In theory, if my battery was dead and the alternator was not working, why do I have power to all the components after jump starting the car?? Does the alternator send 2 different voltages, one to the charging system and another to the normal electrical system to power windows lights etc??

Thanks......

The alternator just pumps 13-14.5v back at the battery while running. The battery acts as a capacitor, absorbing surges and allowing the electrical system to have a "deeper" amp resevoir to handle sudden loads. Technically the car is always running off the battery, the alternator just charges the battery fast enough to stay ahead of the overall load...

When you put enough juice back into the battery to start the car (which takes anywhere from 150-300 amps), you have enough also to allow it to run and operate accesories for at least a few minutes...but depending how much electrical load you have on, it will eventually die if the alternator isn't keeping up with the demand...

The ignition system doesn't take a whole lot of power...they usually run until voltage drops to about 9 volts or so...

So if I understand your question, it's not unusual for a good battery to be able to power the car and everything on it for 15-20 minutes just from a jump start if the alt is dead...longer if the alt is putting out a little charge, but not enough to keep up..

Thanks. I need to test the alternator to see how much it is putting out. Basically, I put a new battery, drove it for 20 mins, and the next day the battery was dead. I was able to jump start it and drive for over 1.5 hrs, but the battery is still dead when I park. My charging light in the dash is working properly, so I don't know why the battery is not recharging while driving, unless the voltage from the alternator is too low, just enough to keep things going......

thanks

You need a voltmeter. You can buy a cheap one at Radio Shack or Harbor Freight. Measure the voltage at the battery with the engine not running then with it running. Running you should see an increase to about 13.5-14.5 volts. If it doesn't increase, the alternator or wiring is bad.

I think you may be looking at the problem backwards, the more likely scenario is you may just have some parasitic load (light stuck on in glovebox, etc)...or occaisionally even a bad diode bridge in the alternator can make the alternator suck up battery power when the car isn't running...

Make sure everthing is off, key out of the ignition and all doors closed, disconnect a battery terminal, and connect a test light between the battery post and cable end...if the light comes on, it's drawing power somewhere...normal parasitic loads like the clock and ecm memory are very small draw...so if the tester lights, open a door or turn the headlights on...if it's just a slight memory keeper draw, the test light will get much brighter when you open the door (it's reacting to the larger current draw of the interior lights)..if it stays the same, you've probably found a large draw...

Then you pull fuses one at a time, when it goes out (or drops intensity back to the weak memory draw), you've found the circuit draining the battery...see what items are protected by that fuse, and check them systematically...usual suspects are glovebox lights, trunk lights, dome light, etc...but sometimes will be something more oddball.

To test if the alternator is the cause, simply disconnect the charge wire (large one that goes from the post on the alt back to the battery)...if that puts the light out, have the alternator tested for a possible bad rectifier diode bridge...an alternator is essentially an electric motor in reverse...instead of using electricity to turn, it turns to produce electricity...the diode bridge is what combines the three phases into one DC current, and keeps the alternator from "motoring", the term used when current flows backward through a generator and tries to make it run like a motor...diodes work like a one-way gate for electricity...

EDIT: Hey I just remembered, Accords seem especially prone to fan relay failures that will make the fan come on after running (normal) but fail to shut down, running the battery dead...check the car 15 minutes or so after shutting it down, make sure the fan isn't running non-stop...

Now if the car is dead immediately after shut-down, then you can ignore all this...the problem is in the alternator or charging system control...all of the above assumes the car won't start after sitting several hours, but not if it's dead as soon as you shut it off.

Thanks for all the info. I will try and remember to post the fix for it. Have not had time to work on it.

i have the same problem with my 92 mustang. i put a voltmeter in between the battery and cable and tried pulling one fuse at atime. got frustrated cuz there was still a draw on the system. so ipulled every fuse it continued to drop a few minutes.. after replacing all the fuses one at a time the draw stopped. now i have to wait till it happens again. imthinking its not a light or switch stuck could it be the alternator although i had it tested and its fine just now it could be something that you said a diode stuck in the alt? thanks for the in put i beentrying everything unhooking all kinds of things to get teh draw to stop and nothing

thanks