Voltage fluctuation

[Mr. Merk]

One thing that has been present since I bought my '88 Carrera a couple months ago is voltage fluctuation.

The lights will dim and the blower slows down. I don't notice any decrease in performance or stereo sound.

I was first thinking (hoping) it is just the voltage regulator but it seems that would point towards a voltage spike, not a drop.

My other thought it that maybe it's not dropping and it is in fact spiking. Because when the lights do get brighter, they are actually pretty impressive. People always say the H5 are terrible, which they are most of the time unless the voltage increases.

I haven't ever driven another Carrera and don't know what's normal.

What I might just do is buy a regulator and take the alternator and have it rebuilt locally just to be safe. I'd hate to spend $300+ on a new one if that's not it but I could live with $75 for peace of mind.

[304065]

[Mr. Merk]

^this guy

genius

[Mr. Merk]

$2.85 shipped from Amazon

[wolds]

check those grounds

[mnez]

That's exactly what mine did when the voltage regulator started malfunctioning. Ended up boiling the battery too. Check your battery for dampness. If so, the whole area needs to be washed out with water and baking soda to get rid of the acid.

[wwest]

A battery cell failing, open or short, can give that result, most often would be a short.

Is the battery old enough to warrant replacement?

[T77911S]

Originally Posted by wolds

check those grounds

do this first. its the cheapest.
clean both battery posts. clean the the connection from battery to the body.
clean the connection from the tranny to the body.
remove each wire one at a time from the fuse block and clean the wire ends. also clean the end of the screw.
clean the contacts for the fuses. clean fuse ends
clean the grounds for the lights and the blower motors. (this is probably where the problem is since these seem to be the only things effected).
dont just check the conections, clean them. even if this is not your problem is does not hurt to do this on the 911, or any other car.

then take the car to someplace like advance and have the charging system tested....its FREEEEEEEE! (adam sandler voice).

[Bleedsblue]

I had the same symptoms, checked the voltage and saw the spikes that mean bad voltage regulator.

The new VR wasn't too bad to install (besides 7, 8, 9mm nuts and screws in tiny apertures) and fixed all my problems, thankfully I caught it before the battery boiled over too much.

[3literpwr]

Same stuff is happening to my '87...

[Noah930]

If you don't buy the cigarette lighter meter posted above, use a length of speaker wire to connect a multimeter to your battery. As you're driving (and particularly when you notice the electrics doing funny things) turn on the voltmeter (which is wedged between your windshield and dash) and see what's going on at your battery. Is the voltage dipping down into the 10-12 range? Or is it spiking to 16-18v?

[wwest]

If you're going to monitor voltage then the best place is alternator connection at the starter solenoid. Batteries represent a HUGE sink of/for voltage spikes.

[timmy2]

Alternator connection at starter is connected directly to the main power lead from the positive post of the battery. I don't think the 0.6 ohm resistance of the cable from the starter to the battery post as measured on my car is going to make much of a voltage monitoring difference if he can actually see the headlights fluctuating in intensity.
Just plug in the lighter socket monitor and watch it. It is how I saw a need to replace my VR when I had the same symptoms. I am lucky to have a remote VR in my '78. No need to pull the alternator.

[Omegablueray]

Same thing happened in 85" Carrera. I knew it was the voltage regulator but decided to change out the whole alternator since one is attached to the other and mine was an original part almost 27 yrs old. I also got a new battery because it was due for a new one. Problem fixed

[wwest]

Originally Posted by timmy2

Alternator connection at starter is connected directly to the main power lead from the positive post of the battery. I don't think the 0.6 ohm resistance of the cable from the starter to the battery post as measured on my car is going to make much of a voltage monitoring difference if he can actually see the headlights fluctuating in intensity.
Just plug in the lighter socket monitor and watch it. It is how I saw a need to replace my VR when I had the same symptoms. I am lucky to have a remote VR in my '78. No need to pull the alternator.

E = I * R Even 0.06 ohms will drop 1.8 volts at a measly 30A alternator output.

All I'm saying is that alternator/VR caused voltage fluctuations will be much more detectable at the alternator.

[Justin@Athens]

FYI the european cigarette outlet is not the same as the standard US outlet. I had to wedge my unit in place otherwise it just would vibrate lose and fall out. +1000 on checking all your grounds first.

[Mr. Merk]

Plugged in my $3 digital Amazon.com voltmeter in to the cigarette lighter outlet and drove it to dinner the other night. Whenever the lights would get bright and the fan kicked up speed it would read 17.1 up to 18.9 volts.

Just ordered this

[mreid]

Originally Posted by wwest

E = I * R Even 0.06 ohms will drop 1.8 volts at a measly 30A alternator output.

All I'm saying is that alternator/VR caused voltage fluctuations will be much more detectable at the alternator.

You may have flunked electrical engineering as 1.8v is incorrect without knowing the entire load. That's only half the equation as you don't know the other half of the load.

Given the symptoms of his problem, the voltage drop is going to be detectable at any point in the circuit.

[MBAtarga]

Mr. Merk - you might want to check out the sponsor of the forum in which you are visiting and posting. They actually sell Porsche parts!
It's not considered in good taste here to be advertising purchases from a competitor.

[rick-l]

Originally Posted by timmy2

Alternator connection at starter is connected directly to the main power lead from the positive post of the battery. I don't think the 0.6 ohm resistance of the cable from the starter to the battery post as measured on my car is going to make much of a voltage monitoring difference if he can actually see the headlights fluctuating in intensity.

Actually the wire from the starter to the battery is 35 mm^2 copper which is about equivalent to an AWG #2 which has a resistance of 0.1563 per thousand feet. So 10 feet would be about 1.5 milli Ohms.

Originally Posted by wwest

If you're going to monitor voltage then the best place is alternator connection at the starter solenoid. Batteries represent a HUGE sink of/for voltage spikes.

see above, that statement does not make sense.


Don't try to educate WWEST. Even when you show him he is wrong he ignores it. Do you really believe he has monitored for voltage spikes by crawling under the car and looking at the starter terminal with a voltmeter or that is just something he dreamed up? Best to ignore him.