Should the voltage be a constant reading or does it fluctuate?

[Nicky Pass]

I never really paid attention before because I usually have the center screen display MPH. I changed the oil yesterday and switched it to check diagnostics as I drove....that’s when I noticed the voltage fluctuate. It would be 12.4-13.2-ish under throttle....of throttle was 13.8-14.2, then idle was 12.4. I never really paid attention before, I keep it on a batter tender when it sits for more then a couple of days. I assume it’s normal...I just never really paid attention.

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[Nicky Pass]

In accessory mode it is at 11.5...so I assume the battery is fine. I always put it on a tender during the week since it’s a “weekend” car.

 

[Nicky Pass]

It’s solid green on my battery tender, which means it’s fully charged. I only have 850 miles on it....it’s not driven much.

 

[Nicky Pass]

The door was open, radio was on and the headlights come on for a bit and it as at 11.5.

 

[torque124]

The door was open, radio was on and the headlights come on for a bit and it as at 11.5.

Engine off ? Normal.

 

[Jetnoise]

I never really paid attention before because I usually have the center screen display MPH. I changed the oil yesterday and switched it to check diagnostics as I drove....that’s when I noticed the voltage fluctuate. It would be 12.4-13.2-ish under throttle....of throttle was 13.8-14.2, then idle was 12.4. I never really paid attention before, I keep it on a batter tender when it sits for more then a couple of days. I assume it’s normal...I just never really paid attention.

Normal

 

[Nicky Pass]

Engine was off, it was 11.6 not connected to the battery tender. Then, I connected to the battery tender, went back to accessory mode (engine not on) and it 12. The last time I drove it was about 3 weeks ago. I let it sit not connected to the battery tender and it started fine after sitting over 3 weeks. I guess the fluctuation when driving is because this time I hooked it up to the tender and the alternator didn’t need zap the batter as much as when it wasn’t on the tender and it sat without being on the tender.

 

[tom_sprecher]

Normal

^^^ This. The computer regulates the output voltage of the alternator depending on current drain of the system.

 

[Demonic]

Normal. You can't read into the tender because unless you ran the charge wire for the tender through the inductive loop of the smart charging system, the BMS won't know you charged the battery so the readings will be a bit off until it relearns the state of charge. TLDR: it's fine.

 

[CycloneRy]

Your alternator output varies on engine RPM as well. It needs some engine RPM to create enough amperage to A) run the car and B) charge what you used outta the battery to start the engine.

This is why its bad practice to fire up a car you don't drive often to demo the exhaust note for your friends only to shut the car off without driving it. You'll never charge the battery at idle.

In the sportbike world this is commonly refered to as new bike syndrome. Never actually ride it at speed, just friends house to friends house in the neighborhood, all the sudden not enough amps to start...

P.S. - Not sayin you were doing this, just explaining the concept..

 

[FLATPLANE]

The car has a smart charge feature the PCM I believe fluctates the voltage to the Battery Depending upon what conditions are.
From All Data

The generator is driven by the FEAD belt. When the engine is started, the generator begins to generate AC voltage which is internally converted to DC voltage. The DC voltage level is controlled by the voltage regulator (located on the rear of the generator) and is supplied to the battery.

The PCM controls the voltage regulation setpoint and communicates this information to the generator internal voltage regulator over a generator communication (GENCOM) communication circuit. The PCM receives generator load and error conditions from the generator over the generator monitor (GENMON) circuit.

This vehicle is equipped with load shed strategy. With the engine off, the BCM monitors the battery state of charge using the battery current sensor attached to the negative battery cable. With the engine running, the PCM monitors system voltage on the VPWR and PSCM .

The PCM monitors the generator current using the generator current sensor attached to the generator B+ battery cable. The information supplied to the PCM from the generator current sensor is used by the PCM to adjust the engine idle stability and torque control.

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