Packard Forum Index » Post-War (1946-54)

Check the 21st electrical diag. Should be on this fine website.
My 23rd, lists "the charge/discharge gauge" as "AMM" which I take to mean Ampere Multi Meter. (There's a "lingo" in naming instruments)
It has both neg and pos leads which would be consistent with ammeter (series) so the needle is indicating what the regulator is doing so to speak, not any actual linear amperage. So I wouldn't overthink this gauge.
The V regulator is an on/off device, not analog. So when the battery is in "range" it only draws power from it - gen is in a "short" condition. When bat V goes below low set pt. voltage, the generator connects or disconnects depending how you view it. When the battery is topped up, the high set pt shuts it off/shorts it again, more of a recycle or bypass as it still spins, so work is input, but the electrons can't flow out the circuit.
So the needle is going to fluctuate according to what the regulator is up to. In between set pts, the deflection will be slight, without headlights, as based on how much (wattage) is being drawn. Once the generator kicks in, it should pretty much peg out "charge" and slowly decrease as it nears set pt. It's the "delta V" (differential voltage between devices) that determines rate of charge, so as it nears "full" the charge rate will slow. Kinda like blowing up a balloon, as it gets near full size, it's harder to blow it up further. The pressure inside is near equal what your lungs can put out, so little volume change.

I recommend a voltmeter for any car with a gen/reg system, 6 or 12 V. It's much easier to see what's going on, you just have to know what the proper cell voltage is supposed to be and that's 2.1V per cell roughly, so 6.3 (2.1x3) or 12.6 (2.1x6) respectively. If V doesn't occasionally go high it's not charging.

I've wired a voltmeter to a standard 'cigarette lighter' plug. Whenever the fancy strikes me I remove the lighter and plug-in the meter. I used the small digital meters found on Ebay, and normally monitor the voltage while I'm underway. Since you'll likely be on the same circuit as the headlamps you should see the voltage drop of that portion of the circuit when the lamps are ON. You'll also be able to see the effect of temperature on the voltage regulator (cold equals more voltage, but not more than 0.2-0.4 volts). Just watch the polarity. For an unmodified Packard the center tip of the cigarette lighter plug will be negative.

dp