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Charging Issues - Round Back Alternator Question
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Author:  REBEL [ Sun Oct 13, 2024 4:35 pm ]
Post subject:  Charging Issues - Round Back Alternator Question
Hi All,
Been a while but I have a question. I have a 1968 Valiant with an original Slant Six. I was having charging problems this season. The car ran dead a few times. I had the battery tested and checked (1 yr. old battery). I picked up a new alternator, put in in and everything starts and has power but I am checking over things with my voltmeter to make sure everything is charging.

My field regulator spade is on the bottom blade of the alternator. My question is should the other blade be grounded?? I have looked and I cant see a definitive answer for my case and model on this.

Here are my readings:
With the key off I get voltage at the output lug of the alternator and no voltage at the field regulator blade. Key on I get around 10.5 V on the output lug and nothing on the field regulator blades. I have continuity from the field regulator connection at the battery over the to the other end of the wire at the Field Reg box. When I start and run the motor the Battery hangs around 12.2 BUT when jumping the field regulator spade on the back of the alternator to ground I don't get engine load or a voltage bump.

My questions are Does the other blade need to be grounded on this alternator for some reason. Am i looking at a bad voltage regulator or bad alternator?

Attachments:
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Author:  SlantSixDan [ Mon Oct 14, 2024 10:57 am ]
Post subject:  Re: Charging Issues - Round Back Alternator Question
Quote:
My field regulator spade is on the bottom blade of the alternator. My question is should the other blade be grounded?
Yes.
Quote:
With the key off I get voltage at the output lug of the alternator and no voltage at the field regulator blade. Key on I get around 10.5 V on the output lug
Should be at or damn near battery voltage. Check for high resistance between alternator and battery and/or faulty voltmeter.
Quote:
I have continuity from the field regulator connection at the battery over the to the other end of the wire at the Field Reg box.
I guess you mean "I have continuity from the field connection at the alternator over to the other end of the wire at the voltage regulator". Good, and how much resistance do you have between those two points?
Quote:
When I start and run the motor the Battery hangs around 12.2
Discharged battery.
Quote:
BUT when jumping the field regulator spade on the back of the alternator to ground I don't get engine load or a voltage bump.
Unclear here whether you mean the second/'extra' field terminal not currently connected to anything, or the active/in-use field terminal.

With one of the alternator's field terminals grounded and the other one connected to the alternator's output stud, you should see your battery charging. Don't rev the engine very high in this condition.
Quote:
Does the other blade need to be grounded on this alternator for some reason
Again, yes.
Quote:
Am i looking at a bad voltage regulator or bad alternator?
We won't know until you ground that second field terminal and run some more tests.
Author:  REBEL [ Mon Oct 14, 2024 3:18 pm ]
Post subject:  Re: Charging Issues - Round Back Alternator Question
Got back out and grounded the other terminal on the alternator and retested everything. Here are the results.

Key off / Output Lug on the Alternator tested again is now at 12.4

The Field Wire from the alternator over to the Voltage Regulator has continuity and hangs around 0.2-0.4 ohms resistance.

I grounded the other terminal on the back of the alternator to the alt body/bracket and started the car. It charges BUT it shot up to over 16v in about a minute at high idle so I quickly shut it off.
I cleaned bolts and areas where the voltage regulator mounts to the firewall and tightened the connections. I also checked the continuity on the ballast resistor to the IGN wire on the voltage regulator.

I am tossing the schematic from my old chiltons in case it will help someone help me, any input is appreciated. Thanks.

Attachments:
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Author:  REBEL [ Tue Oct 29, 2024 5:50 pm ]
Post subject:  Re: Charging Issues - Round Back Alternator Question
I recently got back to looking at my Valiant. I was getting charge out of the new alternator with the one side grounded as I stated in the earlier post but it was overcharging. I suspected a bad voltage regulator and replaced it with a Standard Parts brand unit. Same 2 wire style as the old (the Black Box type). I regrounded the the box to the firewall, tightened the ammeter wires on the back of the dash and after all that I am back to getting NO CHARGE from the alternator. I am not hearing a load put on the engine and the car is discharging the battery as I drive.

I have checked resistance on the field wire as I previously talked about and it was good. 2 questions here:

1. How does the system work? is it voltage or ground applied to the field wire through the box.
2. Where does that signal (be it voltage or ground) come from? I see the wire to the voltage regulator coming from the ballast resistor but I need to know where these wires coming into the ballast resistor and feeding the voltage regulator come from to help understand the problem here. (Do they come from the coil and ign? how do I test for shorts?) Any help is appreciated, thanks.
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