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

I started my car a couple of times, to check if the battery voltage was going up. While running the voltage didn't move from the "6.2 to 6.3" range. No accessories were on at that time, and the gen indicator light doesn't work. I was wondering if the gen needs to be polarized, due to the fact that it's been sitting for 40 years, and who knows what it has been through? I really don't have anything better than a multi-meter to check things. Is it possible it needs new brushes? I don't want to go tearing into it, seeing as how I did that with my starter, and made a simple mistake that cost me $110. If the generator problem can be fixed by polarizing it that would be great. Do you do that with the engine off and key "on", with a jumper lead from A to B terminal? If not, how do I go about doing that? Thanks as always.

-Garrett

Are you sure there is a problem? If you're measuring 6.2 or 6.3 volts then the charging system may be OK, as that is what the voltage should be when the gennie is charging.

Try switching on and off your headlights (with engine running at more than idle speed - say 1500rpm) while you measure the voltage at the battery. If the system is OK the voltage will stay at around 6.3 (as the regulator cuts in and adjusts the generator output). This'll depend on the adjustment/ settings of the regulator.

If the generator isn't charging you should see a drop in the voltage when lights go on but depending on the condition and capacity of the battery this might only be quite a small change. (There could possibly even be an increase ). If no decrease (or increase) then you'll need to do another check: leave the headlights on for a while (around 10-15 minutes should do, which will lower the voltage / charge on the battery) then start the car, watching to see if the headlights go brighter when you rev the engine. You might notice only a very small change in brightness if your battery is in good condition but any increase in brightness means the generator is working.

Try those tests first and see how it goes. There are more complicated ways to check charging if the above methods don't give a clear indication. Best of luck.

Would actually expect to see about 7.2-7.4 volts with the engine running at 1500 or so.

You can try polarizing, you only have to jump from battery to armature for a fraction of a second. If your car is hooked up as originally, that is positive ground, that means battery negative post to the armature post on the generator.

I am guessing that the commutator on your generator has oxidized from sitting and won't conduct. You can clean it up with a bit of scotchbrite.


Easiest generator test in the world is this: Remove the fanbelt and wires from the generator. Ground the field winding to any convenient point on the engine with a small jumper lead. Jump battery power down to the armature terminal. The generator should happily and evenly run as an electric motor drawing oh, eight amps or so. If it doesn't run, runs lumpy, or draws a lot of current it will need some loving.

You can also do this test on the bench with a battery charger, just be sure to ground both the case and the field terminal (positive) and apply neg to the armature post.

I test this way before putting any generator back in. It pre-polarizes. If I have put new brushes in, I let the thing run over lunch time to seat the brushes.

Sounds like your generator is not functioning and I agree with Ross about the voltage you should see across the battery with an engine speed anything above a fast idle.

Following on to Larry51's comment, put your voltmeter across the battery and start the car. If possible pull the front of the car into a darker place like your garage. Put on the headlights, observe their brightness and the voltage at the battery. Increase the engine speed, the voltage should increase to something around 7.2 to 7.5, and the headlights should get noticeably brighter. If not, your generator is not functioning.

Again, as Ross suggests, if it's not functioning the first thing I'd do is clean the commutator. The purpose of polarizing is to induce a small amount of permanent magnetism in the field core and this is essential to instruct the generator's output (polarity). It need only be done once if the generator has been serviced or replaced.

Whether 6.2 or 7.2 volts isn't bad. The real question is the DIRECTION of the voltage. A volt meter does NOT give DIRECTION. By direction i mean is the voltage from generator or battery????

All good suggestions above for diagnosis. But the one test i like best is to start the engine. Then while engine is RUNNING disconnect one of the battery cables. The engine should continue to run (running off of generator). Then try turning on the lites. Mite have to increase engine speed a little over idle.

If the engine will idle with battery disconnected, especialy with headlites on (and maybe very slight engine speed increase with headlites on) then there should be nothing to worry about.

PackardV8, I'd NEVER try that test on a prewar Packard with the earlier style simple generator control. Can't say what would happen with modern voltage regulators but when I did that on my 34 years back, the minute I revved the engine with the battery disconected, the voltage skyrocked, bulbs lit up like the sun, and seconds later every light bulb that was activated burned to a crisp. I assumed this was due to the removal of the resistance of the battery from the circuit. (PS - the reason I remember this so vividly is that even back then, those #3003 headlight bulbs were $100 each or more, if you could even find them.)

And ... doesn't the voltage reading tell you the direction? If it were reversed, the battery voltage would not go up with generator output. Or am I missing something....

Hey Guys,
Thank you for the suggestions. I think what I will do is, try the headlight test first,"luckily one of them works". Then from there, if I am not getting anything, try the method Ross suggested. Will polarizing a generator more than once do any harm?

-Garrett

An AMP meter shows direction, to-or-from the battery in amps. A volt meter only indicates voltage. Volt meter does not distinguish from WHERE the voltage is comming. It simply measure voltage in the entire system (regardless of what is disconnected or not). UNless there is somekind of a new voltmeter offered over the last few years i have not kept up with. Some do show polarity in the DRO type meters.


YEs, in the case of revving ANY generator UNREGULATED to high rpm then as much as 70 or even 90 volts can be produced. But to produce such hi voltage usually requires engine speeds in the range of 2500 and higher rpm.

I thot we were dealing with a POST war Packard in this case anyway which i would assume to mean it has a regulator, not a cut out. Even still the test i indicated was to increase engine speed just a little higher than idle speed.

I really have to diasagree about the diagnosis with a voltmeter. I agree in a simple, static system the voltmeter only showns potential. But in an interconnected battery/generator system, if a battery under load (headlights on, for example) shows an increase in voltage when the generator output is increased, then the generator's and battery's polarity are in sympathy and therefore you do know the direction, from the generator to the battery.

Isn't there an old trick where you disconnect the battery while the car is running and if it shuts off, the generator (or does it only work with alternators) is not working?