Alternator overcharging?

[Wesseat]

When i installed my js alternator 300 amp in my 08 jeep wrangler my voltage at idle was 14.25v. I checked my idle voltage a couple months ago and it was 14.75... Now today and it is 14.85 to 14.91.. I know my agm is weak and needs replaced.. Can a weak battery cause overcharging? I am getting ready to switch to a headway bank and don't want to overcharge it.

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[metalheadjoe 10+ year member]

Sounds like you're splitting hairs.

 

[Wesseat]

Sounds like you're splitting hairs.

Charging a headway at 14.9 wont hurt it?

 

[JW266]

Never seen a bad battery cause overcharging. Bad regulators cause overcharging.

Colder weather will cause a small rise in voltage. I've got a voltmeter in my HU. Cold start in the morning reads 14.2 - 14.4. By the time I get to work it's 13.7 -13.8

 

[Wesseat]

Never seen a bad battery cause overcharging. Bad regulators cause overcharging.

Colder weather will cause a small rise in voltage. I've got a voltmeter in my HU. Cold start in the morning reads 14.2 - 14.4. By the time I get to work it's 13.7 -13.8

I was wondering if the cold temps had anything to do with the high reading... I drove it around and pulled it back in the garage and tested it again and got the same readings from 2 different multimeters. I dont know if im splitting hairs but my expensive xs power agms didnt last very long and i hate to charge my new expensive headway higher than recommend.. I want to do it right. I have my oem alternator and my old lead acid battery that somehow still tests good.. Thinking i probably should swap em out and see what i get.

 

[metalheadjoe 10+ year member]

I was wondering if the cold temps had anything to do with the high reading... I drove it around and pulled it back in the garage and tested it again and got the same readings from 2 different multimeters. I dont know if im splitting hairs but my expensive xs power agms didnt last very long and i hate to charge my new expensive headway higher than recommend.. I want to do it right. I have my oem alternator and my old lead acid battery that somehow still tests good.. Thinking i probably should swap em out and see what i get.

Cold temps fuc*ed my charging system, so removed my JY battery today. I'm too drunk to expand on that.

 

[Wesseat]

 

[2023 LTZ]

Lol
I’ve been having similar problems w my impala. I think the big 6 allows more than designed to flow into the system causing it to operate outside of normal.
I’ve switched alternators a bunch of times but haven’t been able to witness what I’d call “within parameters”.
No cel so I just run it. Fried interstate agms and flooded alike. Flooded seems to last longer in the 13.7-15 continuous charging. I’ve posted on an impala forum but no one knows why it does this or if it’s unusual. Dealer said “you changed the wiring? Any cel?” Nope. “Shouldn’t be a problem then.” This doesn’t help you at all I’m saying I share your struggle bc I’d like to add batts but for now I just keep a flooded in the trunk to switch out if that fr won’t start.

 

[winkychevelle 10+ year member]

I'd probably go lto over lifepo4 or have a circuit breaker wired in that I could disconnect the bank from the starter battery until the alt warmed up

 

[Ridinhi 5,000+ posts]

I took out my amps and volt meter due to me designing a new setup. I have noticed my charging gauge/hand leaning to the right more than normal. Can’t read what the voltage is due to me taking out volt meter. But, my truck act as if it didn’t want to stay yesterday and today. Not sure if it’s related to the cold weather or not. Temps average 7-22 degrees here lately.

 

[Popwarhomie 5,000+ posts]

Could be the cold weather. Could be JS alternators poor voltage regulators. Not the first I have heard of that issue.

 

[some dude]

My 99 Toyota Avalon charges 13.8 in summer, 14.2 in winter on my bass knob voltage display.

 

[winkychevelle 10+ year member]

My truck is up .2v today to 15v and at max voltage is up to 15.5v over the usual 15.4 assuming I turn it up. My alt is set to 14.8v so I don't cook my agms. I wouldn't put lifepo4 cells on that voltage.

 

[Wesseat]

Js alternator replied to my message.. Sounds like they have a fix for my alternator.. What is the best voltage to shoot for when running a headway bank?

 

[winkychevelle 10+ year member]

Js alternator replied to my message.. Sounds like they have a fix for my alternator.. What is the best voltage to shoot for when running a headway bank?

Nothing higher than 14.4 really your best off closer to 14v. This is why lto is so advantageous.

Lifepo4 really doesn't fully kick in till 13.6v in 4s banks
Lto kicks in at 14.4v in a 6s bank

So while lifepo4 will have an overall higher state of charge you will still have to drop to 13.6v before the battery really starts to help.

Alot of guys are running 6s lto and only charging to 14.6v and optimally 15-15.5v is all you need to get maximum value from lto banks.

All battery's have voltage drop but the closer your charge voltage is to the rest voltage the less the change in voltage is thus a less noticeable drop. This comes at the expense of state of charge.