Battery Not Charging

[boboh1]

At the battery terminals I get a voltage reading of 13.3 when fully charged. When the car is running I get a reading of 12.8 volts. I turned off the car and got a reading of 12.8 volts at the field wire with the key turned on. I have a new alternator, new engine compartment wiring, new voltage regulator and new battery cables. Have not replaced the battery from the previous owner. Any ideas? 1969 Dodge Coronet, 383 engine. Thanks.

 

[Coelacanth]

Assuming your alternator is outputting properly, get a hygrometer and check the battery for a dead cell. If your battery is a sealed unit, there are inexpensive devices to test your whole charging system. I bought this unit several years ago, you can find something similar; Foxwell BT100 Battery Tester:

https://www.amazon.com/FOXWELL-FBA_BT100-Analyzer-Automotive-Directly/dp/B01ANF1BRW

 

[PlymCrazy]

Your question is a little unclear.
Why are you concluding the battery isn’t charging?
Are you using a multimeter to measure your voltage?
What is the voltage with a multimeter at the battery with the car running?
A good voltage range with the car running at high idle you should see 13.5ish to 14.5ish volts.

 

[Kern Dog]

The OP explained it clear enough for me. If the running voltage shows less than it measures with the engine off, the system isn't charging.
His question is why.
Poor grounds, not enough grounds, bad voltage regulator, adjustable regulator not properly adjusted, failing alternator....

 

[Don Frelier]

If he has 12.8 volts on the field wire it should be charging. So most likely a bad alternator.

 

[boboh1]

Yes the battery is not charging since I measured the voltage with a multimeter and with the car running only 12.8 volts. Could a brand new alternator be defective?

 

[boboh1]

Maybe running a ground wire from the alternator case to a good ground connection may solve the problem?

 

[MWbirdLOVER70]

Yes the battery is not charging since I measured the voltage with a multimeter and with the car running only 12.8 volts. Could a brand new alternator be defective?

Bad diode in alternator New parts fail this day and age for classics? Nah lol

 

[davek]

take your alternator to a part store and have them check it. You did say it was new.

 

[Don Frelier]

If it's a new alternator it may have both field connections ungrounded.
Check each terminal for ground. If both are open you need to ground 1.

 

[Coelacanth]

Most auto shops can bench test a battery or alternator, good advice there. Or buy an inexpensive tester and do it yourself. That's how I learned the starter in my '05 Magnum, which was cranking slower and slower, was the source of failure in that car's charging system...and not a failing battery or alternator that's not charging enough and causing the battery to get weaker and weaker. The dying starter was needing more and more amps to start the car.

 

[twecomm]

If the alternator you replace was a single field round back model, you may have been sold a square back dual field alternator that requires grounding one of the terminals. Sounds like what Don Frelier suggests is worth investigating. Check out this video.. making dual field alternator work - Google Search

 

[boboh1]

Thanks. I’ll check out the grounding.

 

[boboh1]

Turns out my alternator only has the one single field connector.

 

[rickseeman]

From the description you gave (nothing ever under 12.8 volts) I assume that the car starts, runs and everything functions perfectly?

 

[boboh1]

Can’t say for sure. The car has various other issues and all I can do at this time is start and idle it in the garage for now. I just so happened to decide to see if it was charging or not.

 

[sam dupont]

the rusty circle in the center of this photo is the rear armature bearing. It becomes magnetic when the alternator is being spun by the running motor and a field test is to touch some steel to it. Take care to not touch anything else.

 

[boboh1]

I touched that part with a screwdriver when the engine was off and I did feel a slight magnetic pull.

 

[RJRENTON]

the rusty circle in the center of this photo is the rear armature bearing. It becomes magnetic when the alternator is being spun by the running motor and a field test is to touch some steel to it. Take care to not touch anything else.


View attachment 1710020

WRONG.....it is the rear rotor bearing, not armature bearing, and is totally isolated from the rotor's magnetic field by design. Any current that would be present would cause the bearing to fail due to shaft current flowing thru the bearing to ground. If you suspect a grounded rotating field windings, measure the resistance to ground thru either slip ring to the shaft using a high resistance megohmeter.....it should be infinite....no resistance.
PM me if you don't understand......
BOB RENTON

 

[BB69R/T]

Check your voltage output at the alternator with the motor running. Mine reads between 13v and 14.5 volts consistently. make sure you have a good ground at the voltage regulator ( I am running a mechanical VR) with the firewall. I had a similar charging issure, and at this point it appears the starter relay was loose, so i cleaned the mounting surfaces and used new tooth lock washers and tighented the bolt. Ive had good output numbers so far. my ammeter is reading properly between D/C now and I also have a voltmeter inside the car and it reads a consistant 13 volts when I drive the car.. Good luck.. I hope this helps. you can also check for voltage droppage between the + side of the alternator and + side of battery, and voltage drop between - side of battery and alternator case. 69 Dodge Coronet R/T