72 overcharging

-
P

powerwaggin

Active Member
Joined
Mar 13, 2009
Messages
38
Reaction score
0
Location
Vermont
So, I have checked in now and again for Mopar tips, and the crew here has been extremely helpful over the years, even though I no longer have my '69 273 Dart.

I'm currently running a '72 Dodge W200 (318/727) plow truck and having overcharging issues. I have a new parts-house rebuilt alternator (Carquest) and I've tried 3 different parts-house voltage regulators, but get a steady 15.1-15.3 voltage reading on the battery terminals. I have run a fresh ground wire to the case and the VR body is very well grounded.......VR connector plug is new as are all other wires. Today I set up the charging circuit outside of the truck wiring and got the same results. Any clues or tests suggested?
 
If that Truck has the bulk head connector, and amp gage I would start their. You could have corroded connectors in the bulk head, and also the wires on the back of the amp meter could be loose. Try jigling the connector wires, and see what happens.
good Luck, Dave
 
What battery are you running? I have the same high charging rate but I have the "red" Optima battery and was blaming the discrepancy from factory charging specs on the battery. I have already bypassed the amp gauge (converted to voltmeter on dash).

Satellite stock 318 results after warm-up (perf. viscous drive fan)
Charging Voltage at idle (headlights off) 14.5 Volts
Charging Voltage at idle (headlights on) 12.5 Volts

And I also have the headlight relay kit installed from member "Cracked Back".
 
Last edited:
Yup, same old problem

No particular order:

1...Ground circuit, VR must be grounded to battery NEG "at same potential." Sounds like you have addressed that but I would check
2....Harness voltage drop. Not sure of wiring differences in pickup but the 'general' path of the circuit is battery+----cable ends up at starter relay "big stud"---fuse link---through bulkhead (ammeter wires)---to ammeter----at some point branch off to fuse panel/ headlight switch/ ignition switch------to ignition switch connector----through switch---out switch connector---out through bulkhead on "ignition run" line----branch off to underhood loads, including ignition, alternator field, and regulator IGN terminal

VOLTAGE DROP CAUSES Generally, any bad connection in the path I lined out. This includes the igntion switch contacts themselves, the switch connector, the bulkhead connector, and in some cases, ammeter connections, the terminals, or the interior of the ammeter, and IN RARE cases, the factory welded splice under the dash (assuming your vehicle has this "feature")

3....Weird (sulphated?) battery problem. Check for voltage drop first, then change battery with a known good one

4.....Bad VR which you've replaced.

5....The voltage you are getting is not all that high, but.... LOL

HOW TO CHECK

A...Ground circuit. Warm up get battery "normalized" and make the following check with engine simulating low/ medium cruise, in other words, at a good fast idle. Make check first with everything powered off, and again with heater, lights, radio, etc, running

Stab one probe of meter into top of battery NEG post. Stab other into VR mounting flange, being sure to get through paint, rust, etc. You are hoping for a reading of almost zero, the less the better, zero volts is perfect


B....Harness end. Access as close as you can get electrically to the VR IGN terminal. This is likely the "key" switch side of the ignition ballast. Hook meter to "ignition run" line coming to ballast from switch, and stab remaining probe into top of battery POS post. you want the key in "run" position, engine not running. You are hoping for a low reading, the lower the batter. More than .3--.4V (3/10 of one volt) indicates voltage drop. WHATEVER THIS READING IS gets added to VR set point charging voltage

That is, if the VR is "set" at 14V and you have a 1V reading in your test, the thing WILL CHARGE at 15V

HOW TO FIX

Assuming this is a "drop" problem, the obvious answer is "fix the bad terminal." But a workaround is to use a relay to feed underhood loads. Electrically cut the "ignition run" line coming out of the bulkhead and use that to trigger a Bosch style relay. Feed the relay contacts through a fuse/ breaker off the big starter relay stud. Connect the switched/ load side of the relay contacts to the engine bay end of the wire you cut.

On a side note, one coil terminal of the relay must be grounded. If you like, you can feed that through an unobtrusive toggle, and create a simple 'anti theft' feature.
 
Last edited:
Thanks to all, this gives me a few things to test.
I've had my share of Mopar truck amp meter meltdowns. Being a pretty whipped northeast vehicle, the harness became unworkable so I've been plowing for the last two years, running off a relay switched marine fuse box that I run only start, ignition, heater blower, wipers and lights off of. It has worked great with reliable charging in the 12.5-14.5 range. Charging system is also pulled out of the original harness....the positive field is fed from the same wire that feeds ignition and choke...in my case full 12V with no ballast.

For an independent test, I grounded one of my VR cases right on the battery and ran wires to both fields off the VR connector with similar high voltage results. I'm stumped. Can I still get a "real VR" from Chrysler?
 
67Dart273 has covered it in detail.
I'll just try to get to the crux of the matter.
> The regulator's voltage is what you need to find out.
Then compare it to the power source's output voltage.

When the engine is running, the alternator is the power source. So measure the voltage at its output stud.
The regulator will power the rotor's windings based on what voltage it sees.
As you know the field positive terminal, and the choke and ballast resistor are the closest places to get a voltage measurement for the regulator.
The ballast and the field terminals ought to be the same but meausure at both anyway.

powerwaggin said:
For an independent test, I grounded one of my VR cases right on the battery and ran wires to both fields off the VR connector with similar high voltage results. I'm stumped. Can I still get a "real VR" from Chrysler?
Click to expand...
Really don't know what you're trying to do here.
It doesn't work that way.

The battery is a second power source. At best, it provides power around 12.5 Volts, depending on how much current is being drawn.
The point is whenever the regulator sees battery voltage, it thinks the alternator isn't producing power at high enough voltage.
It's response is to let the rotor draw as much current as it wants.
It does so by internally closing the switch connecting the green field wire to ground.

upload_2019-12-15_23-3-14.png


Bottom line.
Measure the voltage difference between the alternator and the regulator's sense terminal (or as close as you can).
Measure the voltage diffenrence between the alternator case, the regulator case,

(In addition, you can also measure the difference to the battery neg and pos.)
 
Last edited:
Mattax said:
Measure the voltage difference between the alternator and the regulator's sense terminal (or as close as you can).
Measure the voltage diffenrence between the alternator case, the regulator case,

(In addition, you can also measure the difference to the battery neg and pos.)
Click to expand...

This is not correct. I realize that in most of the vehicles we deal with here, the alternator case is "always" grounded to the engine block, and the battery is "always" grounded to the engine block, BUT THE ALTERNATOR MIGHT NOT actually always be. Some alternators require a separate ground wire from a grounding post on the alternator. The case is not grounded to the circuit, or may not be considered a "good" ground.

(The old mid/ late seventies "big frame" 100A Chrysler had a separate grounding wire/ post off the alternator.)

And actually, that is not the point LOL

The ACTUAL point that the VR power and ground needs to see is AT THE BATTERY. Therefore, always check both ground circuit and hot circuit in relation to the battery posts themselves
 
This is a photo, as an example, of the old Mopar 100A large frame unit. NOTICE that the mounting ears have bushings, and these cause the case to be electrically insulated. "C" depicts the very necessary ground lug

Mopar100amp.jpg
 
I bought an adjustable regulator for mine. It has an adjustment pot on the back of it. I used a pair of jumper cables to ground the case while adjusting the pot to 14.7 volts max, I hear that a lot of the new regulators are anodizing the case before assembly and therefore the circuit board inside is not grounded no matter how well you ground the case. That is why I bought.an adjustable regulator from eBay ( only costs about $15.00) let me know if you want one and I'll find the link. Good Luck
 
I have not had time to get back out with the volt meter, but I have several things to try, thanks to all. I'll get some photos and show where I get what in a couple of days.
 
So, I added a 10ga ground wire from alt case to VR to battery to no avail buts it's still a good addition to a rusty old truck....still getting 15.1-15.4V at battery posts with and without loads. I can get a V reading off the splice of my new positive VR (blue wire) connector......is that a good test spot? Then I compare that to output voltage?
 
I believe so. What you want to find out is "if" the VR supply voltage (the IGN terminal) is same as battery. You want the key in "run" with engine stopped. Now measure from battery positive to the VR IGN terminal "or as close as you can get."

Another way to look at this is (with key in "run") to measure battery positive to engine block and note the reading. Then measure from VR IGN terminal "as close as you can get" to engine block and note that reading and subtract the two. Another place to measure the VR is the blue field wire at the alternator. You must NOT disconnect anything to do this measurement. Leave everything connected and 'back probe' the connector
 
With a just-charged battery at 13.1, I measured 13.0 at my ignition circuit connector and got 12.8 at the blue field wire connector.......this with engine off but ignition on, grounding off battery or my 10 ga ground stud.
 
CRAP. If you did that right, it sounds OK. Have you tried another battery? Not sure what else............
 
Last night I tried a battery from car that hasn't been used much recently......measured at 12.4 V. Starting up it read between 14.7 and 14.9 right off, but by the time the choke opened up, there it was jumping up over 15 V again. I just bought a new multi-meter and I have an adjustable VR on order. I also know of a vintage OEM VR that I can pull off a parts truck.
 
Unless we've missed something along the way, I don't know. one last thing you can try.......get the thing as 'normalized' as you can that is fully charged after starting, and warmed up. (VR is temp sensitive and some are temp compensated) Now, with the engine running at fast idle and all accessories off, measure V between the VR IGN terminal and battery NEG post. Also measure between VR IGN and the VR mounting flange, see if there is a difference. Last, after measuring these two points, measure across the battery and double check

If the VR measures closer to correct, that is around 14V to the VR case, you still have a voltage drop problem.
 
OK, so I'll try to do the voltage drop test tonight, but here's some new info. This past weekend when it was 60 degrees compared to "normal" 20 degrees for Dec/Jan in Vermont, I re-installed my almost new battery and fired it up. 14.7 V stone cold......not so scary. At high idle it started to climb but would not hit 15V. Then, after I punched it to pull off the choke, it settled to a 14.6 or .7 I didn't run it long enough to see if it would climb back up into the danger zone, but my thought is that before long it would be nice and warm under the hood. I'm thinking if the VR response is temp related, we might have our answer. My parts guy says that no battery should be subjected to 15+ volts period.....your thoughts? When it's freezing cold the battery won't boil, right?
 
15V is not going to hurt a battery for some period but it will eventually--over a long period---cause it to use water, and corroded metal around it due to gassing and "puking." It WILL shorten battery life over a long period. If you look in any of the service manuals "there used to be" a chart showing some idea of temp change vs voltage output These charts are in the electrical section pertaining to alternator testing and service

The real danger of a cold battery is IF it has been allowed to run down enough that it will freeze---a good battery that is charged up will NOT freeze. You NEVER want to boost or charge a dead/ cold frozen battery.

This chart is out of the 72 service manual. Notice these are not outdoor temps, these are "near the VR" IE under the hood

voltagechart.jpg
 
Now it's back down in the 30's temperature-wise and I'm seeing high 14's but not 15V at cold startup. Once it warms up it settles down to no more than 14.62V. This all seems really good but I'm not sure what I did to "fix" it......The only thing that I did was to clean the cables and terminals really good when I put my good battery back in. All this on the same day the adjustable VR arrived! I think I'll stick with the stock VR unless voltage starts climbing again when it's really cold.
 
powerwaggin said:
The only thing that I did was to clean the cables and terminals really good when I put my good battery back in.
Click to expand...
Making better connections can make a difference!

I'd still check the connection coming off the alternator and the other end of it.
If you are seeing 14 volts or more, power is flowing from the alternator.
If there are voltage drops between the alternator output and the regulator "I" terminal, the regulator will regulate based on the lower voltage it sees.
Lets say the internal set points for the regulator are 14.2 to 14.8 V.
And lets say after start up the alternator is producing providing 15 amps to recharge the battery and run the field and ignition.
If resistance to the 15 amps flowing through the wires and connections causes a 0.5 Volt drop before the regulator I terminal, the regulator will boost the field until the I terminal sees 14.2 to 14.8 Volts. Being the air is cold, that could be 14.8 V at the regulator, bring the alternator output ot 15.3 Volts.
(Neither the regulator nor the battery sees that 15.3 volts.)

As the battery charges, the current drawn drops quickly. When the battery is charged and nothing else is running, alternator will only provide 4 to 5 amps for the ignition and field.
With only 5 amps flowing, voltage drop caused by resistance in the wires and connections goes down. Now maybe its only 0.2 Volt drop.

Make sense?
Voltage drop seen by the regulator depends both on the routing, and the amount of current flowing.
 
An answer has been found.......or at least a solution possibly. I'm going to say cautiously that both cheap voltage regulators were(are) junk. Some day I'll try them out in my '75 D300 dump truck to see what happens.

I had run it the other day when the temp was back down to 9 degrees F. With a resting pre-start battery voltage of 12.6V, it shot right up to 15V once running. Warmed up and idling voltage was 15.1V to 15.3V whether or not I had any electrical loads on it. Enough of this!

I installed a new adjustable VR.

With plowable snow in the forecast, I dialed in the new adjustable VR after getting the engine warm. Right now we're talking 14.10 at idle, 14.3 with a crusty '72 heater blower howling away. Have not run it much but it's snowing hard .......
 
Have you double checked the VR IGN terminal voltage? A second way of checking that---running----is to measure the VR ignition terminal to the VR case. If it is running within a few tenths of 'same as battery' then you can assume there no voltage drop problems.
 
I did a voltmeter check tonight when everything was just barely warming up, while running. From a long pigtail attached at the VR IGN, I measured 13.99V to 14.00V when grounding at the battery. Between VR IGN and the VR case was exactly the same at 13.99V to 14.00V. All this while the battery was at 14.10V between the posts.
 
Last edited:
You must log in or register to reply here.
-

Back
Top