Alternator: Is my charging voltage normal?
 

A little background. I have been noticing over the past few weeks that my starter has been a little big sluggish at turning over my FB. I also noticed that my charging voltage was slowly but steadily going south. I knew I was in need of a new alternator, so I fished my spare out of the basement and took it into Murray's/O'Reilly's to have it tested. It tested good, so last night I swapped pulleys and put in my good alternator. I was always under the impression that alternators were supposed to charge at 14 volts, however mine was sitting at ~13 volts today. Is there another part of the charging system that may be at fault, or does this seem like a normal voltage? I have a double alternator pulley and good belts, so there is no belt slippage. The alternator that I pulled off had, to the best of my knowledge, ~184,800 miles on it, and this one, to the best of my knowledge, has 90k on it and tested as "good" at Murray's/O'Reilly's.

Thanks

-Jim

Jim,

Are you reading the voltage based on what the dash says? If so, mine (and I have seen several other 1st gens the same way) where the dash reads about 1V too low. You should take a multimeter and measure the voltage at the battery. You should be at 13.5v or so.

Since you are showing over 13v, then the system is probably charging just fine. If you are worried about it, O'Reilly's (or whatever) should be able to test your charging system while on the car.

Kent

what did they qualify as good?

it depends a little on RPM, but alternator should be charging 13.5v-14v. at idle it usually drops a little, but still should be more than 12.5, less than that and its running on the battery

My old alternator was charging at one needle above the 12v bar. I'll see if I can dig up a multimeter and see what my new alternator is charging at. I was unaware that there is a ~1V discrepancy between the actual charging voltage and what the gauge says on the dash. I'm also going to have to have my old alternator checked to see if it's good.

How old is your battery? More than 5 years, toss it and get a new one. They rarely last longer than that unless their the uber expensive sealed types.

So you're saying that you changed the alternator but are still having the same (or similar) issue?

I would start by cleaning all connections at both ends of the battery cables. I swear that when I replaced mine with new ones it cured 85% of the issues I'd ever had with the car. :)

And this had better not turn into an excuse for not showing up for the race on the 21st. lol.

ive noticed that too, dash gauge can be pessimistic

you're not the only one!

I agree with all above. I replaced my battery cables with new Mazda ones a few years ago. Made a BIG difference. I could have gone with generic, but the MAZDA ones fit perfectly and look nice. I figure the originals lasted for over 20 years, so the cost difference between OEM and generic is not going to kill me over the next 20 years. :) The old cables would heat up quite a bit if you had to do much cranking (like if flooded). The new calbes get the starter spinning faster and they do not heat up like the old ones did.

The S5 alt with a new 8ga output wire made a world of difference too. Before things would dim or slow when you had the blower going, wipers going, etc. Now they all work great.

This won't keep me from being there, however the lack of paychecks may. I'm still waiting on my first paycheck from work.

I replaced my battery cables the weekend before last. (Copper FTW!) The 7 starts so much easier and doesn't seem to flood as much. I have attached the PDF i followed.

our alternators are wired terribly and with too small of wire. Cut the main wire from the post on the alternator off at wire loom. Run a new 4ga wire from the charging post on the alt directly to the battery. Even if your alternator is dieing this will make it last a lot longer and it will only cost you $10 to do