Bad Alternator?

[JTK]

Like said, if everything was completely dead electrically and then suddenly (maybe after some fiddling?) came back to life. You have a connection problem somewhere.

My guess is as mentioned above. Check those battery cables. If you just replaced the terminals, the cables themselves are likely corroded at one end or both. I've seen them corroded almost the entire length.

 

[mfewtrail]

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.

'Bright Idea' For Short Detection | MOTOR

There’s an old saying that a picture is worth a thousand words. An oscilloscope can sketch a useful picture of the problem you’re chasing, and this includes potential alternator trouble. I first saw an oscilloscope used for alternator diagnosis in the 1970s. Since then, I’ve practiced it with...

www.motor.com

Here's another article from that engineer cited in the above article showing that more than .5v ac "can" be ok: https://www.scannerdanner.com/media/kunena/attachments/4419/updatingyourripplevoltagetutorial.pdf

 

[chemman]

Now if the information provided in these two articles can only be adopted industry wide by manufacturers, service information providers, and service personnel.

As Grube eludes to and Marinucci states - "...a picture is worth a thousand words". An alternator's output observed on an oscilloscope is the way to go for a definitive diagnosis and measure of an alternator's defect(s).

I greatly appreciate the knowledge gained from these two sources. Thank you mfewtrail.

Now to get an automotive oscilloscope to compliment the one in my ham shack!

 

[Donald]

You need to check both ends of the battery and alternator cables. Including grounds. Remove, wire brush or other method of cleaning and reinstall.

Fully charge battery and test the voltage the next day before using the car. If lower try again but now leave battery disconnected and test the next day. An accurate DVM will do for that test.

If easy to pull alternator then pull it and bring to an alternator rebuild shop. They will drive the alternator with an electric motor and test it isolated

 

[benjy]

modern vehicles as well as techy older ones need proper power. recently my audi 2001 TT 225Q 8 YO Napa battery was "acting up" a full several day charge on my C-Tek it seemed OK BUT out for a summer ride it was "acting up" no speedo or tacho reading as well as almost no power + dash lights looked like a christmas tree almost got home, a new wally everstart agm cured all, thankfully!!

 

[Donald]

A bad alternator might not charge the battery fully. But if the vehicle was dead and came back to Iife then it's not an alternator problem. Or there is something beyond a bad alternator if the alternator is bad.

Sometimes corrosion can hide under battery cable insulation.

 

[Tkonrr]

My 2012 Mazda 6 has been a bit sluggish to start since I bought it 2 months ago. It's battery is in perfect health and stays fully charged. Like you, I experienced a couple of no starts with all dash lights, map lights, dome light etc. had absolutely no power and the radio presets got lost. While stranded the second time last week, I found the battery terminals, ground wires, alternator connections to be tight and not corroded. The problem turned out to be a loose connection in a wire attached to the fuse box in the engine compartment. Hope this helps.