22 BRZ, Is alternator output load dependant ???

Dec 29, 2021
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As I was driving around town, I noticed the voltmeter reading on the dash, is swinging between, 12.4 volts and 14.3 volts. Seems strange as I am used to voltage staying constant all the time around 14.3 in other cars. I get home and let the car idle, check battery voltage with a hand held voltmeter and the readings agree with the in dash meter. So I start turning appliances on and off, lights, brake lights, heater headlights all with the engine idling. The results are when there is no load or minimal load is being applied, the voltage drops to battery voltage of 12.6. When I turn on some load, the voltage increases to 14.3 and stays there until the load is removed, then the voltage again drops down to battery voltage. It appears to me that the alternator output is somehow correlated to the load on the system. It’s as if the alternator knows that the battery is fully charged and does not need to output a higher charging voltage. This may be designed in, to remove some mechanical load for purposes of decreasing fuel consumption. I have no problem whatsoever with the battery going dead. Does this sound normal? Has anyone else noticed this behavior?
If look at your vehicles Negative Battery connection you may notice a round or mounted sensor with a wired connection.
If it is surrounding / connected to that or the Positive Battery connection, you likely have an Energy Monitoring Sensor.
That technology will be common with modern vehicles. The design is for "fuel saving".
The alternator senses load and via PWM (Pulse Width Modulation) via the ECM, will charge the battery more or less depending on electrical load.
On yours and other modern models, the battery SOC (State Of Charge) is also monitored. The method behind the madness is to maintain the SOC if for any reason other electric consumers remain ON, depleting the battery. In that case, those energy hungry components are shut down to preserve the battery SOC so that the vehicle is ensured for the next engine start. The images are only an example.


  • Battery Sensor.jpg
    Battery Sensor.jpg
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  • battery sensor.PNG
    battery sensor.PNG
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