Voltage regulation

[PAT4]

After a 2 months storage, I foud my batteries down (watch, alarm ...). I charged them with an Accumate (soft charging system) and they reached 13.6V without any problem after 3-4 days.

When Accumate disconnected, the batteries stay around 12.5V

When I started the 911, I mesured voltage (at the batteries) and found it was moving from 14, 15 or 16 volts with no direct relation with the engine RPM.

I changed the voltage regulator for a new one (901-603-206-02-M14) bought here at PP

and when I started the car, the voltage is now perfectely stable but "only" 13.7 V instead the usual 14.4/14.5 Volt (at the batteries) when engine running (2.000 rpm)

I mesured at the rear of the car, at the new regulator connector. I found around 6 V at one connector, around 0 at other one and 14.1 V and the third one.

Do you think there is a problem around or can I satisfy with "only" 13.7 V at the battery when driving ?

Is this new solid state regulator adjustable ?

[Gunter]

You don't say what year 911.
I assume by the picture it's prior to 1978.
We need to see a picture of your 2CV with the number 75 on the license plate to verify that you are in Paris, France and not in Paris, Texas.

The Voltage Regulator for early 911's is not Solid State, I think.
13.7 V at 2000 RPM sounds good to me.

Test battery at rest 12.5v
test battery at idle 13.0-13.5
test at 2500 rpms 13.5-14.5 MAX

Salut

[rick-l]

I am no expert but if you look at the first chart in State Of Charge vs Voltage Article the line labeled "Rest" is the voltage vs. charge percentage with no current going into or out of the battery. 12.5 volts says 70% charge but there may have been a slight current draw when you measured that and it varies with temperature.

From that chart you can also see why the regulator manufacturer chose 13.7 as the charge voltage, the voltage the alternator is going to maintain on the battery. The "C" on the charge curves is the amp hour capacity of the battery. So for a 90 Amp hour battery C/10 would be 9 amps. So if you maintain 13.7 volts from no charge to full charge the current will be limited by what the alternator will put out until you reach ~ 70% charge and then the curves will shift to the right until you are at full charge.

Here is another good article TI (Unitrode) battery charger. Apparently you want to approach fully charged at a low charge rate or overcharge reaction occurs. At high charge rate it occurs before 100% return capacity has been reached. Overcharge results in hydrogen formation and loss of water.


12.5 at rest = good
VR 14-16 = bad
new vr 13.7 = good

[PAT4]

The 911 is a 2.2 T from 1970 with two batteries in the front.

Sorry, no 2cv at home but a Smart Car you can see in the background, the 2 places car that arrives in USA since the beginning of january !!!

So, the original regulator is not solid state but the replacement one I bought here at PP is, with a visible 2N3055 transistor.

So it appears that I have loss of tension around 0.4 - 0.5V between the rear of the car and the front. BTW, it is not very important : on my 914 there is 1 Volt difference !

So I am going to read articles rick-l suggested

[supdaf]

I just had a charging issue with my 76. What I found was the "noise attenuator" that is in line with the voltage regulator was causing the problem. The attenuator would ohm out good in my hand but the alternator would not charge with it installed. I full fielded the alternator to verify alternator function and now the attenuator is gone and all is well. The connectors are the same so you might check your charging without the attenuator installed as a troubleshooting exercise.

[304065]

Pat,

Judging by the "intermediate unit" on your electrical console you have either a '69 or '70 as this was eliminated in late 1971.

That is a Bosch voltage regulator, of course. It would be somewhat unlikely for you to have a Bosch alternator this late, more likely you have a Motorola-SEV Marchal. It was recommended by the factory to use the same manufacturer of voltage regulator as alternator.



That said, what you probably have is a voltage drop in the run forward caused by oxidation of, in order:

B+ terminal on alternator;
Red wire at Pin #14 of the 14-pin connector, probably oxidized--this carries current to the rear electrical panel to run things like the defroster, etc.
Starter terminal;
Battery terminals

And of course, the grounds are the other half of the current path, so I would check these as well.

Anyway, that's what I think is happening--oxidation causing a high resistance somewhere. The thing to do is disassemble the connections, clean with emery paper until bright and reassemble. This should fix the issue.

Also, I use a Transpo IB301A- which is an inexpensive aftermarket solid-state VR that is adjustable for "set-point." This shouldn't be used to compensate for oxidation, however.

Good luck!

[PAT4]

John,

Actually, I don't know what brand is my current alternator. My 1970 911 is an american one (#9110101614) imported in Europa in 1997.

The old regulator was a Bosch, the new one bought here at PP is smaller but also a Bosch.

So, I will remove the alternator next Week-end to check brushes, clean connections and verify everything.

I will also check the connections (I had problems in the past with the 14pin connector, for the reverse light) and come back to you to for debriefing.

Many thanks