Alternator overcharging when cold?...

[R. Shackleford]

Hey all. Got a funny issue with my '65 belvedere II A318 charging system. On a cold start the alternator puts out 15.6+v at the battery even on idle. After the engine gets to operating temperature everything goes to how it should, 13.5 on idle and 14.4 on rev. I cleaned up the firewall plug but honestly it was very clean to begin with. Never experienced this before so any ideas are good ones.

Recently replaced parts;
Alternator (OE replacement)
Voltage regulator (OE replacement)
Battery

I had replaced the VR last summer then when I realized the battery was not getting a charge. Then everything seemed fine until the bearing started goin out in the alternator so I replaced it with an OE replacement. Then that didn't seem to charge so I replaced the VR again, cleaned up the firewall grounds and now I get the 15.6+v until operating temperature. I have not checked anything under the dash yet so just checking to see if anyone has had this specific issue.

Thanks for reading!

 

[R413]

If you lose ground at VR charge goes wide open to 16+ volts.

How much are you cranking it to do a cold start?

Is there a draw making the battery low on a cold start, thus the 15.6 volts on a startup? Try taking A battery cable off when you park it and connect for next cold start.

 

[R. Shackleford]

She fires right up on cold start so no excessive crankin and I always disconnect the battery at night. Battery sits at 12.4ish before startup. I don't have anything that isn't stock or OE replacement in this aside from a tape deck installed in the 90s and a tach I installed last summer. I've already taken them outta the equation just in case by pulling power and ground from them. I was suggested from a buddy that it may be the ammeter and the shunt inside is giving more resistance until it heats up and the thermal expansion closes the gap a little bit and then flows as it should. Is this a possibility? He's no Mopar guy so not super familiar with the notorious charging system issues. I've been pretty lucky so far so this ones a head scratcher.

 

[Nacho-RT74]

After crank up the engine the alternator will recharge the battery for the lost load due the crank up job. This can take from 3 to 10 minutes depending on alt capacity and load requested after the engine start up.

Maybe this could take a bit more voltage untill get a steady load sourcing

 

[old guys rule]

Hey all. Got a funny issue with my '65 belvedere II A318 charging system. On a cold start the alternator puts out 15.6+v at the battery even on idle. After the engine gets to operating temperature everything goes to how it should, 13.5 on idle and 14.4 on rev. I cleaned up the firewall plug but honestly it was very clean to begin with. Never experienced this before so any ideas are good ones.

Recently replaced parts;
Alternator (OE replacement)
Voltage regulator (OE replacement)
Battery

I had replaced the VR last summer then when I realized the battery was not getting a charge. Then everything seemed fine until the bearing started goin out in the alternator so I replaced it with an OE replacement. Then that didn't seem to charge so I replaced the VR again, cleaned up the firewall grounds and now I get the 15.6+v until operating temperature. I have not checked anything under the dash yet so just checking to see if anyone has had this specific issue.

Thanks for reading!

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Is it a race voltage regulator? Made that mistake once.

 

[twecomm]

Do you have some previous history on this condition you state ? It's quite normal that while cranking, the battery gets depleted some and once started and running, the alternator gets instructed by the regulator to apply a charging voltage until battery is replenished and then settles in at typically 13.6 ish volts. Sounds quite normal to me.

 

[Black_Sheep]

I fought overcharging on my GTX and eventually figured out that low voltage at the IGN terminal on the regulator was causing it. There was high resistance in the ignition switch causing a significant voltage drop in the ignition circuit. Since the regulator senses system voltage from the ignition circuit, it was trying to compensate and essentially full fielding the alternator. A new ignition switch fixed it…

 

[R. Shackleford]

Is it a race voltage regulator? Made that mistake once.

No not a race VR that I'm aware of. Part number says OE replacement

 

[R. Shackleford]

Do you have some previous history on this condition you state ? It's quite normal that while cranking, the battery gets depleted some and once started and running, the alternator gets instructed by the regulator to apply a charging voltage until battery is replenished and then settles in at typically 13.6 ish volts. Sounds quite normal to me.

I do not have any real info on if this was an issue before. All I know is I replaced the battery cause it was 25+ years old, the alternator cause the bearing was makin a lot of noise, then the VR due to the new alternator not seeming to charge. With the new VR it does the 15.6+ when cold. If I put the old VR back on no charge whatsoever. I only crank that starter for maybe 2 full seconds before she fires up on cold but it is the OG starter so maybe thats takin a bigger draw than I think

 

[R413]

Starter shouldn't be a problem with a new battery, especially starting so quickly.

 

[R. Shackleford]

Also I have never seen it go above 15.8v at the highest point, and that was revving up to 4k+

 

[RemCharger]

All I know is I replaced the battery cause it was 25+ years old,

!!!!!!!
Thats a new record in my books!

 

[R. Shackleford]

!!!!!!!
Thats a new record in my books!

Yeah surprisingly enough it was still holding a charge but getting weak