Why is the internal VR preferred?

[FL911SC]

Perhaps another silly question, but that has never stopped me before.
This past weekend, during my first autocross, I found out the hard way that my battery is not being properly changed. I had no problem starting the car until it was on the grid and my turn to go. I turned the key and got nothing. I was able to push start the car and just left it running between runs.

So this week I have been reading up on alternators, voltage regulators, generator lights, blue wires and the other places I will need to troubleshoot when I get home.
During my reading, I have found that when replacing the alternator, it is preferred to replace it with one which has an internal voltage regulator.

My question is, why is the internal voltage regulator preferred over the external one I have now? Even the tech. article the covers the change does not say why you should do this. Additionally it is not one of the “Recommended Upgrades” listed on this site. Intuition would say that the external setup would be preferred since it can be easily accessed for testing and/or replacement. But intuition probably isn’t right on this one and I just want to understand why.

And just to get this question out of the why now, will the new style (internal VR) alternator mount to and fit into the current fan shroud without modification to the shroud? I read the air duct might have to be modified, but is there anything else such as the shroud?

Thanks,
Keith
’79 911SC Targa with original alternator.

[Peter Zimmermann]

Your original type alternator, with the external regulator, is actually far more reliable than the '82> type. It was thought to be the right thing to do to "upgrade" the old style alt/reg to the internal style. But then, after many had been done, it was realized that the internal style had a typical life expectancy of about 40K miles vs 100K+ miles for the external style.

If I was in your situation, I would find a really good rebuilder to do your alternator, and replace the voltage regulator with a new one (I write this assuming a new regulator can still be bought). After a car has been updated to an internal unit, the usual process is to have the alternator rebuilt, and a new regulator installed.

When you update an early car, the air duct has to be modified slightly. The fan shroud is good to go. My shop always stocked one early style rebuilt alternator w/a new reg., and two late style rebuilt alternators. I felt that emergencies required a quick turn around, so we did our best to get a replacement done, at the worst, the next day following a tow in. The ratio of rebuilds, old to new, was mind boggling.

[304065]

It is not preferred. In the 1980s, semiconductor technology had progressed to the point where internal VRs were available. . . .for watercooled cars with the alternator mounted on a bracket in the engine compartment with its own fan.

Our cars have the alternator mounted 2" above the hot engine, and the VR heat-soaks when the engine is turned off. Heat is the enemy of electrical components and the internal VR can be thought of as a giant, solid-state switch which generates its own heat.

I did a Club Race at Gingerman once, hauled there 14 hours, and had the alternator light come on in the race! I thought I had broken the belt so I immediately hit the pits. Turns out it was the internal VR in my alternator, throwing up its hands! When it cooled down, it worked again.

So if you have a 79 with an external VR, keep it as long as you can.

[timmy2]

I have a new internal reg alternator on the shelf for an emergency in case my external reg alt wears out and needs a rebuild. I will keep mine with the external VR until it can't be rebuilt any more... External VR's are readily available. I have a new one installed now and a spare just in case it dies early.


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[FL911SC]

Thank each of you for your response. I guess my intuition isn't too bad after all (even if my logic for keeping the current setup wasn't spot on). If the troubleshooting yields the need for a new alternator, I will look to have the current on rebuilt and replace the voltage regulator.

Mr. Zimmeremann, for what it's worth, our host has the voltage regulators for sale.

I am sure I will have some questions as a result of my findings, but until then... Thanks again.

Keith

[Peter Zimmermann]

Originally Posted by FL911SC

Thank each of you for your response. I guess my intuition isn't too bad after all (even if my logic for keeping the current setup wasn't spot on). If the troubleshooting yields the need for a new alternator, I will look to have the current on rebuilt and replace the voltage regulator.

Mr. Zimmeremann, for what it's worth, our host has the voltage regulators for sale.

I am sure I will have some questions as a result of my findings, but until then... Thanks again.

Keith

Darn; my bad! I thought about checking with them before I added that to my post, but I forgot. Good call!

[manbridge 74]

Someone needs to make a better IR. Many turbo japanese cars have alt mounted right next to the exh manifold. The aftermarket ones are junk but the OE Denso stuff lasts a LONG time.

That said, I'd keep the external reg as long as possible too.

[wwest]

At the very heart, core of alternator use technology, was/is the requirement for SIX high power 80 amp SOLID STATE semiconductor diodes with greater than 50 volts reverse breakdown voltage and EXTREME heat tolerance.

No alternator automotive battery charging/voltage supply system could be possible without those.

Now, I go back to time of/for drilling the rivets out of the old VR case in order to "refurbish", file down, the voltage regulating relay contacts. These contacts open and close at a rapid/variable rate in order to supply the PWM rotor current for correct battery charging, ssytem supply voltage under all conditions.

Each and every time those contacts open the resulting inductive voltage "kick" removes a few molecules from the relay contacts. Very much like your Kettering ignition points, if you've even taken a good look at those upon replacement.

For how many miles was that mechanical VR good for? Like clutch wear, that depends...

How many open/close cycles has a given pre-1980 era VR had at 20,000 miles.

In my experience replacing the VR was in the range of 20-30,00 miles.

Note: Nowadays you can buy a solid state VR that mounts outside the alternator..but can you buy an alternator that requires, uses, same...?

To my mind there is no viable substitute for a modern day alternator with internal (solid state) VR.

[wwest]

Originally Posted by timmy2

I have a new internal reg alternator on the shelf for an emergency in case my external reg alt wears out and needs a rebuild. I will keep mine with the external VR until it can't be rebuilt any more... External VR's are readily available. I have a new one installed now and a spare just in case it dies early.


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Modern technology, highly reliable, solid state external VR's are readily available in the marketplace.

Or, somewhere around here I have a DIY procedure/schematic (circa ~1965) for subbing in a transistor, "powered" by the relay contacts, for supplying rotor current. Zener to absorb/"damp" the inductive kick.

[timmy2]

I'm using the solid state external voltage regulator.
When my mechanical one failed at 82,000 miles, I opened it up to see what had failed and found multiple burnt/ cracked resistors inside and a coil that had failed. It went in the garbage as a new solid state one was about $40, so I bought two...


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[wwest]

Originally Posted by 304065

It is not preferred. In the 1980s, semiconductor technology had progressed to the point where internal VRs were available. . . .for watercooled cars with the alternator mounted on a bracket in the engine compartment with its own fan.

Our cars have the alternator mounted 2" above the hot engine, and the VR heat-soaks when the engine is turned off. Heat is the enemy of electrical components and the internal VR can be thought of as a giant, solid-state switch which generates its own heat.

I did a Club Race at Gingerman once, hauled there 14 hours, and had the alternator light come on in the race! I thought I had broken the belt so I immediately hit the pits. Turns out it was the internal VR in my alternator, throwing up its hands! When it cooled down, it worked again.

So if you have a 79 with an external VR, keep it as long as you can.

"..when it cooled down..."

The six high, >80 amp, current rectifying diodes are under a low more working stress, and subject to the same HEAT level, as an internal VR. VR is only switching, PWM, fully on or fully off, about 10% of the current level of those diodes.

My guess would be that you experienced a failure due more to component, metal, expansion, and vibration.

Solid state components very rarely "cure" upon subsequent cooldown. I have seem them seemingly exhibit that symptom, only to later discover upon reheated to the same level.....

[wwest]

Originally Posted by manbridge 74

Someone needs to make a better IR. Many turbo japanese cars have alt mounted right next to the exh manifold. The aftermarket ones are junk but the OE Denso stuff lasts a LONG time.

That said, I'd keep the external reg as long as possible too.

"...some one needs to make a better IR..."

They have, did, beginning back in about 1980, IMMHO.

Trying to think back about when I last had alternator problems. Keep coming up mostly with memories of the generator era. The only alternator failure that I remember having was in a 1992 LS400. The slip rings were of such "soft" copper that the slip ring brushes, with lots of wear left, had worn those down to the bare alternator shaft.

Oh.... NipponDenso alternator.

[manbridge 74]

Well any maker can have a bad run of slip rings but I'd say that would be the exception on ND alts.

My comment about a better VR needing to be made is meant to be tongue in cheek as many solid state VRs are out there on top of truck engines towing heavy loads in high heat, etc. Perhaps Bosch remans are using cheaper components similar to rebuilt ND parts being cheaper. Hard to argue that remans last longer than the OE ones.

I like the old mechanical VRs if for nothing more than nostalgia and the fact that most old 911s aren't seeing the yearly high mileage they once did.

[HarryD]

Originally Posted by Peter Zimmermann

Your original type alternator, with the external regulator, is actually far more reliable than the '82> type. It was thought to be the right thing to do to "upgrade" the old style alt/reg to the internal style. But then, after many had been done, it was realized that the internal style had a typical life expectancy of about 40K miles vs 100K+ miles for the external style.

If I was in your situation, I would find a really good rebuilder to do your alternator, and replace the voltage regulator with a new one (I write this assuming a new regulator can still be bought). After a car has been updated to an internal unit, the usual process is to have the alternator rebuilt, and a new regulator installed.

When you update an early car, the air duct has to be modified slightly. The fan shroud is good to go. My shop always stocked one early style rebuilt alternator w/a new reg., and two late style rebuilt alternators. I felt that emergencies required a quick turn around, so we did our best to get a replacement done, at the worst, the next day following a tow in. The ratio of rebuilds, old to new, was mind boggling.

Peter would you mind elaborating on the modification to the air duct? I ask because i just replaced the air duct on my alternator as part of my regular cleaning of the top fins of my motor. The old one was missing the second fin. You have me now wondering if i should have let my old one stay.