Alternator

[BAKNBLK]

Seems the Alt has given up, voltage driving will drop to 12.2 to 12.5 then jump to 13+ but usually 12.5 or less. Normally was 13.7to 14v. Drove home yesterday 50 miles, check charging system came up once I got home. Checked battery and it was 12.3v. I have a Odyssey battery and the auxiliary was deleted. Its a '21 with 40k miles. Everything is tight etc. Options? I haven't found a aftermarket like a Powermaster available.

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[jeepoch]

Perfectly normal operation. Alternator output voltage decreases as your batteries become 'charged'. As they drain under load, the alternator has to work harder to restore the battery's internal electrical-to-chemical energy. It does this with higher voltages.

Recall Ohm's Law; I = V / R

For any battery, energy is input with charging potential in the form of coulombs (amount of total electrical charge present). This is directly related to current (I), the amount of charge flowing per unit time. With Mr. Ohm's findings, this means current is directly proportional to voltage (V) and indirectly proportional to resistitive load (R).

In other words, as your battery drains due to higher resistence (larger load), an increase in delivered charge (more current) is delivered by increasing the voltage applied.

Think of your alternater as a charge pump. It works 'harder' (more current) by increasing its output voltage. When the load is lighter (batts are fully charged), then the alternator doesn't need to work as hard, the voltage drops, thus delivering less current (charge per unit time).

No worries, this is a sign your battery(ies) are in good working order. When your alternator remains high continuously, this is when you need to consider replacing things.

Anything from the high 12 to mid 13 volt range is generally a very normal, healthy charging system.

Hope this helps,
Jay

 

[shadango]

Question -- my 2021 2.OT Wrangler shows 14.2-14.5 on the dash readout most times....sometimes down as low as 13.8....thoughts?

Has been this was since brand new, some 40k miles on her now.

I am chasing an ABS/Brake light random issue , replaced both batteries recently thinking that was the issue (OEM original batteries, 5 years old)....and 'overcharging spikes" apprantly can cause ABS issues.....

On my antique and classic cars, I have always figured 13.7 being the right reading while running.....but this new stuff.......seems different.....

 

[jeepoch]

The issue here is the fallacy of the JL's Battery Voltage display on the Cluster's "Electronic Vehicle Information Center" (EVIC) presented value.

Most people falsely believe this is your vehicle's instantaneous Battery Voltage. Nope, not quite right. This is an averaged value of the alternator's output 'effort'.

Think of it more as a guage of how 'hard' your alternator (or rather the entire charging system) is working at charging the vehicle's battery(ies). The higher the value, the harder it's working, and the larger the drag being put on the engine.

I often refer to this value as 'Kumquats' rather than voltage. While the units displayed may have some indirect reference to actual voltages, it is really a numeric value derived by the charging algorithm in software, not as a voltmeter phyisically measuring electrical potential across the + and - posts of the battery.

Again the higher the number of Kumquats, the harder the charging system (as a whole) is working at charging the battery(ies). Nothing more, nothing less. They should have used a bar graph from 0 to 10. Fully charged batteries being 5. More than 5 then actively charging, less than 5 not needing to charge (or draining). Again in measurement units simply relative to 'full'. With the Kumquat meter on the EVIC, somewhere in the mid to high 12v readings can be considered a 5 on the relative charging scale.

Best Regards,
Jay

 

[shadango]

The issue here is the fallacy of the JL's Battery Voltage display on the Cluster's "Electronic Vehicle Information Center" (EVIC) presented value.

Most people falsely believe this is your vehicle's instantaneous Battery Voltage. Nope, not quite right. This is an averaged value of the alternator's output 'effort'.

Think of it more as a guage of how 'hard' your alternator (or rather the entire charging system) is working at charging the vehicle's battery(ies). The higher the value, the harder it's working, and the larger the drag being put on the engine.

I often refer to this value as 'Kumquats' rather than voltage. While the units displayed may have some indirect reference to actual voltages, it is really a numeric value derived by the charging algorithm in software, not as a voltmeter phyisically measuring electrical potential across the + and - posts of the battery.

Again the higher the number of Kumquats, the harder the charging system (as a whole) is working at charging the battery(ies). Nothing more, nothing less. They should have used a bar graph from 0 to 10. Fully charged batteries being 5. More than 5 then actively charging, less than 5 not needing to charge (or draining). Again in measurement units simply relative to 'full'. With the Kumquat meter on the EVIC, somewhere in the mid to high 12v readings can be considered a 5 on the relative charging scale.

Best Regards,
Jay

I have long been a fan of "what is the normal state" of something... obviously for this a guy would have had to own a vehicle a while and paid attention to whatever reading... in this case "volts".

Anything way above or way below the "usual" is when i get concerned......

I seem to be about where "it has always been" so.....gonna try to not overthink.

On my 72 Plymouth, the aftermarket voltmeter regularly reads 14 volts.....folks who seem to know tood me there is a charging problem.

But, for 15 years now it has been fine.....the current battery in the Cuda is 8 years old...so i figure its fine.

But like i said, this new stuff makes me nervous

 

[BAKNBLK]

Ok so what your saying the Jeep display reads +- who knows what voltage..
All I know is 12.3 after driving a hour isn't correct that was measured at the battery engine off. I put it on a battery Tender over night then I checked this am it was 12.8v. Now reading 12.3v 4 hours later..these Jeeps seem to have a large draw when off.

Normal alternator's should provide between 14.2 and 14.5 volts at the battery terminals. In cycling applications, the absorb voltage should be between 14.4 and 14.8 volts, while the float setting (if applicable) should be between 13.5 and 13.8 volts. Should not go to 12.2v driving on the freeway IMO.

 

[58Willys]

Have the battery load tested, it may be failing and not accepting a charge.

 

[BAKNBLK]

Will do.

 

[Wabujitsu]

Will do.

If the battery fails the load test, it may just need to be desulfated. If that is the case and you have a battery charger with some sort of “refresh/recover” mode, I would try to desulfate the battery per the charger’s instructions, and after researching the process thoroughly.

You can add YEARS to an AGM battery’s life with a proper charger.

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