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Posted by: Ansbacher Mar 9 2015, 06:54 PM

Simple question, I think. With engine running and no extra electrical loads turned on, my voltmeter reads a bit over 13 Volts. Turn on headlights and voltage drops to a bit above 12 Volts. Is that a normal drop or is something going on with the voltage regulator or alternator?

Ansbacher

Posted by: r_towle Mar 9 2015, 06:58 PM

At idle, normal.
At high revs, not normal.

Posted by: dlee6204 Mar 9 2015, 07:02 PM

I would say it's normal if Youre reading off the gauge in the center console. The gauge isn't the most accurate for troubleshooting. If you want to really test it, stick a meter on the battery and turn on the lights.

Btw my gauge does the same thing and it charges normal.

Posted by: Tom Mar 9 2015, 07:06 PM

Depends on where the reading was being taken from. On or near the battery, it should remain fairly constant as you turn things on. As you get further from the battery, the loads will have a larger effect on the reading.
Tom

Posted by: screenguy914 Mar 9 2015, 07:43 PM

Unless cranking the engine, system voltage should be about the same throughout the vehicle, including at the battery posts (12+V).

After starting the engine, the alternator's job is to provide enough electricity to recharge the battery and prevent it from discharging during normal operation. At full system load (i.e. all lights and accessories ON), the battery could be receiving up to 14V of voltage from the charging system, but above idle speed.

Sherwood

Posted by: Ansbacher Mar 9 2015, 07:54 PM

Yes, I was reading volts from the center console gauge. Sounds like I need to check it at the battery with my meter tomorrow. Thanks all.

Ansbacher

Posted by: Mike Bellis Mar 9 2015, 08:44 PM

Almost ALL old car alternators make little or no output below 1500 rpm. The exception is some old Dodge units make power at 1100 rpm. Newer cars are different with all the electronic systems many can make power at idle.

Your reading is normal at idle.

Posted by: 76-914 Mar 9 2015, 09:00 PM

That is one inaccurate gage. Everyone has that result; unless you run a dedicated + wire to the gage.

Posted by: Spoke Mar 9 2015, 09:00 PM

The voltage you measure is expected of the center console voltmeter. I checked the voltmeter in my car with my multimeter and it was less than 0.25V different than my multimeter.

The voltage drop you're seeing with the lights on is a simple IR (current x resistance) voltage drop of 40+ year old wiring and connectors. You might get rid of some of the voltage drop by cleaning all grounds and battery connections.

Posted by: Dave_Darling Mar 10 2015, 12:55 AM

The center console voltmeter is mostly there for "entertainment purposes". After you get used to how it works in your particular car, you can also use it as a quick check for if your lights are working. If the voltage drops by less than you expect it to, you may have a burned-out bulb...

--DD

Posted by: euro911 Mar 10 2015, 03:02 AM

My center console voltmeter reads a little above 12v too, but drops dramatically when I hit the brakes or activate the turn signals. One of these days I do need to clean up all the connectors - it's probably just a corroded ground wire.

Voltage readings taken with a VOM (aka: multi-meter) at the battery show the true voltage and it's charging my battery fine

Posted by: somd914 Mar 10 2015, 03:46 AM

QUOTE(euro911 @ Mar 10 2015, 05:02 AM)

My center console voltmeter reads a little above 12v too, but drops dramatically when I hit the brakes or activate the turn signals. One of these days I do need to clean up all the connectors - it's probably just a corroded ground wire.

Voltage readings taken with a VOM (aka: multi-meter) at the battery show the true voltage and it's charging my battery fine

Posted by: The Cabinetmaker Mar 10 2015, 06:04 AM

I'm gonna call foul on the old wiring thing. They showed the same drop when new!

Posted by: euro911 Mar 10 2015, 10:31 PM

32 had passed by the time I acquired the 'BB', so I have no idea how accurate the gauge was when the car was new