How much voltage is supposed to come out of my voltage regulator when measured at the battery? I was checking mine and it remains solid at 15.1 volts even after driving 20 miles. Off the top of my head this seems too high. Shouldn't it scale back to around 13.5 volts for a maintenance charge? I have had no problems with the charging system and the batteries are original. I was just doing a routine check. I used my digital miltimeter to measure voltage. Out of curiosity I then checked my 2000 Camry and the voltage remained at 14.5.

 

That does seem to be creeping up there a bit

 

anybody know what the PROPER SPEC regulated voltage is supposed to be on these trucks?

Mine is an 07 5.9L (I also have dual Optima red tops in it).

I am measuring over 15 volts.
This seems odd, as I am used to regulators maintaining 14v when the engine is running.


Never thought I had a problem, but last week I installed a new inverter. When The engine is running, the inverter flagged an error for over voltage. (over 15 v) and will not operate at that high an input voltage.

I am wondering if I actually have an issue with my truck, or if the inverter is just being too picky.

Lots of searchs and I have come up empty on that spec.

THANKS!

 

How and where are you measuring voltage?

The in-dash voltmeter gauge is not to be relied on for an actual voltage reading.

 

multimeter on the battery.

Whats the reading supposed to be?

 

The ECM controls it. It senses the voltage on the drivers side battery and the ECM also senses the battery temp via sensors under the batteries. First place to check would be the battery connections and then the cross over cable from the passenger side battery to the drivers side battery for a loose or corroded connection. The alternator charges the passenger battery.

 

Around 15V is normal when the ambient temp is around and below freezing.
I see that everyday in winter.
Anywhere between 14.5 to 15 is normal. It depends on ambient temp.

I have an Ultragauge onboard.
The voltage reading I see is the driver side battery voltage.

 

With engine running, measure the voltage between the center of the positive post and the center of the negative of each battery.
They should have the same readings.
Otherwise you have bad crossover cable or bad connection problem in your charging system that would results in ECM overcharging the passenger side battery.

 

I second the replies. Put a set of jumper cables from battery to battery and then check the volts.

 

Spooler,
I think you are suffering misconceptions. The "system" consists of loads and power sources. These are all in parallel. The system voltage is common (the same) in reference to ground (-). In our Dodge, we have two batteries and an alternator as power sources. The batteries can be independently anywhere between 0 V and 13 V depending on that battery's overall condition and state of charge. Once connected together, there will be current flow between the two batteries where the stronger battery will try to charge the weaker battery. This is normal. Assuming that the batteries are serviceable, this balancing current is not a problem and there will be as a result, a common voltage that will reflect the voltage of the interconnected pair. Parallel to the batteries, there is the alternator. The alternator is a 3 phase AC generator that feeds 3 full wave rectifiers (two diodes each) that rectifies the AC current to DC. The voltage of the output is controlled by the excitation voltage applied through the slip rings on the rotor. That excitation voltage is fed to the slip rings by the voltage regulator that continually monitors the "System" voltage. That is adjustable internally on the better alternators. Typically on single battery systems the max voltage will be about 14 V. On parallel dual battery systems, the output voltage will be about 15 V. The ECM has nothing to do with this and there are no battery temp sensors anywhere. When the alternator is outputting current at 15 V, all the loads will be fed by the alternator, as its voltage is higher than the batteries. At the same time, the voltage difference between the battery's state and the alternator will result in a charging action with a current that reflects the voltage difference. The total current output in amperes will be equal to the charge current of battery 1, plus the charge current of battery 2, plus the current of every system consumer that is turned on. There should be no voltage difference anywhere in the "system" if there is, there is a problem.

 

I see you understood nothing that I wrote. I give up.

 

Spoolers post is correct. Other than there is only 1 battery temperature sensor, it is under the drivers side battery tray and can be seen by removing the plastic wheelwell.

If one follows the charge cable from the alternator. It goes directly to the passenger battery.
The ECM does indeed control the alternator output and it is monitoring the drivers side battery thru the engine harness.

It is common to overcharge the passenger side battery on these trucks. There are tons of posts in every Dodge Cummins forum on this issue.

 

I stand corrected. The ECU does act as a voltage regulator through the field terminals and the ECU also monitors environment temperature with that sensor, not battery temp. However, it is against the laws of physics to be able to independently charge a a single battery when they are cabled together in parallel regardless of where the alternator output cable connects.

 

What Spooler was pointing out was that the way 3rd gen trucks are wired, the alternator feeds the passenger side battery directly, while the ECM (voltage regulator) monitors system voltage at the driver side battery. If any voltage drop exists between the two batteries, which seems to be fairly common, improper charging voltages will be the result, as the two batteries are no longer truly in parallel.

 

I'm seeing an anomaly where my charging voltage is hitting 16.5v momentarily. Just started doing it a week ago and only when it's cold and the heater grid is cycling after the truck starts moving. When it hits 16.5v the IP dings and the MIL lights momentarily and the radio resets. I check the IP codes and it's showing several codes for the PDC. This weekend I'll check all battery connections and will pull the fuse box to check all the cable connections including the FCM.