Dead battery - Is the alternator bad?
 

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

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.

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.

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 .

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.

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.

Oops !!!
My English slipped out after a few beers :D
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 .

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

Helpful posts! Thanks!

I just checked voltage with the car off and it's at 12.2V. With the car on, it's 14.3V. So does that mean the alternator is good?

I'm starting to suspect that something is draining the battery from somewhere. When I was driving the car the last time, the radio went out. Now with the battery charged up it works fine. When the car sat for a few days, the battery was completely dead.

Any other thoughts?

If it was the voltage regulator, the voltage would be showing up all over the place on the multimeter with the car on, right? It holds a steady 14.2-14.3V with the car on.

It is within range but how long did you leave it running for ?
it could drop off after a while so put your lights on and keep it ticking over for a while .
what meter did you get.
This type of scenario is why i use flukes with min/max and logging etc.

next you need to disconnect the ground and put your meter across battery- and disconnected - clamp wthen close everything .
This willtell you what your drain is running at .

Ok. I just restarted the car and the voltage is now reading 13.9V. Voltage is going down slowly even with the car running.

Sorry Ian. Don't quite understand. Do I disconnect the ground while the car is running and then check voltage?

Sounds like the regulator and or alternator is going .
It should read steady with a small load on it like lights on .
Everything else turned off , and don't forget the hvac controls ...

The drain check is with everything off to take an amp reading of what you lose from the battery with the car turned off . (Ie: parked over night)

I left the car running for 15 minutes and with the headlights on. Voltage got to as low as 13.48V. Then I turned off the car and the battery is at 12.5V which is slightly higher than earlier i checked.

Ehh electrical gremlins are the worst.

Them figures are t the end of the world .
It dropped but still was high enough to produce a charge for the battery .

Did you get a meter with dc amps ?

Here's a pic of my meter.

http://986forum.com/forums/uploads01...1378591746.jpg

Shall I start removing the firewall cover and get started on removing the alternator? Lol

I can't see properly as I'm in the car on my cell , but it looks like dCA ?
If it is , that is dc amps . Perfect.

Disconnect the ground as described earlier and take a reading .
Make notes and remove fuses one at a time and note what it goes down to .

I forgot to add earlier . Your meter co. e toons must be good .. If using probe pins scrape first and if using clips lamp them on the. Use the grips to clean the surface .

I will be home in an hour so will call back on here but hopeful someone else will rey a out your drain readings if you're having trouble

It's DCA on the left side of the meter.

So I removed the negative cable from the battery.

What setting do I use on thE meter? 200milliamps?

Then with the car off I take a reading at the battery and pull one fuse at a time in the drivers side footwell?

Do I replace the fuse after each reading?

Yeah
That's exactly how to do it .
One at a time and replace after noting the reading .
You should be reading around 20-25 milliamps so if you have a smaller range on your meter it will be fine .
The idea is to find how many mAs your car drains with all doors shut and locked (simulating a parked scenario)
And if it is high enough to flatten your battery you pull one fuse at a time to find out which circuit has a fault causing excessive drain

Thanks for your help.

Before I go check fuses, from what I've seen so far, could the alternator still be good?

Thanks again,
-leo

From your first reading yes .
From your second reading no .
but i'm suspecting a bad connection on your leads or the air kicking in or radiator fan coming on .
We can go back to it later ...
A drain check will eliminate a circuit flattening it when parked
And your initial reading with all fuses still in place will determine that

I'm trying to do an initial reading with the car off, earth off, and I'm getting 0 milliamperes across the battery. Am I doing something wrong?

Yeah you don't go across the battery
Go across the battery ground post and the disconnected battery ground cable

You will also need to pull up the rubber near the hoods latch and use a screwdriver or similar to force the latch lever to the right .
It will fool the car that the hood is shut thus turning off the trunk light and enabling you to lock the car and enable the alarm

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.

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 ...

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

FaceTime would be excellent for this .
Good call !!

I could grab my meter and do a "follow me" thing !! :D
I'm home now , but I see he's offline ...
I hope he didn't blow his meter doing miliamps on a car battery !!

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.

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 :D

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 .....

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.

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 :D

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 :D:D

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 . :eek:

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 :D


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 ...

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 :D

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.

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

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)

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.

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 :D

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