Bad Alternator?

[GMFan]

My 2011 Mazda 6 has lately been a bit sluggish to start. Yesterday it nearly left me stranded in a parking lot. The keyfob didn't work and the car did nothing when I put the key into the ignition. The car was completely dead and none of the electronics worked. It was almost like the car had no battery in it at all. About 10 minutes later after looking under the hood, the car randomly came back to life and it started and everything has been normal.

I took my car to Autozone this morning to have them test the battery expecting to replace the battery. The battery is 3 years and 5 months old. The manager recommended testing before replacing. They hooked up their jumper tester and the battery and starter test came back fine. The alternator came back as "Fail." The printout says:

Battery Results: PASS
Entered Battery CCA: 590
Measured Battery CCA: 577
Battery Health: GOOD HEALTH
Battery Temp: 71F, Expected: Not to Exceed -27F or +140F
Beginning Voltage: 12.5V, Expected: Greater than 12.4V
Voltage Under Load: 11.8V, Expected: No Less than 10.4V
Battery Type: SLI_STD

Starter Results: PASS
Loaded Voltage: 11.7V
Free Run Current: 90

Alternator Results: FAIL RIPPLE OUTPUT
Starting Voltage: 13.9V, Expected: Greater than 12.9V
Loaded Voltage: 12.1V ! (Fail), Expected: Greater than 12.9V
Voltage Regulator: BAD
Ripple Voltage: 0.00 V, Expected: No greater than 0.05V

I took the car to a shop for a new alternator and they are saying the test on the alternator came back as the alternator is okay. The shop said they can replace the alternator, but according to them the alternator tests out okay.

What should I do in this situation? The car has 200K on it on original alternator. Can the test from Autozone be relied upon as accurate? If this does not sound like an alternator issue I'd like to further diagnose before throwing an alternator in it.

Thanks,

 

[supton]

Did you clean all connections? that it came back to life after 10 minutes makes me think of connection problems first.

 

[JMJNet]

Take it to another shop?
What kind of shop did you take it to?
There is also a possibility that the cable is bad from alt to battery.

If you have a load tester, you can test it yourself.
Measure the load without any electrical parts.
Turn on all electrical parts you can think of like AC, Lights (even High beam), etc. then measure the load.
If the voltage cannot be held steady, then the alternator is bad.

 

[eljefino]

Really seems like a connection problem. The battery is supposed to filter at least a little "ripple" so if it doesn't have a real tight connection to the alt, more AC is going to find its way from the alt to the test point and show up as "false ripple." The fact that two independent tests, at two test points, had two different results, supports this.

But the biggest is the car "coming back to life" in the parking lot. What happens there is your bad connection arcs, and leaves an insulating black mark that only makes it worse. Something jarred and re-made the connection. Check everything by taking it apart, not just by looking at it.

 

[GMFan]

Thanks these are great replies. I did replace the positive and negative connections with the generic part store connectors a year ago because the old ones corroded away.

The shop retested and said the bad alternator wouldn’t cause the issues I had. They said loose connection problem, but the connections all looked good.

I’ll bring it back home and break out the multimeter to check the battery connection resistances.

 

[JeffKeryk]

I would start by servicing the battery connections. Maybe throw a charger on the battery for a few hours.
If it is fairly easy to replace a cable, like the ground, with a fatter cable, I would do that. I do this on my 4 banger Hondas. The 6 cylinder cars used a bigger battery and ground cable.
Good luck.

 

[SHOZ]

Make sure the clamps are tight so the cables don't rotate. But don't torque the post. My Hyundais the OE clamps don't fit the aftermarket posts which seem to be smaller than the ones on the OE batteries made in Korea. A tubular spacer stops the clamp from tightening past a certain point. So I took it out and shortened the tube.

 

[Kira]

I would start by servicing the battery connections.

^^SO often this.
Y'all just had a spate of damp weather, no? Water gets in between post and cable clamp if they're dirty. This happened to me on my 3rd day of car ownership. I could see the soaked corrosion hissing as I tried to start the car. All the guys at work broke my spheres because I had a dirty battery.

I'm also a huge believer in battery terminal sealant spray after thorough cleaning.

Re SHOZ' post above: I forget the group numbers (sizes) but my neighbor's car came with a G51 (small) battery. A replacement, bought before I tended the car, definitely had smaller posts. There were electric woes of the caliber you had. I shimmed the posts with sheet copper. Then, when that battery dies a member here quoted me the common replacement for the small G51 and it had bigger posts and the clamps fit perfectly. Can't remember the specifics but you know what I'm talking about.

 

[chemman]

With a helper, have the helper rev up the engine to between 2000 - 3000 rpms, turn the high beam headlights on, and measure the AC ripple voltage between the the negative battery terminal and the battery output terminal of the alternator. If you measure more than 0.05 VAC (50 mV AC), then something is amiss with the alternator's internal diodes.

Good Luck!

 

[Warstud]

Remove the battery cables and clean them where they make contact with the battery . Then go from there .

 

[Kira]

chemman, you sent me to my Ford Ranger notes. I got my truck ~4 years ago and have been jotting things down as I find them.

AC Ripple Test:
Use a Volt meter @ AC volt setting.
Locate B+ connection on the back of the alternator. (Stud with the larger wire connected)
Start engine
Have someone raise RPMs to 3,000 and hold it there
Test AC volts by touching 1 meter probe to B+ and the other probe to Alternator's Case (ground), there is no +/- with AC Volts so color of meter probe doesn't matter
AC Ripple under 0.50 AC volts is passing, so 0.49 is passing but................

I couldn't help but notice an order of magnitude difference between your advice and what I read.

Hmmmm......

 

[eljefino]

I’ll bring it back home and break out the multimeter to check the battery connection resistances.

That won't tell you what you need to know. Just sitting there the resistance is one thing, trying to crank or running down the road are two different scenarios.

Get hands on, and take stuff apart to check. Battery terminals, engine grounds, the positive distribution block at the fusebox or starter.

 

[Warstud]

Bad Battery - will usually occur when you go out and start it and it slowly starts or dont start at all .

Bad Alternator - will usually occur while your driving . Your headlights and dashlights will get dim . The blinkers will quit working .

Everything thats electrically controlled will gradually quit working . Keep an eye on the voltage gauge on the dash to see if it gradually goes down .

 

[JMJNet]

There is also a possibility when the alt is weak but not bad yet.
If you have a shop specializing in rebuilding starter/alternator, bring it to them.
They are hopefully more knowledgeable on electrical issues.

 

[SHOZ]

Cheap plug in volt meters are good as unless you know what is normal for your car you don't know. I have a OBDII display running all the time showing coolant temp and other things.

 

[Marcozi]

chemman, you sent me to my Ford Ranger notes. I got my truck ~4 years ago and have been jotting things down as I find them.

AC Ripple Test:
Use a Volt meter @ AC volt setting.
Locate B+ connection on the back of the alternator. (Stud with the larger wire connected)
Start engine
Have someone raise RPMs to 3,000 and hold it there
Test AC volts by touching 1 meter probe to B+ and the other probe to Alternator's Case (ground), there is no +/- with AC Volts so color of meter probe doesn't matter
AC Ripple under 0.50 AC volts is passing, so 0.49 is passing but................

I couldn't help but notice an order of magnitude difference between your advice and what I read.

Hmmmm......

THIS! The voltage regulator, which typically contains the diode pack, is likely bad. Here's a link to a picture of a full wave rectifier: https://www.electronics-tutorials.ws/diode/diode_6.html

 

[chemman]

chemman, you sent me to my Ford Ranger notes. I got my truck ~4 years ago and have been jotting things down as I find them.

AC Ripple Test:
Use a Volt meter @ AC volt setting.
Locate B+ connection on the back of the alternator. (Stud with the larger wire connected)
Start engine
Have someone raise RPMs to 3,000 and hold it there
Test AC volts by touching 1 meter probe to B+ and the other probe to Alternator's Case (ground), there is no +/- with AC Volts so color of meter probe doesn't matter
AC Ripple under 0.50 AC volts is passing, so 0.49 is passing but................

I couldn't help but notice an order of magnitude difference between your advice and what I read.

Hmmmm......

Kira - in the last line of your posting above the Hmmm... you have 0.5 V AC listed for the AC ripple. That is 500 mV AC, which is one heck of a lot of AC ripple.

If I cited 0.5 VAC to you 4 years ago (I honestly do not remember) then I made a mistake in that posting.

 

[Kira]

You were not the source. They come from everywhere. When I read something good, I jot it down.
This wouldn't be the first time I discovered a plain old error or data which applies to some specific vehicle.

 

[zzyzzx]

I'm thinking that this could be an intermittent problem caused by worn alternator brushes.
Try getting one of those lighter socket plug in votmeters and drive with it in and see how the voltage varies.
Based on my personal experience higher revs = alternator stops working but will start back up once the RPM's die down.

https://www.amazon.com/INNOVA-3721-Battery-Charging-Monitor/dp/B000EVWDU0

 

[f355spider]

I'm thinking that this could be an intermittent problem caused by worn alternator brushes.
Try getting one of those lighter socket plug in votmeters and drive with it in and see how the voltage varies.
Based on my personal experience higher revs = alternator stops working but will start back up once the RPM's die down.

I friend of mine had a problem with the "batt" light coming on in his Ferrari. He took the car to both an ORiellys and an independant Ferrari shop and both told him is alternator/charging system and battery tested fine. At home, he pulled the alternator out of the car, took it to a reputable alternator rebuild shop and they put it on their testing machine and ran it....tested fine initially. After 20 minutes, it got warm, the voltage dropped. Bad voltage regulator. They said the oem Nippondenso alternator otherwise looked fine, replaced the regulator and sent him on his way.

A device like you suggest would have caught his problem on his first drive I'm sure. He could have easily spotted the drop in voltage when warm. Ferraris have gauges for water temp, oil temp and oil pressure...but not voltage. For that you get a "batt" light, like every other car.