Alt putting out 16 volts

[Garys1969RR]

My voltmeter shows 16, sometimes * 16.5 volts going to the battery with the engine running. So I checked the field wire voltage at the alternator with the key on, motor not running. The field wire is getting 11.25 volts, with key on and the motor not running. Then I check battery voltage and it is showing 12.25 volts under the same conditions. Is this right? Doesn't the ignition switch feed power to the voltage regulator and the field wire of the alternator from the battery? shouldn't I have the same voltage at the field wire and the battery?

 

[Sixpactogo]

You will lose some voltage through the system. A volt seems a little high but if the Alternator is sending 16+ volts to system when the engine is running, I would suspect the regulator as the culprit.

 

[R/T Boy 67]

If the voltage at the regulator is lower than battery voltage, then there will be an overcharge condition. The regulator thinks the battery voltage is lower than it is and charges accordingly. It could be a bad connecter or some added draw on that circuit, etc. Check the bulkhead connecter.

 

[Mopars & Missiles]

Most likely got some corrosion at a connection in the battery sense wire, this will cause increased resistance which in turn lowers the sense voltage at the regulator. The regulator responds by increasing the output of the alternator, which is exactly what it is supposed to do when sense voltage is low. Find and remedy the source of the voltage drop (corrosion/resistance) in the sense line to the regulator and it will work just fine.


I guess to be totally thorough with this problem, you have to ensure that the regulator ground is the SAME as battery ground. Otherwise you again will have a voltage drop that tricks the regulator into thinking that the battery voltage is low and hence, increasing alternator output.

 

[Garys1969RR]

I guess I'll run a dedicated wire from the battery ground to the reg body. That would eliminate that possible problem. Also, I can disconnect the regulator plug, and measure voltage going into the regulator. It should be the same as what the field wire of the alt has.

 

[Garys1969RR]

So there should also be a wire coming off the ignition switch that sends battery voltage to the regulator

and field wire, Right? Is that normally a dark blue wire ? Here is a pic of the blue wire, coming off the regulator, and going to a junction. It is showing slightly lower voltage,with key on, than what i measured directly off the battery .

 

[Garys1969RR]

So the blue wire is the battery sense wire?

 

[moparnation74]

Most likely got some corrosion at a connection in the battery sense wire, this will cause increased resistance which in turn lowers the sense voltage at the regulator. The regulator responds by increasing the output of the alternator, which is exactly what it is supposed to do when sense voltage is low. Find and remedy the source of the voltage drop (corrosion/resistance) in the sense line to the regulator and it will work just fine.


I guess to be totally thorough with this problem, you have to ensure that the regulator ground is the SAME as battery ground. Otherwise you again will have a voltage drop that tricks the regulator into thinking that the battery voltage is low and hence, increasing alternator output.

Great post MM!

 

[Mopars & Missiles]

I guess I'll run a dedicated wire from the battery ground to the reg body. That would eliminate that possible problem. Also, I can disconnect the regulator plug, and measure voltage going into the regulator. It should be the same as what the field wire of the alt has.

For your ground connection, yes that may work, but all you need to do is verify with a DVM that you have 0.0 Vdc between the battery negative post and the BARE metal case (no paint) of the voltage regulator. If you measure "some" voltage between those two, then you don't have a perfect battery ground at the regulator.

As for the "field wire" voltage, NO that is the output of the voltage regulator, not the input and it should not be the same. Check the terminal on the voltage regulator that is labeled "BAT", this is the battery reference voltage INTO the regulator. This is the voltage that SHOULD be the same or very nearly the same as the voltage measured right at the battery positive terminal. Any difference in voltage between these two would indicate "voltage drop" in the wiring, connections, and/or ignition switch prior to the voltage regulator.

With a FSM and studying the wiring diagrams, you can easily trace these circuits through the car. It does take a little patience, but you would be surprised how easily (and cheaply) you can usually correct this problem.

 

[Mopars & Missiles]

Also, all I've said here is in regard to Factory OEM wiring. Yours has obviously been altered at some point in time, so you may have a little more work to do to find the problem. I see a lot of "less than perfect" aftermarket wiring connections.

 

[Mopars & Missiles]

So the blue wire is the battery sense wire?

OK, just refreshed my memory with the FSM wiring diagram. The wire directly from the battery or battery sense wire is "16DBL". This means a 16 gauge wire that is Dark Blue.

Also, in one of my previous posts I referred to the battery sense wire as being labeled "BAT" on the voltage regulator. That is WRONG, it is labeled "IGN" of course this means Ignition. Sorry about that.

One more thing, please in the future try to include the information on what car you are working on. In your case, its fairly safe to say you have a '69 Road Runner, but SO MANY times someone asks a question without providing this basic information and expects correct answers. Evidently they think every car is the same, or everyone on this board has the exact same car that they own.

 

[Mopars & Missiles]

Let's see a photo of your Voltage Regulator. From that other pic, it appears you may have a '70's and up style regulator installed, not the OEM '69 style.

 

[Garys1969RR]

Let's see a photo of your Voltage Regulator. From that other pic, it appears you may have a '70's and up style regulator installed, not the OEM '69 style.

OK, sorry bout that. It is a 1970 Dodge Dart. Newer style solid state voltage regulator. 440 Auto. Pretty much all stock, except for the B Body drive train. AKA 440-727-8 3/4 rearend. And the ignition has been modified to use an MSD 6-AL, with timing retard box added. It has a Paxton blower also, hence the timing retard box. I'm considering going to a GM HEI module to simplify things.

 

[Garys1969RR]

Anyway, I ran a clip lead directly from the battery to the dark blue wire which goes to the regulator and 1 side of the alternator field. Apparently the regulator senses battery voltage from this blue wire, and then grounds the other field wire to complete the circuit. That energizes the field in the alternator, and causes it to produce charge voltage from the output lug of the alternator. With this wire hooked from the battery to the blue field wire it then charges normally, at a steady 14.5 volts. Without this jumper wire hooked up, it charges at 15.5 to 16 volts, and makes the lights flicker brighter. Also with the jumper wire in place, it continues to run with the key shut off. So the field/regulator wire is also supplying the ignition system with power. With Halloween being so close, I'm beginning to feel as if the electrical system is haunted, LOL. So it helps to review this stuff, and I will eventually figure it all out. Your ideas and suggestions do help. Thanks.

 

[R/T Boy 67]

When I got my 67 coronet it had mopar electronic ignition installed, and it got it's power from that same ign. on blue wire. The extra load reduced the voltage in that circuit and caused an overcharging condition. I put in a relay to run the ignition and it cured the problem. If your ign. System is run off that circuit it could cause your problem.

 

[Garys1969RR]

Yes that makes sense. So the relay is actuated when the ignition switch is turned on? And then that relay completes a direct circuit of battery to field/regulator circuit? Is that how it works? Then I won't run ignition or any other circuit off that wire. Sounds fairly easy. Thanks!

 

[R/T Boy 67]

I used the relay to power the ignition. The blue wire from the ign. switch activated the relay and also went to the voltage regulator. The relay draws very little power. I used a fat wire from the starting relay stud to the ign. relay, and from the ign. relay to the ign. system. I used a fuse in the wire to the ign. relay. Hope this makes sense.

 

[Garys1969RR]

Oh. I see now. Someone on A Bodies used the same type of relay to get a steady and full battery current to the regulator, then ran the ignition directly off the ignition switch. So this is just the opposite. But getting the same results. Thanks for the info.

 

[Nacho-RT74]

Also with the jumper wire in place, it continues to run with the key shut off. So the field/regulator wire is also supplying the ignition system with power.

It is indeed the same wiring. It feeds alt field and ballast resistor too so then the coil which makes to keep running a points car. When ECU, it also feeds the Ignition box, so another reason to keep the car running.

You just need to make a good wiring mantenience. I bet you'll find some wires, terminals and cavities toast at bulkhead ( not just blue wire but main charging system ones, thick red and black ). Check also dowm the column, the ign switch harnes, another weak spot.

 

[R/T Boy 67]

The reason I ran the ign. off the relay is because the 18 gauge blue wire is too small for most aftermarket ign. systems. With a relay you can run 12 gauge wire directly to the ign. system.