'73 Charger ammeter only shows charging when RPM is increased

[Charger Fan]

Recently had to replace a bad alternator on '73 Charger. I noticed today when the car is running at idle speed the ammeter shows discharge. If you give it some gas and raise the RPM the needle swinger over to charge but drops back to discharge when you take your foot off gas. Any suggestions where to start troubleshooting?

 

[BeepBeepRR]

Voltage regulator would be my next guess.

 

[toolmanmike]

Idle speed? ANy electrical accessories on? I can watch my turn signals blink on both of my Mopars. The alternators don't have much output at idle.

 

[Don Frelier]

Sounds pretty normal just depends on how severe the discharge is.

 

[kiwigtx]

My fuel gauge needle moves when I push the loud pedal. Alternator require a tad over idle speed sometimes if there is significant electrical load.

Not much...but a little helps.

 

[Rusty knuckles]

Voltage regulator for a start. Could be blown diodes in the alternator too. I had that happen once. Charged down the highway but not in town.

 

[w.Hudson]

Compare pulley size on the old alternator verses the replacement alternator.

A smaller alternator pulley will help it charge at idle speeds as it increases alternator speed.

 

[BB69R/T]

My Recently had to replace a bad alternator on '73 Charger. I noticed today when the car is running at idle speed the ammeter shows discharge. If you give it some gas and raise the RPM the needle swinger over to charge but drops back to discharge when you take your foot off gas. Any suggestions where to start troubleshooting?

I had a similiar problem. The first place to start is check the voltage at the battery with the motor at idle. It should be in the range of 13.5 to 14 votls. 2nd place is to check voltage (idle) at the alternator. you should get similiar numbers at the alternator. 3rd would be to check voltage drop (at Idle) between + post on the alternator and + post of battery. then check voltate drop between alternator case and - side of battery. numbers should be less than 1 volt. my ammeter does the same thing. I installed a volt meter as well, and when ammeter needle is just left of center, my voltmeter is reading a solid 12. 2 volts. hope that helps

 

[oldkimmer]

Put a know good battery in it. Kim

 

[RJRENTON]

Recently had to replace a bad alternator on '73 Charger. I noticed today when the car is running at idle speed the ammeter shows discharge. If you give it some gas and raise the RPM the needle swinger over to charge but drops back to discharge when you take your foot off gas. Any suggestions where to start troubleshooting?

IMO......TURN UP THE IDLE SPEED AN BCH...about 800 rpm in neutral would be a good starting point.....
BOB RENTON

 

[Geoff 2]

Fit a smaller alt pulley.