BlackCab

I have a very sad problem. I got back in town after being gone one week and my 1990 C2 wouldn't start. It turned over once and that was it. The car jump started right away. I drove it around and it started several times that day and the next morning, no problem.
I had a rebuilt alternator installed about 2 months ago because the car wouldn't start when I got in to drive home after dinner one night. It could not be jump started that time. The battery is new from January, 2003. I took it to a friend of mine yesterday. We hooked up a voltmeter. With the car off, the reading was 12-something. While idling, it was 13.2-13.4. There was no significant change when the radio, heater, lights were turned on. He suggested that the voltage regulator wasn't picking up and that I had a bad alternator. I took it back to the guy that put the alternator in and he tested with a digital voltmeter. It said "charging system normal". The readings were all essentially the same. It kept saying "system noise" though. They thought that the batter was dead and that there is no way I could be driving all around after the jump start if the alternator wasn't working. They pulled all the fuses out of the front box and put them back but he wasn't using an ampmeter at that time. He then installed a new battery (after that, the voltmeter still read "system noise"). We had the hood light off and everything off. I have a sneaking suspicion my problems aren't gone. Is it possible that there is a drain or that the alternator is bad? Any thoughts (besides that this message is too long?)

Doug H

I once had a bad problem with a 944. I could not keep a battery charged and I replaced the altenator several times and put new batteries and etc. in it. I latter heard that it was probably a ground issue.

DavidI

I'd be very tempted to work through the procedure in Adrian's book for checking the alternator and battery voltage - your idling voltage is marginally low, so perhaps the alternator is not quite right. The testing steps work through battery, alternator and regulator and current leaks - highly recommended.

Lorenfb

If you suspect a drain, then you need to test for it with a milliamp-meter.
The 964 alt. usually only charges to 13.5 to 13.8 and not the like the 911
3.2 which charges to 14.5. The max. drain should be less than 70-100 ma.

If the rebuilt alternator has a junk regulator, then the noise being picked
up could be the result of it. Any alt. regulator is a switching regulator
and not a linear regulator which means that it is either "on" when the
voltage is below the threshold or "off" when above. Some regulators
produce more noise than others.

Good Luck
Loren
'88 3.2

BlackCab

Thanks, I hadn't gotten there yet in the book but I'm flipping there now. That is interesting about the regulator. I was thinking that less than 13.8 with the car on was too low. I'm going to find a milliamp-meter and test for a drain. Hopefully with any luck I can avoid the multiple batteries and alternators! Thank you so much.

Adrian

I am afraid I am going to have to step in and disagree with you on a number of points Loren.

The voltage regulator is never off. If it is, the voltage to the rotor of the alternator is effectively zero and the alternator output voltage drops to zero. The VR control the field strength of the alternator rotor at all times. It is this rotating magnetic field (electro-magnet) which creates the AC output of the fixed windings. The voltage regulator of the 964 is an analogue device.

If you are checking for a current drain you use a decent multimeter such as a Fluke. I have a Fluke 87 but other Flukes or equivalents are just as good.
You select a meter which has the ability to read three decimal points. 0.000 range selection.
When you first hook up you select the highest current rating which is normal 10 amps. On some meters this means putting the red or positive probe into special socket. This is fuse protected. If the car is drawing more than 10 amps the fuse will blow and not the meter.
When you are set up and hooked up then you use the range switch to read the lower current readings. In my book you are shown images of the meters that I use.

The normal current drain for a stock standard (no after market alarms fitted) 964, 89 to 90 is 8 ma with alarm off and 13 ma with alarm on. A stock standard 91 to 94 it is 8 ma with alarm off and 20 ma with alarm on.

The maximum allowable current drain is 90 ma with all after market systems installed.

One very important point. Never do a current drain check 20 minutes after shutting the engine off using anything less than 10 amps selected first on your meter.

Never do a current drain check when your engine is hot.

These warnings are to save your meter not anything to do with the 964.

The alternator/regulator assembly is capable of a maximum output of up to 22 volts. Relay R34 provides 22 V overvoltage protection to the PDAS/ABS or ABS only systems.

The minimum output with battery charged for ANY automobile charging system is 13.8 volts. This maintains a 1.8V differential which provides a constant charge to the battery underload. If the voltage is lower than this the charge rate is too low. If the output of the alternator is less than 13.8V at idle with the battery fully charged then you have a potential problem. After a cold engine start up the voltage should be around 14.2V. I was only playing with this the other day. All German cars use the same parameters which are an industry standard if you like.

The 964 is fitted with a brush type internal regulator. Electrical noise for it to have an impact has to be imposed onto the output voltage and somehow get past the battery (which acts like a great big capacitor and sucks the ac voltage off).
All other noise is induced directly into the wiring. This was an issue on some early 964s and was resolved by the installation of an electrical suppressor in the engine bay electrical panel.
The most common source of electrical nosie problems which are directly related in sound to movement in engine rpm are the ignition wires. An insulation test of the spark plug wires is recommended. There are other areas to look as well but you start there. Always check the putput lead from both coils to the caps. Check for arcing to the body around the coil mounting area.
Ciao,
Adrian
964C4

Lorenfb

Sorry, you're wrong about alternator regulators. Take one out and check
it on a bench test. If the regulator weren't a switching regulator, it would
dissipate a huge amount on power, since the field winding is just 3 to
4 ohms resistance. At 14 volts thats almost switching 50 watts by the
regulator.

The field winding integrates the switching current which results
in a constant output voltage. That's why if you view the voltage ouput
of an alternator with a scope you'll see a ripple (varying) voltage. This
ripple is in effect the "noise" referred to by some alternator testers.
If one of the diodes fails, then ripple/noise increases significantly.

Next, the current on ANY late Porsche ('84 and up) RARELY gets below
25 ma. The 8 ma quoted only exists in ones dreams. Also, Bosch regulators
used on the 964 alternators are set to 14.35 which results in the
battery voltage being NO more than 13.6 to 13.8 after the voltage
drop from the rear to front. This lower voltage has resulted in many 964
alternators being incorrectly replaced by some shops.

If you're refering to the Paris-Rhone 911 3.2 alternator shown in the
in the 964 book (pg 383 - incorrect alternator for 964), then the
battery voltage does get to 14.2 as the regulator is set to 14.75.
The 964 uses a Bosch alternator, i.e. the first 911 alternator Porsche
used again since the late '60s.

Have Fun
Loren
'88 3.2

Adrian

I will keep dreaming then Loren because I am not quoting Porsche figures I am quoting my own figures and other cars I have measured.
Ciao,
Adrian
964C4

BlackCab

Loren,
Am I interpreting you correctly? It seems like you're not saying that the regulator is "off" but that by 'switching' you're talking about AC and DC current? That's what it seems like you mean because in the next sentence you're talking about ripple voltage. Are you meaning that some AC gets through and it increases in the case of a failed diode? That makes sense to me.

Lorenfb

An Bosch alternator & regulator works as follows:

1. The regulator senses the battery voltage via the DF pin which
goes to the alt. light in the instrument cluster.
2. When the voltage drops below the preset threshold of 14.35,
then the regulator switches "on", i.e applies full voltage to the field.
3. When the battery voltage reaches about 14.35 , then the
regulator switches "off".
4. The regulator has what's called a hysteresis of about 200 to 300
millivolts between the "on" and "off" voltage points.
5. If the battery is low or there's a lot of accessories running,
then regulator stays "on" longer, i.e. the duty cycle of the alternator
increases and vice versa.
6. All alternators are three phase units, i.e. one set of windings thru
diodes conducts current while the other two "go along for the ride".
As the rotor turns, the set of diodes and windings conducts.
This also contributes to the ripple (small A.C. voltage - millivolts)
on the battery.

Bottomline: Think of an alternator as a voltge source with very low
internal resistance which is switched "on and "off" to apply voltage
to the battery.

Good Luck
Loren
'88 3.2

Adrian

Dear Loren,
I am afraid that in nearly 30 years I have never ever seen or heard such a description before. You certainly did not go to the same college and study the same books as I did.
Ciao,
Adrian
964C4

PS: I also have to visit your facility. You seem to have invested in some serious test equipment. I have rarely seen even Lucas, Lear, TRW or Bosch facilities with the test rig to check out brush type integrated voltage regulators. Normally they are thrown away and a new one installed.

Doug H

My car idles at 13.8 with my stereo on which is quiet a load. I have three amps and each one has separate digital voltage meters hooked up. Don't know what it is when I turn the stereo off because the meters go off too. Battery should be 12.4 with a good charge. Are you sure his issue could not be grounding.

If he has a decent load that is constant because something is screwed up shorting somewhere, 13.2 to 13.4 sounds reasonable for a healthy alternator.

Adrian

Dear Doug,
You are correct. One of the issues is age. Negative battery cables corrode. Earthing points corrode. This will drag the voltage across the battery down.
A simple removal of the battery terminal connectors and a bit of a clean up some sometimes do the trick.
I know the load you put on the system, I have seen the pictures. You are still maintaining 13.8V which is correct. Dropping below this level indicates something is wrong. Coupled with a flat battery clearly something is wrong and all the talking in the world ain't going to fix it. Somebody has to go through the current drain process and the earth strap and lead checking process.
Another issue is battery capacity. 964s each batteries especially ones that are not the correct capacity. 72 amp/hr or higher and 88 amp/hr for a cab.
A lot of people put in 66 amp/hr batteries and they are killed off quite quickly if you drive in winter.
Ciao,
Adrian
964C4

Lorenfb

Bosch alternators with an alternator light provides good diagnostic capabilities:

1. The light must be "on" with the key in the run position w/o engine started if not;
a. field winding is open or,
b. bulb is bad or,
c. brushes on regulator are bad or the regulator itself or,
d. slip rings are worn.

2. The light must be "off" when key is in "off" position if not then a shorted diode
in the alternator.

3. The light must go "off" when engine is started if not;
a. light glows dimly,
I. and does not get brighter at higher RPMs - poor connection from alt. to battery
II. light gets brighter at higher RPMs - an alt. diode is open or a field diode
is open
b. light glows brightly always - a shorted stator winding

A simple alternator regulator test method:

1. ground the case tab of the regulator
2. connect a variable voltage source (0 to 20 volts) to the DF tab (connects to
the alt. field spade in the alt. (one of the two brush terminals)
3. connect a volt meter between the plus terminal of the voltage source
and the other brush of the regulator
4. vary the voltage source and measure where the voltage switches between
zero and the source voltage, that's the regulation point of the regulator.

The alt. regulator provides a switched ground to one of the two field winding
terminals. The other field terminal is basically always at 14 volts.

Have Fun
Loren
'88 3.2

ian c - u.k

hi adrian
you mentioned before about cabs having a bigger battery .
so i enquired at my local dealers before i returned the bosch silver i had just bought ........
they told me the batteries are same apart from rs which is smaller .
i also had a look on PET and couldnt find any info .

i can still return the bosche one , so can you please tell me more about this bigger battery

thanks