Alternator issues

SomethingElse

I'm currently trying to fix my electrical system. The battery isn't being charged by the alternator when the car is running, voltage drops slightly on engine startup and slowly decreases as car is left running. The battery terminals read approx 12.5V. When I switch the key to the ON position, the main alternator post has the same voltage as the battery and the two other wires have the same voltage as the battery also when I disconnected the clip from the alternator and tested them. Should all three wires to the alternator be 12V?? I'm currently thinking it might be one of the cables damaged but I am having trouble tracing them.

Any ideas would be greatly appreciated!

Waterson

If battery voltage is decreasing once engine is running you have an issue with your alternator. The 12V feed into the alternator on the small gauge wire is to power the diode/rectifier pack and most limelt though you sont state what car toi have, the alternator bulb on your dash. Once the alternator is charging, 12V is output in the opposite direction along this small gauge wire and the two opposing voltages put out the dash bulb.
The voltage drop at cranking is due to the large load consumption of the starter turning over the engine and is normal. If the voltage drops below 10V it may be an idea to get your battery tested.
If your alternator has a clutch pulley, check that this has not failed and may be freewheeling under higher RPM, this not generating charge.

scannerd

If your alternator is working correctly you should have 13-14v at idle, not 12.5, if you have a multi meter look up "diode test for alternator"

CJhaughey

You can buy rebuild kits for most alternators from Ebay, there is a guy called Goldlion electronics based in Mayo that sells them if you want to do it yourself.
Small money to fix that way.