Charging voltage

Tom in TN

Tom in TN

Senior Member
Stock 1955 Fairlane. 6 volt, Positive ground with a reed top Optima battery.
Checking for voltage at battery while running and I get 6.82v.

This seems a bit low, anyone know what it should be?

Car is a 69K mile original and the generator has never been serviced.
Maybe it's time?
 

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Tom, think something in the 7.2v. range would be what you'd expect on your Optima. Maybe also check your voltage regulator??
 
I wouldn't worry about it as long as it is higher than 6 volts. What is the voltage of the battery after it sits overnight? Above 6 volts? Also, AGM batteries take a different charge rate than the original lead acid. I have them in my work pickup, which came with lead acid, and the voltmeter reads lower but the batteries are never dead.
 
Tom, your voltage regulator is adjustable. Might try that before spending for a new regulator....although it may come to that!!:)
 
I put a digital voltmeter in the glovebox of my 54 (stock 6 volt system) and can watch it while I drive. It is very interesting comparing it to any other car that has 12 volts, even to my 57 with a stock 12v charging system. The 6 volt system does not put out a lot of amps, but it does the job with stock accessories just fine, although a bit eccentric.

At an idle, with nothing turned on (heater fan, headlights, radio all off) I will see anywhere from ~6.5 volts to 7.x volts. Factory amp gauge will show a slight charge. If you run the engine at a higher RPM, (highway speeds) that value can go much higher, I've seen 8.1 volts with no load. My car is completely stock. I purposefully keep the radio on all the time to keep the voltage at a max of 7.5 volts or so. I've tried different voltage regulators and I get the exact same behavior.

Now, if you turn EVERYTHING ON at idle speed, (heater on high, radio, high beams) it will show a significant DISCHARGE on the factory amp gauge, and the voltmeter shows 5.7 volts, give or take a few tenths. If you drive the car and get the RPMs up, it will show a charge and the voltage will go up to 6.9 or so. Completely normal.

This is all with a fully charged battery. If for whatever reason my battery was run down (leaving lights on all night etc.) then it will show less of a charge and lower voltage at all RPMs until the battery is charged up.

My 57 with stock 12 volt system, does not have such a wide range of voltage and is much more stable. At an idle it will not go below 12.5 volts with everything turned on. Still only a 30 amp generator, but the extra voltage works much better than the older 6 volt system.

So Tom, the 6.8 volts you have idling seems completely normal to me, and if it goes up with more RPM, or down with more load, it is operating as it should. I actually like the characteristics of the 6 volt setup, it taught me a lot about charging systems in general.

Here is a similar voltmeter to the one I'm using, even though it's meant for 12 volts, it works perfectly on 6 volts:

https://www.amazon.com/Voltage-Wate...otorcycle/dp/B08LDHRG5J/?tag=atomicindus08-20
 
My '55 showed up with an 8V battery setup. That battery was replaced by a correct 6V one, I reset the voltage regulator to 7.2V and all has been good since.
 
So, it appears that the gen and reg are doing their part..but the starter solenoid and/or starter might be rolling over after 68 years and 69K miles...at least it sure looks that way.

Thank you for the replies fellas...esp rjlester...that write up took some time and i find it very valuable- thank you.
 
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