When it rains pours...

I noticed my Charger wasn't charging (via the ammeter). It went from a heavy discharge at idle to breaking even (dead center) when I revved it. I checked the voltage at the battery (running) with 12.2V @ idle and only 12.5V when I revved it. This alternator used to put out 14.5V all day long.

Alternator is a 100 amp Tuff Stuff unit (8 years old at this point) and car has 40 amp electric fans. I inspected the wiring and connections and all looked good. Wiring is reproduction installed around 12 years ago.

I went ahead full fielded the alternator (to eliminate the regulator).
- voltage at the blue field wire tested at 11.9V when I pulled it (battery voltage was 12.2V)
- I plugged this back in and pulled the green field wire
- I connected a remote starter to the (green wire) field terminal and ground

The alternator definitely kicked on and slowly climbed to 12.8V very very slowly. I revved the motor (while full fielded) and it slowly climbed to 13.8V (maybe took 30 seconds).

This seems very slow compared to what I have seen when I full-fielded alternators where they would jump to 15+ volts immediately.

Can I pretty much assume this alternator is dying? Anything else to check since I eliminated the VR?

if full fielding the alt didn't change, it is the alt. Mostly sure diodes banks

Thanks, Nacho. I just wanted a sanity check to make sure I wasn't missing anything.

it's toast

IF its the diodes banks ( positive or negative ), having the replacements they are easy to replace at home. No need for special tools, just 1/4" socket and some other.

they can be checked in fact without dissasemble the alt, just using the VOM leads from exterior on OHM function ( middle OHM scale should be enough sicne they use to be on 100-400 ohms rate ), since diodes banks are accesible.

They can be even visible damaged/burnt.

Here I show how the diodes can be tested for positive bank. Same aplies for negative diodes bank but againts the alt case not the stud and swaping around the VOM leads.

( I can't recall right now if the positive lead of the VOM must be on stud or diodes to check the positive bank, but if doesn't work just flip the VOM leads around ).

All 3 diodes should register same value

If diodes bank came out damaged, there are replacement kits. NOW, I'm not sure if any diode bank will hold the Tuff Stuff alternator output rate.

https://store.alternatorparts.com/partno605.aspx

or diodes banks separatelly if just need one of them

https://store.alternatorparts.com/chrysler-square-back-rectifier.aspx

( I bet there are cheaper sources for this )

they sell the same diodes bank for all their ( quickstart ) alt output rate kits

the next thing it could be damaged is the stator being some of the windings broken/burnt. The Stator can be checked but alternator needs to be dissasembled. Stator can be also replaced BUT I think this could be provided just by Tuff Stuff. This is the bigger difference on the alternator ouput rate.

Rotor can get damaged too simply testing for continuity between brushes and being isolated from chassis, But on this case you wouldn't register any kind of charge or voltage variation like you described making the tests.

Nacho,

That is what I am afraid of (that OEM rebuild parts won't work for the high-output alternator).

I just replaced some fuel fittings so I had to run the car for a while to check for leaks. Guess, what? Alternator is now charging. Cold the alternator was at 14.5V down to 13.8V when the car was good and hot. Under a big load (AC on, max blower speed), the alternator was holding at 13.1V at around 900 RPM (out of gear idle).

I guess I will just have to keep an eye on the ammeter for awhile. I do have a pretty good battery (big Interstate 110 minutes reserve) so hopefully if the alternator chokes, I can get it home before it dies.

The diodes can be heat sensitive: You tests do not look encouraging IE:
and

I would repeat the last test (load) with the RPM up to 2-2.5K and see what the readings are.

I wouldn't say that in the diodes bank case. Definitelly brushes and isolators are the same... Stator I don't think so of course. Rotor dunno.


Now, about the SUDDENLY working alternator... check the field brushes assemblies. Fuel line runs at a side of the alternator and maybe playing around, the brushes were moved/relocated. We are talking about an 8 years alternator? but... how many miles or how much time you have run the engine ?

Once I got a melted isolator and brush inserted in it, making to loose the contact with rotor trace ( I have a pic of that... somewhere )

Editing
Found the pic. Somehow the brush could got heat enough being able to melt the isolator and get inserted into the plastic

Sounds like the alternator belt is slipping to me not making the alternator spin at the higher RPMs needed to make it work like it use to

Alternator is 8 years old - maybe 2500 miles on it? My fuel line doesn't run near the alternator as I have a totally non-stock carb/intake/spacer.

The only thing I can figure is that I was doing work under the hood to replace the fuel inlet fitting/filter/hard line and perhaps I bumped something and made a loose connection? I have no idea what it could have been as I looked at the two field wires, ground, and output connections on the alternator.

I did fire it up again and took it for a short drive. Per the ammeter, it's charging normally, even with the AC/blower motor on.

Of course when the car is heat soaked and then driven in 90+ degree heat, it likes to be finicky with idling but that's a whole other story.

The belts may have been slightly loose so I just tightened them up. Cranked the car and still charging

why I never think on the belt ? LOL:

well, Is not common a belt gets loosen just like that!

Well I think my charging issue is back...

Based on my ammeter, I am charging from a cold start but that quickly starts to level off where I am running slight discharge at speed and a significant discharge at idle. I show 12.1V at the battery when the car is running (hot) - even when rev'ed up.

Since I full fielded this alternator before (and it didn't help), I will assume my VR is fine. I went ahead an ordered one of those fancy 130amp Tuff Stuff alternators which is pricey but will help with my electric fans.

The only other thing I can think of is the battery going bad. It is from 12/14 but it is a high end Interstate battery which I have kept on a battery tender when the car was sitting for a while. I am leaning away from this as this battery spins the motor like a top. Could a bad battery cause this type of behavior?

full fielding elims everything except the alt. I would check the brushes. got another alt you could sub in for a quick test?

Maybe, depends on what he did. The alternator requires 12v on one field terminal (this is hot whenever the key is in run) and ground on the other (this comes from the VR). If he had an issue with the keyed 12v side and only grounded the other terminal then he hasn't eliminated everything but the alternator.

Well I pulled the alt and battery and took them to AdvanceAuto (hold the eyerolls). Battery tested fine, alt tested bad. I will let everyone know what happens when I get the new alt swapped on.

when I full field I get it on a fast idle/jump one field terminal to ground/feed 12V to the other field terminal. this eliminates the ign sw/ground & any else except the alt. this would be a good time to clean all terminals/connections including ground paths especially with the higher output alt on its way.