Voltage Regulator Malfunction???

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Creedmoor

Recovering Fordaholic
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So I was being proactive and while the 318 in my 68 Barracuda was warming up, I stuck a voltmeter on the battery terminals. I was showing 15.06 - 15.13 volts. Pretty sure that’s too high. Shouldn’t it be more like 14.2 volts? I don’t want to cook a battery - they’re getting pretty spendy nowadays.

Located my voltage regulator but it doesn’t look like what I was expecting. Is this some sort of solid state replacement for the big brick I was expecting? What should I be looking for as a replacement? This thing only has the two wires going to it.
Appreciate any advice! Thanks.
FFAB07A1-6343-448B-9A62-EBD987640B1B.jpeg
 
Looks like a "race only" unit that basically full fields the alternator voltage output. Not good for street usage.
 
It could be that high normally, if the battery is in a state of discharge. While it is warming up isn't necessarily the best time to test the charging system. You should test it again after it is completely warm and possibly even after driving some.
 
3 things...
Screenshot_20230318-224052~3.png

  1. My money is that there is an adjustment in that hole (red cir.)
  2. Check voltage from the green area to the negative terminal on the battery, it should be 0v
  3. Most likely you can replace the VR with a standard grounded field regulator for a 68.
Screenshot_20230318-224649.png
 
Last edited:
VR's are temperature sensitive.

You need to check voltage when the engine bay is warm, the battery is "normal" temperature and the charge is normalized.

Also MOST these girls if they have not been improved, have VOLTAGE DROP in the ign1 "run" ignition line, which is the line from the key that powers ignition system and VR. This occurs both in the ground circuit (more rare) but mostly the hot side, in the bulkhead connector/ ammeter circuit, and ignition switch and connector

TO CHECK IT

Turn the key to "run" with engine stopped. Stab one probe into the battery + post, and the other connect to the VR IGN lead. You are hoping for a very low value, the lower the better. If it's more than about .3--.4V (3/10 of one volt) chase through that circuit and find out why

Also check the ground side. Run the engine on high idle, and check this first with all accessories off, and again with heater, lights, etc powered on. Stab one probe of your meter into the top of the battery NEG post, and the other into the mounting flange of the VR, HARD. Again the lower the reading the better, zero is perfect
 
If I remember correctly, that regulator is just a "marine" version, that Chrysler listed as a "P" part and charged more. They did similar for a lot of parts.
 
If I remember correctly, that regulator is just a "marine" version, that Chrysler listed as a "P" part and charged more. They did similar for a lot of parts.
That may be the most reasonable I've heard yet. One "famous" person on here has claimed that they are "race only" (because Mopar claims they were) and that they don't properly regulate at the correct voltage, but, (he admits) because they have epoxy paint--well SO?? Scrape off the paint so it properly grounds the thing. ---You know---like any other VR
 
That may be the most reasonable I've heard yet. One "famous" person on here has claimed that they are "race only" (because Mopar claims they were) and that they don't properly regulate at the correct voltage, but, (he admits) because they have epoxy paint--well SO?? Scrape off the paint so it properly grounds the thing. ---You know---like any other VR
Again if my memory is correct. The original regulators for the single field wire alternators were mechanical (had points inside) and were electrically "noisy". The later regulators were electronic and had a much "cleaner" output, and better regulation. The Mopar "race" regulators, and the marine regulators were electronic, but were direct replacements for the mechanical regulators. These worked better with the Mopar OEM electronic ign systems when they were installed on the earlier cars.
PS: the old regulators (mechanical or electronic) controlled the 12v "hot" side of the field. The newer style electronic regulators controlled the ground side of the field.
 
So I was being proactive and while the 318 in my 68 Barracuda was warming up, I stuck a voltmeter on the battery terminals. I was showing 15.06 - 15.13 volts. Pretty sure that’s too high. Shouldn’t it be more like 14.2 volts? I don’t want to cook a battery - they’re getting pretty spendy nowadays.

Located my voltage regulator but it doesn’t look like what I was expecting. Is this some sort of solid state replacement for the big brick I was expecting? What should I be looking for as a replacement? This thing only has the two wires going to it.
Appreciate any advice! Thanks.
View attachment 1716065779
That's pretty typical cold at start up.

The regulator on the car is a solid state replacement. While it looks like the MP P part painted black, the numbers on the top indicate its probably made by or for Standard Motor Parts or such.

You can do the test suggested above to determine if there is resistance in the run circuit. However with that regulator you will have to back probe the connector with red wire. Note the ammeter position when you do the voltage drop test. It should be slight discharge, but people sometimes tap into that circuit for additional stuff (such as electronic ignition, electric choke, stereo, electric fan). Those will increase the current a little or a lot.

Some other test you can do are:
a. Measure the voltage at the battery once the battery is charged. You'll know its recharged by looking at the ammeter.

b. Measure the output voltage of the alternator. If its the same as the battery during charging, then suspect a drop in the run circuit. If its higher than the battery during charging, then suspect the alternator output and battery charge lines. A variation on this test is to get the battery charged, and then add accessory loads such as the headlights and heater fan. Without a relay harness, lights will add a load of 12 to 15 amps to the output circuit.



Back probe into the input connector on a SMP VR-128
1679316991710.png


Another issue that comes up is with replacement alternators. Replacements, especially the revised squareback, have a higher field current draw than the originals. I wrote to SMP to ask for the specs on the VR-128, and they only had the dimensions. :( It would not be surprising that the electronics can handle 3 to 4 amps fine, but not 7 amps or more.
 
New ones of these are available with upgraded circuitry inside. Not sure if the one posted is old style or new.
3 things...
View attachment 1716065832
  1. My money is that there is an adjustment in that hole (red cir.)
  2. Check voltage from the green area to the negative terminal on the battery, it should be 0v
  3. Most likely you can replace the VR with a standard grounded field regulator for a 68.
View attachment 1716065818
 
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