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It should be 13.8V but seems to move around some. Alfa did some screwball things to the wiring so the regulation is not very good.

The big wire should go the fuse box first then from the box to the battery. So any voltage drop to the box is compensated. but Alfa ran a short run to the battery. So as the system loads up it overcharges the battery by what ever the voltage drop to the box is.
That is why batterys don't live as long as they should in the alfa.

So 12.3 is way low my guess not charging at all.
 

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alternator output

I believe most Bosch alternators have a nominal charging output of 14.4v. This would be at the terminal on the back of the alternator.

As previously commented, any resistance in the circuit will create a voltage drop at/across that resistance. So the voltage you see on the dash volt meter or at the battery, etc. will be less. Hopefully not too much less.

You are probably seeing only the battery voltage. You might only need a new regulator.

Do you have 12v at the D+ terminal. Does the Alt light come on? If not a burnt bulb or bad connection to the lamp or the fuse will prevent 12v from reaching the D+ terminal on the back of the alternator. If 12v is not present here the alternator will not work/charge.
 

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Actually they'll produce GOBS of voltage as my 300ZX showed the other day when the internal regulator failed.

It's the regulator that keeps it, or should keep it, in the 13.6 to 14.5 Volt range. I have had a regulator fail and pull the voltage low like yours. 12V or less.

Another thing that can cause it is one (or more) diode bank going out in the alternator. I've had that happen, too.
 

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Discussion Starter · #6 ·
I changed out the bad alternator with a 'good' one We had at the shop. Its pumping out 13.4 volts. It also has that frigging annoying bearing sound. Oh well. I'm might have my other one with the good bearings rebuilt, or even better yet, swap out the regulator on it and get it bench tested. If the regulator was bad would it be generating the 12.3 volts or nothing at all?
 

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The big wire should go the fuse box first then from the box to the battery. So any voltage drop to the box is compensated. but Alfa ran a short run to the battery. So as the system loads up it overcharges the battery by what ever the voltage drop to the box is.
That is why batterys don't live as long as they should in the alfa.
I'm unclear what you're meaning or trying to say here - bit confusing.

However, the Milano/75 setup is not unusual, as far as I've seen. It is typical for the alternator to feed directly to the battery, and the battery to feed directly to the starter motor and fusebox.

The 'problem' that I've found, is that the 75 wiring is not very thick, and the junction boxes scattered around the engine bay are prone to corrosion.

8awg (American Wire Gauge) from the alternator to the junction box is technically ok over its short distance, for a 70A alternator, but it's pushing the limits. 8-10awg from this junction box to the battery (for the purpose of recharging the battery), and 8awg battery-chassis groundwire are also pushing the limit. What looks like 4awg to the starter motor is ok; I haven't isolated the powerwire from the starter motor to the fusebox yet, but I don't think it's very thick.

If you want to do upgrades, then I recommend changing the alternator wire to 4awg, and the battery-chassis groundwire to at least 4awg. If, as I suspect, the wire from the starter motor to the fusebox is 8awg, then I would upgrade this to 4awg.

:)
 

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alternator testing

do not disconnect the battery while the engine is running to test the alternator, this can cause damage to the alternator or other electronics.

do not full field the alternator, Bosch does not recommend this as damage can occur to on board electronics.
the Milano/75 with the 2.5 engine should have a Bosch K1, 14v 55a alternator with an integral regulator.
The voltage at B+ and D+ should be the same or very close. If the voltages are not significantly the same it could be that a diode or winding is defective.

If you have access to an ocilloscope you can look at the ac ripple voltage on top of the dc voltage. A regular lumpy pattern should be visible. if any of the lumps are missing it could be indicative of a bad diode or a winding which is open or grounded.

If the regulator is bad the alternator could put out 12.3 volts but more likely the regulator is bad and you are reading the slightly undercharged battery voltage. A fully charged battery should be 12.6 volts. If less than 12.4 volts charging is recommended before testing the charging system.

as the brushes wear output can decrease, you may notice noise in the radio or other audio electronics powered by the car.
 

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"I'm unclear what you're meaning or trying to say here - bit confusing."

It has to do with where the regulator sence is. in this case the lamp is used as the sence
it will try its best to keep the voltage at the lamp 13.8V but the lamp gets is voltage from the fuse box. so if the lights are on and set the blower fan is on and heck let put on the seat heater and the rear window heater. so lets say we get 2 volts drop from the stud on the fender to the fuse box. the light will see 11.8V the alt will crank up until it current limits over charging the battery or push the battery to 15.8V (this is why you get the bulge in the battery on a alfa and short battery life) so lets say it made it to 15.8V the voltage at the fuse box is now at 13.8V but a ton of wasted current is going into the battery. if the alt went to the box first then the battery. it would boost the voltage to 13.8V at the box (15.8V at the alt stud) and 13.8V to the battery so no wasted current and no undue stress on the alt or the battery.

now if the regulation point was moved to say the stud on the fender it would be a whole lot better as the voltage would be stable there. you still would get the drop from the stud to the fuse box but the voltage going critical things like the injection would see a much more stable voltage. and the stress on the battery and alt would be reduced big time.

I think this is one of the things auto manufactures do a lot, cut corners.
By not running the thick wire from the box and back they save some cost.
and yes the regulation suffers and battery don't live long but as long as it gets past the warranty period it is not there problem.
 

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I do recall that around the time I first got my Milano (early '90s) there was an old Alfa hand (Fred diMatteo, IIRC) who was selling a replacement regulator for Bosch equipped cars that bumped up the charging voltage by a few tenths of a volt. The normal setup was considered marginal at that time.
 

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Sly,

All true, but a couple of minor points:

It has to do with where the regulator sence is. in this case the lamp is used as the sence
In the Milano/75 a resistor in the ARC control box is used instead of a lamp.

I think this is one of the things auto manufactures do a lot, cut corners.
By not running the thick wire from the box and back they save some cost.
and yes the regulation suffers and battery don't live long but as long as it gets past the warranty period it is not there problem.
It's even worse because the cheap [email protected]%$ds only have to run a thin wire back to the battery from the other side of the lamp/resistor as it only has to handle the current through the lamp/resistor.
 

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...now if the regulation point was moved to say the stud on the fender it would be a whole lot better as the voltage would be stable there.
Actually, the 'regulation point', or system voltage signal, comes from the most stable point there is; the field diodes output INSIDE the alternator. This output is also alternator terminal D+, the wire that feeds alternator output voltage to one side of the warning lamp. The other wire feed to the lamp, or switched side, comes through the ignition switch and the fusebox. If the voltages from both circuits is the same (zero voltage potential), the lamp is out. If the voltages are not the same, there is a voltage potential at the lamp so the lamp will light. The intensity of the light is proportional to the potential.

Voltage drop in the switched circuit has no effect on alternator output voltage.
 

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The lamp wire is the reference single.
Craig is right is is a resistor in the ARC in this case. but still the reference.
The LED used in the ARC could not be used as it would have a voltage drop across it and mess up the regulation.
It is also used to trickle start the field magnet.
If you lower the voltage of that wire the voltage will go up coming out the stud. There should be a limit will where it will go into a fault if it is too out of wack. So it will not send 100V-300V out unless the regulator shorts out. which is rare but happens time to time. and if the battery boils dry you fry the radio and all the bulbs pop first. and then everything else if not corrected ASAP.
The onewire Delco Remy's work the same way and is more or less a twin of the one wire bosh system.

There is no auto charge system that regulates to the stud that I know of. Even the old generators had the sence feed off the key power. And most ran the main feed to the fuse box(if there was one) or junction box then back to the battery. so even a old generator would compensate for voltage drop as long as the generator could keep up.
 

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so lets say we get 2 volts drop from the stud on the fender to the fuse box. the light will see 11.8V the alt will crank up until it current limits over charging the battery or push the battery to 15.8V (this is why you get the bulge in the battery on a alfa and short battery life) so lets say it made it to 15.8V the voltage at the fuse box is now at 13.8V but a ton of wasted current is going into the battery. if the alt went to the box first then the battery. it would boost the voltage to 13.8V at the box (15.8V at the alt stud) and 13.8V to the battery so no wasted current and no undue stress on the alt or the battery.

now if the regulation point was moved to say the stud on the fender it would be a whole lot better as the voltage would be stable there.
Voltage drop in the switched circuit has no effect on alternator output voltage.
@ slyalfa: thanks for the explanation and example; it makes sense. I presume that a healthy voltage regulator would not allow voltages as high as 15.8V, and your example is just that, to make a point.

However, like papajam, I have always presumed the voltage regulator - inbuilt into the alternator - does not rely on feedback from anywhere but it's own output. As such, the voltage at the stud or ARC is irrelevant to the voltage regulator.

Having said this, I have not studied the wiring schematics in detail, but will do so, out of interest. In particular, the attached pic is the feed from the alternator in my 3.0. What is the 'light green' wire, which is connected to the alternator? I have presumed it is an output from the alternator, perhaps to ARC; but is it an input to help feed back to the voltage regulator?

Btw, the wires are hopelessly thin, by today's standards. I will be rewiring my car and replace the 8awg (alt to stud), and what looks like 10awg (stud to battery), with 4awg to the battery via a distribution block.

:)
 

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OK, following up to my own question about the green wire. Referring to the relevant ARC and 'charging' electrical wiring diagrams, it looks like an output wire from the alternator, to ARC, to provide a warning if the voltage ('Generator Efficiency') is low/faulty.

So I presume it has nothing to do with regulating the voltage.

I therefore remain confused by slyalfa's description, and cannot understand how voltage at the 'stud' or fusebox or ARC can make the alternator and voltage regulator 'increase output'. The bottom line being: where is the voltage regulator sensor?

I believe it to be built into the alternator/voltage regulator. And that the voltage regulator would produce voltage up to around 14.4V, and not be designed to pump out anything over this (ie: nothing like 15.8V). Sure, if more power is being consumed by the car (headlights, radio, demister, etc), the voltage regulator and alternator would attempt to increase output, but only to a maximum of 14.4V and 70A (or whatever the max outputs are for these components), and subject to engine revs (ie: alternator pully/rotor speed). If power consumption (by headlights, radio, etc, etc) exceeds the supply, then the car would experience 'voltage drop'. So be it, that is the typical limitation of virtually any vehicle.

Am I missing something?

:)
 

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I have always presumed the voltage regulator - inbuilt into the alternator - does not rely on feedback from anywhere but it's own output. As such, the voltage at the stud or ARC is irrelevant to the voltage regulator.
100% correct. Just to clarify the 'but it's own output' part though means the alternator output, NOT the regulator output. The regulator does not output anything; it simply completes the field winding circuit by varying circuit resistance to ground.

What is the 'light green' wire, which is connected to the alternator? I have presumed it is an output from the alternator, perhaps to ARC; but is it an input to help feed back to the voltage regulator?
It is both an input and an output.
With key on engine off (KOEO), switched power goes to one side of the charging indicator lamp. Power then goes from the other side of the lamp, through the green wire, to the alternator D+ terminal. The green wire at this point is an input. Since the alternator is not outputting anything, the voltage potential at the lamp is at maximum so the lamp glows bright. Upon engine start and the alternator starts outputting (voltage building at the field diodes output), the D+ terminal then becomes an output. If (when) alternator output voltage at the D+ terminal and the switched voltage at the lamp equalize, there is now zero voltage potential at the lamp and the lamp goes out. At this point, the green wire is nothing more than one half of the warning lamp circuit. One could now disconnect the green wire from the alternator and the alternator output would not change.

The bottom line being: where is the voltage regulator sensor?
The field diodes output inside the alternator (which is also alternator terminal D+).

As previously mentioned, with KOEO, the voltage on the D+ terminal, having come through the indicator lamp and green wire, also provides for field winding excitation. This allows the alternator to start outputting at a low RPM. However, even with the green wire disconnected from the D+ terminal, the alternator will still start to output on its own BUT only at a much higher alternator RPM (like 5000-ish).
 

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As previously mentioned, with KOEO, the voltage on the D+ terminal, having come through the indicator lamp and green wire, also provides for field winding excitation. This allows the alternator to start outputting at a low RPM.
slyalfa said:
It is also used to trickle start the field magnet.
Ah, of course, go it - thanks: ignition power generates the magnetic field in the rotor windings.

On re-reading slyalfa's posts, it makes more sense. Cheers guys.

:)
 

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...ignition power generates the magnetic field in the rotor windings.
Yes, but ONLY on initial start up. Field power then comes from the field diodes (D+) once the alternator starts outputting.

And again, this initial field excitation voltage is not mandatory for the alternator to start outputting. Without this initial voltage, it'll just take many more revs before things start to happen.
 

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Correct charging voltage is 14,3-14,4V, nothing over. Action must be taken if the charging voltage is under 14V although things can work under that too, but the charging will be too bad!

G.K.
 
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