Contour Enthusiasts Group Archives Forums Modifications Duratec Performance alternator

i know on older cars you can unhook that battery and if the car stays running then it is a bad battery but i did this on my 96se tour and it died if things havent changed any (i am sure they probably have) then my alternator is bad right.
is there some reason you cant unhook the battery on newer cars.

PLEASE HELP

I didnt know that was a viable option to test an alternator on any car.... That said, the best way to test an alternator on our car is with a volt meter. Take all readings at the battery's terminals. First, with the engine off, you should read about 12.5 volts. Start the car, and the voltage should go up to 14.5 volts. Turn everything you can on (ie. lights, brights, fog lights, radio...) and the voltage should not go under 14 volts at idle. Rev the engine up, and it should jump right back up to 14.5 volts. If all that checks out, the alternator would be fine... -Nick

Is your battery light on? If it's on, chances are the battery isn't getting charged from the alternator. If the light isn't on but you keep having battery problems, it's probably the battery gone bad.

If you remove the battery cable you will kill everything. In the old days you could do that, but not on fuel injection cars because the fuel injection system runs off of 12volts. You are simply unpluging the juice to your injectors and ingnition system.

When running the car sources it's electricity from the alternator. If you disconect the alternator the car will run on the battery. If you disconnect the battery the car will run on the alternator. Under heavy electrical load the alternator can be taxed to it's limit. At those times some current flows from the battery to make up the differance. If there are no accesories, lights, etc. on the car runs from the alternator. The alternator and battery are in parellel. The reason the alternator charges the battery is because it puts out about 14VDC. The battery fully charged is about 13VDC. If you put a voltmeter across the battery terminals with the car running you should see 13.5 to 14.5VDC. If it is less than that there are several things that could be wrong:

1> Battery
2> An electrical short
3> Faulty alternator

PLEASE PEOPLE!! DO NOT REMOVE THE BATTERY CABLE WHILE THE CAR IS RUNNING.

Modern automobiles Use the battery as a capacitor, to help iron out voltage ripples that are small, and easily absorbed by the relatively large battery. if you remove that battery from the curcuit, it is possible that voltage spikes and dips can fry ANY electronic component in the system. PLEASE DONT DO THIS. It works fine on any car without a computer, IE pre-80 something (depends on model) BUT CAN CAUSE many electrical problems, from killing voltage regulators to outright killing the ECU.

PLEASE DONT DO THIS, USE A VOM to check your alternator, or take it to someone who knows how to test it. If you take it to a mechanic that pulls the cable off while the car is running, you should start running..... to another mechanic.