Charging Voltage

[MChessick]

Alternator Charging Voltage

Anyone know what the voltage should be reading measured at the battery with the truck at idle? I think mine may be high. After an hour driving on the highway, I had a reading of 14. 25 volts measured at either battery using a volt meter, not the guage in the truck. A low battery will charge at 14 volts for awhile until it comes up and the regulator will kick it back. I am not sure if I have a problem and certainly do not want to roast 2 good batteries.

Thanks



Mark

 

[jakprince]

14. 2 volts sounds good to me. I wouldnt be worried about it.

 

[Tmartin000]

I am seeing 14. 75 as a nominal charge voltage... . as seen through my Fluke DVM. I am really glad your starting this thread... I was wondering if mine was too high. .

 

[Riverrat]

14. 5 V is normal max output for most alt.

 

[kscheffler]

14. 4 is optimum for extended battery life given the normal operating temperature, as the temperature rises the charge voltage should be reduced. After 14. 4 "off-gasing" occurs and is not good. 14. 75 for a lead acid battery is not good have your voltage regulator checked. .

 

[p-Bar]

Remember their is a sensor in the batt box if it gets too hot it stops the charging. In the old days it used to be 13. 8 volts max , but I guess with the crappy headlights in these trucks the higer voltage will get a few more lumens out there.

 

[MChessick]

I hear what you are saying but a fully charged battery is 12. 75 volts. In any other car I have had the alternator charged at 13. 5 volts and reduced down from there as the battery recovered from starting the car etc. How can 14. 25 volts all the time not cook the batteries? I am sure this is my ignorance on the subject but it doesn't make sense to me.



Pitcru

 

[Hoefler]

The alternators voltage will increase as the load increases. Lights, blowers, injection system, fuel pumps, etc. . Anything electrical requires the alternator to increase output to maintain them. To increase your amperage output, you will get an increase in voltage.

 

[JMerola]

This is a great thread. Over the last couple of months, I have been driving a couple hundred miles a day back forth to work. Over the same time period, I have noticed some leakage around the caps of both batteries (which didn't exist prior). Batteries are 2 years old.



Is this an overcharging issue? How do I measure the charging voltage (engine RPM... )? Should I have the voltage regulator checked as well?



Thanks for the help,



Jason

 

[Pawpaw]

From the 04 Service Manual:



VOLTAGE REGULATOR



DESCRIPTION



The Electronic Voltage Regulator (EVR) is not a

separate component. It is actually a voltage regulating

circuit located within the PCM (Powertrain Control

Module) (within the ECM for diesel engines). The

EVR is not serviced separately. If replacement is necessary,

the PCM must be replaced.



OPERATION



The amount of direct current produced by the generator

is controlled by EVR circuitry contained

within the PCM. This circuitry is connected in series

with the generators second rotor field terminal and

its ground.



Voltage is regulated by cycling the ground path to

control the strength of the rotor magnetic field. The

EVR circuitry monitors system line voltage (B+) and

battery temperature (refer to Battery Temperature

Sensor for more information). It then determines a

target charging voltage. If sensed battery voltage is

0. 5 volts or lower than the target voltage, the PCM

grounds the field winding until sensed battery voltage

is 0. 5 volts above target voltage. A circuit in the

PCM cycles the ground side of the generator field up

to 100 times per second (100Hz), but has the capability

to ground the field control wire 100% of the time

(full field) to achieve the target voltage. If the charging

rate cannot be monitored (limp-in), a duty cycle

of 25% is used by the PCM in order to have some

generator output. Also refer to Charging System

Operation for additional information.





Bob

 

[Tmartin000]

From what I understand about AGM, Spriral or flood cell battery technology, all three of which cost a fortune and ---In my opinion ARE worth it, need higher voltages to maintain their effectiveness, then this higher charge voltage are perfect for them. I love the fact they don't give off any gasses and corrosion problem goes away. Maybe these are a great solution..... IF the factory batt's don't hold up.

 

[MChessick]

Thanks Bob, great bit from the service manual. I guess everything is ok then.

Thanks everyone for the info.



Mark

 

[kscheffler]

AGM batteries should be charged to 14. 7 volts to maintain the battery life. Since the voltage regulator limits the charging to 14. 3 to 14. 4, I discharge my OPTIMAS 2 to 3 times per year with an inverter and trouble light take it down to no lower than 11. 7 volts. Then I charge with an adjustable voltage charger with the max charge set to 14. 7. Works great for truck and boat. It is not important to charge AGM to 14. 7 every time but it is important once in awhile to fully charge.

 

[Tmartin000]

My issue thus far with two trucks and four Optimas were a failure by first year on two of the four. Seems if you have the need to REALLY discharge the one closest to the starter (pass. side) repeated cranking did it for me... . they never really come back. Both of my Diesels did this.



kscheffler-- Good to know. Seems without taking precautions you and me both give, these Optimas "may not" be the end-all beat-all of auto batteries.



Maybe the Blue ones are best... ..... ??????



Tom

 

[BK]

Lead acids batteries, and the wet and "gels" cells are really the same,

will see a terminal voltage after they've been fully charged but stabilize of 12. 6Vdc, or 2. 1V per cell.



After removing the charge, they will very slowly float down to 12. 6 or 12. 75.

If you put a very minor load on it, it should go down to 12. 6 more quickly.





Lead acids have two rated float voltages, for cyclical use and for storage use.

For storage use they want 13. 6Vdc as a float voltage @ 75DegF.

For cyclical use they want 14. 1Vdc as a float voltage @ 75DegF.



The lower the temps, the higher the float voltage is recommeneded to attempt to charge the battery well and to retain capacity.

Down to about 25DegC @ 14. 7Vdc.



The higher the temp, the lower the float voltage as to not heat the battery to much and reduce it's life. The high end escapes me now. . I don't remember the max temps and related voltages. . but it gets down to 12. 9 if I remember right. - yea its barely charging. . so you may get a hint that under the hood we are beating the daylights out of these batteries.



When storing a lead acid battery, wet or gel or agm or what every you want to call them. . they should be stored with a charge float voltage of 13. 6vdc. Like when you store your trailer.

Some DC supplies in the trailers that also charge the batteries, have a switch 13. 6 or 14. 6.

The 13. 6 is for storage long term.

If you've been unhooked for some time and running on battery and only expect to be plugged in for a few days and expect most of your trip to be like that (cyclical), the 14. 6 should be used. Back to 13. 6 for long term storage.



Cars and trucks are considered cyclical use.

So normally you will find it around 14. 2 - 14. 7 .

In the old days the old mechanical regulators had a either or. . 13. 6 when it was hot and 14. 6 when it was cold.

A lot of the new electronic regulators have more steps.

So when it's real could out you may see it some what higher than when it was a bit warmer.

Plus it all depends what else you have on and what the RPM is.

Typically at idle the alternator can't handle full loads or even half load, and charge the battery at the same time after starting.

There's a rating and usually the FSM calls out the RPM to check the full output current of the alternator at.

So if the heater grids is one, and the headlights, and your at idle and just started the truck. . the voltage across the battery is going to be real low. . lucky to be 12. 6 , Just too much of a load at idle

 

[jelag]

BK's advice is right on the money... He understands batteries, and charging systems... I'd like to add..... the more discharged the battery is... . the lower the voltage and the more charge it will accept from the temperature controlled voltage regulator in the PCM... ... . no only does the battery have a lower voltage when its discharged but it has a lower resistance... . which is why you would see higher current going to the battery when its low... .



When the battery gets fully charge the resistance increases... and so does the voltage... . so little or no current flows from the charging circuit to the battery... .



Hope this helps... .