fpena944

A couple of nights ago I went to start my car and CLICK, battery dead.

Now this the same battery I replaced one year ago so I thought that was a bit unusual. Got the car jump-started, went for a drive and figured it was an anomaly.

Same thing happened last night so I knew I had an issue. I did a battery drain test using my multimeter and found that the car really isn't pulling any amperage when at rest so I headed to the local auto parts store for an electrical test. They told me the battery and alternator were fine but the voltage regulator is faulty.

I had my alternator replaced back in 2010, does a regulator go bad that quickly?

What does it take to replace? Is this a DIY job or take it to the mechanic?

Also how is it that if the voltage regulator is dead when I go for a drive the battery does still manage to get charged?

Anything else I should test for?

Paul Waterloo

They said the alternator was fine but the voltage regulator was bad? LOL....it sounds like they know nothing about electrical systems.

There is no separate voltage regulator, it's built into the alternator.

What voltage is the battery at while the car is running? You need to measure this with a volt meter.

fpena944

It was at an O'Reilly Auto Parts store. Of course he had to tell me about the Boxster he used to own.

The voltmeter on the dash shows just under 14 volts. I just hooked up the multimeter and at idle it is around 13.9, throttling to about 2k RPM it pretty much stays in that same range. Is that within spec?

gnat

Paul's right, test the voltage while the car is running. It should be between 13.5 and 14.5 volts. If the VR is bad it will fluctuate wildly and go well above 14.5 volts.

How long are your drives? If they are short enough it could simply be that you aren't recharging it after cranking. I have a 10mile commute which is not enough to fully recharge the battery after starting it so it will progressively get harder and harder to start until one of us takes it out for a much longer drive. Then it will be fine for another couple of weeks (not driving every day).

sjg1138

Actually the voltage regulator can be replaced. I had the same issue. The voltage regulator is on the outside of the alternator and can be removed and replaced. I did it and it fixed my charging issues (well this and the replacing of the infamous Y cable).

https://rennlist.com/forums/996-foru...rt-number.html

I wonder if the the added resistance of a corroding Y cable connection causes the Voltage Regulator to go bad sooner than it should...

gnat

Yeap, that is good. 12v is what you should see when the car is off and on should be in the 13-14.5 range. Sometimes it can fluctuate a bit, but overall it should be stable. Sounds like your issue isn't the VR from my experience.

fpena944

Based on what you're saying it appears my battery and charging system seem to be working, would you agree?

As for how I drive the car...Well I used to drive my car daily but for the past 2 weeks it's been less frequently used. Now most of my drives are under 15 minutes with the exception of the drive I took the other day closer to 30 minutes. But it hasn't sat more than 3 days consecutively yet.

Could this still be an issue even though the car reads almost 14 volts being produced?

Aside from my driving habits, any other thoughts on what it could be?

gnat

Sitting for a long period on a fully charged battery will indeed drain it, but based on your described driving habits I suspect (like me) your battery is never getting fully recharged after cranking.

Find an excuse to take it for a good long drive without stopping and re-cranking (maybe an hour or so) where your RPMs can get all over the place (the higher the better). Then see how it acts.

I suspect that you just need a battery tender to help you recharge after the short drives. Or just drive it longer distances

Paul Waterloo

Does not sound like any issue with your charging system. I would have to see, but isn't it the Y cable that allows the high resistance connection which causes the starting symptoms you describe?

I would have to go back and review the threads (which I have not book marked) but I believe that's true....but could be wrong. Search for it...the threads are easy to find.

mcbit

The VR can certainly be changed independently of the alternator.

Paul Waterloo

I'm not saying that's the case, but it's not like the guy who did the testing even knows this.....he did not remove it, excite the alternator separately, and then give his diagnostics.

fpena944

Drove it for a while yesterday and when I came back out in the evening to crank it up the car started without incident.

I imagine if it was the charging system then my car would have killed the battery by the time I arrived, right?

I won't be using it in the next couple of weeks so I'll put the battery tender on it so I don't have to worry about a dead battery when I return.

Thanks everyone!

gnat

So the same solution to most 996 woes then. Drive more

It all depends on what the problem is.

If your alternator is fine, but your battery won't hold a charge then the car will run perfectly fine once it's started.

If your battery is good, but the alternator's stator is failing then it won't put out enough AMPs and you'll be driving off the battery. Sooner or later you'd drain it enough that the car would stall. How long depends on how bad the stator is (e.g. are you still getting some or no power from it).

If your VR is failing you can get all kinds of whacky symptoms and depending on the electronics in the car (general, not 996 specific) this is probably the most dangerous. The VR's purpose is to keep the voltage stable between 12 and 15 volts (typically right around 14). Some electronics don't tolerate the voltage swings well and it can damage them.

An easy way to diagnose electrical issues in older/cheaper cars is by watching their headlights. I don't know that it works with HID/LED lights though. If you let the car idle/maintain a steady RPM and the lights change their intensity, then you probably have a VR issue. If they are dim at idle and get brighter as you raise the RPMs, then your stator may be going (still could be a bad battery).

The really old school test of your alternator was to disconnect the battery while the car was running. If it shuts of, the alternator is bad. This is no longer advised with computer based cars though as you can damage them in the process.

fpb111

Some VR info.

fpena944

I think the issue was not driving enough. No problems since I took the long drive. While I'm away I'll put a battery tender on it.

But my question now is, how do those in metro areas that usually only require short drives handle this? Seems pretty inconvenient especially if you have your car parked in a parking garage - how do you keep the battery charged in that case?