Alternator

[nofishfisherman]

Are there any easy ways of checking to see if an alternator is going bad?

 

My Mazda 3 would not start yesterday morning but I was able to jump it when I got home from work.  I removed the battery and brought it in for testing and it tested bad so made the replacement. 

 

The car has 107,000+ miles on it which seems to be around the time alternators have gone bad in other vehicles I've owned. I drove the car to work this morning (only 2-3 miles) and I started wondering about the alternator and if there is a way to test it before it goes bad and leaves me stranded somewhere. 

 

I saw elsewhere some saying you can start your car and remove the negative cable from the battery and if the car still runs the alternator should be good, although I saw else where that you should absolutely not do this because of potential electrical issues.

 

I'm just wondering if there are any reliable ways to check the alternator at home with limited auto skills. 

[pikestabber]

1 hour ago, nofishfisherman said:

I saw elsewhere some saying you can start your car and remove the negative cable from the battery and if the car still runs the alternator should be ...

 

Yeah, don't do that... You can end up doing some serious damage to your car. Lots more computer "stuff" in newer cars to fry out.

 

Bring it to a part store...almost all of them can grab a voltmeter and test your alternator. Most will do it for free. I just replaced my battery a couple days ago for a similar problem and it turns out the alternator was shot, too. One can kill the other, and vice-versa, too. Their fates aren't always tied together, but I agree you'd be wise to get your alternator tested.

[pikestabber]

...assuming you can still drive it, that is... You can get a voltmeter for about $20, give or take, and if you aren't comfortable testing it yourself, you might find a buddy who can? There's a lot of info online to help, too.

[PurpleFloyd]

The old timer trick was to touch the center of the back side with a screwdriver. If the alternator was charging it would have a magnetic charge and pull the tip towards it  if it wasn't charging there would be no magnetic charge. 

[nofishfisherman]

I think my neighbor may have a volt meter that I could borrow, I can try testing it that way before escalating further. 

 

 

[Mike89]

I'd just go the auto parts store where they will check it for free.  done it before and they are very helpfull.

[delcecchi]

3 hours ago, nofishfisherman said:

I think my neighbor may have a volt meter that I could borrow, I can try testing it that way before escalating further. 

 

 

Watch for the the harbor freight coupons.  Periodically they will have one for a free voltmeter with any purchase.   Then go buy some screwdrivers or a tape measure (can never have too many of either) and get a free voltmeter.  

 

Then, measure the voltage across the battery with the car running.  If it is more than like 13 volts (anyone know what it is actually supposed to be?) at least the alternator is putting out something.  

 

My experience with modern cars is that if the battery is more than about 4 years old, you are on borrowed time.  

Edited March 16, 2017 by delcecchi

[nofishfisherman]

The battery was several years old, don't remember exactly how old but it certainly wasn't anywhere close to new.

[Jeremy airjer W]

1 hour ago, delcecchi said:

Watch for the the harbor freight coupons.  Periodically they will have one for a free voltmeter with any purchase.   Then go buy some screwdrivers or a tape measure (can never have too many of either) and get a free voltmeter.  

 

Then, measure the voltage across the battery with the car running.  If it is more than like 13 volts (anyone know what it is actually supposed to be?) at least the alternator is putting out something.  

 

My experience with modern cars is that if the battery is more than about 4 years old, you are on borrowed time.  

13.75 is good

14.25 is great

14.5 is really good.

Roughly......

 

Ill second the remove the cables with the vehicle running. Not a good idea.

 

As far as getting a heads up on an alternator failure. Think of it as a light bulb. Can you tell when a light bulb is ready to fail. Probably not. It will work great one minute and you go to turn it on the next and it is done.

[nofishfisherman]

16 hours ago, Jeremy airjer W said:

 

As far as getting a heads up on an alternator failure. Think of it as a light bulb. Can you tell when a light bulb is ready to fail. Probably not. It will work great one minute and you go to turn it on the next and it is done.

 

Thats always been my experience.  The alternator failed in my other vehicle awhile back and left me stranded with a 3 year old and our new born baby in the car, not an ideal situation.  That's what I was hoping to avoid by getting a heads up on if the alternator was on its last legs.

 

I did take the car to an auto part store last night and they tested the battery, alternator, and starter and all passed so it looks like the culprit likely was just the old battery that I replaced.