Alternator diagnosis
 

Hello, the battery recently died on me. Bought a trickle charger, charged it all the way up. Multimeter readings:
Car off: 13.28V
Motor on: 11,76V

Drove it for a bit, new readings:
Car off: 11.8V
Motor on: 11.2V

Is my alternator broken? Ground leakage? I think the fuse is fine, checked it. any advice would be appreciated.

Sounds low on the battery, how old is it?

https://cimg6.ibsrv.net/gimg/www.s2k...55cff281ba.jpg
The alternator is not charging the battery. With the engine at idle, the volts across the battery should be 13.2VDC or more.

Battery failures are much more common than alternator. Note the Engine Running and Engine Off dividing line in the nice chart above.

Battery voltage of a fully charged battery after "resting" -- neither charging nor discharging -- for at least 12 hours should be at least 12.7vDC. Don't quibble about 12.6v. :) Note "fully charged" and "resting." Any lower than that indicates a bad battery. Put the battery on a decent battery charger at least overnight.

BUT based on your measurements your alternator is not fully charging the battery and will, in fact deplete it. To charge a battery requires a higher voltage (1v will do) than the battery already has. Anything lower than 13.7vDC at the battery terminals of a good battery when the engine is running indicates a bad connection to the alternator or a bad alternator.

Pick the low hanging fruit first, that's the battery. Borrow a good battery charger, charge it for 12 hours (24 is better) then rest it for another 12 before checking the voltage again. If your battery is good check the connections to the alternator and the alternator itself.

-- Chuck

ive already bought a trickle charger, 4 hours after a full charge the battery was above 13v. so probably the alternator. what are my next steps?

It's starting to point to the alternator or its connections but recommend checking battery voltage after a longer period of resting. Also a $20 battery checker can give information how the battery handles loads like starting. Link to the Harbor Freight version but there are dozens all made in the same factory in China that look like this.

https://www.harborfreight.com/100-am...Code=102&gQT=1

https://www.harborfreight.com/media/...200&fit=bounds

-- Chuck

ill look into that. how can i check the alternator connections? in case the battery isn’t the problem?

I'd start looking for another alternator. :)

Connections/connectors are the weak point in any circuit so check the mechanical connections and for clean contacts. Tedious and probably acrobatic to check them. Contact cleaner and treatment with DeoxIT D100L is what I use anytime I find a connection even slightly dirty especially connections exposed to the elements like under a car engine. DeoxIT seems expensive but a 25ml bottle will last forever 'cuz you're only using a drop at a time. I'm sure there are other similar items.


-- Chuck

Many parts stores will test the alternator for you. It takes about 10 min to pull it off the car. Yes it can be wiring issues so need to make sure all connections are good and tight, but given your running voltage it is for sure not charging the battery.