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Discharging battery while car running


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2001 Boxster non-S USA, shipped to Finland one month ago and started to experience this problem.

I found similar posts here in the group and mostly alternator, voltage regulator, ignition switch or bad battery was blamed.

I noticed the problem when couldn't start the car anymore even though I was just driving it. I thought the battery is dead and went to get new, tested battery. The car started happily with the new battery, but after a while same problem.

I charged the battery and ran some tests:

1) Battery connected, ignition on, car not running: battery voltage 13.0V

2) Start the car > battery voltage jumps to ~14.5V for a few seconds

3) Car running on idle battery voltage starts to drop steadily and after a minute or two it is 12.35V

4) Revving engine doesn't change battery voltage at all

5) Battery seems to stay at this voltage (~12.35V) at least for few minutes until I turned engine off

6) I repeated above three times with exactly same results

Everything turned off the idle current consumption is 30mA.

Ignition turned on the current consumption is 2.8A.

Obviously car is not charging since the voltage is around 12.35V. But it seems to be charging for a while when engine is started.

How can I narrow down the problem? I don't want to change alternator and/or voltage regulator and still experience the same problem.

Any help greatly appreciated!!

Timo

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Your voltage numbers are normal in my opinion. As long as your not running under 12 your car is simply responding to demand...like after you've ringed it out stating it up.

What does "wont start" mean? No cranking at all? Some? cranks but won't kick over?

Regards, PK

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Your voltage numbers are normal in my opinion. As long as your not running under 12 your car is simply responding to demand...like after you've ringed it out stating it up.

What does "wont start" mean? No cranking at all? Some? cranks but won't kick over?

Regards, PK

You have probably seen my recent post on battery / alternator problems. Turned out is was a loose positive connection from the engine to the battery.

My advise would be to check all connections really carefully before throwing money at new parts.

Just my $0.02...

Joost

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Your voltage numbers look low to me. My alternator cranks out something like 13.6 volts when the car is running. I think you're going to have to get a new one.

Try starting the car and then disconnecting the battery. It should keep running if the alternator is good.

Don't parts shops in Finland do free battery/alternator testing like the ones in the states do?

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You didn't indicate how many miles on the car. When the alternator died on my '01 Boxster, a few dash lights came on intermittently for a week or so, then one day the whole dash full of idiot lights came on and the car died. Happened when the car was about 4.5 years old around 35K miles. Dealer replaced the alternator and all has been fine ever since. Be forewarned rebuilt Boxster alternators are expensive, and new ones are outrageous. Later I replaced the battery, and it wouldn't hold a charge at first. Put it on a maintainer for a few driving (actually parking) cycles, and now it holds a charge just fine. Dealer said it was normal and some new batteries don't hold a charge initially.

Like you said, you've seen all the ignition switch posts. Lots of weirdness attributable to bad ignition switches, so if you have the original style, that might be a good place to start.

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"Try starting the car and then disconnecting the battery. It should keep running if the alternator is good."

I'm not an expert, but I think running the car without the battery connected will cause more harm than good. The battery is a buffer for the entire electrical system.

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"Try starting the car and then disconnecting the battery. It should keep running if the alternator is good."

I'm not an expert, but I think running the car without the battery connected will cause more harm than good. The battery is a buffer for the entire electrical system.

True. It could damage the computer. I'm used to working on pre-computer cars. I'd say drive it to the Finnish version of Autozone and have them test the charging system. They should be able to tell you immediately what the problem is.

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Thanks for all the replies!

Still I have the same question that how can I narrow down where the problem is (VR, alternator, somewhere else)?

Is there some more tests I can run?

As I describe in my first post, it is charging for a minute or so and then goes discharging. I don't think this points to any faulty connections.

I don't have too much faith on "Autozone" and similar, anyway they try to sell parts.

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Try, turning accessories on one at a time while running and see if you have a voltage drop that isn't corrected by the voltage regulator

Also drive it around for a 1/2 hour and check the voltage while still driving turning nthings on and off. Further , I believe you can hook you DMM to about any 12v lead in the car (cigarette lighter comes to mind) while you drive around (or run the DMM wires directly off the battery and over or around the windshield to DMM, or even tuck it under the windshield wiper)

Autozone does not hire the brightest. Fortunately their test equipment is designed with that in mind. I've never had them try any undue pressure, I attribute this to there not having any parts for it and, the car just befuddles them. Plus, don't work on commission where Ilive.

Regards, PK

Edited by pk2
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Thanks for all the replies!

Still I have the same question that how can I narrow down where the problem is (VR, alternator, somewhere else)?

Is there some more tests I can run?

As I describe in my first post, it is charging for a minute or so and then goes discharging. I don't think this points to any faulty connections.

I don't have too much faith on "Autozone" and similar, anyway they try to sell parts.

The testers they use at Autozone, O'Reilly's, Napa, etc. read your battery charge. Then they read your cranking amps. Then they read your alternator output. Then they test the voltage regulator diodes. You might be able to rent one if you don't trust their people to stand there and read it.

If it is charging and then goes to discharge, my guess would be bad diodes, which are in the voltage regulator, but again, without running tests, it's all just a guess.

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I got it fixed - the voltage regulator was bad.

When I described the problem (charging for a while and then not) to car electrician he said that it sounds like a voltage regulator problem.

With that I got new VR from Bosch (old part was F 00M 145 225, new is F 00M 145 350), paid 68 euros. The next step would have been to replace the alternator itself.

I was able to replace VR with instructions I found from this forum. THE MOST HELPFUL INSTRUCTION WAS TO TURN ALTERNATOR LITTLE BIT CLOCKWISE TO GET IT OUT.

Thanks to everybody!

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