What does your voltage gauge read when its running during the day with no lights, and then at nights when your head lights are on AND when when you hit the brakes ? And what would be a good solid voltage reading from the gauge?

 

well, i'll tell you what my SAFCII says for voltage.

when the car is OFF the battery reads around 12.0 volts, with some lights on it'll dip down to maybe 11.5 volts.

when the car is ON at idle, i see around 13.8 volts.

when the car is ON while driving (above 3k rpm), i see consistent 14.0 volts or so.
i think 14 volts is what you should see regardless of load when you are driving.
if turning on accessories drops it down a lot then you may have a problem.

- Aaron

 

During the day with no lights - about 13.9
Night with headlights on - about 11.9
At night with headlights on and hitting the brakes - about 11.5

This is with a VDO voltmeter.
I'm running a Racing Beat dual-sheeve pulley which is also underdriven that doesn't help on my crappy 1987 alternator. :P


-Ted

 

hmm, ok maybe you WILL see a siginificant drop then.

i have an S5 though with stock pulleys, if that makes a huge difference...

i'm just going to say that below 12 volts while driving is probably bad

 

Yeah, anything under 12.6 volts and you are starting to run on battery power instead of alt power.

And you need to see 13.5 volts just to charge a battery.

I usually see around 13.9-14 volts at night with the lights and brake on, and around 14.3 during the day.

 

I noticed with stock pulleys my NEW Autolite ALT has a charge cut off of 800 RPM, so if I where to use a underdrive I wont be charging unless im up over 1500 RPM.

 

Only if you buy a 50% underdrive pulley, which would be pretty silly. Most are 20%, so charging would start at 1000rpm. Underdrive alternator pullies are just a bad idea for street cars. Look at Ted's numbers...

 

I have the same symptoms as Reted,
can I replace the voltage regulator inside the alternator?
my 90 n/a has only 80 k miles, or should I just walk into an advanced auto and get a reman alternator?
damn dimming lights,

 

if the rest of you electrical system is working fine, upgrading the alternator is something people who are having voltage issues can look into.
there was a thread or something somewhere listing the alternator output ratings.
basically:
S6 > S5 > S4

and of course a lot people do not like the S4 alt at all. i've had no problems with my S5...

 

S4 - 70
S5 - 80
S6 - 100