Thread: Alternator Output Nanocom vs Voltmeter

Hi Craig and the voltage at your battery is going to be the more accurate reading.

Anything that derives it's voltage reading from anywhere else in a vehicle is susceptible to voltage drop.

You already posted up a perfect example of erratic voltage readings when the headlights are turned on.

Try turning your demister on and watch the amount of voltage drop that can cause.

The demister in some vehicles actually draw far more current than the headlights do.

This difference in voltage readings, depending on where you source voltage, is why these plug-in cigarette lighter socket voltage monitors are not that accurate and can easily be u a volt or more lower than the cranking battery voltage.

The engine revs will also effect voltage readings and give the wrong impression of the alternator not being up to the job.

+1^^^, also what you see with nanocom is only the feed to ECM on that particular circuit not the alternator's direct output cos you get it on live data readings from the ECM on instrument mode or fueling inputs and that voltage can be affected by many factors... if you want the direct reading you must connect o voltmeter to the hardwired circuit which goes from the alternator to the interior fusebox(FL1 -150A)