Update - PROBLEM SOLVED!! alternator charging wide open!!!

[str12-340]

So the car is a 70 Dart with a 318. Optima battery, stock AC alternator and stock voltage regulator. All have worked fine in the car for over 2 years. Car just got a basically stock rebuild on the engine. All worked fine for break in and I started driving it around to get 500 miles on the engine. After 150 miles of driving with no issues over a two week period, suddenly alternator charges wide open. I pulled the plug on the voltage regulator to keep from over charging the battery and limped it home. I figured the voltage regulator died, but have tried two others with same result - plug the voltage regulator in and the alternator charges wide open. Battery has usual charge, about 12.7 volts sitting, when the regulator is plugged it it slowly climbs over 14 volts and the ammeter says it is charging wide open and I pull the plug.

What are my choices for source of problem? Where to start first?

 

[mikebee]

it's the alternator.i just had the same thing happen to my van and checked everything out and it ended up being the alternator.my first thought was the regulator too.

 

[67Dart273]

THIS IS IMPORTANT!!!

I pulled the plug on the voltage regulator

You pulling a field wire off at the regulator or at the alternator?




If you pull the plug AT THE REGULATOR and this "kills" charging, then this shows the regulator wiring "has control" of the alternator

What I mean is, there is not a short in one brush holder at the alternator

Make absolutely certain that the regulator is GROUNDED

Make absolutely certain that both connections (especially the blue IGN wire) of the regulator is making connection at the regulator plug terminal.

At this point I would "jumper" things with clip leads. That is, finds some screws to make connections in the regulator plug

Jumper across from the regulator plug to the regulator with clip leads.

With key in 'run' but engine off, compare the "blue" regulator IGN terminal to battery +

Best way to do that is to hook one meter probe to battery + and the other probe to the regulator blue IGN terminal. You hope to see very little reading, the less the better. More than a couple of tenths of one volt means trouble.

 

[srduster340]

I would get rid of the ammeter first. You can get a voltmeter and swap the ammeter face so it looks stock. I use a Ron Francis regulator. My alternator stays at about 14V at idle.

 

[str12-340]

so I printed out what I got from 67Dart273 and will try that in a little bit. This is 70 so transistorized regulator, I pulled the two wire plug from the regulator. I've tried two other regulators, one new in the box and got the same results. That means the bolts went in and out of the holes twice, so it seems if it was not grounding through the bolts that would have cured it. I've got a spare alternator so I'll try that later too.

67dart273 - about the test between battery + and blue ignition terminal, do you mean the terminal on the regulator or the terminal in the wire plug? I don't understand what this test tells me? Thanks for the help!

 

[BillGrissom]

Re your last question, you are measuring the voltage drop from BATT+ to the Vreg "sense wire" (also its supply). If you get too much drop on that path (fuses, key switch, bulkhead connectors), your Vreg will think the battery voltage is too low and command more from the alternator (when not needed). That is a common problem which causes over-charging.

Unlikely the drop is in the ignition switch. Now if you had a GM Cobalt ... (very funny).

 

[67Dart273]

Here's the thing..........

It is common for one of the brush holders in the alternator be be grounded. This is a crap shoot. If this (wrongly) grounded brush is hooked to the green field wire, the alternator charges wide open like yours is doing

If it gets hooked to the blue field wire, it can burn up the ignition harness.


If the above is the trouble, unhooking the connector at the regulator will NOT cause the alternator to stop charging.

So It is important to know (we aren't there) whether you are actually unhooking at the regulator, or at the alternator field wires

So...........

Assuming you ARE unhooking the regulator connector, I would say you have the following troubles.....

Unlikely you have so many bad regulators............

Might be a regulator grounding problem. VERY important to get the regulator grounded. If no other way, run a bolt through the regulator flange, with a wire to the engine block and try that

If not the ground, it might be a bad connection in the regulator connector, IE wire blue wire broken inside the regulator connector.

 

[str12-340]

so here's what I did - I started the car with everything in place as it was (still charging full bore) and I measured volts at the battery and got 14.30 and then at the Ignition 1 terminal at the ballast resistor - 13.85. That's a pretty significant drop. Since I had another alternator, I put that on and restarted the car and low and behold the ammeter started coming down over 5 minutes. Voltage at the battery charging is 14.3 and steady, disconnecting the battery positive cable and checking the battery itself - 13.76. I let the car runs for 20 minutes and checked it all again: 14.3 at the battery connected, 13.78 at the battery disconnected, 13.76 at Ignition 1 at the ballast, all holding steady. So just out of curiosity I got the voltage regulator that this all started with and put it back on the car - after some charging after the start it all settled down to the exact same figures as with the new voltage regulator.

Thank you to 67dart273 for the help - I think I understand the system better than I did when I got up this morning! I'm going to take the bad alternator to a local rebuild shop (1 guy who has been doing this for 20 years) and see if he can figure out what happened. I was disconnecting the voltage regulator at the regulator itself (two wire big plug) and that shut the alternator down every time, and yet replacing the alternator fixed it - like you I don't understand how this could be.

mikebee - thank you for prompting me to switch the alternator. I still don't understand how this could be it. but there is no arguing with success!!!

One thing is for sure, I think I should get off my rump, pull out my wallet and replace the 44 year old forward wiring harness. Parasitic losses in a dozen places could account for the voltage drop and the old wiring under the hood, subjected to outside air, and the heat of 44 years of running the engine is usually toast long before the stuff inside the car. The car is a show car, but gets driven to shows hundreds of miles away (that's 3/4 of the fun!) so the last thing I need is an electrical issue 500 miles from home!

 

[BillGrissom]

Good work. The underhood copper in the wire is usually fine, it is corroded connectors (high resistance) and brittle insulation (shorts to gnd) that cause problems. Carry some alligator clip jumpers, some 14 awg wire, and a spare ballast and you can often wire it to get home.

I did that to drive my 64 Valiant home 90 miles after buying it. The ignition switch wiring was butchered so I just jumpered from BATT+ to ballast to coil+ and another to alt field to recharge (after battery ran down) and drove it home. My son drove our minivan so could jump me, though probably wouldn't be hard to get a stranger to help you jump a classic convertible. Everybody was waving and asking when I stopped for gas and parts ("I used to have a slant six, loved it"). You are almost a celebrity.

 

[str12-340]

So after all of this work swapping alternators, voltage regulators, hooking up an aftermarket ammeter, I finally have a for sure final diagnosis.

The Optima battery had one bad cell. Somehow, when this happens it sends a signal to the voltage regulator and alternator saying..."FEED ME!!!" so the alternator continues to charge a battery that is for all intents and purposes fully charged. The Optima battery dealer had a device that they use to test, charge, load Optima battery and when they pu it on the charge function the battery continued to demand juice even though the thing was carrying 13 volts already.

THANK YOU to evrybody that helped to brainstorm solutions!!! It was a big help in finally figuring this out...

 

[BillGrissom]

Somehow, when this happens it sends a signal to the voltage regulator and alternator saying..."FEED ME!!!" ... the battery continued to demand juice even though the thing was carrying 13 volts already.

To clarify for others, there is no mysterious digital signal communicated between the battery and alternator. 13 V is too low. Most voltage regulators are set to maintain 13.4 V. You also have drops before the Vreg sees the voltage, so it might have seen 12.5 V, thus commanded more from the alternator (via applied field current). Even with the alternator outputting strongly, the bad battery was sucking up the current, not letting the voltage on the bus increase. Many auto parts will do a free battery test on the car.