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Odd voltage regulator issue

hunt2elk

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Got this car put back together 4 years ago. Everything in the electrical system is new except the ignition switch. Car is a 1970 and using this style alternator.
During restoration I installed a brand new USA made MP 3438150 voltage regulator. It was working great for 200 miles and then I noticed the operating voltage had dropped from 14.2 to 13.2. Had the alternator checked and it was fine. Called Summit and they sent me another Mopar regulator under warranty. While I was waiting for that, I bought a couple of Standard VR125's (made in China). I put one of those on and everything was fine again. Last summer I noticed the volt meter was running over 15, but chalked it up to cheap gauges. Finally got around to replacing them with some good Autometers. I now have 5000 miles on the car. Same high voltage as before, and this time I verified it with a multimeter. Was running at 15.5 volts. So I dug out the warranty replacement MP that Summit sent me years ago. Installed that and the voltage was right at 14.2. Life was good for a week, but now the voltage has dropped to 13. Dug out the second Standard VR125 I bought previously. This one is putting out 15.4 volts. So I have 2 Mopar 3438150's that both started out good and then went to regulating around 13 volts. 2 Standard VR125's. One ran for quite awhile ok and then over regulates at 15.5, and the second one is 15.4 out of the box. All 4 of these units were bought at the same time. Anybody else ever had a crazy situation like this? Are there better regulators I could try?

20210913_182420.jpg 20210909_141058.jpg 20210909_141230.jpg 20210913_165726.jpg
 
You could have a problem with the plug. If there is a poor connection that could be your problem.
 
Got this car put back together 4 years ago. Everything in the electrical system is new except the ignition switch. Car is a 1970 and using this style alternator.
During restoration I installed a brand new USA made MP 3438150 voltage regulator. It was working great for 200 miles and then I noticed the operating voltage had dropped from 14.2 to 13.2. Had the alternator checked and it was fine. Called Summit and they sent me another Mopar regulator under warranty. While I was waiting for that, I bought a couple of Standard VR125's (made in China). I put one of those on and everything was fine again. Last summer I noticed the volt meter was running over 15, but chalked it up to cheap gauges. Finally got around to replacing them with some good Autometers. I now have 5000 miles on the car. Same high voltage as before, and this time I verified it with a multimeter. Was running at 15.5 volts. So I dug out the warranty replacement MP that Summit sent me years ago. Installed that and the voltage was right at 14.2. Life was good for a week, but now the voltage has dropped to 13. Dug out the second Standard VR125 I bought previously. This one is putting out 15.4 volts. So I have 2 Mopar 3438150's that both started out good and then went to regulating around 13 volts. 2 Standard VR125's. One ran for quite awhile ok and then over regulates at 15.5, and the second one is 15.4 out of the box. All 4 of these units were bought at the same time. Anybody else ever had a crazy situation like this? Are there better regulators I could try?

View attachment 1166057 View attachment 1166065 View attachment 1166066 View attachment 1166067
First of all, the origional alternator was a round back style, depending on origional accessories, it was either a 37 amp or 42 amp either single or dual sheave drive. Most aftermarket replacement alternators are the square back alternator design shown. Their capacity very depending what the origional unit came from. The regulator you show is correct for either styles of alternators. Internally, they have components that vary the alternators field voltage to provide a nominal 14.5 system voltage. There is an internal voltage divider network, inside the regulator, that also provides temperature compensation to allow for cold weather, allowing higher system voltage and lower voltage in hot weather. Because of the origin of these internal items, the ×/- tolerances on these components are likely causing the disparities. In addition, insure that the case is securely grounded to the engine block with its own wire. The field current is low, 5-6 amps, at maximum charge rate, a 14 AWG wire is sufficient. I'm sure others will have their own ideas and suggestions.
BOB RENTON
 
The harness was a new M&H when I built the car. Terminals look good but I will ohm them out tomorrow. Just remembered that a guy gave me this meter years ago. Oddly, both Mopar regs test good and both Standards test bad.

20210913_194134.jpg
 
First of all, the origional alternator was a round back style, depending on origional accessories, it was either a 37 amp or 42 amp either single or dual sheave drive. Most aftermarket replacement alternators are the square back alternator design shown. Their capacity very depending what the origional unit came from. The regulator you show is correct for either styles of alternators. Internally, they have components that vary the alternators field voltage to provide a nominal 14.5 system voltage. There is an internal voltage divider network, inside the regulator, that also provides temperature compensation to allow for cold weather, allowing higher system voltage and lower voltage in hot weather. Because of the origin of these internal items, the ×/- tolerances on these components are likely causing the disparities. In addition, insure that the case is securely grounded to the engine block with its own wire. The field current is low, 5-6 amps, at maximum charge rate, a 14 AWG wire is sufficient. I'm sure others will have their own ideas and suggestions.
BOB RENTON
When I had the alternator rebuilt, they replaced the 37 amp internals with a 60 amp version, I don't think that has anything to do with my problems though. I do have a seperate ground wire from the mounting bolt to the battery. It is probably only a 16 gauge wire. I think I am going to redo that with a 14.
 
As previously stated the Mopar voltage regulators need to be earthed to work properly.
Might pay to check yours - paint can get in the way.
 
stock fields wiring is actually 18 gauge.

No need for a ground wire between alt to the batt, as far the mounting bolt area is clean and the ground wire between block and batt is also tight and clean.

Sure I'd check the ground between reg and firewall. Not saying is that but worths checking that.
 
My brother had a ‘70 Challenger back in the 80’s that constantly drained the battery. He had it to several garage’s and even an electronics specialist. They gave up. I found it to be the ground on the voltage regulator.
As previously stated the Mopar voltage regulators need to be earthed to work properly.
Might pay to check yours - paint can get in the way.
 
As previously stated the Mopar voltage regulators need to be earthed to work properly.
Might pay to check yours - paint can get in the way.
Yeah, I have the paint scraped off where the bolt head rides. I'll stick a star washer there as well.
 
The 14.2 to 13.2 might be the temperature compensation if the 13.2 was with a hot engine compartment?
I have been using the Transpo C8313 adjustable regulator in the '71 Charger with a 136 Amp Denso alternator.
 
The 14.2 to 13.2 might be the temperature compensation if the 13.2 was with a hot engine compartment?
I have been using the Transpo C8313 adjustable regulator in the '71 Charger with a 136 Amp Denso alternator.
Learned something new today. I didn't realize that the output voltage is supposed to drop as the regulator heats up. Guess that's what Bob was referring to in an earlier post. So my 13.2 is no doubt ok after I have the car heated up. I feel better about that than the 15.5 volts put out by the Standard vr125's. It still seems weird that the Mopar ones will put out 14.2 all the time for a couple hundred miles, and then drop after being in service. I will check out that regulator you mentioned.

20210914_085930.jpg
 
Learned something new today. I didn't realize that the output voltage is supposed to drop as the regulator heats up. Guess that's what Bob was referring to in an earlier post. So my 13.2 is no doubt ok after I have the car heated up. I feel better about that than the 15.5 volts put out by the Standard vr125's. It still seems weird that the Mopar ones will put out 14.2 all the time for a couple hundred miles, and then drop after being in service. I will check out that regulator you mentioned.

View attachment 1166196
YES....THIS IS EXACTLY what I was referring to. Car batteries require a slightly higher charging voltage when cold than they do when hot, hence the ambient compensation (temperature change) afforded by the voltage regulator. This is accomplished by positive temperature compensation (PTC) resistors as part of the internal voltage divider network of the voltage regulator which controls the transistor that is switching the alternators field current and ultimately alternator's output voltage.
BOB RENTON
 
The temperature compensation is so you don't overheat a hot battery and boil the electrolyte.
Many newer cars have a temperature sensor in/under the battery tray to better monitor the batteries temperature.
Also the regulator senses the battery voltage closer to the battery. The battery sense, the regulator power in our regulator version, can be an issue with trunk mounted batteries. You can mount the regulator near the battery and power the regulator from the battery through a relay, just need a longer field wire from regulator to alternator.
 
Have you checked for voltage drop between the battery positive post and the ignition 1 terminal (regulator reference) at the regulator while under running load? Any resistance at any connection in between will cause a higher-than-normal charge voltage measured at the battery. Beginning in 1970, column mounted ignition switch, the Molex connection at the bottom of the column has been a problem since very early on. Bulkhead connections, specifically Ignition 1 and battery charge terminals have contributed to high voltage drop.
 
Have you checked for voltage drop between the battery positive post and the ignition 1 terminal (regulator reference) at the regulator while under running load? Any resistance at any connection in between will cause a higher-than-normal charge voltage measured at the battery. Beginning in 1970, column mounted ignition switch, the Molex connection at the bottom of the column has been a problem since very early on. Bulkhead connections, specifically Ignition 1 and battery charge terminals have contributed to high voltage drop.
I'll do those tests next time I am out in the garage. I am thinking everything is ok basically because only the Standard regulators are passing high voltage. The Mopar ones are more inline with spec, although may be a tad low.
 
I replaced my '74 voltage regulator when reinstalling the engine a few years ago. Didn't think to check charge rate until one of the many charging issue threads popped up here. Found I was actually at 15.3 volts. After chasing the problem a while I discovered the ignition switch itself was causing "ignition 1" voltage drop which in turn told the regulator it needed higher charge rate. Replaced the ignition switch and the charge rate dropped to 14.7. Since the '74 is still in restoration mode I didn't worry about that slightly high voltage at the time.

Now that we are closer to being on the road I readdressed the issue a couple weeks ago. With aid of a very understanding auto parts store, I bought a new (different brand) regulator and my cold charge rate is now 14.3 volts.

SPECIAL NOTE: While chasing the voltage drop start at the regulator connector while still connected to regulator; then go to the bulkhead connector (outside and inside). Don't stop there. check both input and output side of that ignition switch!!
 
Yes, excessive internal ignition switch contact resistance contributes to the total voltage drop measured. After correcting any voltage drop issues found, still don’t like the charging voltage at the battery, there is a good quality adjustable regulator available from the aftermarket that can be used to dial in the desired voltage at the battery.

regulator.jpg
 
One good thing to do to our older Mopars is put a relay in to power the voltage regulator battery sense circuit. Later Mopar did this on some cars and called it a field loads relay. Basically to take the 12 volt key run wire to the reg and run that to a relay coil and then ground the relay coil. It will only power when the key is in the run mode. Then wire the relay right from the battery to the voltage reg volts sense circuit. It works great because you eliminate the ign switch and any bad connection between the ign switch and reg. You get battery volts right to the reg. It will let the reg see a much more accurate battery volts.
As for the volts changing yes all factory voltage regulators sense ambient temps as it raises the set voltage in colder weather. But that said when its 80 degrees out it may charge at 13.6 and when its 20 degrees it may be at 15. But I have never seen any change a full volt from underhood temps as eng warms up. Yes they sense ambient outside temps and adjust the voltage setting accordingly. But as I said I have not seen any change much if any just by the eng underhood temps. In the summer my volts is around 14.2 and it stays at 14.2 from a cold eng to 190 degrees in the eng. I may be wrong but I believe they only sense the volts at key on and keep that setting until the next start. Good luck with it. Ron
 
The field load relay function used on later models is ( as far I recall ) to activate the field circuit JUST when in run and not cranking due the low voltage the field circuit gets while cranking throught the ballast saving the regulator from sensing that low voltage and trying to compensate
 
The field load relay function used on later models is ( as far I recall ) to activate the field circuit JUST when in run and not cranking due the low voltage the field circuit gets while cranking throught the ballast saving the regulator from sensing that low voltage and trying to compensate

Yes it did that but the main reason Mopar went to it was to eliminate the wiring going through the firewall and the ign switch as it just takes the hot from the battery right through the relay to the field and to the regulator volts sense circuit for a better voltage sense and less voltage drop to the field circuit in the alt. Ron
 
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