R66

I have a 10DN 35 amp alternator, electronic voltage regulator, and 1 year old battery holding 12.54 vdc at rest. The ignition system is a Chrysler magnetic reluctor pickup and amplifier box with a 1.3 ohm ballast resistor.
While troubleshooting an ignition electrical problem, I put volt meters on the battery and ignition point side of the ballast resistor.
At idle, the alternator is charging at the battery 13.9 vdc +/- and at the ballast resistor (negative side of coil) 9.3 vdc +/-.
While driving the car, above 1000 rpm, the the alternator is charging at the battery 14.1 vdc +/- and at the ballast resistor 10.5 vdc to 11.1 vdc +/-.
The readings are taken with only the radio and ignition system drawing a load during driving, and of course the brake lights occasionally.
I was expecting the voltage reading from the alternator to decrease as the alternator charges the battery after starting the car, however, it does not seem to change after a 1 hour cruise at various speeds it remains constant at ~14.1 vdc. The battery returns to 12.5 vdc +/- after normalizing for more than an hour or so with no load.
Am I wrong in my expectations to see the alternator fluctuate charge of the battery like the voltage meter on a battery charger?
I am concerned the battery may be failing or I still have a short causing a constant draw and alternator charging.

Thanks,
Ron

jim lockwood

You are concerned that the alternator output doesn't drop to a maintenance Voltage after the battery is fully charged? Am I reading that correctly?

Assuming so, my observation is that lowering the output Voltage to a maintenance level isn't a universal trait of charging systems and almost certainly not a trait of older, dumb alternators. The dumb alternator of my 2004 2500 Dodge truck puts out 14.0 - 14.2 V continuously, for example. The charging system in my 2017 travel trailer, in contrast, does reduce the Voltage to the batteries once they are fully charged. Of course, that's not an alternator; it's a smart charging system.

Anyway, my point is that I don't think anything is wrong with your 10DN-based charging system.

jforb

Are there any trouble symptoms? I mean, does it not have enough juice to start the car some times?

The voltages you report sound reasonable to me....

R66

No trouble symptoms, just needing an education to assure my limited electrical knowledge is not missing a problem. I was thinking the old mechanical voltage regulators didn't hold the charging voltage steady like what I am seeing.
Don't want to have a "Tow of Shame" on a flatbed again, it has made me paranoid I guess.

Thanks Gentlemen,
Ron

Desert Nomad

That's interesting. I just changed my battery and checked my charging voltages to insure my alternator was functioning properly. Statically, engine not running, I have a battery voltage of 12.88 V. Starting engine at idle @ 650RPM, voltage doesn't change much until RPM hits 700-800 then voltage starts rising to 13.5, 13.8, and up to 14.8 at over 1,000 RPM. It settles to around 14.6 - 14.8 and RPM's over 1,000. This is with no load on the system. I have the original 37 amp alternator with the mechanical regulator. I've never had any charging problems and the last battery lasted 7 years. What R66 mentioned above, I don't think the old mechanical regulators do hold voltage steady like the new electronic types do, based on my results.

dplotkin

Charging current drops off as a battery reaches full charge and voltage will drop some, but not much. An ammeter in a car with a newish battery will show a hefty current draw after cranking that quickly levels off as you drive. A voltmeter will show alternator output voltage which is generally steady given steady RPM. Does not sound as though anything is wrong to me either.

Dan