Charging intermittent, sometimes it does sometimes not

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cawcislo

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Took my 70 duster for a drive today. For the first 5 miles or so it was charging normal per my aftermarket voltage guage. 14 volts, then when I looked back at the guage it went down to 12 volts and stayed there for another 5 or so miles, no matter the rpm, at idle at stop lights etc. Then it came back to life and charged at 14 volts again for another 5 or so miles then it went down to 12 again. When I got back home I checked the wires at the alternator to see if I had a loose connection, but they seemed okay. Do I need to look for a pinched wire or loose connection somewhere else or could this be a dying alternator or dying voltage regulator? Let me know where I should start. Thanks.
 
Sounds normal to me. As the volts of the battery drop the regulator ups the voltage to charge the battery, once charged the regulator dropped the volts. I assume you don’t have electric fans and added draw items thus you’ll see more fluctuation on the gauge, running fans and such will keep the gauge pegged in the 14 area trying to keep the battery changed...
 
Chrysler regulators can vary the current with temperature, even the newer solid state ones.

An intermittent connection could also cause it. I have a finicky jumper wire bypassing my ballast that has caused me a similar issue.

The current will vary depending on electrical load, but the voltage should always remain between 13-14.5 except maybe at idle where it will drop slightly under 13v depending on load (headlights, fans, etc). But over 1k it should be over 13v.
 
If the 12v is happening at slow idle, IE at a light with foot on the brake, this would be normal. But voltage should come right back up to "nominal" 14V as RPM is increased and you start to drive

This sounds intermittent

Check field circuit, especially look for bad brushes, loose connections. Check voltage supply to VR IGN terminal.

Check charging path (output) Monitor output right at the alternator output stud and see if it goes down with battery voltage, or whether it "spikes up" at some point and battery dies down. This would indicate an intermittent open/ bad connection in the charge wire path, wire end terminals, bulkhead connector, ammeter, etc
 
Well my intermittent issue turned permanent. The whole drive today 20 plus miles was at 12 or slightly below. I had a new alternator as a backup so I decided to swap it in. No change runs at about 12 to 12.1 volts no matter the rpm. Checked connections at multiple points and didn’t see any frayed, loose broken connections. What should I trouble shoot next?
 
Start as if a new problem. Troubleshoot it

I treat the charging system as several sections

1...Charging path. This is the main charge line/ path from alternator output stud to battery. OEM path is output stud---BLACK wire to / through bulkhead connector---to ammeter---out ammeter on RED---through bulkhead---fuse link---to battery

2...Field path. The VR gets power from the IGN1 "ignition run" and the alternator field gets power from the same place.

VR MUST be grounded.

Alternator field current path is from ground--through VR---out on GREEN--to one field---through field---to light blue to IGN1---key/ etc/ battery

TO TROUBLESHOOT you need regular tools, a 12V test light, and multimeter, and some alligator clip jumper leads

IT IS A GOOD IDEA with a "new" / rebuilt alternator TO CHECK that neither field terminal shows continuity to ground. Ohmeter should show infinity/ open from either field to alternator case.

Remove GREEN field wire at alternator. Clip an jumper to the disconnected alternator field terminal, turn the key to "run." Check voltage at light blue field terminal, leaving it connected. Should be "about same as battery." If you disconnect/ reconnect jumper in quiet and subdued lighting, you should see and hear a small spark, showing current through the field circuit.

You can double check that by setting your multimeter up for high current (10A or 20A scale) and put the meter in series with the jumpered field terminal to ground.

If this seems good so far start the engine, with meter monitoring battery voltage

Slowly bring up RPM watching battery voltage. Try not to allow battery above 16V. If no change, move meter to alternator output stud and ground. Recheck. If voltage goes way high, the charge path is open, such as bad connection at ammeter/ bullkhead terminal. If voltage stays 12V or lower, the thing is not charging

At that point recheck that you have power to and current through the field and if so, replace alternator

IF SO FAR ABOVE causes a charge, this shows the alternator is good. Reconnect everything "normal" and recheck. If no charge, now we check field circuit and VR

With everything re-connected normal, remove VR connector. "Rig" a jumper between the two VR connector terminals. This can be done with small machine screws. This puts full battery power from key to the GREEN wire. So disconnect the light blue field wire and jumper that alternator terminal to ground. Again run engine, monitor battery, see if it charges. If it does charge, and you are CERTAIN the VR is properly grounded, replace the VR

VR GROUNDING. Absolutely MUST be grounded. Scrape around mounting holes on firewall and VR and mount using star lock washers
 
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CHECKING FOR VOLTAGE DROP

Once you have fixed the basic "no charge" problem, time to check for system voltage drop to make sure it will not over charge (over voltage).

Turn key to "run." Connect meter to "as close to" VR IGN terminal as you can without disconnecting wiring. This is likely the IGN terminal on the ballast resistor. Stab other probe into top of battery + terminal. You should read very little voltage, the less the better. If you read more than .3V (3/10 of 1 volt) you need to chase down why. Typical drop is in the bulkhead connector terminals, the ignition switch connector, or the switch itself

ONE WAY to "fix" this problem is to add a relay for underhood "ign run" loads. Electrically cut the (usually) dark blue "ign1" "Ignition run" wire coming out of the bulkhead. use the bulkkhead end to trigger a relay, and connect the remaining cut end to the relay load contact. Feed the relay contacts with power/ fused/ breaker off the starter relay "big stud." Ground the remaining relay coil. You can feed this through an unobtrusive switch for an 'easy" anti-theft switch

VR GROUND. The VR ground path can have voltage drop as well. To check, do this:

Run this test with engine running at "low to medium cruise" (fast idle) and with battery/ engine warm and normal. Run test first with all loads off, and again with heater, lights, etc, turned on

Stab one probe into the VR mounting flange. Stab the other into the top of battery NEG post. As before, you are hoping for a very low reading, zero is perfect. If yourread more than .2--.3V improve the grounding from battery/ engine/ firewall.

A good way to do this is to buy a short starter cable, "eyelet to eyelet." Look at your pass front head (v8) The same holes are on the REAR of the driver's head. Use a short bolt, connect the cable back there. Connect other end to good solid bolt through firewall, or to one master cylinder mounting stud.
 
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If the alt has a lot of mileage, I would suspect the brushes are worn out. Just like an electric drill that has brushes, the brushes eventually wear out.
 
If the alt has a lot of mileage, I would suspect the brushes are worn out. Just like an electric drill that has brushes, the brushes eventually wear out.
With a 50 year old car whose knows how many miles are on anything.... now that I swapped in a new alternator my problem should have been fixed (unless the new alternator is faulty). So I’ll have to troubleshoot per 67dart273’s instructions above. Just waiting for the weather to cooperate. We got 6 inches of snow yesterday so I’m not too keen to be troubleshooting in the cold.
 
Update. Tested alternator. With the green field wire unhooked and that field terminal on the alternator grounded just off idle the volts started climbing quickly to 14..15... so alternator does charge. Looks like VR.
 
Update. Tested alternator. With the green field wire unhooked and that field terminal on the alternator grounded just off idle the volts started climbing quickly to 14..15... so alternator does charge. Looks like VR.


Make CERTAIN VR is grounded, and that connector is "tight." "Work" it in/ out several times to scrub terminals and "feel" for tightness. Sounds like you are on right track
 
So I did one last double check of the voltage regulator, unplugged it and plugged it back in, checked the ground, there's a star washer thee and its grounded just fine. No change. Swapped in a new voltage regulator, boom fixed. Volt meter showing just under 14 volts at idle and 14 as i get more rpm. Thanks for the help 67dart273.
 
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