Battery Voltage

Rouxzy · 09-04-2002, 04:00 PM

I've had problems with my battery not keeping a charge or not charging, can't quite figure it out. When the car is off I get a reading across the battery terminals of 12.35 volts. When the car is running I get a reading of 11.92 volts. Is this normal? Every now and then the battery will not have enough volts to start the car. My question is this. Is it a bad battery, voltage regulator, or alternator? How do I test to find out for each?

Jorgeman · Jorgeman's Garage

Roux--NOT GOOD! If that voltage doesn't get up into the high 13's/low 14's (volts) when the car is running at over 2000 RPM's then your alternator or voltage regulator (or both) are at fault. The voltages you reported are guaranteed to run you battery down to the point where it won't start the engine.

Face · 09-04-2002, 04:25 PM

Rouxzy,
There are a few recent posts on this same general question with much more detailed replies than I can spout from memory. Do a search for Alternator/Battery/Voltage Regulator and you will find the answers you seek, grasshopper.

Cheers,

Rouxzy · 09-04-2002, 06:19 PM

Thanks guys, I did do a check on past threads and it does sound like the alt. but why doesn't the light come on?
If in fact I do need to replace the alt/reg what do you suggest? Purchase rebuilt or have mine rebuilt. I'm willing to pay extra for quality.

Early_S_Man · 09-04-2002, 06:33 PM

Dors your alternator warning lamp come on when you first turn on the ignition, or never at all??? If it isburned out, that is why your alternator isn't putting out anything! Burned out bulb = no pre-excitation field current!

Wil Ferch · 10:06 AM

Guys:
Early-S-Man is right on the money.
First..check the bulb, it should go on when you first turn the key and don't yet start the engine. As you turn further and the engine starts, it should go off.
Next...regular batteries should show about 12.6 standby volts. This is "full charge". From memory, this drops off rapidly . Something like 12.4 volts is only 75% charged....12.2 is 50% charged, and anything under 12V is essentially "dead". Very fast curve. When charging, as was said...look for 13.8-14.4 volts ( or so) charging value, especially at 2000-3000 rpm.

I've had my alternator repaired by a trusted local shop...had them put in new slip rings and good quality bearings..I brought them the Voltage regulator to install. I then put the whole shebang back in the car. Maybe $75-$120 to do it right, outside of the VR cost. BTW...Porsche VR is about $150...shop around...
I found a German HUCO VR for about $50...and it looks better made, with a larger heat sink, than the OEM French made part.
--Wil Ferch

Face · 09-05-2002, 09:05 AM

And if you do end up needing a rebuilt alternator complete with VR and a 3-year warranty (in the $160 range) look here - Jerry recommended them to me. You won't find them cheaper than that and most "local" rebuilds only offer a 1 year warranty.
http://autoexpress.safeshopper.com/684/cat684.htm?524

Cheers,