please help, not getting enough voltage from amp

[baddest65]

please help, not getting enough voltage from alternator

edit: the thread title should actually read: please help, not getting enough voltage from alternator

hey guys, i have a powermaster 140 amp alternator that i recently installed in my 1965 stang again, after it had been repaired by powermaster for not putting out enough voltage. i got it back and they had a test sheet that was signed and said that it was now working as it should.

anyway...the car had been sitting for a couple of weeks ever since i installed it again

the battery was strong enough to crank the engine for some time, until the carb got some gas in it. it fired up and i let the car run for about 5 minutes. and i made sure that the alternator was triggered on by revving it past 1500 rpms.

anyway...when i put the car in drive, turn on the headlights, and then the brights...it dies. and i can see the voltage go lower as i'm turning on the lights.

also, if i turn on the lights, and the blinker, sometimes it dies too. and i can see the volt meter guage go up and down as the blinker is turning on and off.

could this be a bad ground? the alternator again?

also...after those 5 minutes, i turned the car off, disconnected the battery, and tested the battery, and it was only reading 11.92 volts...i'm pretty sure it should be reading higher than that right?

it's an optima red top battery and i've already cleaned the posts. i've had the battery in there a few years...maybe 4 years?

any advice???

 

[baddest65]

any thoughts?

 

[tweet66]

Sorry I'm not of much help but I wouldn't mind knowing myself. I'm having a similar problem with my 69 Falcon.

 

[tweet66]

Sorry I'm not going to be much help, but I wouldn't mind knowing myself. I'm having a similar problem with my 69 Falcon.

 

[Bonestock2k]

That battery voltage is a little low but to be expected if it's not being charged. With the engine running check the voltage at the battery with a digital volt meter - if it's being charged by the alternator it will read somewhere around 13.5 to 14 volts. If not I would take the alternator to nearest auto parts store and have them check it for proper output - most provide that service for free. That will get you a lot closer to figuring out what's wrong. I assume your drive belt is tight? I've seen batteries go TU in 4 yrs also, even so called good ones. One good way to test battery is with a hydrometer - check each cell for specific gravity - they can be purchased cheaply.

 

[1969mach1351]

Like Bonestock said I'd check the voltage with it running it should be around 14 volts. I recently heard that the Optimas are only good for about 4 years or less but I'm not sure about that. Optima claims they last twice as long as "normall" batteries. If it's your battery it should be able to watch the volts drop after you turn off the car. With the car off it should stay stable at about 12.5 volts.

A hydrometer is a good way to test other batteries but you can't on sealed batteries like an Optima.

 

[baddest65]

thanks guys. i'll check it out.