Dead battery - Is the alternator bad? - 986 Forum - The Community for Porsche Boxster & Cayman Owners

3point2 · 08-25-2013, 02:39 PM

Hi-

I was driving one day on the freeway and the radio shut off and I couldn't get it to turn back on. However, the car was running fine. I pulled the car into my garage that day, armed the car, and came back 5 days later to find that my battery was completely dead. I took the battery to Autozone to have it checked out and they said it is fine.

My next thought was the alternator needs to be replaced. But I was thinking that since the battery completely drained after sitting in the garage for 5 days, it may be something else that's draining the battery. Or is this normal with a bad alternator? Could it be the voltage regulator or something else?

Thoughts?

Thanks for any help!

-Leo

thom4782 · 08-25-2013, 04:06 PM

You might be on the right track. If it is the alternator, then your left driving off the battery. It will drain and eventually die. And that might explain your dead battery. Only way to really tell is to get the car started and measure the alternators output. I know I'm stating the oblivious but that's where I'd start.

tonycarreon · 08-25-2013, 04:31 PM

did the battery light come on? how far was the drive from the dead radio to home?

when my alternator died, the battery light came on and the car died after about 15 miles.

Ian c · 08-25-2013, 05:00 PM

You need to get the battery charged and back on , then check voltage .
12vdc on the battery 13.8vdc running .
Then disconnect the earth and put your multimeter on miliamps and see what your drain is with everything turned off .

3point2 · 09-06-2013, 03:25 PM

Thanks for the replies.

No battery light came on. It drove fine on the way home the last time except the radio died. And then when I came home a few days after the car was parked tor restart it, the battery was completely dead. Can the battery completely drain that fast on its own even when the car is turned off?

I'll pick up a voltmeter and check the voltage tomorrow.

What is the earth connection? Where is it located?

Thanks again!

cas951 · 09-06-2013, 05:26 PM

Quote:

Originally Posted by 3point2

Thanks for the replies.

No battery light came on. It drove fine on the way home the last time except the radio died. And then when I came home a few days after the car was parked tor restart it, the battery was completely dead. Can the battery completely drain that fast on its own even when the car is turned off?

I'll pick up a voltmeter and check the voltage tomorrow.

What is the earth connection? Where is it located?

Thanks again!

He meant Ground cable. The black cable at the battery terminal. If you have a volt meter connect your wires in series from the neg cable to the negative battery terminal. If there is any voltage drain it will show on your meter. You can disconnect your fuse 1 x 1 till you no longer see any voltage reading with the voltmeter.

I'd start with the radio fuse first.

Ian c · 09-07-2013, 06:22 AM

Quote:

Originally Posted by 3point2

Thanks for the replies.

No battery light came on. It drove fine on the way home the last time except the radio died. And then when I came home a few days after the car was parked tor restart it, the battery was completely dead. Can the battery completely drain that fast on its own even when the car is turned off?

I'll pick up a voltmeter and check the voltage tomorrow.

What is the earth connection? Where is it located?

Thanks again!

Quote:

Originally Posted by cas951

He meant Ground cable. The black cable at the battery terminal. If you have a volt meter connect your wires in series from the neg cable to the negative battery terminal. If there is any voltage drain it will show on your meter. You can disconnect your fuse 1 x 1 till you no longer see any voltage reading with the voltmeter.

I'd start with the radio fuse first.

Oops !!!
My English slipped out after a few beers

Yeah , earth is ground .
You will need a multimeter with milliamps to do the fuse check easily but you can pull all suspect fuses , and any non critical fuses , and work that way .
It will just take longer .

If you are going to buy a multimeter , get one with voltDC , voltAC , continuity/ohms , and amps/miliamps . This will cover most of your uses around the home and car , and once you have one you will find uses for it

An analog is accurate , but I suggest you get a digital .
Have a look on transcat for a fluke , and you can probably pick up a bargain on Craigslist or eBay .

Ian c · 09-07-2013, 06:54 AM

Just had a quick look on your local CL ...
This would be more than ideal for 75 bucks if it has leads etc .

fluke multimeter

Or this one for 100 .

http://sfbay.craigslist.org/pen/tls/4043200302.html

This one is older , but cheaper . At 60 bucks

http://sfbay.craigslist.org/sfc/tls/4047183659.html

dghii · 09-06-2013, 07:49 PM

If your battery and cables are ok, you most likely have a bad voltage regular. The regulator is on the back of your alternator and is a generic part which costs less than $50.

My car did the exact same thing back in mid May. It finally through an overvoltage code. This repair is not too difficult but will test your patients a bit. Lots of good write ups available.

Rickinduncan · 09-07-2013, 03:41 PM

Follow the above instructions. As a test that your doing it right, turn on your interior light and close the door. With one light on, it should read around 200 miliamps on your meter,or simply leave a hood open.that should also give you a reading of around 200 miliamps . Turn the light off, or close the hood,and it should read zero, or something very small.

Ian c · 09-07-2013, 03:45 PM

Are you staying online for a while rick ?
I'm only stopped at Starbucks for a few mins on the way home ...
It would be great if we could get him on his way while he's got the tools out ...

Rickinduncan · 09-07-2013, 04:10 PM

Sure, but in this day and age, it's almost worth while to place a phone call, or at least FaceTime

Ian c · 09-07-2013, 04:47 PM

FaceTime would be excellent for this .
Good call !!

I could grab my meter and do a "follow me" thing !!

I'm home now , but I see he's offline ...
I hope he didn't blow his meter doing miliamps on a car battery !!

Rickinduncan · 09-07-2013, 05:05 PM

On second thought, FaceTime wouldn't work. We'd spend all our time viewing each other's p cars, and I'd end up feeling bad because mine hasn't been washed in 12 days. And if he did go 'post to post' he definitely blew the fuse in his tester.

Ian c · 09-07-2013, 05:10 PM

It sure would make this easier though ..
I've just read some of my replies and a mixture of "iPhone thumb" and autocorrect makes them almost illegible

Ian c · 09-07-2013, 05:14 PM

I think I'll just type an "how to" essay and he can read it when he's back online .

My best guess upto now (not knowing the drain mAs) is a bad connection between alternator and battery , bad battery , or faulty ignition switch .....

Rickinduncan · 09-07-2013, 05:24 PM

My best guess is a corroded ground strap. So ...... How many days since you've washed yours? Maybe I would have won the FaceTime car view.

Ian c · 09-07-2013, 06:36 PM

It's too dark to take pictures now , but .....

I run instrumentation-tech. crews on power plants and where I'm at now one of the final things that needs doing on this site is remove a big pile of dry dirt/dust that has been there for about two years , so we can do a db check on the 6 new jet engines we just fitted running full-on , all at once .
This means Over 50 trucks loaded with dirt and dust doing continuous journeys past my car .
And a water truck going 8 hours a day trying to keep the dust down , but mainly creating puddles of mud .
That , and the fact I haven't washed it since BEFORE a full day of autocross about a month ago , probably makes your car look like a garage queen next to mine

The boxster doesn't look TOO bad though , that's only been at the plant once this last week ....
But judging by people reactions on here when i posted pics of the pink wheels , it probably would look better to most if it was caked in mud

Ian c · 09-07-2013, 07:13 PM

Forget that essay for now .
On the way home I had to call at Barbour frieght to buy a soldering iron to de-amber my headlights , and noticed they have a multimeter with everything needed apart from audible continuity for around $5.00 .

With hindsite , I should have just bought one tonight to assist my essay with pics .
But I will go buy one tommorrow , and take pics of me doing a basic "battery issues" check .

I will then start another thread detailing the steps needed to work through electrical gremlins

It does not have a continuity function so I will use one of my flukes for that part , as that is a vital "quick 'n' easy" test that is VERY valuable when working on car electrics ...

I don't expect everybody who works on cars to spend hundreds on fluke meters , but the $5.00 harbor freight meter at a minimum should be in everybody's toolkit

They also have one with continuity on sale at the moment for $20.00

The one 3.2 bought from RadioShack looks similar , and is not too much money at $20 if you have an RS nearby but no HF , but there is one with continuity for a few bucks more ...

dghii · 09-07-2013, 07:43 PM

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.