reveal problems unless they are more extreme. And by then its often too late.
V = I x R
V/I = R
1.6 Volts/ 20 amps = .08 ohms

Back to finding the problems.
One problem is resistance in the circuits.
The ignition and field current on a stock 70-71 will be around 5 amps. More if a newer alternator has been installed. Same if an electric choke installed, etc.

We don't really need to know the exact current, but its useful to keep in mind if you decide to use the voltage drop to hunt for resistance points.
Follow the path the current was taking and look at all the connections along that path. Also look at places wires for those ciruits can get get exposed to chafing or heat or strain.
Click to expand...
I did that and looked at the entire loop from battery termal wire all the way to the ammeter and bulkhead both sides no wire issues or connector issues everything clean tight
 
Red arrows show connections where resistance may be occuring.
1732830507969.png
 
After 30 minutes post charge battery is down to 12.01 so its slowly dropping after charge
 
J.B. said:
I did that and looked at the entire loop from battery termal wire all the way to the ammeter and bulkhead both sides no wire issues or connector issues everything clean tight
Click to expand...
Then youll have to use voltage drop to test.

One quick way is to turn the headlights on with the engine off, key off.
The ammeter should show about 12 amps discharge.

Measure the voltage at the battery positive, then at the alternator bat stud. There's no current in the alternator output wire so we're just using at as an extension of the probe. Any difference we measure will be due to resistance between the battery positive and the main splice.
We can do one better by measuring direction from the battery poitive to the alternator stud. This eliminates ground path losses.
 
If I remove the green field wire from the back of the alternator and then place a wire on that field terminal and run it to battery ground the alternator sounds and battery starts get 13.87 volts and charges
 
Mattax said:
Then youll have to use voltage drop to test.

One quick way is to turn the headlights on with the engine off, key off.
The ammeter should show about 12 amps discharge.

Measure the voltage at the battery positive, then at the alternator bat stud. There's no current in the alternator output wire so we're just using at as an extension of the probe. Any difference we measure will be due to resistance between the battery positive and the main splice.
We can do one better by measuring direction from the battery poitive to the alternator stud. This eliminates ground path losses.
Click to expand...
Here is photo of discharge gauge with lights on and the results of the test

Start of test battery at 12.00 and alternator batt post 12.00



11.64 positive battery terminal


Alternator batt post 10.30

IMG_1794.jpeg
 
Btw this is for
My 1973 Cuda no one ever answers on the ebody but systems are all the same
 
J.B. said:
I did that and looked at the entire loop from battery termal wire all the way to the ammeter and bulkhead both sides no wire issues or connector issues everything clean tight
Click to expand...
Did you test for voltage drop under load at every point of connection?

If you have a wire with 15 strands in it
The load is shared by each strand.

Now let's say you have the same 15 strands but 14 of them are broken.

Now all the load has to be carried by the one strand.

Both the first and second example will show the same resistance on an ohm meter. But under a 5-10 amp load the first example will have a 0.08v voltage drop. But the second will have a 1-2v voltage drop.


The single strand under load increases in resistance.


Thing about an interstate with 4 lanes all the cars can pass past a point on the side of the road at full speed

This is all 15 strands working correctly


Now block off 3 lanes and the traffic crawls.

This is with 14 of 15 strands broken



If it's late at night and there is only one car for miles that car can pass that point at full speed regardless if it has 4 lanes or 1

This is how your ohm meter works.
 
Last edited:
Dana67Dart said:
Did you test for voltage drop under load at every point of connection?

If you have a wire with 15 strands in it
The load is shared by each strand.

Now let's say you have the same 15 strands but 14 of them are broken.

Now all the load has to be carried by the one strand.

Both the first and second example will show the same resistance on an ohm meter. But under a 5-10 amp load the first example will have a 0.08v voltage drop. But the second will have a 1-2v voltage drop.


The single strand under load increases in resistance.


Thing about an interstate with 4 lanes all the cars can pass past a point on the side of the road at full speed

This is all 15 strands working correctly


Now block off 3 lanes and the traffic crawls.

This is with 14 of 15 strands broken



If it's late at night and there is only one car for miles that car can pass that point at full speed regardless if it has 4 lanes or 1

This is how your ohm meter works.
Click to expand...
Ok i just went out and started from the battery, battery with lights on 11.80, checked connection at starter relay 11.80, the checked the fire wall side bulkhead red 11.8. Next i checked the red connected post at back of ammeter and the result was 10.30. Is that ok or not ok thats the first change of signal from what battery had
 
Just went out and tested my 67 dart.

Last driven yesterday or Tuesday for 30+ minutes.

Key off, doors shut, no accessories on.

Battery plus to minus post 12.66v

Alternator output post to Battery minus post 12.66v

Key off, doors shut, headlights on.

Battery plus to minus post 11.96v

Alternator output post to Battery minus post 11.53v

0.43 voltage drop
 
Dana67Dart said:
Just went out and tested my 67 dart.

Last driven yesterday or Tuesday for 30+ minutes.

Key off, doors shut, no accessories on.

Battery plus to minus post 12.66v

Alternator output post to Battery minus post 12.66v

Key off, doors shut, headlights on.

Battery plus to minus post 11.96v

Alternator output post to Battery minus post 11.53v

0.43 voltage drop
Click to expand...
Im thinking my ammeter is the culprit evwrything is good up until i get to the post, when i get to the red post on back of ammeter thats where i get the big drop from 11.8 to 10.30 giving me a 1.5v drop
 
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