Quote:
Originally Posted by 68 Z/28
 sounds like it could be either battery or alt. jump it then pull off the neg. bat. cable and if it stays running your battery is the problem , if it stops , prob. the alt. |
I'm no genius auto mechanic but I have heard that is not a good thing to do. It can damage the diodes in a good alternator due to reverse voltage spikes created when the load is removed when the alternator is spinning creating current.
A lot of times a sudden problem like that can be caused by a bad battery/shorted cells. In a lead/acid battery there are six cells that provide 2 volts each. When I lived in Phoenix the heat just killed batteries, was lucky to get three years or so out of them in my and my wifes car. Car would start fine one day, next day turn the key and boom, cell shorts. One time I had two cells short at the same time. When I put a volt meter on the battery, car off no load/lights etc., read 8 volts so two cells were shorted. My S-10 did it here in Indy not too long ago, one day fine next day won't/barely cranks. Measured battery voltage, 10 volts = one cell shorted.
If you have a volt meter and can measure your battery voltage with car off and no loads it should read 12 volts, with engine running if the alternator is functioning properly it should read about 14 to 14.5 volts. Alternator is three phase with a diode rectifier for each, if one diode is bad so one phase gone it will read somewhere between 12 and 14 volts. That can gradually cause the battery to loose charge but generally not a one day fine/next day not thing. Also if you do have a shorted cell you want to get a new battery right away before the excessive load on the alternator overheats it causing it to fail. I suspect you have a bad battery, if you are unsure you could remove it and take it to an auto parts place and have it load tested.
P.S. BTW if you don't know, ALWAYS remove the negative cable from the battery first. Ever seen the end of a wrench melted off in an instant when someone put it on the positive and the other end hits grounded metal somewhere? With the negative cable off battery is isolated so no current can flow if the wrench touches something when removing the positive cable.