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Discussion Starter #1
Hello,

I recently had a newly rebuilt alternator fail on my 72 GTV - all is well now but in checking my voltage over the weekend, I find the following:

After a drive (car still warm) the voltmeter showed:
12.6 from the battery with the car off
13.7 volts while running
13.2 volts with the headlights on
After letting the car idle for 5-7 minutes, the meter read 14.4 - 14.6 volts with the car still running.
The battery is 3.5 years old

Is this normal? I am pretty good with turning wrenches but no scholar with electrics.
All terminals are clean and tight - the fan belt is tight and new.

Thanks all,
John
 

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12.6 car off is great
13.7 running isnt bad
13.2 hl on is too low

A big change five minutes later doesnt make any sense and makes me question the voltage regulator. Im using an inexpensive internally regulated alt from a later spider, drop in replacement.
 

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If it does not go above 13.7 in normal use then it is OK. !4.6 is unlikely to cause problems if it is only for a few minutes but it will cook the battery if it is always like that. I agree that something is not right and it is most likely the voltage regulator. You should at least keep your eye on it.
 

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OK, I switched the voltage reg from a newer style (sourced from an Alfa parts guy), to the original style that was on the car when I bought it 4 years ago.
Here are my readings - so much more consistent:
Battery - 12.6
Running cold 13.9 1800 RPM
Running with headlights on - 13.8 - 2000 RPM
Running with headlights off - 13.9 - 2000 RPM
Idle - 13.9 - 14.0 900 RPM

Photo 2 is the original reg (as if you guys wouldn't know)!

Big difference!

Thanks everyone
John
 

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13.9 at idle is pretty healthy.

A failed rebuilt alternator may indicate poor quality, but why did you get it rebuilt? If you fry more than one in a row, there might be an intermittent short in the car.

Ages ago during a national convention track day, we had to use a fire extinguisher on a GTV with some underhood smoke. Once everything was under control, I noticed a new alternator, new regulator, new battery. I asked the owner if he'd had recent electrical problems - which was an obvious yes. I eventually noticed the car had been recently converted from Spica to carbs, and the wire that fed the decel switch had been left live, bare and loose. After taping up some wires he was able to drive the car, enjoy the convention and go home.
 

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Discussion Starter #6
I am working on a 74 GTV restoration. It did not come with an Alternator - a friend gave me one and said it needed to be rebuilt so I had it done last spring. I stuck it on a shelf as it waits to be installed in the project car.
About two months ago, I had an electrical issue and it seemed it was the alternator so I installed the rebuilt alt. On a trip to NH, I kept losing power but I did make it to my destination (the alt. we replaced was actually OK).

My friend brought the old alt. to NH and I swapped it out and all was well. The reason I made this post is I am trying to get more familiar with the meter so I decided to check the voltage to make sure all is still OK. This is when I discovered the variation in the voltage settings.

I hope this makes sense!

Thanks all!
 

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OK, I switched the voltage reg from a newer style (sourced from an Alfa parts guy), to the original style that was on the car when I bought it 4 years ago.
I am skeptical that those "newer style" regulators are better than the original style. Yes, the newer ones are electronic, which you'd think would be better. But that 14.4 - 14.6v reading certainly wasn't better!

I had a similar problem after substituting a solid state regulator for an original unit; in my case it put out such a high voltage level that it fried my Pertronix ignition and stranded me in the middle of nowhere. Reinstalling the original regulator restored proper voltage levels.

There's nothing wrong with the original alternator-regulator system. But, if you want to upgrade things, go with the later model, internally-regulated alternator that r-mm refers to in post #2.
 

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I'm using the AL16X from a reputable ebay seller of rebuilt items whose name I forgot but was widely vouched for here. It was $150 some time back and makes a steady ~14v at idle or load. Since I added relays for the headlights where the old volt reg was, I appreciate the simple internal regulation.
 

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I bought a BNR uprated alt for my 86 Alfa, and it eats voltage regulators, puts out lower volts when engine bay temps heat up and struggles to keep up with lights with relays, the blower motor, and electric engine fan. Voltage gauge goes to 10, multimeter tells me 13.5 or so.
 

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Hmmm... is the voltage gage reliable? If yes, there is a loss somewhere. Maybe a bad connection, or a severe current draw that sinks the voltage. Either cause will play havoc with the regulator and alternator.

Using a digital voltmeter, check the voltage drop on each wire that is connected to the alternator, This is done by placing the tip of one probe on a terminal at the alternator , and the tip of the other probe on the terminal at the other end of the corresponding wire. For example, one probe on the voltage stud of the alternator and the other on the battery post. With the battery in the trunk, it's a bit harder but needs to be done. Also measure voltage drop between the alternator body and ground, ground and engine, and battery negative and ground. Make sure you don't short anything along the way.

None of the reading should be more than a few tenths of a volt.
 

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Discussion Starter #13
Thank you, Yves!

John
 

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FWIW, the single best improvement I've seen in charging system performance came from installing a larger positive cable from the alternator to power stud on the driver side inner fender, and adding a ground wire directly from the alternator housing to the car body.
 

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Discussion Starter #15
Power stud? Please clarify.
Thank you
John
 

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Follow the fat red wire from the alternator to the driver's side inner fender. Little black box with a cover.
The stud is under the cover and distributes voltage to almost every circuit on the car.
 
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