Alternator overcharging

-
Go Mango

Go Mango

Never enough beer...
Joined
Jun 3, 2018
Messages
942
Reaction score
1,646
Location
Avon, Indiana
Recently replaced the alternator on my 70 340 Dart. The new one has a smaller pulley and now I'm getting 17.3 volts at fast idle. Could pulley size be causing this? I've checked the wiring, and have repaired/ replaced some of it myself. I've got .1 ohm resistance in the charging circuit, which to me is pretty good. I've also checked for voltage drop with the engine off, which was also negligible. Maybe need a new regulator? Everything is grounded very well.
 
most of the overcharging problems I delt with were traced to the bulkhead connector check for burned or melted connections and corrosion . make sure your regulator is grounded real good .
 
I bypassed the bulkhead connector with both wires on Monday because it was definitely a bad connection. The voltage regulator has the same potential to ground as the left cylinder head and the negative battery post. Bypassing the bulkead connector solved the melting wire insulation under the dash, but not the overcharging. To me, 17.3 volts at idle is asking for a battery explosion.
 
That VR is smoked! sub in a replacement, before it sets your car on fire.

No, the pulley size is not the source of this issue

The VR is either not finding the battery, or it's hung up WOT, or, I suppose there could be a dead short from battery to ground thru a device or connection somewhere, sending the VR into overdrive, but then the smoke would be the telltale,not lol.

So shut the engine off and look for an off-draw; if none found, replace the VR
 
Last edited:
I'm replacing the regulator as soon as I get off work. And I've checked, can't find any ,"off draw"
I'm no automotive electrician, but I am a real IBEW local 481 industrial electrician. This one has got me fuddled, but I agree about the regulator.
Thanks!
 
Thread moved to "Electrical and Ignition".
 
If this is a solid state regulator it very likely is NOT a bad regulator

HOW did you check voltage drop? The way I do this is follows:

Access as close as you can get to the regulator IGN terminal. Do not disconnect anything, as you want the current load to be "as normal." Usually, the ballast resistor "key side" is what you want. Probe that and the battery POS, with key in "run." ANY drop there is added to the VR nominal set point of 14, AKA if you read 1.4V that would be a charging figure of 15.4.

ALSO CHECK ground drop. Run this check running at "medium cruise" RPM both with accessories off, battery "normalized" and thane again with heater, lights, etc, running

Stab one probe into the VR mounting flange. Stab the other into the top of the battery NEG post. As above, you want to see the less the better, zero would be perfect

IN RARE CASES I've seen claims the battery itself caused this problem, so you might swap in a good know battery to test
 
It looks like an older voltage regulator.
The steps you suggested are exactly what I did yesterday afternoon. Never thought about the battery though. I'll try that if a regulator doesn't help.
Thanks
 
Not sure an alternator can overcharge. The voltage regulator's job is to limit the voltage it receives. Sometimes you will find a bad VR, but usually you will find it is not grounded well enough. I typically run a new ground wire rather than relying on VR to body ground. Also, virtually every Mopar I own had worn VR mounting holes and the VR doesn't mount as tight as I would like.
 
The regulator mounting screws have the same potential to ground as the negative cable to the cylinder head. But I'm going to run a new wire anyway. Worth a try.
Thanks
 
Mopar to ya said:
Not sure an alternator can overcharge. The voltage regulator's job is to limit the voltage it receives. Sometimes you will find a bad VR, but usually you will find it is not grounded well enough. I typically run a new ground wire rather than relying on VR to body ground. Also, virtually every Mopar I own had worn VR mounting holes and the VR doesn't mount as tight as I would like.
Click to expand...
I think that's only approximately correct;
as I understand it;
the VR reduces the fieldcoil strength in response to the voltage it is reading on the sensing wire. If the sensing wire voltage is low, it increases the fieldcoil strength, by grounding it. The Alternator immediately goes to WOT. The VR sees the sensing voltage going up, past it's internal set point, and throttles back the fieldcoil by opening the circuit, and the alternator stops charging completely,( well not completely completely,lol) . This cycle happens IDK how many times per minute, but the battery sees the average of WOT and way less than WOT, as this is going on; which is supposed to be about 13.2 to 14.2 on most systems, GMs not included; they run closer to 15.2.
If you momentarily ground the green wire coming out of the fieldcoil, you will see what your alternator is capable of putting out, with whatever battery voltage is coming down the blue wire, and at idle. This is called full-fielding. You will probably see the 17.3 that was listed in post #1. The VR was full-fielding. The only way it can do this is if the ground back to the Battery is 100% A-OK. If the ground was open circuit, it would not charge at all. If the ground was poor, anything can happen, so you always start by proving the ground, when diagnosing a low-charge. Not so with a 17.3 charge rate; that is about max, at idle, with a fully charged battery.She's stuck on WOT.
 
Last edited:
Go Mango said:
The regulator mounting screws have the same potential to ground as the negative cable to the cylinder head. But I'm going to run a new wire anyway. Worth a try.
Thanks
Click to expand...

Yes, that is how it is supposed to ground, but they never seem to. Both my running Mopars have wires run for ground and my Duster will also when I get it running.
 
The regulator mounting screws have the same potential to ground as the negative cable to the cylinder head. But I'm going to run a new wire anyway. Worth a try.
Thanks
 
I'm guessing the field wire off the alternator should NOT have continuity to ground?
 
So with the field wire unplugged, and the regulator unplugged, I have continuity to ground. Spliced in a new wire, fired it up, and eureka! Problem solved! 12.47 volts at idle! Thanks for all your help guys!
 
Go Mango said:
So with the field wire unplugged, and the regulator unplugged, I have continuity to ground. Spliced in a new wire, fired it up, and eureka! Problem solved! 12.47 volts at idle! Thanks for all your help guys!
Click to expand...

I would have suggested that, but the readings you indicated (charging) usually that problem will drive the battery "sky high" depending on battery charge, etc. Some guys have blown out lamps, headlights, even
 
You must log in or register to reply here.
-

Back
Top