Strange Voltage

[BassAddictJ]

When I start my car my voltmeter hooked into the 12v ignition reads 14.4v for the first few minutes after starting the engine, eventually dropping to 13.8v. The voltage while driving will randomly drop from 13.8v all the way down to 12.5v, then eventually within about 10min later work its way back up to 13.8v over the course of 10-20sec. Only times I see the amp effect the voltage is when playing full tilt. Even then sometimes it'll be sitting at 12.5v, and then i play full tilt and the voltage does not move or go under 12.5v. Then still playing full tilt it will eventually work its way up to 13v. Often when the voltage is at 13.8 i play full tilt and the drop is to right at or around 13v. Although the voltmeter is on the ignition side, it is always within 0.1v if not dead on with readings on the back battery and amp at all playing volumes.

It's weird to be driving and see the voltage go from 13.8v to 12.5v. Even reving my rpm's has virtually no effect on boosting the voltage when its hovering around 12.5v.

Stock 120amp alty
Stock bat is in the trunk, connected to + on alty
Back battery (d3100) is hooked up to the + on the alty (only connected to front bat at alty + terminal).
1/0 with big 3, solid chassis ground.

any thoughts to why this voltage is fluctuating?

[BassAddictJ]

anyone?

[smoka]

If it drops voltage with your audio off, then it sounds like you might need to get your alt tested. Could be a problem with the voltage regulator?

You can rule out your batts by just hooking up one at a time and see if you still get the random voltage drop.

[KyleBechtold]

is your belt squealing? slipping?

[boostet-bird]

its more than likely the voltage regulator in the alt my car did the same thing and thats what was wrong with it im just gonna put a 250a on mine

[blackdragonaudi]

It's likely that when you first turn it on the engine RPM's are slightly higher than at normal idle. So when it finally warms up the voltage drops a tad.

[18inchjeepin]

new gm cars do this, shut off the alt when the batt doesnt need charging, and its computer controlled, it *****!!!

[BassAddictJ]

these voltages are with the car on.

i'll try it with the one bat at a time

no belt noises.

yeah the 14.4 at first and then a slight drop i knew was normal....but the later fluctuations i thought were strange. so if it is the fact that the alty is being computer controlled, why is it not seeing that the d3100 is needing a charge? how does this switch work and is there any way for it to recognize the d3100 and be left on?