Charging system has been bad for years probably?

[KPB]

Hi,
70 Challenger 383, I have a feeling that the charging system has been bad for years now, but wonder how it was possible to not really notice it. I try to make a long story short. First of all, I don't drive very much unfortunately, maybe 1000km a season, usually I charge the battery and it lasts until I take it out again late November. This year it was harder to charge somehow, so I had the battery on my watchlist. Still, went for a 300km drive recently, with couple of starts, stop and go, idling. Worked fine. The next week battery was dead. So I started investigating. I thought something drains the battery maybe, but no loads registered on the multimeter.

I remember measuring the battery voltage while motor running a couple of years ago, just around 12,5 volts, suspicious as I had expected around 14, but well... had no issues, uncommon car, maybe that's correct...? And I forgot about it.

Well ammeter is like frozen, so likely disconnected, I found the shunt wire from alternator main plug directly to battery.
I measured alternator, main plug = battery voltage, field 1 (blue) 0 when ign/off, around battery voltage with ign/on. Field 2 (green) 0 when ign/off and barely some voltage with ign/on. I bypassed VR by connecting field 2 directly to battery while running, still get 12,5 Volts at battery. -> So I suppose alternator is dead.
But also VR seems bad, it has ground on the screw, ign voltage, but measuring between both pins at 20kOhms I get no reading (either 0.00 or infinite, can't remember right now).

So everything points at bad alternator and VR, would you agree? But how on earth was I able to drive it for years without noticing anything? A few 100 km.

Another question: can I somehow identify the current alternators amperage, to get the correct spare part?

Thanks in advance for any help and your opinions...

 

[Challenger RTA]

But how on earth

You answered your own question.

 

[Challenger RTA]

Posting the diagram below to help you understand you already might.

Check the grounds on the motor, chassis by the battery, alternator mounting bolts. Be sure they are clean and tight. The battery cable can corrode an 1" inside the insulation and cause a problem.
Once again Check alternator mounting bolts. I had a problem there I'll explain.

 

[Challenger RTA]

I had a car that was giving me charging issues as you explained. I change alternator from a car that I know was good also the battery. Never had a problem with the car I swapped the battery and alternator to. Before and after. Same problem went on for a few years. Cleaned all grounds, positive cables. Ground and positive connections. Took both fuse boxes out and cleaned. Not to mention the gauge cluster, computer connections, dash harness, engine harness. Rear harness check for shorts and grounds while it was still installed. Thought that will fix it. NOOP!

Understand this is a newer car and this is what the wiring consist of.

 

[Challenger RTA]

So now for the rest of the story. I Don't Quit! I'm smarter than a rock, I think!

So like I said I know the battery is good. Check yours's out first take it and auto parts store and have them check. Alternator same have it check. I would bet there good. Next the questions is that are the bulkhead connectors good and all the other charging connections. But one. I'll explain.
I was looking at the engine compartment. Going over in my head what I did and and what I missed. As I looked at the alternator positive connection and thought did that a few time. Looked at the mounting and adjustment bolts ok did that. As I looked at the motor where the alternator mount, mounts. A dim light came on and got brighter. Took the mount off. Cleaned mount, bolts, bolt holes. Put it back together and never a problem since. It's been years.
This might save you a lot of time. Think simple.

 

[KPB]

Hi,

I measured resistance of ground from battery to block, to alternator screws, to alternator case, to VR... Everywhere around 1 Ohm...ish.

Then from battery positive directly to alt main plug the same. I left out bulkhead path for now due to limited time and space, and as there is the shunt wire alt to battery anyway. So basically the circuit battery +/- to alternator +/- seems ok, no significant resistance.
Having battery voltage at blue field and shorted green field to ground there should be somewhere 13+ volts right? Still getting like 12.3 volts directly at alternator (main plug to case) as well as at battery.

Honestly I can't think of anyone here that still can benchtest an alternator... Just changing parts...

Bzw it's a square back alt, probably not correct for the year but should not be a problem?

 

[Challenger RTA]

This is for stock Mopar charging system.

1:With the key in the off position should have on the alternator output battery voltage.

2:The field wires should both read zero we should have no voltage.

3: If there is voltage at the field wires with the key off, there is a wiring problem.

4: If no voltage here at the alternator output with the key off then we likely have either a dead battery or we have a wiring problem or blown fusible link.

5: With the key in the on position. there will be voltage at the alternator output, it's going to be lower than what it was with the key off, because the entire vehicle is energized. The voltage drop is going to be more you can still you can see it went from
12 and a half down to 11.7. Still going to have near battery voltage.

6: What's important. With the key on. The field wires should have voltage. It won't be full battery voltage but it's has power coming to the alternator and it will be a lot less on one side and one side is high. That's the inlet so that's power going into the field windings.
The other one, the one that's low is the output from the field windings.
The output from the field winding is what goes back to the voltage regulator.
The voltage regulator on this is simply a switch ( Remember it needs a good ground to function.) all it's going to do is connect this field terminal here to ground and when it connects it to ground electricity then flows through the field windings energizing it and causing the alternator to charge.

 

[Challenger RTA]

7: Run test: This is for stock Mopar charging system.
Before doing the run test you're going to want to connect directly to the field output terminal on this alternator with some sort of a jumper wire. You can remove the existing field wire if it helps you to get to it. Use a jumper wire that comes back to the battery and it's not connected to anything right now. Have the voltage meter connected to the battery. Just checking battery voltage 12.3 volts there abouts. By touching the jumper wire to the negative terminal.
Just grounding it you can hear the engine loaded up because it's pulling a load and our voltage runs up to 14. That tells you that when the field in the alternator is energized it's charging. The alternator is good. Now you know that it's not an alternator problem at this point. If it's not charging you have a no charge scenario but this passes then you know it's the voltage regulator or some wire up until it it's most likely the voltage regulator and that's all it takes to diagnose the charging system on one of these
Here again If the any ground is bad or loose. it won't charge correctly or reliability. They become phantom grounds that just keep haunting you! That being the Voltage regulator ground, chassis ground, engine ground, Bolts, bolt holes, nuts and mounting brackets. 99% of the time there overlooked. The whole car is a ground.
That's all I have to say about that!