Overcharging battery to a little over 15v

[mpro69rr]

I posted this in electrical but didn't get much response, trying here.

Having a little overcharging problem, 69 RR 383 4 speed, all new wiring for the whole car with the MAD wiring. At idle I get 14.4v to 14.5v on Dakota Digital gauges (matches volt meter at battery), when revved to 4000rpm I get 14.9v to 15v. Also I had a 95amp powermaster alt (duel field with one FLD grounded to alt case) but that went up 16v at 5000rpm so I switched to my current alt (single field). not sure of the amp. Below are the tests I did, all while running:

1. Battery ground to VR IGN 14.5v, same as battery
2. Battery ground to (unconnected from alt) FLD wire 11.5v
3. Battery ground to stud on alt 14.5v
4, Battery 12.4v to 12.6v
5. Ground at VR is good

Everything seems to check out except, why only 11.5v at the FLD wire? I also unplugged the FLD wire and the battery did not charge. I have a feeling, while driving, if it goes to 5000rpm it will go over 15v. Why the increase in voltage while going up in RPM? I had another VR I tried and same thing. I finally found a VR with a volt set at 14.5v so that should be here next week. Will this solve my problem?

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[steve340]

The voltage pumped out by the alternator should drop back as the battery charges up. This is controlled by the regulator. This stops you "cooking" the battery. You may need to drive for a few miles before this happens dependant on how much electrical load there is.
Does this happen?
Very basic explanation for over charging - the battery cannot hold the charge or the regulator part is not working correctly.
This causes the alternator to continue to try and charge the battery.

 

[RemCharger]

Allow the battery to fully charge on a good charger before moving on to diagnosing

 

[mpro69rr]

The voltage pumped out by the alternator should drop back as the battery charges up. This is controlled by the regulator. This stops you "cooking" the battery. You may need to drive for a few miles before this happens dependant on how much electrical load there is.
Does this happen?
Very basic explanation for over charging - the battery cannot hold the charge or the regulator part is not working correctly.
This causes the alternator to continue to try and charge the battery.

I wonder if the battery ever had a full charge because the volts should drop when its full, good point. I'll have to check that.

 

[mpro69rr]

Allow the battery to fully charge on a good charger before moving on to diagnosing

Good idea, that way I'll know, like what steve340 was saying. I'll charge it up this weekend. Can't be the VR because I used two new ones, I always carry spares. The battery is not that old so I am also wondering if something else caused the new battery to degrade. Does anyone know why I would only get 11.5v on the FLD wire? It being that low how could it signal the ALT to charge at 15v? Like I said in my post, I used two different ALTs, one single field the other double field, can't be the ALT? I better see if the battery can hold a charge first.

 

[steve340]

Look at the FSM for a description of how it all works. I am no expert but -
I think the field wire is how the regulator adjusts the alternator output and how the regulator senses the battery is full - you may be on to something with your 11.5V

 

[mpro69rr]

Look at the FSM for a description of how it all works. I am no expert but -
I think the field wire is how the regulator adjusts the alternator output and how the regulator senses the battery is full - you may be on to something with your 11.5V

Yes, if the IGN terminal is 12.5v and the battery is 12.5v and the FLD wire is 11.5v that means the ALT is getting a signal of 11.5v and adjusting for it, that would mean the VR is bad and who knows I could have two bad VR's because they are Chinese junk! Does this sound correct, can anyone confirm this? I have a new VR coming that volt sets the VR to 14.5v and below. If its not junk it should work. I also bought a 1970 adjustable electronic VR and I may install that with my powermaster two field ALT and wire it up. I can adjust it to whatever volts I want. From reading all the threads on this forum people say that's a better way to go.

 

[mpro69rr]

Can anyone comment if I am correct above? It sounds correct but not sure of the 11.5v at the FLD wire. Thanks!

 

[oldkimmer]

R u still going thru the bulk head connector or is it bypassed? R the wires tight on the back of the gauge?

 

[mpro69rr]

R u still going thru the bulk head connector or is it bypassed? R the wires tight on the back of the gauge?

bypasswd, MAD wiring.

Overcharging problem solved