Acceptable Battery Charge Volt Range -- 15.5 too high?

[mrmolding]

So, I've looked and looked and I see most posts mention that 14.8 is optimum. I recently added one of those ashtray USB ports with a volt display and it sits on about 15.2 to 15.5 volts at idle. It does not go up very much when I raise the RPM, and I have not taken it out for a drive, but I'm wondering if this is too high? I found a few posts that mention that 14-16 volts for a mopar is normal on A Bodies forum but could not find anything definite here. To double check, I hooked up a multimeter to the battery terminals and got 12.6 and then when it started, it got about 15.5 same as the USB adapter.

I'm running a Powermaster 95 AMP alternator with a charge wire.
I swapped out the Mancini repro voltage regulator to the autozone one that came with the car, no difference.
Just for fun, I removed the charge wire -- same result.

Is this alternator overcharging? Am I overthinking this?

 

[Aron Gleason]

Anything over 15 volts is too much. Mine sits at 13.7 idling. Driving it should be 14.2-14.5 volts

 

[mrmolding]

Anything over 15 volts is too much. Mine sits at 13.7 idling. Driving it should be 14.2-14.5 volts

Thanks!!! So all that’s left is the alternator.

 

[Aron Gleason]

Thanks!!! So all that’s left is the alternator.

You're welcome

 

[Aron Gleason]

I run a old ac delco 1 wire alternator that's rated about 45 amps. Powers my fuel pump, electric fans. And my battery is in the trunk with a battery disconnect switch.

 

[mrmolding]

I run an old ac delco 1 wire alternator that's rated about 45 amps. Powers my fuel pump, electric fans. And my battery is in the trunk with a battery disconnect switch.

I actually have an nos 55 or 60 amp round back I got from another member a few years ago. I think I’ll try that tomorrow. I appreciate the help!

 

[Aron Gleason]

I actually have an nos 55 or 60 amp round back I got from another member a few years ago. I think I’ll try that tomorrow. I appreciate the help!

No problem. Hope it works out for you.

 

[72RoadrunnerGTX]

Check the voltage drop between the battery positive and the ign1 terminal (blue wire) at the voltage regulator while the charging system is operating.

 

[hunt2elk]

Anything over 14.7 or so makes me nervous. These cars were originally designed to operate between 13.8 - 14.2 volts. I would check all your wire connections as well as the voltage drop through the ignition switch. Grounds are very important as well.

 

[Darter6]

13.8 - 14.2 volts.

This is what I was taught back in the day.
What year is your car? 70 up uses a electronic VR . Lately part store replacements are in the 15+ range.
If you car is older and has been up-graded to the electronic VR you may want to try this.
I got a 70 up adjustable VR and set it at 14 V . Works great. Mopar Action Magazine did a article on them.
Found it on e bay.

 

[Sixpactogo]

I doubt that the alternator is the culprit here. They try to send around 17 volts to the system. It is the regulators job to keep the voltage to around 14 volts. I would be looking closer at the regulator and grounds. The regulator needs to have a good case ground since that is where it gets its reference. If you have a digital ohm meter, check to see if you have less than .5 ohms between regulator case and battery neg.
15 volts will cook your battery in short order.

 

[72RoadrunnerGTX]

I agree it’s likely a refence voltage issue, however its much more likely on the positive side, ign1 at the regulator. Too many connection points between the battery positive and the reference sensing ign1 at the vr to build-up resistance over time. The bulkhead connections, ignition switch connections, and the ignition switch all can contribute to a low reference voltage at the vr. Again, no more than .5 volts total voltage drop on the positive side as well.

 

[RJRENTON]

Out of curiosity, HOW are you measuring the voltage? With a digital meter, such as a Fluke meter or an old ANALOG meter like a Simpson 260 or equilivant. Analog devices plus the operator's interpretation of the reading is may cause the inaccuracy and the assumed result.....rather than tfying to determine where and if a few tenths of a volt exist. There is no exact, not to exceed number, maximum a lot depends on the battery's state of charge and it's age. Just my opinion of course.
BOB RENTON

 

[mrmolding]

This is what I was taught back in the day.
What year is your car? 70 up uses a electronic VR . Lately part store replacements are in the 15+ range.
If you car is older and has been up-graded to the electronic VR you may want to try this.
I got a 70 up adjustable VR and set it at 14 V . Works great. Mopar Action Magazine did a article on them.
Found it on e bay.

It's a 70 Road Runner. It was already converted from points to an ECU and the Electronic Voltage Regulator when I got the car. I've since replaced every wire in the car -- all harnesses, battery cables, etc. I even got a new VR mounting plate from Roseville Moparts and made sure the firewall was grounded. Anything incorrect with the VR I purchased?

The VR is this one:
Mopar Performance Voltage Regulator

This is the alternator:
Powermaster 7018 Powermaster Retro Alternators | Summit Racing

I sent an email to Powermaster and the tech responded and said 15.5 is too high and told me to make sure that the alternator is grounded. Huh! Pretty decent customer service!
Thanks everyone! I'll check all of the suggestions this evening.

 

[mrmolding]

Out of curiosity, HOW are you measuring the voltage? With a digital meter, such as a Fluke meter or an old ANALOG meter like a Simpson 260 or equilivant. Analog devices plus the operator's interpretation of the reading is may cause the inaccuracy and the assumed result.....rather than tfying to determine where and if a few tenths of a volt exist. There is no exact, not to exceed number, maximum a lot depends on the battery's state of charge and it's age. Just my opinion of course.
BOB RENTON

Multimeter in the battery terminals. It's just a cheapo one I got in a kit from Amazon. I agree that I thought either the multimeter or the USB/Voltmeter for the cigarette lighter might be cheap, but since they both read the same value, I'm willing to believe either one of them. Battery is a about a year old from NAPA -- correct for the car and reads 12.6 when the car is off. Thanks!

 

[Darter6]

a lot depends on the battery's state of charge and it's age.

Agreed ^^ Try to do a load test to see if the battery drops no lower than 10 V .
If you don't have a carbon pile load tester,places like Auto Zone and other parts stores will have a tester.
The Mopar VR you have should be ok. But it may still be set high.
Remove some paint from the rear side of bolt hole and from firewall for a good ground.
The Powermaster alternator is doing it's job. The VR is not.

 

[mrmolding]

Agreed ^^ Try to do a load test to see if the battery drops no lower than 10 V .
If you don't have a carbon pile load tester,places like Auto Zone and other parts stores will have a tester.
The Mopar VR you have should be ok. But it may still be set high.
Remove some paint from the rear side of bolt hole and from firewall for a good ground.
The Powermaster alternator is doing it's job. The VR is not.

Ok. So possibly a grounding issue is causing two different voltage regulators to give same result? Does anyone have a link to the adjustable voltage regulator?
That’s my main hangup and I go back to alternator. I’ll double check grounds. Thanks!

 

[RemCharger]

The only adjustable vrs I'm aware of is the old mechanical type.

 

[72RoadrunnerGTX]

The only adjustable vrs I'm aware of is the old mechanical type.

Transpo C8313

 

[RJRENTON]

Ok. So possibly a grounding issue is causing two different voltage regulators to give same result? Does anyone have a link to the adjustable voltage regulator?
That’s my main hangup and I go back to alternator. I’ll double check grounds. Thanks!

The Mopar electronic voltage regulator has provision for user adjustment. The regulator works using an internal voltage divider network that has temperature compensation that is set by design, with in a range found to be acceptable. The electronic voltage regulator controls the field voltage/current of the alternator's rotating field with an internal NPN transistor by turning on/off (current sinking circuit) to keep the alternator output voltage relative constant(established by the internal voltage divider network) while the amps produced by the alternator is determined by the connected load's requirements. Just insure that the electronic voltage regulator case is grounded as this is a fundamental requirement.
BOB RENTON