Low output at idle w/ac on?

[mopower76]

I know I’ll probably get some crap from some of you guys, but this is about my fifth Avenue and not A Body!

I believe it has a factory 65 amp alternator I could be wrong, but it is the original alternator put on in 1987. This car has 40,000 original miles but had been sitting since 2003 when the original owner passed away.

I’ve mechanically gone through the entire car and the electrical system checked out fine a year ago when I first started daily driving the vehicle now in the last two months while driving with the AC on or any other accessories playing at a stoplight the voltage drops down below 11.
While driving, it’s putting out 13 to 13.5 V.
I guess my main question is is there an upgraded alternator that will bolt on? I know I’ve used high output Police spec alternators in the past and smaller Denzo units on engine swap cars over the years, looking for quick easy over the shelf and reliable with high output at idle!

Thanks for helping in advance!

 

[Murray]

Alternator should be putting out about 14.4, you are low. Do you have a square back alternator with electronic VR? This should work well at idle. Sometimes we can cheat a bit by turning up the idle a little.

 

[MadScientistMat]

There was a 100 amp truck alternator introduced around 1989. Should be a pretty direct swap if you use the V belt pulley.

 

[Bewy]

If the original alt was 65 amp, & there have been no electrical add-ons, then it doesn't need a bigger alt. A bigger alt is heavier & uses more hp.

You could have something draining power; alt may need to be checked; they have carbon brushes like an elec drill. A/C compressor could be faulty/dragging causing an increase in current consumption.

 

[Kern Dog]

While driving with the AC on or any other accessories playing at a stoplight the voltage drops down below 11.
While driving, it’s putting out 13 to 13.5 V.
I guess my main question is is there an upgraded alternator that will bolt on? I know I’ve used high output Police spec alternators in the past and smaller Denzo units on engine swap cars over the years, looking for quick easy over the shelf and reliable with high output at idle!

Thanks for helping in advance!

Alternator should be putting out about 14.4, you are low. Do you have a square back alternator with electronic VR? This should work well at idle. Sometimes we can cheat a bit by turning up the idle a little.

I have noticed the same thing in my '70 Charger. The engine side harness was replaced 11 years ago. I did the MAD bypass and changed the instrument panel to a Dakota Digital with a voltmeter.
Idling with the A/C on, headlights and foot on brake put the voltmeter below 10 volts. I have the stock 60+ volt squareback with the stock type electronic VR.
I would just default to a Denso alternator but I don't know if they came with dual groove pulleys. I'll check with RockAuto and report back....

 

[mopower76]

I can’t remember what the number of groves or the year to look for the denso alt to use… it’s been a long time now!

It is original electronics with a voltmeter, and I’m sure the alternator is just slowly dying out. Like I said before, this wasn’t happening with the same accessories running just a month ago or less.

I haven’t gotten the alternator checked yet but again I’m just looking for something with a little better output at idle. It will have an aftermarket audio system runs high current amplifiers nothing outrageous, small clean and simple.

I like the idea of the 100 amp truck alternator, I’ll look into that! Thanks for the suggestions everyone!

You guys are the reason I always post electrical issues on this web board no matter what the style car!

Mopar to Ya!!!

 

[str12-340]

Is there not an idle kicker that bumps up idle speed when you turn on the AC? If there is one is it actually functioning????

 

[AJ/FormS]

WHOA!
do a full field test.
Make sure the battery is up to voltage.
Put a voltmeter on it.
Disconnect the field wire off the alternator, it should be blue.
Run a jumper wire (at least 14ga) from the battery to the wire you just took off.
Start the car and check the output voltage, at idle, theb at 2000rpm..
Change your voltmeter from DC to AC and repeat.
return the engine to idle, remove the jumper, and reconnect the field wire
Results;
1)There should NOT be any A/C in the system which indicates a blown Diode in the Rectifier-section. The alternator is not yet junk, you can take it apart and replace the diode fairly easy........ if you can find a diode, lol.
2) As for DC output, IDK the factory specs anymore so I'll guess.
At Idle I want to see at least 2 volts higher than what the battery has at rest.
At 2000rpm, I'm expecting to see over 35VAC.

If your alternator can do this, look elsewhere.
like maybe the throttle-kicker.

 

[67Dart273]

Some ting wong. I do not believe those cars had the old style full current ammeter, and it SHOULD have a square back. Either there is something wrong with the charging system, AKA wiring, ?? or somehow a rebuilt ended up on the car that is WAY below amperage, That is, maybe you really have a 35-40 alternator thanks to some cheap rebuilder.

I would get into the manual and run a field test. Turn "stuff" on to cause a load, and then monitor battery voltage vs the output stud of the alternator, which will tell you some about voltage drop from the alternator to the battery.

Also with a bunch of accessories on, jumper 12V to the field and see if the low RPM voltage keeps up. Be careful with this and monitor battery voltage while doing so. Don't (try not to) let it climb above 15.5-16 or so.

 

[mopower76]

Thanks for these suggestions!!! It’s been a rough couple of weeks, I’m working on multiple projects, getting one ready for the Duck Tape Drags in Tucson next month and another ready to sell and on my way home from my 40 hour, Whitey (5th) lost all coolant from the top of the aluminum timing cover!
In all my years I’ve never experienced this happening. It must have had corrosion I don’t see when replacing the timing chain and water pump.
So… the 5er is parked for now. Too much on my plate to mess with it right now.