Alternator Overcharging maybe?

[Noman]

I have a 77 M885 got it about a year ago and have slowly been fixing this and that as time allows. My current problem is it maybe over charging and I can't figure out why. So this is what I have, at idle I get 12.5-13 volt at the battery which is to be expected with a 70s charging system, but when you bump up the RPM I quickly get 15.7 volts at the battery. What I have done so far; if you unplug the regulator then it drops to battery voltage, a new regulator gave me 15.6 volts at the battery so I put the old one back in and returned it, I checked and cleaned ground to the regulator even ran a jumper to negative on the battery no change. I don't want to swap alternators just to test mine and have no wish to tearing in the wiring harness with out good reason. So are they known for running a little hot in the voltage(what is your voltage at the battery)? I know that this is not ideal but is it really a problem. Oh and yes I do have a the amp gauge bypassed. Thank you and this is a great site wasted many an hour on it.

P.S. I have been thinking about just putting in an AC Delco 12si and being done with it, has anybody done this?

 

[gimpyrobb]

Charging should be 14.4. Why not take your alt to a starter/alt/gen shop and have it tested?

 

[MatthewH]

Sounds like either a bad connection in the wiring, or a faulty alternator. My M887 did the same thing. New volt reg, made sure it had a good ground, and a new alternator solved the problem.
Alternators are cheap for these trucks, cheaper than that Delco 12Si you want to make fit. Last one I bought was like $60 with a core

 

[Carlo]

Are you taking volts at the battery or alternator?

 

[tennmogger]

Have you checked your batteries? A high resistance cell or cells will not load the regulator until voltage rises. The alternator is able to put out over 15v so it's probably good, IMHO. You swapped regulators so that might rule out regulators.

[Edit] took out my reference to 24v, duh]

Bob

 

[Noman]

Update - I went and double checked my battery passed a load test with flying colors. I also check my remote voltage and it came up the same as the battery. So I think I can rule out any wire fault. Lastly I did find this page last night (http://www.allpar.com/fix/codes/sensors/charging.html) and did the the checks on the page passed all of them. Haven't taken the alternator to a shop yet because at the moment this is my day driver and the closes thing to a alternator shop is the local parts with the kid behind the counter who has never see any thing older that a 97 civic. So have not ruled that out but I will have to pull the alternator in the parking lot and that has to wait tell the weekend.

In the mean time I ran a jumper of the hot side of the battery in to the cab so I can use my multimeter while I drive around maybe this will give me some insight to the cause. I will keep every one updated on my redneck volt meter.

Thank you

 

[74M35A2]

If the alternator has a remote voltage sensing wire, that may be dropping voltage, so the alternator is increasing it's voltage to compensate. Sorry, I don't know this vehicle or what alternator it has. Most people are happy with their Delco conversions though in other areas of this board. Fully charged battery voltage is 12.8V, so anything over that is charging, but, it should never be 15.0V or higher. Some regulators are temperature compensated, but likely not in the 70's era. Does your bypassed ammeter have anything to do with it?

I had a Mustang in which the regulator stuck full on, and it caught the harness on fire. Get it fixed quickly, you are boiling your battery.

 

[Kerogane]

We had a lot of trouble with these trucks losing ground form the neg. cable to the radiator SUPPORT causing overcharging. Should be an extra wire on the ground cable held to the rad. support with a 1/4 inch bolt.

 

[pigpen60]

Check the plug at the voltage regulator, if the voltage sensing wire is broke/whatever it will charge wide open

 

[armydodge]

Its not enough to bypass amp gauge alone..
Have you run another wire from alt to starter? heres a good info link. http://www.allpar.com/history/mopar/electrical.html
See paragraph on wiring harness corosion and particularly, converting to 80's style wiring.
If you want you can measure volts/amps into bulkhead connector (direct from alternator) and out of bulkead connector and see whats lost between there and ignition/amp gauge.
Kerogane is 100% right about grounding to rad support. Do it if you haven't already.
Went through this on my 75 and fixed it by cleaning all grounds, making SURE voltage reg is well grounded at firewall, and running the additional wire with fusible link to starter relay.This takes care of dumping all those amps through the firewall and even if those wires are still there, provides another path for juice to get directly where it should in the first place.
The volt reg works by putting out full volts and grounds itself intermittently to keep volts where they should be. If the reg cant achieve a good ground... volts will be too high and cook your battery.
Let us know how its going, this can be frustrating. I have more info if you need it

 

[busbart]

Well, I had the same problem, (actually still have the same problem) and I found that Dodge has in the under the hood wiring a point where a couple of copper wires are welded together. from that point goes a voltage sensing wire to the external voltage regulator. Or at the weld or in those wires by now you find a lot of corrosion (black or green wires) which causes extra resistance= the voltage regulator senses too little voltage, and tells the dynamo to sent some extra volts to the battery and with that is cooking the battery.
I changed out the regulator and the dynamo for new ones, and that did not make any difference.
so now I'm having a new set of electric wiring ready to install, and then I think my problems are gone.

 

[WVCB]

Lots of good info here: http://www.madelectrical.com/electricaltech/amp-gauges.shtml I did the fix on my 77 and it solved several issues.