ELECTRICAL Diagnoses

[ParadiseXJ]

I'll apologize in advance, because this not a Jeep tech question, but it happened while I was WORKING on my Jeep :wierd:. Please move or delete if I'm going out of bounds.

02 Nissan Sentra - my commuter. Battery light came on, no change in running. 5 miles later car died, like everything died, dead. AAA guy jumped it. It started. Removed the jumper, died. Got towed home.

Battery 3 yrs old - put on charger overnight
Alternator 8 months old
No slipping belts
Weak point is the + battery connection - need a new one.

After 24 hr. charge, battery reads 14.2v, off charger 13.xx, started 11.8 (measured AT post and at ALT feed).

So is it the ALT, the battery (and bad connection), or is there a relay/fuse on newer cars that could blow, leaving me stranded.

 

[Nely87]

Your alternator is bad. While the cars running you should be seeing about 14v.

Sent from my SGH-T959 using Tapatalk

 

[Saudade]

but it happened while I was WORKING on my Jeep :wierd:.

Well, that's a bit of a stretch...

I would agree it's likely the alt. They can typically be tested at your local autoparts store.

 

[ParadiseXJ]

$#&@ = Darn!

I have an extra Jeep Alt? Whaddya think.

 

[kastein]

Sounds like alternator or perhaps a fusible link in the wire from the alt B+ terminal to the battery to me. Stick a voltmeter on your alternator's output right at the alt, if it reads OK or even too high there is a chance it is good. Then measure voltage from alt B+ terminal to battery positive terminal, if there is more than a volt or so of difference, you have a bad wire or fusible link/fuse.

 

[ParadiseXJ]

Thanks, I'll give that shot. I replaced the alt 8 mos. ago, new, not reman.
...too bad though I'll have to take the Jeep to work

 

[ParadiseXJ]

Thanks for moving this. I felt like a dork not knowing where to post it...now I know.

I tested the battery after a day of not being on the charger...never made it to 12V.

I tested the battery after I disconnected the charger and started it. 11.8V

I checked the main alt bolt thru the VM to ground...11.8V

An interesting note: The gen light went out when I revved it over 1200RPM...but no change on the VM. Still 11.8

I put it on the charger @ 10A. NO change, still 11.8.

Could there possibly be some other reason that it's not going over 11.8V. Could a bad battery "refuse" the charge. Just a thought. Electricity is Greek to me...and it's not the charger or the VM...I did the same test on my MJ and got good numbers...tween 12.5 off and 13.9 running.

 

[kastein]

I don't believe a bad battery could do that, all it could do is draw a ton of current to bring the voltage down and you would notice that. Other things that should be checked - make sure your ground from the battery to the chassis is good, make sure the ground from the engine to the chassis is good (you can do these with a voltmeter while it's running, measure voltage from chassis to battery negative and from chassis to engine, if either one is over a half a volt or so, post up what it is... I would expect no more than a half a volt.) Another problem that could be causing this is an issue with the field coil in the alternator, if the field coil wiring, slip rings / brushes, or coil itself have a problem there will be no magnetic field to energize the alternator so it won't produce any power.

PS - no worries on the thread being in the wrong forum, it's like 3 mouse clicks to move it.

 

[ParadiseXJ]

I talked to a friend today. If the battery charger goes to 0 after 24 hrs. then it's accepting the charge, don't know if it has a choice. It's not the cost of the alt that bugs me...it's that it'd take 1/2 hr to do on my Jeeps. 2 hours on the Nissan. F

Battery after 24 hrs on charger...12.7 static, 11.8 running, 14.2 on charger

Good news: Alternator on warranty