Okay so Ive had my GS4 about a month. When I got it the battery was fading and when it finnally died I swaped it out with a new one. Since I had no prbs until yesterday. I had just added a mid power amp running to mid level 12's at med-low gain. 42mi to work, no probs, 30 mi home, probs. The car started acting like it did when the other batt was almost dead. When i would push the brakes it would kill the stereo and then come on again. I made sure this wasnt a brake prob. I turned on the head lights and same thing. The stereo returns no matter how long the other lights are on, it just seems that the initial spike drops the voltage below what the stereo wants. The batt light never comes on. On the way in today no probs. Since day one i have noticed that my dash lights kind of flicker. At first i chalked it up to the bad batt and figuered the were fickering with the revs of the alternator. But after the swap it still did it, and now im worried maybe there is a prob in the elec system. My thoughts are that the alternator is over charging the batt. I know I have a good batt, and the alternator is pushing 12.4++ at idle. Any thoughts?? Also when i was playing with it yesterday I tried turning off the A/C and the problem left which made me belive it was to much drag on the drive line and the alternator couldnt keep up, or that turning off th A/C was just enough boost in voltage to keep me from shutting down the radio....

 

Hello There,
It looks like it is time to get the alternator and the rest of the charging system checked out. The output seems to be too low. At idle, with no accessories on, your nominal voltage should be in the area of 14.3 to 14.4 volts DC. !2 volts is just barely charging. Eliminate the obvious things like slipping/worn alternator belt, or loose connections first.

If you have a lot of high powered accessories, it may be wise to step up to a higher capacity battery..800 to 900 amps of cold cranking power as a back-up. I am not sure if you can get a larger output alternator than the factory provides for your car, but it sounds like you need a bit more reserve.

In any event, have that alternator checked with a professional volt/amp tester that can simulate real world driving by imposing the same load that headlights, A/C, and other accessories do while driving.
Good Luck!
GSEREP1

 

You can almost always get a higher output alternator, even if it means swapping in an alternator made for a large truck (with new brackets). Just about all Toyota alts can be rewound. Check with a local RV dealer, as they can probably rewind your alt for a higher amperage output.

12.4V is what the battery should be at rest. If this is your voltage with the car idling, then i'd say your alternator is beginning to fail. Either your alternator, or your voltage regulator.

At idle, 13.8V is about on par. I can't say for sure what the GS series will read at idle as I don't have one (yet ) but should be in the ball park figure of 13.8V with 14.4V at cruising RPM's.

Keep in mind, as the car runs, there should be no draw from the battery (the battery after the car is started becomes a load on the electrical system). The draw should be coming from the alternator, with large power consumption being drawn from the battery (which hopefully, you don't do). 500 watts (with a sine wave, which nobody ever really does at ~Fs of the sub) is drawing at least 40 amps and since no amp is 100% efficient, even more is being lost to heat dissapation. Since music is so dynamic, luckily you'll probably never reach those peaks in current but for very brief moments in time.

If you're playing bass heavy music (???) then you'll probably be more affected by current draw from the audio system.

In any case, your voltage is way low. Time to test the alt and the voltage regulator.

Tim