Is my alternator working?

[henko]

I made the cardinal sin of reversing polarity on my jumper cables the other day - that made me feel like a real idiot.

I swapped out the battery and the car now starts fine (it was acting funny on the old battery which was old anyway).

The "charging" light on the dash is not lit up, and the car runs fine. How do I know the car is not just running off the battery? How do I check the

I got a new voltage regulator to begin with, hoping that my alternator was spared from my stupid mistake.

[sindo57]

if the alternator is working fine you should be able to turn the car on and then unplug the battery.. if the car turns off then you need a new alternator.. if not than your good... this is the cheap easy way to find out if you broke it or not

good luck

[henko]

Thanks - I tried that and it ran fine and I let it run for about 30 seconds. There was chime coming from the fuse box but other than that everything was fine! Phew! I did not feel like spending $400 on an alternator. So it seems my old, discharged battery took one for the team. Rest in peace!

[Eagledriver]

Turn the ignition switch to on but don't start the motor. Your battery/charge light should be on. If it is and it goes off when you start the car, your system is working fine. The check you did will tell you the same thing but it can also damage your alternator. Another way to check is with a voltage meter. You should have about 12.5 volts with the motor off and 14 with the motor on.

-Andy

[don gilbert]

do that check on a motronic car one to many time and it will cost more than 400.00

[James Brown]

yeah, best to get a voltmeter. I removed the useless oil quanity gage and got a voltmeter from Palo Alto. good peace of mind. and looks great!

[T77911S]

Originally Posted by sindo57

if the alternator is working fine you should be able to turn the car on and then unplug the battery.. if the car turns off then you need a new alternator.. if not than your good... this is the cheap easy way to find out if you broke it or not

good luck

thats not a good thing to do with todays alts. you could do that with the old stuff, like VW's with generators, but i would not do it with an alt. i forget why. i think you risk blowing a diode.

best is to check with voltmeter. if you do not have, go to advance or autozone, they will check it for free.

[RWebb]

1st reason - it presents an open condition (no load) to the diodes that rectify the waveform to create a DC voltage; this is likely to blow them up = $$

2nd reason - as per above posts, it can send spike and/or over-voltage to the engine computer (Motronic "brain") that runs the engine in all 911 1984 & later; this is likely to blow it up = $$$$

[mxessin2]

A safer way to check -

Step 1 - With the car turned off take a volt meter and check the voltage at the battery posts. It should read around 12 volts.

Step 2 - Start the car and check the voltage of the battery at the battery posts.
It should read 13.5 - 14.5 volts.

[twistoffat]

Alternators rely on teh battery to regulate the current. Donīt uncouple the battery while running as it could fry the alternator. Iīve also heard that the surge can fry your computer

[dshepp806]

Huge gamble disconnecting it while running....please don't ever do that again.....or you may be in for more than you realize.

Bad advise on your 911,..careful,..careful.

Best,

Doyle

[vintage guy]

+1....Don't run your car with the battery disconnected.