Before I get roasted I did a search and read all the posts on this subject. When I drive my Mercury it shows around 13.5 in the voltmeter. It does seem to fluctuate a lot. Some times it will go as high as 14 or more. If I shut it off and start it up again a lot of the time it reads below 11 volts. Around 10.7 or lower. I have replaced the belts and put an engine to frame ground strap on the car. I has a chrome alternator with a chrome pully. Could that affect it after it gets hot? Sometimes it will pop back up to 13.5 but I thinking it shoudn't fluctuate so much. The engine is a HAMB favorite, 350 Chev . Does it sound like a voltage regulator? Thanks guys.
There's a plug in with a white and red wire on the side and a post on the back with a heavier wire bolted to it.
Thats the reg old GM. If your not sure of the alt. go by the starter gen. shop and have them check it on the car. My $0.02 are going to say the voltmeter is not real correct. If the headlights are good and bright at night I would forget it. IMHO
sounds like the style of alternator that needs "excited" to charge...does it go up when you rev the motor?
It has Dakota digital guages. The lights do dim when the voltage drops. It seem like revving it when it's down doesn't affect it too much. When I turn on other accessories it does drag it down weither it's reading normal or low. Sometime, like I said it will pop back up by it's self. Maybe I do need to try the rev it up thing. I read it in an older post too.
13.5 IS ok everything above 13.2 is charging, and remember a battery dont need to be charged all the time, and the voltage will be lower then. But usullay not below 13.2-13.4 Volts An Alternator should start to charge at idle or just above. Id take a good multimeter and measur the voltage on the battery post. To see what the voltage is there. And go from there.
Take that thing to your local parts store and have em spin it up to see if the internal voltage regulator is working evenly. Does this car have a mechanical fan or an electric fan? Older SI series alternators just can't keep up with decent sized fan plus accessories at idle speeds. Good luck!
Read voltage at the battery terminals with the engine off. Right around 12.2 volts indicates a sufficient state of charge.
Could be one of three things. As posted, use the battery to check your voltmeter, noting this reading. Then check the sense and field wires going to the alternator to make sure they have a good connection. The sense wire is especially important as this will tell the alternator to charge up if the voltage is low. The other two things are the internal voltage regulator and the diode trio. Usually the voltage regulator when faulty will do what you say it is doing. The diode trio when faulty (in my experiences) will cause the charging voltage to go high by .6V (ie: 14.2 to 14.8V). Like what was posted, take it to a shop and have the alternator tested, both loaded and unloaded. My feeling is the sense wire is intermittent, which is where I would start after getting the alternator tested. (Make note as to what the voltage is when being tested)
Ditto, as I was thinking the same thing. Pull the clip, and check the sense wire (the one that folds over and goes to the Bat terminal on the alternator. Also check the smaller wire on the clip, and trace it all the way back to the idiot light, or the ignition switch. This is the exciter wire. In any case, volt meters are real simple, and I believe your voltage is actually changing, and you have a problem. P.S. Solder the connections, and use heat shrink tubing to finish the ends.
Another possibility ia a loose alt. belt. To check it try to turn the alt. pulley by hand if you can get it to move without belt moving it's not tight enough. When ever you put a load unto the alt. it will actually slow engine down and if belt is loose it starts to slip enough to lower voltage output.