wrustywrench

I know my alternator is working,,but I have a question.

13.8 ,13.9 volts cruising. but in town the voltage on the dic drops to 13.1 , sometimes as low as 12.8.( lights and ac off, fans kicking on and off ) I know that low rpm with fans on will do this, but this seems to be temp related to how hot the alternator is. . stays lower until car cools off ( after setting) ,...I have check solenoid connections, but its a bitch due to LG long tubes.

Seem almost like it heat related.

Is there a chance that the voltage regulator is breaking down at higher temps?

I do not get low voltage warning.

73Corvette

What are the temps?

wrustywrench

my coolant temp is only 180.. I may just be paranoid... car is maggied and fan do kick in sooner.

popshumphrey

Mine does this too! 97 coupe. Will run 13.7 when cool temps and when it is hot outside will drop to 13.2 or so. Measurement at the alternator is 14.1 and at the battery posts. I too have checked the grounds and the solenoid connections. Maybe not checked enough. It has worried me for a year. No DIC messages. Just paranoid about the voltage issue. Even tried to get 73vette to steal me a new alternator, but to no avail. Keep me posted. What year is your vette?

popshumphrey

Yes I have been made aware of that. Maybe rusty wrench was not. However, I did replace my ignition switch to no avail. Rusty - that might solve your problem though.

Pounder

mine never drops below 13.6 or so ????? mostly runs at 14 plus ???

reath1

Charging voltage will drop some depending on temperature. Perfectly normal.

popshumphrey

My 98 never drops below 13.6. This is a 97. It may be that the ignition switch from auto zone was not the best choice. I have to apologize for hijacking the thread. Rusty wrench try the ignition switch. Bill curled has posted hoe to test it.

GCG

As mentioned above, difference in readings between the DIC and directly at the battery/alternator are caused by the DIC being downstream the ignition switch. The real voltage is the one measured with a multimeter directly at the battery/alternator.

Voltage at the battery and alternator should be the same or very close. If not, chances are the connection at the starter solenoid is loose and/or dirty and/or corroded.

Charging voltage dropping a bit (as measured directly at battery/alternator) at high temperatures is normal. When a battery is hot it should be charged at a lower voltage than when it is colder, and the voltage regulator in the alternator has a temperature compensation circuit that provides that adjustment.

vigman

Just FYI.. I have a NEW GM ignition switch, changed out the starter, cleaned ALL grounds, Have a NEW Optima red top and the voltage diff between the CIG lighter and the DIC is about .5 volts higher at the cig lighter, which seems to match what's across the battery...

Are you sure that when you say it's COLDER , could it also be POST START... the voltage appears to be slightly higher as you are " re charging " post start...

Mike

GCG

Just to clarify, different voltage values when reading directly at battery/alternator and what the DIC reports is something different than charging voltage dropping a bit at high temperatures.

The PCM does not control the charging voltage. The only thing controlling that is the alternator's voltage regulator.

After high temperatures have set in, with a corresponding adjustment in the charging voltage, if a car is turned off and then restarted it is not going to go back to 14v unless it is allowed to cool down before restarting.

Bill Curlee

VOLTAGE DROP TEST!!!!!!!!!!!!

Obtain a multimeter. Select DC Volts, 0-20 VDC scale... Attach one lead to the positive battery terminal and the other to the BATT terminal on the back of the alternator.

Theoretically, When ALL connections are 100% pristine, you should see 0.00 VDC between those two points . The alternator BATT terminal attaches to the starter solenoid main terminal and the battery POS wire also attaches to that post. That's how and where the battery gets its charging voltage.

IF,,,,,,,,,,,,,,,,,,,,,,,, You see VOLTAGE between those two points, there's a POOR CONNECTION that is causing a voltage drop and you will see it on the meter as a VOLTAGE READING.. You may have to scale the meter down to get an accurate reading.. The bigger the voltage reading, the poorer the connection is.


VOLTAGE TEST: With the engine OFF,,, measure the BATT terminal to chassis ground. You should see FULL BATTERY VOLTAGE.

With the engine running, you should see FULL CHARGING VOLTAGE on the BATT terminal and the same voltage on the POS BATT TERMINAL on the battery.

Check all that and report results....


BC

bluemike28

Was there ever an update on this?