Factory ammeter

I'm curious while were on the topic wouldnt the voltage regulator protect the wiring even if you had a 60. Amp alternator? Or does it do something different? I tested my voltage regulator today with a ohm meter I'm getting 3.80 ohms @20 is that a good reading?

dartfreak75 said:

I'm curious while were on the topic wouldnt the voltage regulator protect the wiring even if you had a 60. Amp alternator? Or does it do something different? I tested my voltage regulator today with a ohm meter I'm getting 3.80 ohms @20 is that a good reading?

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No ALL the vr does is maintain proper output voltage. If the alternator is a 30, 40, 60, 180, it can put out that amperage if the battery is low enough, AKA after the lights been left on, or if there are a lot of accessories, IE electric pumps, fans, big stereo, whatever.

67Dart273 said:

No ALL the vr does is maintain proper output voltage. If the alternator is a 30, 40, 60, 180, it can put out that amperage if the battery is low enough, AKA after the lights been left on, or if there are a lot of accessories, IE electric pumps, fans, big stereo, whatever.

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So the alt only puts out the amps needed to maintain the battery? For example it will put out more amps if the battery is low charge vs full charge?

dartfreak75 said:

I tested my voltage regulator today with a ohm meter I'm getting 3.80 ohms @20 is that a good reading?

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What type of meter? Not sure what you mean by @20. I ask because most digital meters will give automatically scale to show ohms, or megaohms; while most analog versions there is a scale to set and then read. With the scales sometimes you have to multiply.

As far as the VR in your '75, no you can't test it that way.
The 'I' terminal checks the voltage in the run circuit. Depending on the voltage level, it powers transistors which control how much current can run through the alternator's rotor. Basically it controls the other terminal's connection to ground, opening and closing it as needed.

dartfreak75 said:

So the alt only puts out the amps needed to maintain the battery? For example it will put out more amps if the battery is low charge vs full charge?

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Yes a low battery will draw more amps. With a charger we can reduce the amps a low battery draws by reducing the voltage of the power supply.
A photo sequence of that in this post.
It's like a light bulb in that regard. If the lightbulb is connected to a power source at lower voltage, it will draw less current and dim.
When the battery is connected to the car's power system, the recharging voltage is somewhat fixed. The only limitation is the alternator's capacity to produce power.

As far as the alternator output goes, it only puts out the amps needed to charge the battery and whatever else is running.

Mattax said:

Yes a low battery will draw more amps. With a charger we can reduce the amps a low battery draws by reducing the voltage of the power supply.
A photo sequence of that in this post.
It's like a light bulb in that regard. If the lightbulb is connected to a power source at lower voltage, it will draw less current and dim.
When the battery is connected to the car's power system, the recharging voltage is somewhat fixed. The only limitation is the alternator's capacity to produce power.

As far as the alternator output goes, it only puts out the amps needed to charge the battery and whatever else is running.

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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Alternator 101

Mattax said:

whatever else is running.

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To give some idea of the current demands of a mid 70s A-body, this is the breakdown of the alternator output of my Grand Wagoneer measured with a clamp meter.
Its pretty similar in terms of electrical equipment and lighting.

I looked up the part number on my alternator it says it's a 65 amp.
https://www.autozone.com/batteries-...ctured-alternator-7516/335737_1359382_0_24380

Mattax said:

What type of meter? Not sure what you mean by @20. I ask because most digital meters will give automatically scale to show ohms, or megaohms; while most analog versions there is a scale to set and then read. With the scales sometimes you have to multiply.

As far as the VR in your '75, no you can't test it that way.
The 'I' terminal checks the voltage in the run circuit. Depending on the voltage level, it powers transistors which control how much current can run through the alternator's rotor. Basically it controls the other terminal's connection to ground, opening and closing it as needed.

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Sorry I just saw your message. This is the setting I used its 20m on the ohm settings I watched a video and a guy was testing mopar vr he was getting 1.85 ohms

This is the video I was referring to @Mattax

dartfreak75 said:

Sorry I just saw your message. This is the setting I used its 20m on the ohm settings I watched a video and a guy was testing mopar vr he was getting 1.85 ohms

View attachment 1715604291

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20k not 20m lol

dartfreak75 said:

Sorry I just saw your message. This is the setting I used its 20K on the ohm settings I watched a video and a guy was testing mopar vr he was getting 1.85 ohms

View attachment 1715604291

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Thanks. That's fine. Don't what I wasn't thinking. I forgot about non-autoranging digital meters...

dartfreak75 said:

This is the video I was referring to @Mattax

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I don't have time to look at that this AM but off the top of my head I can't think of how small differences in resistance would indicate anything.
With no power connected to the 'sense' terminal , the field terminal to ground should be very low resistance. That's about it.
One of the other guys may have more insight.

This is a simplified VR diagram that Chrysler used to illustrate how this type of regulator works.
When the voltage at I is below something like 13.7 Volts, the Zener diode signals the transistors to complete the field circuit to ground.
That allows current to flow through the windings of the alternator's rotor. That current through the windings creates a spinning electromagnetic field.


If voltage at I is a little higher than 13.7, rapidly opening and closing the switch reduces the magnetic field strength.
There may be a third path through a resistor so there's actually three paths. That's how the earlier electromechanical ones work.

dartfreak75 said:

I looked up the part number on my alternator it says it's a 65 amp.
https://www.autozone.com/batteries-...ctured-alternator-7516/335737_1359382_0_24380

View attachment 1715604280

View attachment 1715604281

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7516 is an interchannge part number.
65 amps is probably, uh maybe, the maximum it was supposed to produce when regulated to 12 Volts.
It might be exactly the same output as a Chrysler unit that the shop manual says will put out 41 amps at 1250 rpm when regulated to 15 Volts.

Not sure if this is useful to anyone, but I have some wiring diagrams on the charging system and ones for the entire car (2 are version I've remade myself to make poster size printouts for my garage)

Index of /car

dartfreak75 said:

This is the video I was referring to @Mattax

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That video is specific to that company's adjustible regulator.
It looks like a mopar type regulator case with a Wai Wei Transpo regulating unit soldered and potted into it. Seen those for sale at some of the same places that sell alternator parts for repair.
Probably what you are watching is an adjustable resistor in a circuit between the sensing terminal (i) and the field terminal.

Mattax said:

That video is specific to that company's adjustible regulator.
It looks like a mopar type regulator case with a Wai Wei Transpo regulating unit soldered and potted into it. Seen those for sale at some of the same places that sell alternator parts for repair.
Probably what you are watching is an adjustable resistor in a circuit between the sensing terminal (i) and the field terminal.

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Thanks man so is there any way to check and see if mine works? Or should I just replace it ?

dartfreak75 said:

Thanks man so is there any way to check and see if mine works? Or should I just replace it ?

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Off the car you need a special tester that is powered. So the short answer is, off the car, no.
On the car it's pretty easy. Procedure is in the shop manual.
Charge the battery fully.
Place positve probe or clip of the voltmeter onto the ignition circuit some place close to the regulator. The 'run' terminal at the ballast resistor is a good location.
Connect the negative probe to a good ground.

Start the car. Watch the voltmeter and keep an eye on the ammeter and rpms.
manual says target 1250.


With nothing else turned on and the battery charging done, voltage should stay pretty steady regardless of rpm.
That still leaves the possibility of resistance in the wiring, but the regulator itself is working.

Mattax said:

Off the car you need a special tester that is powered. So the short answer is, off the car, no.
On the car it's pretty easy. Procedure is in the shop manual.
Charge the battery fully.
Place positve probe or clip of the voltmeter onto the ignition circuit some place close to the regulator. The 'run' terminal at the ballast resistor is a good location.
Connect the negative probe to a good ground.
View attachment 1715605734
Start the car.
View attachment 1715605717

With nothing else turned on and the battery charging done, voltage should stay pretty steady regardless of rpm.
That still leaves the possibility of resistance in the wiring, but the regulator itself is working.

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Ok I guess I will just have to wait till I get the car put back together lol

Honestly, if the ammeter is showing normal charging and discharging I don't worry about it.
If the ammeter is showing excessive charging, then I do a quick check of voltage at the battery.
The reason excessive charging raises a question about voltage regulation is that the battery will attempt to overcharge when supplied with power above 15 Volts.

Of course the other reason there might be higher/longer than normal charging is the battery was heavily discharged. In which case just try to keep the rpms low and get it on a charger as soon as possible.

Since you have things apart.
Resistance at the connections circled in red, or the wires connecting them, will cause the alternator to produce power at higher voltage than it should.


Poor connections or wiring in the battery feed/charge line will cause the battery to undercharge and/or take longer to recharge.
While not good, not quite as serious as the issues created by the ones above.

I’m having an overcharging problem, I’m getting 16 volts out of the batt. Lug on the alternator, but 14.5 at the battery and starter relay. I have tried 3 regulators and 2 alternators no change. I’ve checked the green field wire and it’s fine between the alt and vr. Where do I go from here? It’s a 75 duster.

gm1236 said:

I’m having an overcharging problem, I’m getting 16 volts out of the batt. Lug on the alternator, but 14.5 at the battery and starter relay. I have tried 3 regulators and 2 alternators no change. I’ve checked the green field wire and it’s fine between the alt and vr. Where do I go from here? It’s a 75 duster.

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This problem has nothing to do with regulator. Your battery voltage is not bad. What this is, here, is simple voltage drop in the harness, in the circuit path from the alternator to the battery. Depending on how big the altlernator is, and how hard it is charging at the time, this may be anywhere from "sort of acceptable" to note even on the acceptable planet.

The charge path in a stocker is alternator......black output wire.........through the bulkhead connector..........to the under-dash welded splice------through the ammeter and the ammeter connections---------out on the red wire--------back out through the bulkhead connector---------through the fuse link-------to the starter relay stud---------and to the battery.

EACH POINT separated by dotted lines is a point of potential voltage drop. The potential "worse offenders" are likely the ammeter, the bulkhead connector, and maybe connections at the fuse link. Also "in the mix" are the wire end terminals at the alternator, the ammeter, and the wire end on the fuse link to the starter relay.

This drop is going to depend on how much current the alternator is putting out, IE how low the battery is, and how much in the way of load/ accessories are powered at the time.

HOW TO FIND this drop? This could be a "wrong path down the wrong road" in this case because of the changing load. You may have to figure out how to add load to maintain the charge rate. Not sure what the easiest way, maybe leave the headlights on, engine off, for 15 minutes, then make tests "quickly" and don't run the engine more than you need to make the test. In other words, you don't want the battery to charge up while you are making measurements. Turn on loads in the car, like lights, heater blower.

So follow the path I laid out. "Clip" one lead of your meter to a point at one end....either the battery end or at the alternator end.........and leave it there until you find the biggest drop

Clip up your meter, start the car, take a reading. Kick the thing up onto the fast idle cam to maintain RPM, or screw in the idle screw, again, so RPM stays at 'low to medium cruise'

Take a second wire hook to the other probe of the meter. It needs to be quite long so you can reach into the passenger compartment. You want to get "as close" as you can to the black charge wire INSIDE the car. One accessable point is the "hot bus" on the fuse panel. Find the "hot" end of the fuses that are "always on." So with key off, probe the fuse panel and find which fuses are "hot." Pull one of them and determine which end of the fuse is hot. Clip your meter probe to that.

So now you the meter clipped to the alternator output, and the "hot" buss in the fuse panel.

Start the engine, make sure it is charging "hard" and the loads are turned on, and take a reading. You are hoping for a very low reading, the lower the better. While it is running/ charging, go out to the engine bay side and WIGGLE the bulkhead connector, see if the reading changes lower or higher.

Diagram out what you measured each point and write that reading down.

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What you just measured is where the alternator output comes into the passenger compartment on the "black wire" side of the alternator. Now you must find out if the ammeter is adding "drop." So we need a connection in the RED wire circuit INSIDE the car BEFORE it goes through the bulkhead connector. This might be more difficult.

See if you can reach up and clip your meter lead onto the RED wire at the ammeter. Do this with battery ground disconnected!!!! If you cannot do that, crawl in and identify the bulkhead connector cavity where the big read ammeter wire connects....on the INSIDE of the passenger compartment. "Back probe" that and run your running/ charging test again. If the reading is the same as before, or maybe, say, only a tenth or two volts more, then you can assume the ammeter connections are OK.

Now move to the engine bay side. "Backprobe" the red wire terminal coming into the engine bay and connecting to the fuse link. As before, start and run the engine, measure that. WIGGLE the bulkhead connector See if the reading changes.

Next, clip to the starter relay "big stud" and check that reading when running, and last RECHECK at the battery. Should not change between these last two readings. If it does, you have a problem between the fuse link and the battery

READ the MAD article, this covers the how and why we have problems. The diagram on that page is a great basic diagram of the main power problem area

Catalog

gm1236 said:

I’m having an overcharging problem,

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Ok. First - Do you mean the ammeter is showing charge all the time?

gm1236 said:

I’m getting 16 volts out of the batt. Lug on the alternator, but 14.5 at the battery and starter relay.

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This means there is resistance to flow between the alternator and the battery.
It should not result in the battery overcharging. 14.5 Volts at the battery is normal and the battery should charge normal unless it is run down, low on acid or otherwise damaged.
If it is very low on charge, it will draw a lot more current than when slightly low. (See the photo sequence in this post for example of this.)

To narrow down the problem, check
The Ammeter reading. The ammeter will indicate how much current is flowing to the battery for recharging.
Since the battery charge rate may change (should go down as the battery recharges after start), recheck the ammeter after making voltage measurements.

Recheck the voltages at the alternator output and the battery.
This time also check the voltage as close to the voltage regulator as you can probe. (read post 67 for more details)


Additionally, check for voltage drops in the ground path between the body and the alternator housing.


Check for voltage drops in the ground path from the battery. Note the ammeter reading even if zero. This very important.

With an analog meter the black probe will need to be on the ground of the power source.

If the voltage drops in the ground bath that current is flowing is minimal, then procede to look for voltage drops in the output lines and connections.
Post back here with what you're finding and people can help.

Note: If the ammeter is pegged or close to pegged, shut the engine off! Stop testing. Get the battery fully charged on a charger and if possible tested.
A pegged ammeter is a shutdown situation.

Note 2: Visually check the power circuit wiring. It probably looks something like the diagram, but especially for '75 this should be verified. If the car has rear window defroster grid it will have a slightly diferent wiring path. Some have mentioned seeing remote shunt ammeter wiring on '75s. If you see multiple fusible links, that would be an indication of this or a heavy duty wiring arrangement.

Thank you both 67dart273 and Mattax, I’ll runs some tests tomorrow. I suspect the bulkhead connector could be the problem. I’ll post what I find. Thanks again, I know how much work it is to wire a long reply with diagrams. You two know you stuff!