37 Packard 120 Overcharging??

[pint4]

I am trying to trouble shoot a problem with the electrical charging system on my 37 Packard 120 with Autolite voltage regulator and generator.  My gauge on the dash  is pegged out showing I am charging at maximum.  I had the generator and regulator both taken to a local automotive generator rebuilder shop and they said both checked out good.  Any ideas as to what to try next?  The generator has been rebuilt and the wiring in the car has a new harness from Wiring Unlimited.

Thanks,

Bob

[Owen_Dyneto]

Sounds like the field is grounded.

[pint4]

Owen-Not sure what a grounded field is?  Can you describe what to look for?

Thanks,

Bob

[Owen_Dyneto]

If you ground the field you bypass the regulator and the generator will put out it's maximum.  This could happen in a number of ways, faulty regulator, broken insulation on the generator's field post, broken insulation on the field wire to the regulator that allows it to ground, internal fault in the generator including even replacing the generator label tag and using too long a rivet which penetrates the field winding and grounds it.  Remove the field wire at the generator; if the generator output drops to zero the fault is between the generator and the regulator, if it continues to have max output the fault is within the generator.

[pint4]

Owen,

I brought the generator and voltage regulator to the shop that rebuilt it and had them test it.  They said both generator and voltage regulator tested good.  Wouldn't they have noticed the grounded field problem when they did their test?  

Thanks,

Bob

[Owen_Dyneto]

Not necessarily.  If they just tested to see if the generator produced an output, it would have passed the test. 

[HH56]

And as O_D pointed out, it could also be wiring. Having everything connected and in the car and then doing the tests in the order he suggests you can soon narrow things to a place of interest.  If it does point to the wiring and regulator side, after making sure none of the field wire terminals might have gotten bent to accidentally touch ground verify the mounting of the regulator.  Some regulators have an exposed resistor on the back side which is in the field circuit.  If something happened and that resistor was bent where it can touch metal and became shorted it would provide the symptom you describe.

[Matt Harwood]

This thread was extremely helpful to me today. My '41 Cadillac was showing a pegged ammeter, and while I first thought the battery was really low, after about 45 minutes of driving and no change made me realize that something was amiss. So I did the tests that Owen Dyneto suggested and by pulling the field wire from the generator, the charge rate dropped to 0. So it's not the generator, correct? Then I tested the two wires going to the generator for continuity and they're good and the insulation is apparently intact, so they're not touching and grounding out to each other. So that leaves the regulator, right?

 

What I have is a 3-terminal Delco regulator, just like zillions of other cars. By testing continuity on the terminals of the regulator, I found that by touching the field terminal and the engine block, there's continuity, so something in the regulator is grounding the field terminal, hence the over-charging. So something in the regulator is grounding the field terminal. Am I correct in my assumption and a replacement voltage regulator should cure the problem?

 

Thanks for the advice, this was perfect timing for me. Hope Bob gets his Packard back on its feet, too!

[HH56]

Your test would indicate the problem probably is in the regulator but the fact the field is reading as grounded on a VOM is misleading.  Here is a fairly typical diagram of a regulator controlled charging circuit.  There are minor differences between brands but the principle is the same.  

 

Note there is one resistor grounded at one end and tied to the field terminal on the other end.  The other resistor is tied to a point which has voltage coming from the generator.  There is also a direct connection to ground via the normally closed contacts in the current and voltage sensing parts of the regulator.  With the regulator just sitting the closed contacts are why you are reading the field terminal as grounded.

 

When the unit is operating the grounded resistor always provides some connection of the field to ground so there will always be some output.  As the generator starts providing voltage the other resistor provides a bit of voltage feedback into the field circuit and contacts in the current and voltage sensing portions start rapidly opening and closing to provide the solid ground for max output.  By virtue of the contacts rapidly changing the amount of resistance the field sees to ground the voltage output is stabilized at the set level.

[Matt Harwood]

Hmmm. So I bought a brand new US-made 6V regulator and popped it in there and polarized it correctly by jumping the BAT and ARM terminals, as the instructions say. The ammeter is not hard-pegged all the way, but it's still running at close to full output (90%) and staying there. It's twitching a bit, but never comes down to 0. Even at idle it's charging with the headlights on, so it's obviously putting out plenty of juice. New regulator apparently did not cure the problem. Shows a rock-solid 6.8 volts at the battery while running and about 7.4 volts coming off the generator. I don't know what that means, but I was measuring stuff thinking it would be helpful.

 

So the generator is making electricity, that's good, right? Wires are not touching or frayed, so there's nothing amiss in the wiring. Battery seems plenty healthy (less than a year old). Still a regulator issue? I honestly don't know what to do next.

 

Any thoughts?

[Matt Harwood]

Doing some reading, I'm seeing that 6.8 volts at the battery might be too low, and therefore the voltage regulator is mis-adjusted. Looks like the generator is putting out the correct 7.4 volts but the voltage coil in the regulator might be set too low. Therefore, it's trying to increase current to get the voltage up (Ohm's Law), correct? By adjusting the voltage coil to read an output of 7.4 volts, current output should come down, correct?

 

Now, how to adjust this thing...?

[HH56]

Assuming the voltage difference happens all the time -- with or without headlights -- what is disturbing is in a circuit that should have minimal load with everything off you have a voltage drop of  .6 volts over approx 10 feet of wire. The voltage at the battery should be essentially what you are seeing at the generator.  I don't have a Cadillac diagram to see if they do anything different with the charging circuit than Packard but basically, once the regulator cutout relay closes the generator output is fed thru what for all practical purposes is straight pieces of wire to the battery.  If Cadillac uses an ammeter that should be the only thing in the middle and those can also be considered a piece of wire.  To get that much voltage drop would seem to indicate a resistance somewhere in the circuit or a battery that is pulling a considerable load.  Have you verified all the connections are clean and tight -- battery, generator, ammeter, solenoid -- and used a hydrometer on the battery to see if there is a bad cell?

[Matt Harwood]

Talked to my mechanic later in the day and he suspects the battery. I've got it on a slow trickle and we'll see if it's topped off tomorrow. His thought was that all was well, but the 10 minutes of idling I did simply wasn't enough to top off the battery. That would explain the low voltage. Will report back tomorrow and we'll see what happens. Hopefully it's that simple, but this is my car, so it's probably something ridiculously obscure instead.

Thanks for the advice!

[West Peterson]

I just had this problem on my '40 Packard. It ended up being the generator, which had just recently been "rebuilt" for the 2nd time. After doing all the electrical tests, we determined the problem was the generator. I opened it up, and realized that very little "rebuilding" had occurred. Plus, one of the two brush springs was not very tight, which may have caused the intermittent problem I was experiencing, before the problem of the meter being pegged on full charge. I sent the generator to another rebuilder, told him to replace the brush springs, bad wiring, and while he was in there, I had him install sealed bearings. Works like a champ now.

[Matt Harwood]

Looks like the battery was very soft. It took more than 24 hours to charge it on a trickle charger, but I wanted to be sure it was topped up. I'm surprised that it spun the engine so vigorously and wasn't fully charged after 45 minutes of driving with the ammeter pegged, but it sure looks as if it was WAY down. Car started easily like it always does and after about 15 seconds of fully charging, the needle slowly dropped down to 0 and stayed there. Turning the lights on showed a momentary twitch, then it settled out at 0 again, working properly. Woo-hoo!

 

Now I'm wondering if the regulator really was bad or the battery was just really, really low. I guess having a spare regulator isn't a bad idea and it works properly so I'm not going to mess with it now.

 

Thanks for all the great advice, this was a very helpful thread that I hope helps someone else in the future!