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Voltage

Ranger16

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What is acceptable voltage @2000 RPM with lights on?

I replaced my alternator a few weeks ago with the same 35 amp alternator and after cleaning the wire contacts I noticed it would now hold 14v at idle with lights on. Last night I went to a cruise night and ran the usual 14 - 14.5v, but on the way home with lights on, I noticed it was running about 12.2 -12.5v @ 2000 RPM, less at idle, but lights did not dim. Normal? Acceptable? Why the change? Color me confused.
 
Alternator quit charging completely, that's why you are seeing 12.5 V. That is the battery voltage only and will continue to drop as you drive. Should stay at about 13.5 to 14.0 V if system is charging correctly.
 
Had that problem with one of our vehicles it turned out to be the alternator wasn't putting out full charge. If I drove with ac off I had no problem but the extra power for the ac was enough to drain the battery. I'd have the alternator checked even though it's new it may be faulty...
 
I would check for loose or broken wires first, could that simple... Here's some good information to start with... Get out your test light & multi meter & start doing a few tests....
Very important that the regulator case "sees" a good ground...

Do A test... key to "run", unhook GREEN field wire from alternator. It should be 12V as battery....if OK, next GROUND this terminal... Start the car. FULL fielding OUTPUT of alternator ...about 1500 to 2000 RPM voltage should increase... if not bad alternator......


1969 Chrysler Imperial Charging System Diagnosis Service Guide from the Master Technicians Service Conference Session 256


 
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Great video. Just watched it after my earlier post. Good info.
 
Alternator quit charging completely, that's why you are seeing 12.5 V. That is the battery voltage only and will continue to drop as you drive. Should stay at about 13.5 to 14.0 V if system is charging correctly.
Drove all the way home and it never dropped, except at idle, but it does make me wonder about the alternator.

I watched the video.
dizzy.gif
I'll have to watch the part about testing the alternator again. After reading all your responses, a faulty alternator seems logical. That would REALLY piss me off.
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Mopar from the 60's with the stock charging system will have the headlites dim some at idle at night.


Mopar Headlight Dimming - MyMopar.com - Mopar Headlights
Mopar Headlight Dimming from mymopar......
Dim Headlight Syndrome
Since we have had so many questions about dimming headlights when the engine is at idle, I have decided to explain the problem here and hope it will help allot of you out.

The headlights (and all of the other lights on the car) go dim for only one reason, that's because the system voltage drops below the normal voltage of 14 volts. Voltage is electrical pressure just as water pressure makes the water come out of a faucet. The greater the pressure (voltage), the faster the water comes out. Loose the pressure (voltage) and the water come out slower. Loose electrical pressure and the lights get dimmer. Amperage is electrical volume and since your headlights and standard electrical options are less than the amperage (volume) capabilities of the alternator, voltage should remain in the normal range (14 to 14.4 volts). So, why does the voltage go below normal? First thing to be sure of is that the wiring is not restricting the flow of current to the system. This can be done using a digital voltmeter. Connect the positive(+) of the meter to the battery stud of the alternator and the negative (-) of the meter to the POSITIVE of the battery. Run the car with the lights on (to create a load) and read the meter. You should not read more than .3 to .7 (that is tenths) of a volt. Do the same with the negative side of the charging system. Connect the negative (-) of the meter to the alternator case and the positive (+) of the meter to the NEGATIVE battery terminal. More than that and you have wiring that is not allowing normal flow of electricity. (Hint, did you check the bulkhead connector for a hot or burned connection?)

Now for the more probable cause of your problem. The same type of Chrysler alternator was used for many years and all had the same physical shapes. However, the electrical characteristics changed over the years. Before 1969 the alternator was a rather low output (37-42 amps) and was used with a mechanical regulator. The rotor installed in these alternators had a field current of 2.3 to 2.7 amps. In the later 70's the windings in the rotor was changed and had a much higher resistance. Over the years the alternators have been rebuilt so many times that the rotors generally don't get tested for the correct application and a higher amp rotor could be installed in an alternator that it was not designed to be in. A higher output alternator will give you more amperage capacity, but only at higher engine RPM's and will usually not do as good as a lower amp alternator at low engine RPM's. Later model high output alternators are designed to give good output at low & high RPM's and the engine idle is usually 200 -300 rpm's higher than your classic car. So the moral of the story is that there is a good possibility that the alternator on your car was not rebuilt with the correct parts to operate as it should on older cars. If the same alternator was installed on a 70's car with an electronic regulator and a few hundred higher engine RPM's, you would never have a problem.
 
Just one more thing to muddy up the waters. The spade style connectors on the field tabs can spread and loosen. If you wiggle them to get them off or on, you are spreading the connector. Eventually you may notice they get a lot easier to get on or off. They might even get to a point where they will fall of on their own simply due to engine vibration. Obviously, the looser they become, the more it degrades the integrity of the connection. This is true with all the many spade style connectors in the Mopar harnesses.
 
That field connector came off pretty hard. I just started it and the voltage gauge stayed at 12v or less. Napa is getting the alternator back tomorrow. It's already on the work bench.
 
Went to pick up the new alternator at Napa. Found the pulley dinged badly as though it was dropped. No faith left in their quality control. Got a refund. Have a new (reman) on order from Advance/Carquest. Could be from the same company for all I know. This one is identical to both the OEM and Napa, but is 60 amp vs the OEM 35. Everyone tells me I can run a higher amp with no problem. Supposed to be in by noon tomorrow (Thurs).
 
Hmmm...all that reminds me why...I had my old one rebuilt local.
i think running a 60 amp alternator is much better for me,the factory 37amp needs to be at lease 60amps, i would not go past that range though,i have a electronic voltage regulator and it stated not to exceed 60 amps.i do not have any power draining accessories,just factory equipment.
 
i think running a 60 amp alternator is much better for me,the factory 37amp needs to be at lease 60amps, i would not go past that range though,i have a electronic voltage regulator and it stated not to exceed 60 amps.i do not have any power draining accessories,just factory equipment.
My understanding is that a larger amp alternator accomplishes nothing unless you need to draw more amps such as with a large aftermarket stereo system. On a standard '69 Road Runner with basic factory electronics, the extra amps are just there so to speak.
 
Well, the NAPA alternator DID fail after only 5 weeks and was the problem. New alternator installed and the voltage gauge is back to 14.5 v.

P.S.
Sure hope I am right in the previous post as this one is a 74 amp, not 60 as I was told.
 
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