Dead battery - Is the alternator bad?

[Ian c]

Originally Posted by dghii

Dude,
Quit checking molecules and stuff. You have a bad voltage regulator. Disconnect your battery. Remove your alternator and replace the regulator.

You will not be able to detect a bad regulator with a DVM. It will not spot a bad diode within the regulator. Your problem is that the voltage coming out of your alternator (the output is the regulator) is all over the place and makes the electronics in your car do really weird stuff.

Your car did not develop fantom current draws overnight. Don't overthink this. This maybe a Porsche, but its really just a car.

Ahhhh ....
The good old "diagnose with your wallet" theory

[cas951]

3point2,
Your chrging seems fine to me. As long as the Alt output is 14+ volts with no load you should be fine. If you want to test further let the car idle, turn on your lights, AC, and other accesories to see what voltage you have at the battery.

You should have 13+ volds.

What you have is a drain when the car sits for awhile which drains your battery. This is why Ian and I suggest you use the voltmeter and pull your fuse out 1 x 1.

If you don't find the culprit from the fuse the likely cause is either the starter or Alternator or bad Ing switch.

[Ian c]

Indeed .
I suspect he's decided to give up and go get drunk

Hopefully he'll be back tommorrow and we can carry on with the online diagnosis

An alternator and voltage regulator can be working fine yet not put out enough volts to charge a battery .

The fact his is putting out enough on its lowest reading (2nd test = dropping) , and his battery DCv reading went up indicating a fuller charge , leads me to look at other things as I mentioned in my "best guess" post .

I had a read back earlier, and depending on the mA drain test results , the ignition switch is edging its way towards the number one on my list ....


(Radio fail)

[dghii]

Originally Posted by Ian c

Ahhhh ....
The good old "diagnose with your wallet" theory

No. A 3 time Boxster owner who had the EXACT same problem 3 months ago and who fixed it after diagnosing the problem.

You want to verify you have a bad regulator? Get an oscilloscope and look at the output of your alternator. You'll see that you're missing (at least) one of your diodes.

[Ian c]

Ive had a bad diode draining the battery , also a bad connection on the alternator , a bad battery connection , bad radio , bad ground , bad ignition switch , bad alarm , bad immobiliser , bad door switch etc etc etc .

You could well be correct , you could well be wrong .
You could scope it to test , or you could meter it .

I too had the EXACT thing happening within the last 3 months on my boxster ....
It was the ignition switch ...

I'm used to diagnosing before ordering parts and scheduling labour ....
It's what I do for a living , and have a huge amount of test gear at my disposal ( each Instrument tech working for me carries about 20Ks worth in their toolkit)
If I did it by guesswork and throwing money at it , no matter what past experience tells me , I'd be claiming unemployment

This is me diagnosing using experience .
Just a pity the guy had allready been to the main dealer , then 2 specialist that diagnosed with his wallet first ....
http://www.volkszone.com/VZi/showthread.php?t=850130

[dghii]

I understand that you wrench for a living and appreciate you taking the time to help a fellow owner. If these were expensive parts requiring lots of man-hours to replace, I'd be right there with you.

I've replaced ignition switches on Boxsters because of weird symptoms (radio on/off), lighting, AC blower working sometimes but not others. Never had the ignition switch determine what the charging voltage went to my battery, nor cause otherwise working accessories to suddenly draw more current and run down a battery.

Hopefully, he'll get it sorted out.

[Ian c]

I suspect on of the aircon faults caused by the faulty ignition switch was causing the drain , but never really diagnosed it as the switch was known faulty so got changed out.
After this , When the car was driving again I had no fault

It had BAD problems with the key not springing back after activating the starter , and sometimes being difficult to remove ...

[3point2]

Thanks for the replies! Yes I did take beer break and friend stopped by an ended up abandoning the car to continue with the beer and a BBQ lol

Ok I'm back on the car now and am going to begin the fuse check and drain. I'll be posting updates here shortly. Thanks so much for the help!

-Leo

[3point2]

I have the positive cable connected to the batter and the negative cable disconnected. I have my meter set at 200 milliamperes and touching the red meter cable with the negative battery cable post and the black meter cable to the disconnected ground cable. And I'm getting 0 readings. I've adjusted the scale but still no readings?? What am I doing wrong?

I checked the voltage on the battery and its still reading 12.2V so the meter is working.

Thanks,
-Leo
510-710-8320

[cas951]

Originally Posted by dghii

I've replaced ignition switches on Boxsters because of weird symptoms (radio on/off), lighting, AC blower working sometimes but not others.

I don't mean to hijack this thread but I just realized this could be the problem I'm having.
My Bose system is acting really weird. It started with audio fading from low to high volume. Now when I hit a bump on the road it turns on or off on it's own. When I want to turn it on I get nothing. When I hit a slight bump on the road the radio comes on automatically. This was on my last road trip last weekend.

I went for a long ride yesterdday and the radio did not turn on at all. Drove over 300 miles.

[Steve Tinker]

Leo...
Try attaching the red probe of the meter to the end of the ground cable and the black probe of the meter to the battery terminal. You had the polarity wrong and depending on the meter it may not indicate any mA drain.
At 12,2 volts your battery is barely 50% charged.

[3point2]

I tried reversing the cables as you had mentioned and still no readings.

[Steve Tinker]

Just to verify your Ma scale is working, switch on an electrical load (interior lights say) still with the battery negative terminal disconnected and connect the meter up in series again in the Amps scale.
The meter should show a reading (the load of the interior lights) when you connect the meter across the end of the cable and battery.

[3point2]

I am using a different meter. It works now. I'll be posting results shortly. Thanks!

[3point2]

I pulled each fuse and all the readings are at 1.70 amps. No big fluctuations anywhere.

Is that ampere normal?

[Ian c]

Originally Posted by 3point2

I pulled each fuse and all the readings are at 1.70 amps. No big fluctuations anywhere.

Is that ampere normal?

No it is not .
1.7 mA is normal .
Are you sure you're reading it right ?

If the meter you're using now is the same as the one you posted a pic of earlier , what are you set to in the dca range ?

[Ian c]

It looks like we missed each other again while I was out today , and you're offline now just as I'm getting ready to watch a movie


Here's a few more quick tests if you're still working on it .
With your meter in the same position , click over to Vdc ... What are you reading volts?
You need to clarify that your drain is 1.7 mA ...
Next do the same check on the alternator connection BATT . What are you reading mA?
(Be carefull not to touch this wire to anything !! The best way is to disconnect the battery then remove and secure the wire with the test leads fitted , then reconnect the battery. )
While you're in this area , a alternator drain can be checked at the same time (preferably with assistance so nothing shorts) . Does the battery mA reading drop when the alternator is disconnected ?
Next reconnect everything and go from the alternator BATT , to ground and set to ac volts . With the engine running and lights on , What are you reading ~voltsAC ?
Now you need to do your first test again
Across the battery with the car running with lights on for a few minutes , what are you reading Vdc ?
What are you reading immediately after turning the car off ?
Turn the lights on for a few minutes , then take a reading again .
Finally , if you can , disconnect the battery completely and take a reading after around 30-60 minutes . Then again in the morning .