Charging issues

[DK832]

My 69 with 351W has suddenly developed problems with keeping the battery charged. We use daytime running lights here in Denmark, so drain is higher than most Mustangs usually have.

My voltage drops below 12V if I idle along in traffic too long and even after a highway cruise is still just 12.4V or so on an Optima red. This is measured with a meter directly on the battery terminals of course, engine off, without any lights or accessories on. At idle without anything turned on I get 12,2V and dropping. At 3.000rpm it charges @ about 12,8-13V without lights or any accessories on. A swap to a known fresh standard 45amp acid battery yields same results even though voltage @ 3.000rpm is up to about 14,0V.

The generator is about 7 years old with 25k miles on it, belt is not slipping as far as I can tell. Ground connection from battery is good.

What then is the most likely culprit? Generator or regulator or...? HELP!

 

[Max Power]

It seems that you are getting a slight increase with RPMs, so that tells me that all circuits are probably good, and your regulator is probably goos as well. I would suspect alternator output.

Not sure if this applies over there, but many good parts shops here can bench test your alternator for output. I always do that before replacing, and usually just buy a new regulator anyway, because they are cheap here.

Your mileage may vary....

 

[67-in-pieces]

Maybe try a new alt and decrease the pully size on it, just a bit. Should charge at idle with a smaller pully, I would think.

 

[TOM B]

65 to 70ish mustangs had low output alternators and when you reved it up the lights get brighter. Many people including me went to a "Powermaster"
Alt. It puts out 100 + amps and is made to bolt in, and gets rid of that pesky voltage regulator too. all my charging problems just went away and have bright headlights now too.

 

[DK832]

Thanks for the input. I was figuring on the Powermaster 100 amp (or Summits house brand). Do I order the one with internal regulator and eliminate the one on the inner fender? Are all Ford alternators interchangeable? I search Summit for one for 69 Mustang with 351W and get none. For Ford, 351W I get the Powermasters etc.

 

[geostang351]

Same problem here. Good thread.