Low Charging - Alternator Problems?

[FastSVO]

Hi Guys,

I have a 165amp 3G alternator (large case) on my '91 that was purchased from a reputable seller on ebay aka "[email protected]" a few years ago and not many miles have been driven on the car (it's been in storage mostly).

Ok, this alternator has always done an excellent job of charging the system and the other night I noticed the alternator gauge was staying down below the 1/4 mark and would not budge as the rpm's rose.

Put the charger on the battery and was surprised to find that it did required some charging time (car ran pretty good before hand).

So here are tests that I have performed so far:

Engine not running & ignition on

1) Disconnected the D connector with the 3 wires and measured the voltage on the lt green/red wire = 12 volts CHECK

2) Reconnected the D plug to the alternator and probed the greed/red wire. I should be seeing 2.4 - 2.6 volts here but I got 3.8 volts ..... a problem? I understand if I had no voltage at all here, then I would have had a failed regulator.

Engine Running & ignition on.

1) Probed the green/red wire and I should be seeing battery voltage minus .25 to 1.0 volt. My battery at this time was @ 12.92 volts (discharging?) and probing this area got me 12.15 volts.

2) Probed red lead to the charge stud on back of the alternator. The battery at this time was showing 12.5 volts. The Charge stud varied on my DVM between 18.10 - 19.15 and sometimes just 1_.__ (did it exceed the value? DVM set at 20volts DC).

Is my alternator perhaps overcharging the system here? Does the 3.8 volts received from the D plug point to a bad voltage regulator? Bad alternator?

I have yet to pull the 200 amp blade fuse and measure the resistance.

Any help would be appreciated here.

Thanks in advance,

Eric

 

[HISSIN50]

I would not run the car again till the alt is bench tested at the parts store. If ok:

KOEO, do you see battery voltage at the charge stud? If not, the charge-cable fuse is probably blown or the cable is open.

What did the S and A wiring show on the regulator?

The A circuit should be very close to actual battery voltage (less than .50V is acceptable, but I like to see less than half that). If this circuit is bad, it can cause overcharging.

The S circuit should float 1/2 battery voltage or so.

If the car was charging at 19+ V, you should be blowing bulbs and electronics.

 

[FastSVO]

I would not run the car again till the alt is bench tested at the parts store. If ok:

KOEO, do you see battery voltage at the charge stud? If not, the charge-cable fuse is probably blown or the cable is open.

No and I found this to be odd. I am planning on checking the fuse today.


[/QUOTE]What did the S and A wiring show on the regulator?

The A circuit should be very close to actual battery voltage (less than .50V is acceptable, but I like to see less than half that). If this circuit is bad, it can cause overcharging.

The S circuit should float 1/2 battery voltage or so.

If the car was charging at 19+ V, you should be blowing bulbs and electronics.[/QUOTE]


The other pins I am assuming? I don't remember seeing any voltage - will have to double check. Should I measure with KOEO?

Thanks,

Eric

 

[HISSIN50]

Yep. I'd be all over that charge cable and its circuit protection.

The regulator plug (3 wires that you were messing with) is labeled with A, S, I nomeneclature. The green/red wire is labeled I, for instance.

You can check the A circuit KOEO or KOER.
S can only be checked for voltage KOER. You can test the wire for the circuit KOEO (disconnect the stator plug and the reguator plug and do a continuity test between the two).

 

[FastSVO]

Yep. I'd be all over that charge cable and its circuit protection.

The regulator plug (3 wires that you were messing with) is labeled with A, S, I nomeneclature. The green/red wire is labeled I, for instance.

You can check the A circuit KOEO or KOER.
S can only be checked for voltage KOER. You can test the wire for the circuit KOEO (disconnect the stator plug and the reguator plug and do a continuity test between the two).

By the stator plug, you are referring to the single plug (white wire) that goes to the alternator?

What would allow a 200 amp fuse to blow like this? I have my alternator mounted low due to the blower...possibly water got splashed on the alternator?

-Eric

 

[HISSIN50]

Yep. The stator loops from that lone port to the S terminal on your regulator. In stock Fox III form, it's a convoluted pathway, and how yours was done varies by how you wired up that part of the circuit while doing the 3G retrofit.

Most of the time I've run across a blown fuse, it's because the ring terminal on the power cable is real close to the alternator body. Something flexes or is set atop the alt and it shorts the power cable (battery) to ground (the alt body). Water splashing should not cause an issue.

The fuseholder itself could also have failed (plastic melts, and with some fuseholders the bolt that secures the fuse-legs recedes out of the bottom of the fuseholder. This can lead to a short to ground if that bolt touches something metal).

 

[FastSVO]

Most of the time I've run across a blown fuse, it's because the ring terminal on the power cable is real close to the alternator body. Something flexes or is set atop the alt and it shorts the power cable (battery) to ground (the alt body). Water splashing should not cause an issue.

BINGO!

I found the wire had melted against the body of the alternator. Have a look...

Can I just add some more heat shrink tube and electrical tape and call it a day?

Seems my fuse is blown:

I am going to replace the fuse, but is it still necessary to pull the alternator out and have it tested? Could have the alternator been damaged by this?

You have been very helpful and wanted to publicly thank you for all your assistance and knowledge.

Regards,

Eric

 

[HISSIN50]

Eric, with any luck the alt is fine. It'd be nice to bench test it but there should be no harm in fixing the wiring, renewing the fuse, and seeing what the alt does. That's why the circuit is fused in the first place.

FWIW, if you have a 4 AWG charge cable, I would go for a 125 or 150 amp fuse. 200 is a bit much for 4 AWG. As you know, Napa, Pep or a stereo store should have a fresh fuse for you.

If you have slack in the cable, another ring terminal, solder pellet, heat shrink and a torch, I'd solder a new terminal onto the cable. A failing eyelet connector will cause issues down the line (if you leave it, look for signs of it getting abnormally hot, especially if it was a crimp connector. I'm not a big fan of those). You'll often see the strands entering the eyelet actually turn black.

I've used an extra charge stud nut to shim the cable eyelet away from the alternator housing (so you'd have the bare charge stud, a nut, the eyelet, and then another nut that secures the eyelet). This isn't great but it reduces the chance of this happening again. You can also get a charge stud extension here (about 4/5 of the way down the page)

RJM Injection Tech Alternator Accessories & Parts

Thank you for the kind words. Nice work figuring out the issue and let us know how it finishes-up Eric.

 

[FastSVO]

FWIW, if you have a 4 AWG charge cable, I would go for a 125 or 150 amp fuse. 200 is a bit much for 4 AWG. As you know, Napa, Pep or a stereo store should have a fresh fuse for you.
.

Even if my alternator's output has been increased to 165amp?

I'll head over to the parts store tonight and try my luck.

Thanks,

Eric

 

[HISSIN50]

Even if my alternator's output has been increased to 165amp?

I'll head over to the parts store tonight and try my luck.

Thanks,

Eric

You want to fuse for the weakest link. In this case, 4 AWG would be the weaker link (than the 165 amp alt rating).

You'd be hard pressed to need that 165 amps anyhow. E.g., the stock large-case 3G's often bench tested at about 160-170 amps but their circuit protection was rated below that. I always run a fuse lower than the alternator's max rating.

If you want, grab a 150 and a 200 amp fuse. If I'm wrong, you'll have the 200 to toss in (I always keep a spare fuse in the glovebox anyhow). If I'm right, you'll have a little more circuit protection in case something like this happens again.

 

[grn92conv]

Probed red lead to the charge stud on back of the alternator. The battery at this time was showing 12.5 volts. The Charge stud varied on my DVM between 18.10 - 19.15 and sometimes just 1_.__ (did it exceed the value? DVM set at 20volts DC).

Hissin50's right. The fuse protects the circuit/the wire. A 165a (130a) 3G alternator, if really loaded up, will usually only see a little above it's max idle output, maybe 100~110amps. Most people selling alternator upgrades, go higher on the fuse rate (usually 200a), so there's less explaining to do << That might sound crappy, but it's a hard sale, selling a guy a 200a alternator, then giving him a 150a fuse on the power wire. The fuse isn't going to usually blow, except from ground short (like you had) < for that failure the fuse (150 or 200) didn't much matter.


Hissin, you got a kit or just a alternator from me? You didn't like my crimps, man?
If you ever need anything else, give me a shout. I'll cut you a deal. I've seen a few times where you put in a good word for me and I appreciate it.

 

[HISSIN50]

Hissin, you got a kit or just a alternator from me? You didn't like my crimps, man?
If you ever need anything else, give me a shout. I'll cut you a deal. I've seen a few times where you put in a good word for me and I appreciate it.

Hey Mike,

No you did fine man. I got a ~170 amp (IIRC) big case 3G from you for my '94 GT. Long before that [when I got the car] I noted the stock 6 AWG cable dropping over 500 mV so I swapped in a 4 AWG cable at that time.

I also bought a spare reg from you a little later.

I'd have liked to get your cable but I'm poor so I reused mine (it was only dropping an avg of ~0.05-0.10 V).

As for my comment, it would not pertain to your cable but backyard crimping methods. I've seen people use lineman's pliers or a hammer and punch to crimp lugs and that leaves me a little cold (I like to use pellets instead of a poor crimp - that was my only point).

For those interested in an alt, I do recommend Mike's stuff (I also recommend them often in PM's - I get a lot of alt PM's). His customer service is outstanding (we had a part failure out of the box, and though no one's fault, Mike took care of it immediately and free of cost to me). I've also inquired about 6G parts for a family member's car and even if he didn't have the part, he recommendeed who would. That's top notch in my book.

 

[grn92conv]

Thanks, JT.
I fired at you on the corral.

Mike