Underpowered alternator

[JBFury]

So I've got the stock alternator on the Fury and I believe it's 60 amps if not mistaken. I have working A/C and when I'm driving with my headlights on, A/C on and come to a stop I can watch my dash lights start dimming while waiting for the light to change. Once I'm moving everything brightens back up and we're good. I've tested the alternator, the battery and recently installed a new voltage regulator. There are no broken or damaged wires, belts are all new and tight. The alternator charges the battery when the A/C is off nor will the car won't die when it's on, but the voltage drops sub 13 with medium or high blower speed. I've gone as far as to remove the alternator and battery and have each tested at various supply stores in my area, all confirming they are both in good working condition.

My question is this, is it possible that the alternator is simply underpowered and bumping up to a 75+ amp alternator would solve the issue? I've also considered it could be the A/C clutch but wanted to get some background on alternators for these cars and if they historically have had issues with being underpowered for cars with accessories.

 

[Aspen500]

It is completely normal to have the lights dim, blower fan to run a little slower, etc. at idle. Also, keep in mind the car runs off the battery, the alternator is only to maintain the battery charge. I know your battery is good (you had it tested) but a weak battery will cause the lights to dim even more at idle. As long as the battery voltage is maintained above 12.6 volts, it's all good.

Even a battery that's too small can aggravate the situation. That's why vehicles with high system loads need a bigger, higher amp hour battery, which has little to do with the CCA rating. It's why some cars are fine with a 50aH battery, but others require say,,,, a 90 amp hour or more one. (numbers just randomly chosen).

 

[JBFury]

Thanks Aspen500, the battery I have is a cheap no name budget battery with 450 cold crank. May upgrade and see if that helps. I am glad to know that's not uncommon. Much appreciated.

 

[Mikes5thAve]

If the dimming is very noticeable it's a sign of a bad voltage regulator.
The alternator is more then enough for a stock car. It's when heavy electrical loads are added like police use, a lot f stereo equipment etc that it's time to look for an upgrade.

 

[BudW]

There are three things to increase alternator output:
More copper windings inside either field, for stater or both).
Increase the amount of voltage needed to increase the field. Cars have a max voltage of 12 volts (varies from 0 to 12 volts), but if one use 24 volts you "could" double the output amperage.
Increase the alternator RPM.

Most cars - the alternator will just put out enough amperage to power the vehicle at idle (if that) then start putting out 14ish volts around 1500 RPM. What you describe might be normal - but won't know until more testing is done.

Chrysler alternators have three phases. The other two (or one) phases will still work if one (or two) leg(s) fail - but alternator output will be at 66% (or 33%) of rated output. Most people will not notice if one leg (or phase) of alternator goes out, but when the second leg goes, then people start to notice things are not quite what they should be.

Going back to your question about alternator output. A person can install a 100a (which is optional for all FMJ's), 120a (for some M's) or even an aftermarket 200 amp alternator - but you do risk other problems.
My '77 FSM shows (for the alternator output wire):
Standard - 14 gauge
65a option - 12 gauge
100a option - 10 gauge

My '86 FSM went AWOL so not able to look up the details on it - but wire sizes are larger. Either way if your electrical load hasn't changed (monster stereo system, electric cooling fans (or whatever) I'm not sure you will want to upgrade the alternator (and corresponding wiring harness) for your car.
Don't forget the fusible link is also rated for alternator amperage as well. If you have a power draw more than fusible link is rated for, it will melt.
The fusible link is the bigger issue, but even pumping 100ish amps through a normal wire rated at 40 amps could result "in a bad day". The last thing we need is a fellow member to ended up using his car "as a BBQ" (intended, or not).

If your alternator was tested and it tested OK - then I have no reason to doubt the findings. I will say that Chinese voltage regulators are junk - which is about all you will find new now days. The original voltage regulators are, for the most part, reliable (don't fail that often) and finding a good used one would be a better bet (or finding an NOS regulator).
The alternator is a somewhat more common item to fail on our cars - but even then it is not as often as other brands are.
BudW

 

[Duke5A]

The factory charging system on these cars was junk even with everything functioning as it should. Swap it all out for a 60 amp Denso alternator. I ran one when I had a 360 for about eight years. Rated the same, but the idle charging is leaps and bound better. It won't dim the lights anymore. I would have kept it, but after going with fuel injection and electric fans I needed to step up. For a factoryish car, it's perfect.

Alternator
Bracket Kit

 

[69-]

If you upgrade the alternator by sizes, consider upgrade your wiring. Easiest solution would be a 10 gauges (or even 8) additional feed from the alternator stud directly to battery positive.
But this would make the ammeter (in my 79 LeBaron) inoperative.
So also consider a voltmeter to check on the electrical system.

At least, the 79 ammeter is of the shunt type design, eliminating the need to feed full alternator amperage through the bulk head (twice), as earlier versions did, e.g. my 69 Charger.

 

[BudW]

Thank you @69- . That is what I meant by having a bad day (ie: your car turning itself into an expensive BBQ pit).

If a person is going to upgrade the wiring, it also helps to also install some kind of a fuse into that circuit, rated around your alternator output rating. Fusible links are not fun to work with. Blowing a fuse is far better than melting your harness (or catching your car on fire).
A volt gauge is more informative than an ammeter is (to be, anyway).
BudW

 

[69-]

Although I personally really, really like the ammeter (and knowing about the drawbacks).

Most common reason for earlier Mopars turn into BBQ pits: wiring. Ammeter (my Charger's ammeter pressed stud connection showed burning marks when I replaced it... ), splices, bulkhead - All of them with too much load, a little too much dirt (providing for unwanted resistance) and FUMB - up in flames.

 

[Aspen500]

You can get a repro voltage regulator and they are made in USA, at least the one I have was. Only downside is the mounting holes are for A, B,E body not F. I made an adapter plate to use one. I wanted a good regulator and, for it to look "stock".
You can kind of see it behind the washer reservoir.

 

[Cordoba1]

I had the same issue, JBFury. My Cordoba had the original, factory alternator. I also have a newer stereo, an under-seat subwoofer, and like to run the AC on high. Although my modest stereo doesn't draw that much more power, the ALT light would flicker to heavy audio volumes. I invested in a Powermaster 1-wire alternator. Problem SOLVED. So easy to install: Remove old alternator, tape off the regulator leads (so easy to return to stock if someone wants to) and connect the one and only wire needed: The main power lead. I have had no issues with the unit, strong charging, and my lights and fan remain at full speed even while at idle. The Powermaster units are not inexpensive, but they are a nice upgrade that actually simplifies the installation.

 

[XfbodyX]

My biggest issue with factory alternators is burning them up with high rpm. Dont know about the Denso but the powermaster one wire has bearings vs bushings making it a great upgrade if not just for the durability alone.