Alternator doesn’t make sense

[LuvNH]

Been working a voltage problem on a different thread. Short summary is that after other troubleshooting and work, my 911 is producing 16v+. I’m now focused on replacing the VR.

1979 SC with a ‘78 engine. Cleaned nearly all grounds, starter connections good and tight. Resistor installed (5w 91ohm). External VR removed.

Removed the alternator and I’m not sure what I have. The label says it’s a Bosch reman AL400X. The bearing cap on the alt says it’s is a Paris Rhone A14N95 105a. The VR has no meaningful numbers on it at all (on the inside there are some numbers that don’t come up in internet searches).

The Bosch AL400X comes up as 75a.

Called the Pelican peeps and they said that Porsche only made a 75a and a 90a. Same VR for both, btw, which I thought was strange.

After hours of internet searches, there is very little on the A14N95. Found some hits on a Peugeot.

Could the PO have placed a Peugeot alternator in the Bosch case? Could the cap be wrong? Not sure what I should do here.

Regardless, can I use a VR for a 90a one in this? Didn’t think so, but if the 75a and the 90a use the same. Pelican gave me this part number which appears the same. 911 603 913 02.

I know I could leave it with an alternator guy and have him do the once over, but I am trying to avoid that.

[Flat6pac]

Looks like the 6 bolts to attach the air extension are too short.
You need the correct depth fan housing.
The VR is the weak spot in the on board VR.
Bruce

[mysocal911]

Originally Posted by LuvNH

Been working a voltage problem on a different thread. Short summary is that after other troubleshooting and work, my 911 is producing 16v+. I’m now focused on replacing the VR.

1979 SC with a ‘78 engine. Cleaned nearly all grounds, starter connections good and tight. Resistor installed (5w 91ohm). External VR removed.

Removed the alternator and I’m not sure what I have. The label says it’s a Bosch reman AL400X. The bearing cap on the alt says it’s is a Paris Rhone A14N95 105a. The VR has no meaningful numbers on it at all (on the inside there are some numbers that don’t come up in internet searches).

The Bosch AL400X comes up as 75a.

Called the Pelican peeps and they said that Porsche only made a 75a and a 90a. Same VR for both, btw, which I thought was strange.

After hours of internet searches, there is very little on the A14N95. Found some hits on a Peugeot.

Could the PO have placed a Peugeot alternator in the Bosch case? Could the cap be wrong? Not sure what I should do here.

Regardless, can I use a VR for a 90a one in this? Didn’t think so, but if the 75a and the 90a use the same. Pelican gave me this part number which appears the same. 911 603 913 02.

I know I could leave it with an alternator guy and have him do the once over, but I am trying to avoid that.

Yes! The regulator ONLY controls voltage and NOT the amperage.

[LuvNH]

Looks like the 6 bolts to attach the air extension are too short.
You need the correct depth fan housing.
The VR is the weak spot in the on board VR.

Bruce, thanks for the input. Didn’t know that about the VR.

Don’t remember when I took the pic, nor why it looks like that, but the bolts are long enough. Good point though.

I have added the rubber boots. This pic was from my initial removal so I could remember how to install correctly.

[LuvNH]

Yes! The regulator ONLY controls voltage and NOT the amperage.

Really? I was thinking that initially, but a quick google search told me otherwise. That would definitely make life easier for me.

Many thanks!

[mysocal911]

Originally Posted by LuvNH

Really? I was thinking that initially, but a quick google search told me otherwise. That would definitely make life easier for me.

Many thanks!

Don't believe everything from Google, and especially from ChatGPT.

[Jonny042]

Originally Posted by mysocal911

Yes! The regulator ONLY controls voltage and NOT the amperage.

Can't have one without the other, really...

[wazzz]

Well, the voltage regulator, as the name suggests, monitors and regulates the voltage generated by the alternator to keep it within a certain range. As such, it takes part in what we call a constant voltage source (as opposed to a constant current source, that would continuously monitor and regulate the current to maintain it within a certain range).
So yes, according to Ohm's law, all things being equal and the load being a simple constant resistor, voltage and current follow the same curve. But in the case of a car alternator, there are other factors like RPM that dictate the voltage regulation or control. The VR doesn't care about how many amps are drawn, it could even work and regulate the voltage without any current being drawn.

[John W.]

A 75 Amp alternator should be able to generate 75A and a 90 Amp alternator should be able to generate 90A. The voltage regulator maintains a constant voltage say 14.5 V. A voltage regulator can easily work with either a 75 amp or a 90 amp alternator. However, the electrical components used in the regulator must be able to handle the higher current so yes, the same regulator can work for both as long as the components can handle the higher current from the 90 amp alternator. The voltage regulator should have a specification on it as to how much current it can safely handle.

[mysocal911]

Originally Posted by Jonny042

Can't have one without the other, really...

As an example, use a current probe and monitor the alternator charging current for the large Porsche battery, e.g. in a 911 3.2.
When the battery can barely crank the engine to start, rev the engine to 3K. Then check the charging current.
The alternator current will exceed its rating, e.g. over 150 amps, and potentially damage the internal diodes.
So it's NOT a good idea to try and quickly charge a very low state of charge 12V battery, using the alternator.

There's NO current regulation/limit on most alternators!

[mysocal911]

Originally Posted by John W.

A 75 Amp alternator should be able to generate 75A and a 90 Amp alternator should be able to generate 90A. The voltage regulator maintains a constant voltage say 14.5 V. A voltage regulator can easily work with either a 75 amp or a 90 amp alternator. However, the electrical components used in the regulator must be able to handle the higher current so yes, the same regulator can work for both as long as the components can handle the higher current from the 90 amp alternator. The voltage regulator should have a specification on it as to how much current it can safely handle.

It's the alternator's field current, e.g. ~ 4 amps max (3-4 ohms ) and NOT the alternator's output current that affects the regulator.
Typically, the average field current is 1-2 amps to supply the alternator for a low output current of 25-30 amps.

[LuvNH]

Thanks for all the input. Really appreciate the insight on how these work.

Hopefully I’ll be able to report success once I get the part.