Correct alternator Output

[bairdc3]

1980 911sc

Just Rebuilt Marchal Alternator this week and replaced in car, belt is tight. Voltage regulator replaced 1-1/2 years ago.

Light comes on at low idle.

Disappears above 1100rpm

Voltage readings

Low idle 10.8-11.5 volts

2000rpm and above 13.2 volts

Lights on and above 2000RPM 13.1 volts

Fog ligts and lights above 2000rpm 13.0 volts

Radio, amp, all lights and fog lights above 2000rpm 12.9 volts.


Battery is registering weak when a load is put on it. (using Load tester at auto parts store) Optima Battery.

I have read here that the alternator should be putting out anywhere from 13.5 volts to 14.0 volts. Seeing that the Alt ouptut is going down as devices are turned on which is correct, could I have a short somewhere that is causing the output to be low in the first place (max output of 13.2 volts. Or should I invest in a new battery and or another voltage regulator.

[304065]

Why did you have the alternator rebuilt? What were the symptoms?

Where are you measuring the battery voltage? Should be at the battery terminals for diagnosis.

I don't think you have a short but you definitely have a voltage drop, e.g. you aren't seeing the full 14+ volts at the battery. There are probably three reasons why this could happen:

A. The new alternator was installed, and the battery was weak, and the alternator overheated trying to charge up the battery, melting the solder on the diodes, taking one of them offline. A scope would show a missing peak. This is not very likely, but it's always best to start with a fully charged battery even if it means leaving it overnight.

B. Voltage regulator is not sending enough current through DF wire to excite the field to increase output voltage. Could be defective voltage regulator. More likely.

C. Oxidation on contacts at various points in the car that is causing a high resistance, resulting in a voltage drop. Most likely. When you installed the new alternator, did you clean the four wires going to the back down to bright metal? Did you get the nuts on tightly, and crimp down the faston terminal on the black DF wire so it was tight? How are the wires in the 14-pin connector, have they been cleaned? You can use denatured alcohol and a q-tip to clean them, I use electrical contact cleaner and a piece of emery cloth to take off the crud. Also check the wires going in and out of the voltage regulator. If you have an inline noise supressor, take that out of the circuit, just plug the cannon plug directly into the botom of your VR. Be careful, those contacts are old, can be easily damaged by too much torque. That might help. Finally, do you have a nice bright connection at the starter lug, and also a good transmission ground strap?

It sounds like the voltage regulator is trying to do its job, I think some oxidation somewhere isn't letting the current through. It's kind of a chore, but half a day spent cleaning those various spots is your best bet to fix the problem. And unlike replacing stuff, it's free!

Good luck!

[RoninLB]

Warren posted awhile ago that putting a small resistor into the "G" light circuit would properly load the alt at low rpms.

I probably got some of the explain wrong

[RoninLB]

Oh yeah. about your high rpm prob.

I used to "full field" external reg. by hitting the field connector with a jump from the battery hot. I never did it on a Marchal. The "full field" will make the alt perform at Max output.
So, does your alt perform ? gets answered.

[bairdc3]

I am measuring the Volts at the Cigarette lighter using a digital volt meter. http://www.cetsolar.com/voltmeter.htm

The battery was at about 11.2 volts when I returned the Refurbed Alternator to the car.

The battery seems to never take a full charge. I charged it for two days trickle charge at 2 amps only got about 12 volts, charger stated the it was never charged fully. Same thing with overnight charge at 6amp.

I have taken the noise suppressor out of the mix by plugging directly into the VR.

I replaced the Alternator to begin with because it went bad. No gen-light when key turned on and whole car died on the road one night.

When Alternator was out grounded blue wire turned on ingition bright red light on gen-light so the bulb is good.


Tighten all leads on Alternator, I guess I will go back and clean and retighten again.

Battery terminals and ground to car clean and too bare metal.

[RoninLB]

Originally posted by bairdc3

The battery was at about 11.2 volts when I returned the Refurbed Alternator to the car.

ok.. this is what I would do.

I'd check with John C, Loren, or Warren to see if you can full field the external regulator.. at the regulator.

I had a history of getting one in 6 or 8 rebuild alts being NG

[Early_S_Man]

baird,

Specified Voltage range in factory service manual is 13.5 Volts - 14.2 Volts ... remember that your meter's readings can vary due to calibration and accuracy tolerance issues!

Your output at 1100 rpm and below is typical of an alternator below the 'Zero Ampere rpm' ... which tends to get higher as the electrical system ages and corrosion builds up at all of the connections.

The resistor mod accross the warning lamp holder I recommend is designed to increase the pre-excitation current through the field windings, and is described in Tech. Bulletin #1 below.

Your Voltage regulator is working, but all of the wiring connector cleaning John already suggested needs to be done to assure best possible operation!

[bairdc3]

Ok I will go thru all the cleaning john suggested and pull the alternator out again.

Does someone have a pic of where the 14-pin connector is at? So I can go thru that as well.

[RoninLB]

Originally posted by bairdc3
Does someone have a pic of where the 14-pin connector is at? So I can go thru that as well.

on rear of engine comp elec panel.. be careful of flying wires If you open up the male or female side of plug.

[304065]

Ok, the 14- pin connector is a good place to start. They often crack or loosen up with age. New body, cap and pins available (check our host, I got mine from Stoddard)

What you do NOT want to do is open the thing up without a copy of the wiring diagram/pinout for the pins. When you slide the cap off, the wires will go flying out, and they must be reassembled into the plug in the exact order, otherwise bad stuff like fire, etc., can result.

Warren's advice, as ever, is spot on. As the car ages, inevitably there will be high-resistance connections that pop up here and there, which can be fixed with the resistor. Remember that the more current flows through the blue wire, the more heating you will get, however, so it's not a band-aid fix for bad connections.

Good luck!

[targa80]

When the alternator was refurbished were the three exciter diodes replaced. The exciter diodes provide output voltage from the aternator to the voltage regulator. This is not the same connection as the power diode output to the battery. If the exciter diodes are old and degraded from heat they will not output the full voltage as required. I had the glowing light on my 80SC when I bought the car. After troubleshooting the charging system I found the exciter diodes were the culprit. I replaced them with 1N4000 diodes. I did that repair in 1992 and have not had that problem since. You will have to be good with a soldering iron and install the diodes in the correct positions as the old ones.

[bairdc3]

PO had the Optima battery in the car and bought it 10/02. I had no receipts nothing. Autozone found that the battery was week and could not be charged correctly. Spoke to Optima they are shipping me out a new one today, once someone other than myself identified that the battery was indeed bad.

Still hunting the low output of alternator. Tonight I will go thru all the connections as per John's suggestion.

[Superman]

I feel a little sheepish posting after the Great and Powerful Warren has posted, but here goes. I'm glad you're getting a new battery. A battery that cannot come up to 12.5 volts or so is junk. I'd guess your alternator rebuild will be in the $100 - $150 range. That's pretty good considering it's a French product in a German race car. That was a joke. Perhaps two jokes.

At any rate, your new system should work flawlessly making comfortable over 13.8 volts.

[RoninLB]

What's interesting is that Nobody addressed "full fielding" the alternator.. An external regulator system is easy to do. An internal regulator May blow, like the Delco reg.

so my impression is that nobody has even heard of "full fielding" an external regulated alternator ?

Huh ?

[bairdc3]

Well I'll say it HUH?

How do I full field the REgulator?

[targa80]

When I troubleshot the light problem that I was having I did the full fielding test with no adverse effect on the V/R. I used battery voltage from the fuse block in the engine compartment. When I did the test you could tell the engine was being loaded down and the output from the alternator jumped up. I can't remember how high the voltage went though. It has been 12 years since I did the repair. If I remember I physically removed the wires from the connector going to the V/R and connected them individually. So instead of connecting the wire from the exciter diodes I used a jumper wire from the fuse panel.

[304065]

Ron,

What you are describing is applying +12v from the battery directly to the DF circuit. This is the same as applying +12v to the D+/61 terminal-- one brush of the rotor is grounded, the other gets the full +12v. This SHOULD cause the alternator to generate its maximum output for a couple seconds, somewhere on the order of 18V, and it should make a hell of a noise when it does.

That's one way to test it, but you could also cook it if you aren't careful.

[Early_S_Man]

Ron,

I don't use or recommend the 'Full Field test' procedure, because it could damage several electronic devices in the electrical system ... including the battery - especially Optimas, CDI unit, and factory alarm system, if the alternator is left connected to the car's electrical system. The full field test should be limited to no more than two seconds ... so I hesitate to suggest it to everyone! Definitive instructions as to how to conduct the test, and how to interpret the results ... could be considered beyond the scope of most beginners on this board, and blame for fried alternators ... well, I would rather avoid that complication, too!

Traditional alternator test methods, including the Porsche factory service manual, dictate that the alternator be tested completely disconnected from the regulator and electrical system. A variable regulated power supply, power rheostat, two Voltmeters, two Ammeters, and test load resistor are needed to properly load and test the alternator. Since I have all of the required test equipment ... I would rather do the full regular test if I am going to disconnect an alternator. It is possible to test a 911 alternator in the car, disconnected from the electrical system ... but it is probably easier for most to just remove the alternator and have it tested free at a shop.

[bairdc3]

Thanks for all the great advice. What a great group.


How can one comment on technical advice when there is some much great advice? Don't stop keep the advice coming.

I will get back to this I have to wait for my New Optima later this week, I have cleaned all the connections under the car. Ground strap both ends and two cables on the starter. I'll do the engine compartment and areas this week while I wait for battery to arrive. I think I better hold off on then full field test, as a last resort as this may get a newbie like me into some trouble, and I just had the alternator rebuilt. Well someone said 4 out of 10 rebuilds aren't good, but being that the car is 25 years young I would expect some corrosion here and there. Cleaning is order first. More to follow later.

Thanks

[bairdc3]

Ok after a week I have a new Optima battery and have basically only cleaned all the suspect areas under the car (Transmission and starter connections) and the battery ground.

Output I am getting now.

13.8v at the battery running at above 2000rpm

13.6v with headlights and radio, running at above 2000rpm

Is this sufficient? Or should I clean other areas as well (14pin connector and or install diode on Speedo.

If I install diode what kind?

Thanks for everyone's help, I still have a couple of other electrical areas to track down. ie no light at engine deck lid, wiper fluid pump, but all other areas seem to work fine.

Also should the emergency light on dash be somewhat lit when the lights are on? I bought this car in June and never really noticed this to be lit up. It's really bright and of course blinking when it is on, but it is a dull red when off?