Stock Alternator question

I think my alternator went. My car wouldnt start yesterday so I had to get a jump to get home. When I got home I measured my battery. It was at like 12.8volts idle then dropping. When revved it would go up but go right back down. When the engine is off its like 10 volts.

 

Shouldnt it stock be like 14 volts, can anyone give me the specs of idling volt, off volt, and rev volt? Should I buy an subaru alternator or one from a store like napa?

 

I also didnt get a light on my dash for a bad alternator, any idea why? Would a bad alternator relate to it stalling while idling?

Get the battery tested first. Dropping to 10V right after car is shut off sounds like a battery with a dead cell.

 

EDIT: Oh, and if you need an alternator, check prices at your local dealer. When I had a 97 outback and needed one for it, a Subaru alternator was cheaper than aftermarket, and even cheaper than having a local alternator shop rebuild the one I already had...........

You may have free alternator sitting at the dealership thanks to SOA lol. Check on my.subaru.com to see if it has been replaced before.

In my experience 95% of the time that alternators go bad the brushes inside have just worn out, its a pretty straight forward job if you have a decent mechanical know how. My last two bad alternators cost me $5 and $7 each to fix (86 Honda CRX, 85 Toyota Celica Supra), brushes are crazy cheap, and designed to wear.

 

As far as not getting the dash light, thats a pretty weird one, I've always had it come on in cars when the alternator was going out.

 

You should take your car into Advance or Autozone and have them test the alternator (alternatively you can just bring them the alternator in hand if the car is not running).

 

I second the notion of the bad cell in the battery. I used to work at a bike shop on electric bike components and batteries were the bane of my existence. The car would definitely not start if the battery is going bad as it wouldn't have the ability to supply sufficient amperage to the motor. When you pull a large load off the battery the voltage will drop, and if its a weak battery it will drop significantly. Have you tried testing the voltage while your trying to start the car? I would expect if its bad a voltage drop well below 10 would show up.

 

A bad alternator would drain the battery, but shouldn't cause a no-start condition. I've driven (very literally) over 50 miles with a completely tanked alternator and the car was still trucking along.

 

Final Edit: If you jumped the car and then drove it home, I really wouldn't expect the alternator to be bad. If your battery was tanked and the alternator was dead too, you shouldn't have gotten far once you unhooked from the jumping car.

So I went and bought an alternator then replaced it. Before I started the car i tested the battery and it said 12.1volts and when it was running it was consistently 11.80 volts even when running. Do I have a bad new alternator?

It went back up to 12+ volts when I shut the car off ?

Couldn't your battery be warn down some and the alternator hasn't fully charged it back up?

Check your fusible link in your fusebox (if you have one).

I read something that came with the alternator that you need a 15 min break in period of atleast 2k rpms before checking if the alternator is bad.

 

Went on a local drive for 15 minutes and came back and the volts are at 14 finally

 

thanks everyone for their input

 

Now on too the next problems, the IAC making my car die at idle and tires

IF the battery is dead or weak, it could end up killing your alternator. If it won't take a full charge the alternator will run constantly in an attempt to charge the battery.

 

Get the battery tested, its free, and gives you peace of mine if nothing else

I did some testing on the car but then ended up bringing it into the shop

some of the things-

car wouldnt start but start in neutral

gauges died

battery and brake light came on

abs came on sometimes

stalled

I only drove around my neighborhood incase it stalled so I could push it home if I had to lol

then I made it back home, tested the battery 12volts. tested when it was on 11 something. turned the car off. wouldnt turn back on....

 

So i disconnect the battery and put it back on and it starts up no problem?

 

After all that I was so confused I brought it to the shop turns out, its a wire off the postive terminal of the battery. it gave the wrong voltage to the alternator frying the alternator and battery.

 

and my battery was 7 years old, had a crack, and was leaking in my engine bay

I suggest everyone checking the year of the battery.

 

Up to this point, after paying for tires Ive payed almost as much in repairs as I payed for the car. I've only driven it 3k since ive owned it.......pretty dissappointed in the car.

IF the battery is dead or weak, it could end up killing your alternator. If it won't take a full charge the alternator will run constantly in an attempt to charge the battery

 

 

some alt facts. the alt spins all the time when the engine is running. DUH!!

it makes the electricity that the car needs, as much as it needs.(or at least it is supposed to if it is in good working order.)

 

with a good battery and everything off it makes enough to spark the engine.

turn on the heater fan, it makes more. tunr on the head lights, it makes more.

turn on your super stereo with ear drum splitting sound, it makes more.

have a discharged battery it makes more until it is charged back up.

have a battery with a bad cell it makes more, ALL THE TIME, if the battery is never fully charged.

 

the alt will make as much juice as is needed as long as it is needed up to it's max amp output. so a bad battery can hurt it or shorten its life.