Measured both with my fieldpiece multimeter across the battery terminals, and displayed on my speedhut voltmeter in the dash. Somewhere around 14.8V with the engine running and no lights or blower. Anything to worry about here?

 

How soon/long after starting ?

Does it drop after a few minutes ?

 

immediately after. I didnt go for a long drive today but after 5 mins it was still around 14.5 according to my gauge

 

I think that's about right while running. My truck (thru OBD11) reads at 14.3v, so I assume this is normal while alternator
charges battery. Reads at 12.2 when not running.

 

Actually today while driving it never went below 15v. when i shut the truck off it dropped down below 13v within 15 seconds, and on a cold start it somewhere in the mid 12s. IDK why it reads so high when driving. The dash gauge sweeps past halfway too.

 

OK, quick "how it works"

Alternator has a built in voltage regulator that works using PUSH BACK, AKA electromotive force

It should deliver 13.5v to 14.9volts, but there is no exact voltage just a range

When you start the engine the battery needs to output 60-75 AMPS to turn the starter motor
After start up battery is drained a bit, so has low PUSH BACK so voltage regulator ramps up voltage to above 14volts
As battery is recharged its PUSH BACK goes up, and regulator lowers the voltage as it does

If its an older battery i.e. at rest voltage under 12.3volt then it can hold a charge very well so PUSH BACK doesn't go down as much and may stay at 14volts
(At rest voltage is what the battery reads after sitting, uncharged, for at least 2 hours, 8 hours is a better test)

So if battery tests as 12.2volts or lower then its at least 5 or 6 years old and you need a new battery, and running voltage will stay higher

With newer battery, after the 5 minutes of running you should see under 14volts at battery, you can't turn off engine and restart
13.5v-13.8v is the "normal" range for battery/system after 5 minutes or so and until engine is shut off again
If you lights dim at idle then 1 of the Fields in alternator has failed, not a big deal, unless a 2nd field fails, then battery will start to be drained by running engine instead of staying charged up

When you turn on lights or fan to HIGH, you would see voltage drop and then come back up, because PUSH BACK in the system dropped, so regulator turn up the AMP output to maintain the same PUSH BACK in the system

A Voltage regulator can break, and that can ruin a battery, by overcharging it, running it at over 14volts all the time, it cooks away the fluid in the battery
Easy to test for this, have volt meter connected to battery engine running, lets say voltage is 14.5v, raise RPMs to 2,500 and hold for a few seconds, voltage should go up slightly but then come back to 14.5v as regulator adjusts to the higher RPMs
If voltage goes up and down with RPMs then regulator is broken

If battery's at rest voltage is to low then alternator must be run at higher AMP/voltage all the time, this can cause issues with alternator

This is why people often have to replace battery and alternator together, because battery is too old, or has failed in some way, or regulator has gone bad


Battery at rest voltage
12.8v is new battery
12.5v is a 3 year old battery
12.3v is a 5/6 year old battery and time to shop for battery sales
12.2v or less is a failing battery can it ASAP

Voltage in a running engine should never exceed 15volts, that can ruin vehicle electrics, higher than 14.9volts would mean alternator/regulator issue, BUT....if battery is older that could be the cause for this

 

Thank you. So what sort of test should I do to confirm one or the other needs replacement? I know how to do the voltage regulator test. The voltage stays pretty steady at idle and while revving. Turning on the headlights and maxing out the blower at idle causes the needle to dip a few tenths and then slowly come back up. Seems normal, it's just that the needle is over 15v all the time. The battery and alternator have never been replaced. While I can afford to replace both of them at the same time, I don't WANT to replace them both. So any sort of extra tests I can use to narrow it down to one?

 

@RonD I just did an official check with my multimeter and my gauge. I may have been reading my gauge wrong. Also my gauge reads just a touch high. Gauge shows 15.0-15.1V depending on where you are looking. The multimeter attached directly to the battery terminals shows 14.9V and remains there through the operation of the truck. I only idled it for 2 minutes in the garage, but I flipped the lights on and off and watched both gauges. Turning on the headlamps actually causes the volts to MOMENTARILY jump to 15.0 on the multimeter, and then a split second later drops back to 14.85-14.90v. Shutting off accessories does the opposite. Turning off the lights dropped it down to 14.8v and then it came back instantly to almost 14.9. After shutting down the truck the volts went below 13 quickly, and after 10-20 seconds was at 12.6v

 

Test meter on house AC Volts and see what it says, also test 9volt battery if you have one

I would test battery next time you come home, do NOT shut off the engine, just pop the hood and test battery voltage after a 10 + min drive, longer drive the better

As said testing battery after just shutting off the engine won't give you any useful information, needs to sit a few hours

14.9v is fine for the first few minutes
If voltage doesn't change much with RPMs then alternator and regulator are fine

 

This is my daily duty 120 dollar fieldpiece meter, i use it every day on HVAC. I have no doubt it's very precise. I'll check it next time I drive the truck.

 

@RonD After staring at this voltmeter all week I decided to order a new alternator. I got the cheapest one I can find since I don't plan on having the truck more than a year or two more, and I can keep the current one around for backup duty since it still technically works. I would get close to 15.5V idling with the fan and headlights on, and this would drop back to 15 volts when the rpms come off idle. I assume this is some sort of volatge regulator issue. Could the battery be fatigued? Sure. But it cranks up strong every time and has about 12.5 volts after sitting overnight, which is a good battery.

 

Ok new (read: NOT remanufactured) alternator installed. Thanks ford for making this a smooth and easy process, 15 minutes start to finish. So The voltage did NOT come down really at all but I did notice that the voltage stayed very smooth compared to before. I cut on the headlights and maxed the fan simultaneously trying to put a big amp draw on the new unit and the voltmeter did NOT BUDGE. Didn't matter what RPM the needle always stays up near 15V. I also checked the date on my battery. March of '18. It isn't exactly an old battery. Just to be safe I put a trickle charger on it but it was done within a half hour. IDK what else to look at. As far as I am aware there isn't any modules controlling the voltage. I guess I'll hang onto the old alternator as a backup, and just live with the higher voltage.

 

And you left engine running for 5min and it was still in the high 14volts?

Test the voltage at the yellow wire on 3 wire connector with engine running should be same as battery voltage or B+ voltage, high 14's

The yellow wire is the monitor wire, the pushback voltage

Ford did add "smart charging" in the 2000's for used with the new type of Silver Calcium Batteries, so you are only suppose to use those batteries with the "smart charge" system

Not sure what year Rangers used that, but I do remember dealers could reprogram the system to use conventional charging

 

It's a 1993 vulcan. And I tested the battery voltage and it was 14.82V across the terminals in the first few minutes. It didn't change even a hundredth of a volt when revving. I drove to the gas station and back, 7 miles round trip. The gauge showed it was slightly lower, probably 14.7V

 

Did you shut it off and restart it at the gas station ?

 

yes i did lol. It's 3.5 miles from the gas station to my house, about a 5 minute drive.

 

Battery after sitting overnight in 40 degree garage is 12.69V. Seems really healthy

 

Charging system sitting at 2volts over at rest battery voltage will cause early battery failure
Common maintenance voltage is 1.1volt over at rest voltage, so under 14volts for sure, 2+ volts is ReCharge voltage which shouldn't last that long, a few minutes after startup it should start to drop to below 1.5v

Very odd IMO, could be normal just never ran across it

 

Yeah IDK what it is. It behaves just like you said in the earlier posts, the volts come up after engine start, and slowly trickle down over the next 10-15 minutes, but they seem to level off around 14.8v even with accessories running. TBH it's probably been running like this for years and years and the only reason it has become a "problem" now is because I have a quality voltmeter and not the stock dummy gauge lmao.