924Board.org

[changeworks]

Hi Guys,

Ran a quick comparrison of voltage differences as suggested at battery and at alternator the results as follows:

.....................At Battery....................At Alternator
Engine Off ......1234.............................0000
at idle 950 ......1256.............................1398
at 2000rpm .....1294.............................1398-1405(flickering)
at 2000rpm ......1175....(electrics on)......1398-1405(Flickering)
at idle..........................(electrics on)......1398
Engine off ........1210 (rad fan running).....
Engine Off...................(lights on)............0.02

The numbers arent constant little fluctuations, partly the way l have to attach the leads so l can be inside the car (l think), although there is an on off drain/fluctuation with the indicators.

I am considering running a lead directly from the battery to the alternator to see what difference it makes and l have yet to clean the grounds as you suggested.

George
Glasgow
Scotland
_________________
1983 - 924.......

"A mind once stretched by a new ideal will never regain its original dimensions".

[Sleykin]

Sounds like you are on the right track. High resistance between the alternator and the battery (either ground or +) would do that to you. You can measure the voltage from one end of the wire to the other or from the alt case to battery ground with a load (engine running lights on) and the bad wire/connection will show up as a voltage on the wire where it should be very low. When you find a wire with a volt or so dropped across it that will be the bad area.
_________________
Glenn Neff
Medford, OR
87' 924S

[Min]

you can do what slekin suggested, or you can use the 'ohms' function on your multimeter to test the resistance in the wires between your alternator and your battery.

Min

[Smoothie]

Wouldn't it be better to measure for the voltage drop in a situation like this? By my understanding of wires and resistance, you can have for instance an old heavy gauge wire with some oxidation resistance built up in it - that wire may perform just fine with lower amounts of current flowing, but when a larger amount of current closer to the wires' rated capacity is fed, the wires' resistance is enough to block passage of some of that larger current. In other words, an ohmmeter that tests with a small amount of current might read 0 ohms and not necessarily give the whole story on a heavy gauge wire that really should be tested under a heavier load.
_________________
"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[Sleykin]

Smoothie is correct. Unless you have a VERY expensive micro ommeter you won't be able to see the small amount of resistance involved here. For example .. with 1 volt showing in a wire carrying 20 amps you would have .05 ohms of resistance. My $300 Fluke won't measure that reliably on the ohms scale but any decent meter will measure the 1 volt. While that resistance may seem small, it is actually quite large to the voltage regulator that is "calibrated" to the nominal internal resistance of the battery. Now if you see 2 volts on the same wire with 20 amps in it you have .1 ohm. Since he is seeing ~2 volt drop from Alt to battery he is looking for something around .1 ohm in the bad wire/s or connection/s.

_________________
Glenn Neff
Medford, OR
87' 924S

[changeworks]

Hi Guys,

Aint had a chance to do anything yet, family commitments and the weather is not really any good for working out in the street on the car.

However l got hold of the Haynes manual for the wiring diagrams and the Porsche Electronic Technical CD which covers all models. The drawings of the 924 harness and power supply on the CD together with each parts discription make the haynes wiring diagrams more understandable, for me anyway......

Hopefully l can get into the wiring over the next few days..

Cheers

George
Glasgow
Scotland
_________________
1983 - 924.......

"A mind once stretched by a new ideal will never regain its original dimensions".

[Min]

I replaced the voltage regulator on my alternator, and it was working great for about ... 5 minutes ... then it started doing the same thing again, seems I blew another voltage regulator .... any hypothesis on why that would happen?

Min

[Smoothie]

Min - There are some tests of the alternator itself that you might be able to do - otherwise it's time for a pro bench testing. Tests of diodes, amps output, stator, rotor, etc. are shown here - http://www.audiurquattro.de/ralf/infos/pdf/Alternator.pdf
That pdf is specifically for a Bosch 110 amp alt - the OE Bosch alt in the 924 is 75 amps, but most of the info given should apply.
_________________
"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[Min]

after popping that second voltage regulator, I decided since i found a cheap source of voltage regulators(11 dollars canadian) to just replace the regulator on my spare alternator and swap it in(killed the regulator on that alternator a couple years back). Since then I havn't had any problems with it. Charging at 13.76, which is has never done in the time I've owned this particular 924. Thanks for the help everyone.

Min

[Min]

another note, seems the car has alot more power now that its running on 13.7 volts (as compared to 12.7 or 12.8 wich is what it was running before). Does that seem normal?

Min

[Sleykin]

Yes.
_________________
Glenn Neff
Medford, OR
87' 924S

[Sleykin]

Yes.
_________________
Glenn Neff
Medford, OR
87' 924S

[D Hook]

You'd be amazed how much smoother and better it will run if you clean all the grounds; under the hood, under the dash, in the hatch area, etc.

[Paul]

Yep, your ignition system is getting more voltage, so the spark is hotter.

[Min]