I need an advice on how to proceed.
I own a C2 MY05.
I changed the battery last week and the technician told me that my alternator is running too low.

So here are my readings of my alternator and battery:
(The reading of the alternator is taken from the back of the alternator itself - I took the alternator out and connected a cable to the back of it and then reinstalled...)

Running @ 1500-2000 rpm with lights on, A/C on and radio on.

Cold engine:
Alternator: 14,30V
Battery: 13,80V

After 5 minutes:
Alternator: 14,00V
Battery: 13,60V

Hot engine (15 minutes):
Alternator: 13,80V
Battery: 13,30V

Questions:
1) is it normal to have a 0,5 volt drop from the alternator to the battery?

2) Is it normal that the alternator drops from 14,30V to 13,80 as soon as the temperature raises up?
Should I change the regulator perhaps?

3) What are your readings at the battery terminals?
Are mine readings in the average or is my alternator too low?

4) Should I consider changing the cable from the alternator to the battery?

Thanks a lot

 

The early 997.1 (2005, 2006 and perhaps even 2007) have had some issues with the alternator cable and the starter cable. The issue is seen mostly when the engine is hot.

Replacing the cables has helped a few people. It is a very embarrassing shame for Porsche to have designed such poor cables. In addition, they are rather expensive and not easy to replace.

I am sure other people will chime in with more details. My 2006 C4S has the starter cable issue, and cranking a hot engine is tedious and pathetic sometimes. When cold, it is always great.

For the battery, during the winter, I use a floating charger from Black and Decker $20 at Home Depot, and do not worry about the charging voltage. Works perfectly.

Yves

 

I have been at the dealer and watched a tech install one of these very cables, he mentioned it was more frequent repair. The chargings AMPS out of the alternator will initially be high after starting and decrease shortly after when the battery no longer needs it... But volts are a different story, they will increase with rpm to the set voltage by the regulator. To my knowledge.... I could be wrong.

 

You ought to check your alternator cable - it is known to lose contact in some cases.

 

Try checking the difference between the battery voltage between terminals and the voltage from alternator to ground with the key out and doors closed, lock the car with the hood open. The only thing on will be the engine 'hood' light. Have a look at the thread on battery cable/current loss on renntech.org where paulspeed chimed in.
Voltage should be just about the same.

 

Half a volt is top of normal range for voltage drop between batt. voltage and back of alternator. All your voltages look mostly normal, but your tech could have been talking about an amp load test. Your alternator is rated at 150 Amps and a load test should be at least 80% of that (120A) for a good alternator.
Ben