Voltage / charging issues

[Sinister]

How large should it be? I assume you mean the gauge of the cable?

[klueless7571]

I should think 4 gauge or larger. You could get by with smaller if that's all you've got lying around. It's not as though these are permanent connections. If the wire starts to feel warm, just turn off the ignition and disconnect.

Derek

[Sinister]

I was thinking of maybe just running a long VMM probe from the alternator to the battery, to measure Vdrop. Would I damage something by doing this, with the wire being too small? How would that short something, as hinted above?

[klueless7571]

Well, you need to disconnect the existing cable to the battery. Then run your temporary cable from the alternator to the battery. You cannot just run your VMM because you'll fry the meter. There's a lot of current running through there. You've got to be careful not to short anything with your temporary cable. Use a continuous cable and make sure it is secured at both ends. If one end comes loose while your engine is running, it would not be a good scene.

Derek

[Sinister]

To measure Vdrop, I thought you had to have the regular cable connected AND the VMM connected as well, and, since current takes the path of least resistance, I would ONLY show voltage on my VMM if there was resistance in the other path, and the voltage I would see, would be the voltage drop.

Can I do it this way?

[klueless7571]

I thought you wanted to test if the cable was the source of your problems. Hence, disconnect the existing cable, and run a different cable from the alternator to the battery to see if your problem still exists. Why do you even need to connect up the volt meter? You already know there is a voltage drop between the alternator and the battery in your current setup. The mysterious voltage drop is the reason we are going through this whole exercise. Unless I misunderstood your problem description...

Derek

[Sinister]

I wanted to rule out what someone posted above, i.e,. that there is really no voltage drop, but rather, that the voltage reads lower up front, due to an accesory drawng too much amperage. Could that be a possibility?

Regardless, even if there is a voltage drop, it would be the cable or a conenction in one of the segments of the cable, or the junction box, which would be hard to determine?

[klueless7571]

Your problem is rather difficult to narrow down. If it was me, I would start with disconnecting the battery cable, and running a direct cable from the alternator to the battery. Hopefully, the voltage at both ends would be identical. Let the car run for 30 minutes. When everything is warm, see if the voltages still check out OK. My guess would be "yes". If some of your other accessories are draining too much power, and your alternator is not providing sufficient output, you would be able to tell by measuring the voltage at the alternator. If you have an amp meter, you could measure the amps that's going directly to the battery through the new temporary cable, and the amps going to the rest of the car. End of test.

If all your measurements are good, then at least we know that your alternator is good and providing sufficient output for your accessories. Then the next step would be to disconnect the power cable, section by section, and examine and replace as necessary. I wouldn't be able to help you there, as I have no clue as to where and how the cable is routed.

Good luck!

Derek

[Sinister]

Thanks. Thats the main problem. The way it is routed, its a PITA to get to each section.

Has anyone else measured what their numebrs look like?

[Sinister]

Hi. Some news:

I have narrowed the problem down to the alternator. Even on a test bench, when applying heat form an ordinary hair dryer, voltage drops. Clearly the alternator cannot produce the amperage when it gets hot.

This is the third alternator I have used on this car. Either they are all faulty or they are under-rated for the car?

[Sinister]

Does anyone know if the Bosch High Output (200amp) alternator is available for the 996T?

[niceguy]

I believe I read somewhere saying that if you bench test your alternator and there is Vdrop as it gets hotter, the voltage regulator (removable & changable) is the problem. Voltage regulators do wear over time.