'71 Duster 340 Battery getting overcharged

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MrDuster

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Fella's, please help me solve this problem I'm having. Stock '71 street car with 1 year old auto zone replacement alternator (has only 1 field instead of two--blue wire goes to the field and green goes to nothing...alternator has std post for black wire to battery). No aftermarket amp-drawing stuff installed in car. NAPA Legend battery (new one in now). Voltage regulator on engine back firewall infront of driver has a two prong connection with one blue and one green wire..That's what I got, here's the story...This morning I saw white residue around the battery and attributed to a battery that was venting too much...cleaned it up and drove 30 miles. When I opened the hood to show a car buff the engine we both noticed the battery bulging and it seemed hot. I also noticed paint peeling above the battery on the underside of the hood. I drove straight to the nearest NAPA store and got another battery as the guy there thought a plate must be shorting out in the battery...although he mentioned it could be my voltage regulator. Getting home I tested the battery and found it was being charged at 16.83 volts! Buddy helped me troubleshoot. With voltage regulator plug disconnected pulled 17 volts-all measurements at the battery on the posts. We disconnected the hot wire on the back of the alternator and taped it off. Voltage was now 12.8 before and after starting...that made sense! We also noticed a red wire going into a black plastic splice which was starting to melt with a grey wire coming out going into the main wire firewall harness--that's going to need attention. I don't know how to test a voltage regulator or how one works...seems odd to have only the alt field wires running to it...but that's what it looks like...and one of the field wires-the green one, has no place to connect on the back of the alternator...does that need to tie into the blue wire? Sorry if this is confusing...I'm tired after helping a friend build a deck today and am going to bed. Tomorrow's a busy day, but I should have an hour around noon to work on the car and troubleshoot more. Sorry for the long post, but wanted to give more rather than less....any help appreciated!
 
I'll check the grounds tomorrow. A new VR was my first thought too, but I want to be sure I'm not going to damage it by not providing the two field inputs it normally receives. Still bothers me the green field wire is disconnected. Thanks for the ground input...so many times cleaning a ground has solved my problem and best of all it doesn't cost anything!
 
MrDuster said:
Fella's, please help me solve this problem I'm having. Stock '71 street car with 1 year old auto zone replacement alternator (has only 1 field instead of two--blue wire goes to the field and green goes to nothing..!
Click to expand...


Your voltage regulator is no longer in the circuit. Here's how the 70 and later systems work

Refer to the simplified diagram from MyMopar

Dual_Field_Alternator_Wiring.jpg


The blue field wire comes direct from the switched 12V "ignition run" circuit. The 70/ later regulator GREEN wire controls sort of "the amount of ground" on the green wire.

YOU MUST HAVE an isolated field alternator (2 field terminals) in order to use the flat 70 and later regulator

You have three possibilities

1...Take a real good look at your alternator. Post a photo if you can. Some modern rebuilts are actually an isolated field unit that has one terminal grounded. In that case you can get different brushes and convert the unit, or maybe just some insulating washers and "unground" the brush

2...Replace the present alternator with a 72/ later (called a squareback, do not accept the older "roundback) and hook things up correctly

3...Keep the present alternator and buy a 69/ earlier replacement regulator

Below is a couple of different alternators. The one on the left is a special unit. This is an inferior old roundback, which originally came BOTH in 69/ earlier with grounded field, and 70 / later with isolated field. The one in this photo can be set up for EITHER and as shown has a grounded field

The right side photo is a "squareback" the better, newer design. All of these are "isolated field" (2 field terminals"

squareroundcomp.jpg


Below is a "rebuilder's hack." What this is, here, is an OEM 69/ earlier (grounded brush) with the grounded brush in place. The rebuilder has drilled an extra hole at 12 o' clock to insert an insulated brush and "convert" the unit to isolated field. These, for the most part, are a poor idea.

128306-500-0.jpg
 
67Dart273, You always have great information on electrical issues. Great job.
 
Concur, Thank you 67Dart273...just getting my coffee and out the door after a quick read, plan to digest your info later today and post a couple pictures of what I have. Can you shed some light on how a voltage regulator does what it does? It appears both field wires from the alternator hook directly to the voltage regulator with no other input...just curious. Also plan to remove the voltage regulator I have and clean it up good as I thought perhaps it is grounded to the firewall--am I wasting my time??? I suspected the auto zone "guru" wasn't such a "guru" when he told me it was a direct replacement and I could leave the other field wire off with no problem.
 
MrDuster said:
. Can you shed some light on how a voltage regulator does what it does? It appears both field wires from the alternator hook directly to the voltage regulator with no other input...just curious. Also plan to remove the voltage regulator I have and clean it up good as I thought perhaps it is grounded to the firewall--am I wasting my time??? .
Click to expand...

Look at the simplified diagram. The "I" terminal goes to 'switched ignition' and that branches out and feeds power "to" the blue field wire.

On the 70/ later systems, the VR is powered off the switched ignition, same as the pre-70. The DIFFERENCE in 70 / later (isolated field) is that the VR controls the 'amount of ground' via the green field wire. In other words, what you have done is to power the alternator field, and permanently grounded the "normally green" wire connection, thus "full charge"

GROUND.........The regulator and ignition box MUST be grounded. Scrape around the bolt holes and get some star lock washers.

MrDuster said:
. I suspected the auto zone "guru" wasn't such a "guru" when he told me it was a direct replacement and I could leave the other field wire off with no problem.
Click to expand...

He very well could have cost you some trouble, like a blown up stereo or lights or other damage. With no regulator, the only thing preventing the voltage from going sky - high (over 100 volts) is the RPM, the condition and output of the alternator, and the load on the system, IE "how big" is the battery
 
Thanks again for the info. It appears I have one of the squareback/1 field alternators. I am posting pictures of what I have and I'll clean up the grounds and get the right square back 2 field alternator on Saturday...hoping the auto zone manager will help me out with the price. If he doesn't or one isn't available, what would you do with what I got? My green wire was not connected to anything as per the auto zone guru's advice...it was just hanging out there all lonely...what would be the impact of that? Basically one field is not showing up at the voltage regulator, but I don't know how that baby works...The two tied up rounded insulated connectors you see were from the original alternator decades ago...I've had this car awhile...don't even remember the change...but it must have been due to needing an alternator that had different connectors and not wanting cut off the original wire connectors.
 

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Forgot to add this picture of the red wire which connects to a grey wire which appears to take power through the firewall connector...needs addressing due to the black plastic connector melting...hopefully attributed to the current issue I'm having.
 

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Hi,

The alternator in your picture is a "round back", not a "square back". A 71 should have a round back alternator with an isolated field or two field wire connections. If you only have one field connection they gave you the wrong alternator, one that is for 69 or earlier. The round back type with two field connections was for two years only 70 and 71. The square back came in in 72. You can use it on your 71. The green wire goes to one field connection the blue wire goes to the other.

As to your "autozone expert" if he knew anything he wouldn't be working at Autozone for minimum wage. I would take the one you have back and insist on the right one. Better yet get your money back and find a real auto parts store.

The alternator you want will have two field connections with insulated brush holders.
 
To add to the above (and repeat what I said) I WOULD NOT ACCEPT a "roundback" even if it correctly has two field terminals

This is because the squareback (re read my earlier post) is a superior design, and puts out more power at lower RPM.

To add to what Pete said above, I've never been sure what year was the change to "squareback" but if you as for a 73/ 74 that is what you should get on the counter.
 
Thanks guys... Won't go to hard on the "expert" at autozone. I accept responsibility for what I put on my car...it didn't "feel" right...I should have known better. I'll let you know what happens.
 
MrDuster said:
My green wire was not connected to anything as per the auto zone guru's advice...it was just hanging out there all lonely...what would be the impact of that?
Click to expand...
To answer your question directly, in addition to what the others have stated, the idiot crackhead at AutoZoo sold you a alternator with one of the field connections grounded. That is why there is no connection for the green wire from the regulator. The result is you have full charging system voltage on one field connection and ground on the other so you get all the voltage the alternator can produce at all times.

With the correct alternator and the regulator connected the voltage regulator controls the alternator field voltage by interrupting the ground circuit. The blue ignition wire on the voltage regulator in essence tells the regulator what the current voltage is so it can adjust the alternator output accordingly by varying the the field current to ground. Basically, the field current acts as the throttle control for the alternator output voltage.
 
Thanks Rustedwrenh. I'm off to help a buddy build a deck now...but I hope to pull the alternator tonight and go see Autozone tomorrow or Saturday for sure. I think I'm getting a basic understanding f what's going on. The green wire IS important as it controls the alternator like a throttle...but the alternator I have has that field grounded and there's no input to the regulator so it can't control the alternator output even though the regulator would like to as it is seeing high voltage from the blue wire input...did I get that right?
 
To answer your question how Vreg works. It senses the voltage difference between its case and its blue wire (IGN, which also powers it). It strives to keep that difference at ~14.2 V. If too low, it conducts more (thru its transistor) to ground which is the "field current", which increases the alternator's "main current" output. If too high, it lowers the field current.

This is a proportional control system, similar to the thermostat in your coolant system. The reason they do "low side control" is that transistors work better that way. Today, they can do "high side control" easily and there are electronic Vregs for the older "grounded field" alternators.
 
Thanks Bill, that along with what the other fella's have chimed in with has given me a much better understanding of what's going on...understanding electricity past V-IR was never a strength. Does it matter which field gets the blue and which gets the green wire? I called auto zone and they have the square back 2 field alternator in stock...so I can get rid of my round back (Pete-don't know why I called it a squareback earlier...think I'm tired). I plan to make the swap out tomorrow. Looks like the VR is only $14 so I might pick up a new one just in case the old one is bad. Also plan to get some star washers and clean things up good so it'll make a good ground. I'll let you guys know how it all turns out.
 
It doesn't matter which color field wire gets connected to either field terminal.

Good luck with your repair. Let us know how it turns out.
 
Got the two field square back from auto zone...they replaced the wrong one field alternator with no hassle. Put a VR on order as it was cheap and thought my decades old one could possibly be bad. Put the new alternator on and was happy to see 14.2-14.4 volts at idle. Ran the throttle up and was disappointed to see 17 volts. Shut it down and cleaned the VR bolts and star washers up real good and tried again...same thing. Wiggled wires and noted the green wire was getting hot. Shut it down and going to wait for the VR to come in tonight at 9pm...hope to pick it up in the morning around "honey-do" yard work. Hoping the new VR fixes my high voltage problem now that I have a two field alternator. I'll keep you updated.
 
I would not bet the VR is the trouble. "Start over" now with troubleshooting

1....Very first thing to do is make sure the VR acually has control of the field, IE not a field wiring problem OR one brush grounded. Disconnect the VR plug, run the car and see if it charges. It should NOT

2....Next look at voltage drop, both the supply to the VR and the ground. With key on but engine stopped, measure voltage between the blue field connection and battery +. Do this with everything hooked up "normal" that is, "back probe" the terminal. You are hoping for a very low reading, below .3V (---3/10 of one volt). If you read more, you have voltage drop in the path from the battery to the VR

3....Check ground. This is going to have to be somewhat interesting because it's overcharging. Start and run the engine, and check first with all loads off, and again with lights, heater, etc turned on. Get the engine up to some RPM around 14-15V on the battery. Then take your meter as before.......

Stab one probe into the top of the battery NEG post, and the remaining probe into the VR mounting flange. You are hoping, again, for a very low reading, zero is perfect. This shows ground side voltage drop. More than a tenth or two, you need to improve the grounding from battery--engine--body
 
OK--followed the troubleshooting steps above and got a big red flag at step 2.
1. Does not charge with VR disconnected.
2. Did exactly as described and read 12.6 volts. From 67Dart273's post it appears I have voltage drop in the path from the battery to the VR. Could this be due to a bad voltage regulator? If not, what would be my next step?
Thanks...I'm off to run errands and pick up a new VR from auto zone...might not need it, but figured it was so cheap it would be worth keeping as a spare as the one on there is so old.
 
No, voltage drop is not a function of the VR, voltage drop is a harness / connector / switch problem

FIRST thing I'd do is double double check what you think you found. Also bear in mind the trouble could be RIGHT IN the VR connector itself, either broken loose inside the rubber, or just corroded, loose, not making contact.

So let's double check. "Work" the VR connector in/ out several times to scrub the terminals clean and to feel for tightness. Pull it off and inspect with a flashlight for corrosion or damage

Let's RE check voltage.

Set meter for voltage.

Turn key to "run" with engine stopped

Probe the blue field terminal with one meter probe, leaving the connection normally hooked up.

Stick the other probe directly onto the battery POSITIVE post.

What is the reading?
 
12.38V...all connections cleaned up. I have a new VR...should I do the same check with it? Don't know if I'll fry it. It looks like there's 12+V coming to the blue wire with the ignition switch on, but engine off. V is 0 at the blue field on the alt with the VR cap on and 0 at the VR blue wire cap with ignition off. I'll go re-read your last couple posts and double ,double check readings again.
 
The check I outlined is with key ON. "in run." Are you checking this to ground, or what?
 
Great advice to double, double check my work. After studying post #4 diagram and making a chart of voltages at every point, I went to work cleaning and measuring V with the key on and off. Finally got no voltage drop between the positive battery terminal and the alternator blue wire measured at the alternator with everything hooked up. Ran the motor and had the same high voltage as soon as rpm got up above idle. Decided it must be the VR and put the new one on. At idle battery was being charged as 13.4V and at 2500-3000 rpm 14.5-15V...seemed to average around 14.7. Should I declare victory or is 14.7 too high? The only thing I don't like is the voltmeter in the dash fluctuates rapidly intermittently at idle...is that normal? Seems to stay steady around 13.5-14 volts at high rpm. I had the ammeter gauge faceplate redone with a voltmeter face when a FABO member redid my gauges a year or two back. I made a wiring mod to take the ammeter gauge out of the main power line to keep an ammeter gauge failure from stranding me. The gauge now receives power off the main line. The main wiring harness was redone back in '94 and it hasn't had too many miles on it since then, but a lot of sitting around.
 
Soon as I posted I saw your question. I thought I did it right, but I can't be sure...hence my making a chart and methodically checking again...and again. On my chart I had .75V the first time, then 0 the next two times with the switch on and checking from the positive post. I'm out of troubleshooting practice, so I do appreciate you questioning me doing it right. I think the old VR had some internal issues which might have caused such a large V drop. The red plastic housing flashed on from probably an internal short when I pushed it on and off with the key on...I had the cap to measure correct voltage from the ignition circuit and pushed the cap on with the key still on...the lit up red plastic housing kind of surprised me.
 
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