Alternator high voltage? (15.3V)
 

Hi, thought I should run this by you guys to get a feel for my options.

Alternator failed 2 years ago on my F150 2003 Super Crew 5.4. Got a new Wilson A-261 installed plus new battery.

And a few days ago trying to start the truck after 3 weeks of standstill the battery was drained so much that it had to be charged before I could start. I drove about 3-4 hours, but noticed the dash voltmeter showed a higher reading than usual. I measured the alternator voltage to 15.3 Volts when I got back home.

Battery, after standing overnight measured 12.1 volts, maybe a bit low?

I have a Haynes manual which lists some troubleshooting options, one of which suggests measuring between alternator test points A to battery and F to ground. Problem is I see no accessible test points ...

Circuit to field fuse is OK, 0.6 ohm. (Manual suggested high resistance > 10,000 ohms there could result in high charging voltage. I am an electronics guy, and 10,000 ohms seems an awfully high resistance...)

I am not really very experienced with vehicle electrical circuits, so I am wondering if these test points are at the back of the alternator facing the engine block? Or non-existent on some alternators?

I am at the point now to take the truck in to the shop and have the alternator diagnosed, unless someone could give me some pointers for trying to fix it myself...

Anyone here that would suggest a good brand of alternator?
Preferable a brand where I can change out the internal regulator myself if need be.

How long did you charge the battery prior to driving ?

My thought, the battery went too flat, and is not having a sense of humor about being charged again on the truck.

If you did a quick charge ( like an 8A quick charge ) you might want to try a longer charge cycle, and after completing check it to see if the battery is holding the charge.

If you can disconnect the batteries and have a meter and charge you can do a quick test at home.

have the battery stand alone ( at the very least have it disconnected from the truck's system ).
Charge the battery on a 2A setting until fully charged. Once charged, take a voltage reading and record it. This should be in the 13.n range, on the low side, 12.9 / 12.8. If it is 12.6 that could be acceptable a battery that is getting to its last legs. The more than 12.6 V should be at the battery just after charging.
Let the battery sit for 3 to 4 hours, take another reading, should be within 0.2 / 0.3 VDC of the 1st reading.
Let the battery sit overnight and take another reading, should be what the 2nd reading was +/- 0.10 / 0.20 VDC of the 2nd reading.

This should put the overnight ( unhooked ) reading within ~0.4 VDC of the fully charged reading. If the battery is 1.0 VDC off the 1st reading, the battery is not holding a charge on its own, and should be replaced.

The alternator is not made to change a low battery continual basis, and is putting too much strain on the alternator.

Worth a try to see if the issue is the battery or the alternator. A load test on the battery is a good idea if it passes the home test, with summer coming up, heat is a worse killer of a low battery than cold.

It sounds like you need a voltage regulator. The battery won't cause the voltage to go too high.

Thanks for the replies.

The battery was not totally flat, it turned the engine but not enough juice to start it.

I then charged the battery with a fully automatic charger for about 1/2 hour. No setting for low or high charge current on the charger.

As Takeda said, would the alternator put out higher voltage than normal on a low battery?

After I first posted here I fiddled some more today, checking connections etc, measuring voltage drops while engine was running. Did not find anything obvious, but noticed that the voltage had dropped somewhat to 15.1 Volts. Weird (to me).

Why the battery should be drained at all after 3 weeks may be a sign it is failing I suppose, or maybe drained by some faulty circuit. I will check that tomorrow.

15.3 is not a high voltage condition for the alternator.

The range on the cluster is :

6.2-9.1 volts, low voltage mark and below.
16.9-19.1 volts, high voltage mark and above

You are still in the normal band at 15.3 VDC, nothing is confirmed to be pointing at an issue with the alternator as of now, too many unknowns.

3 weeks on the battery could be a battery on the way out or parasitic loss in the system.

If you only have an auto charger without settings, take the battery and alternator into a reputable shop and have both of them tested.

The load test on the battery will take a bit, as they will need to properly charge the battery before doing the load test. Autozone is not a place to do this at, they have a fixed load test and put it on the battery in the state it is in, where a real load test the battery needs to be properly charged before the load test and the amount of the load depends on the size of the battery.

To be able to point to a cause of the issue without additional testing is just a SWAG. Might as well flip a coin for diagnoses and resolution.

Aye the alternator is fielding to high.

Either the regulator or a bad battery.

Could you get another battery to test the alternator?

He is measuring the voltage at the battery, and 15.3V is TOO HIGH! The correct MAXIMUM voltage is 14.2Vto 14.6V:

http://www.madelectrical.com/electri...witworks.shtml

Another good reference for auto charging systems:

http://www.bcae1.com/charging.htm

I am getting my information from the Ford service manual, not some random web site.

Try using something other than generic concepts when working on a Ford F150 and steering members in the wrong direction.

You don't understand what your reading:

6.2-9.1 volts, low voltage mark and below.
16.9-19.1 volts, high voltage mark and above

For instance, from the numbers you posted, 10V would be normal, but your
battery would be dead with this voltage.

There is nothing unique about a F-150 charging system.

I don't understand electrical on F150s...:confused:

Sure let's go with that................

Some more information...

I measured the current draw from the battery, repeated several times:
(all doors closed, ignition key out, hood light disconnected)

At time of connection: About 0.5 amperes
2-3 seconds later : About 0.4 amperes
13 seconds later : About 0.25 amperes (Computer goes to sleep?)

250 mA is too high in my opinion.

So something is draining the battery.

I disconnected alternator completely, because fact is that the output voltage is higher than normal, so this is suspect. No change in drain on battery however...

Next step is removing fuses one by one to isolate the circuit that drains on the battery.

What is the normal drain on the battery with no faults?

~50ma

https://www.f150online.com/forums/4541288-post3.html

MGD

Do you have any axillary lighting or sound system (amps etc)?

What is the current range (MAX) on your meter you were using?

Thanks for the link to battery drain information.
Seems I need to observe over a longer time, my little test was rather short, maybe less than a minute.

I have no extra equipment installed that could drain the battery.

I also live in an area where it gets really cold in winter, -30C is not rare, and I usually drive to town for shopping every 2-3 weeks, about 1 hour drive each way. Which means the truck is not used for 2-3 weeks.

So far I have not had problems with the truck standing that long, except now of course with this new problem re. high voltage and drained battery.

I cannot help wondering if those two things are related, but as I mentioned above, completely disconnecting the alternator did not change the measured current drain on the battery.