I have a 2011 Nissan Frontier Pro-4x. I want to get a general idea how much power I could draw from my alternator while driving. For that, I want to find out how much power my truck uses in the first place.

My alternator produces up to 130 amps, assuming a voltage of 14 volts while driving, around 1820 watts

How can I find out how much energy my truck consuming and how much do I have left over, with truck driving on a highway, lights off, stereo on, etc.? Is it possible to measure power consumption of the whole system using some kind of tool?

2 Answers 2


I would suggest using a clamp ammeter that supports DC measurements too. They have measurements up to quite large values, for example my UT203R supports measurements up to 600 amperes and can measure currents as small as few hundred milliamperes with an acceptable accuracy.

Not every clamp ammeter supports DC, some support only AC. So choose carefully.

Find a good model that supports DC, start your vehicle, let it run for half an hour to ensure the battery is fully charged (or else you measure charging current too which you probably don't want to measure), then zero the ammeter with a button (needs to be done due to stray magnetic fields) and put the clamp ammeter around the alternator positive wire. It has to be around the positive wire only, if there's a separate negative wire you can't put the clamp over both wires at the same time or else the currents cancel out.

It should give you a pretty good indication of the amperage.

Set the electrical devices as you wish (e.g. lights off, stereo on if you want), but you probably can't do the measured when driving on the highway so simulate that by asking someone to rev your engine to cruising RPMs while you do the measurement.


Headlamp bulb 60/55 W and there are two so 120W on full.

Heater motor about 10A

Wiper motor 10A and so on.

But use an ammeter - used to be fitted as standard - now aftermarket and more accurate. The old 2” ones were just an indication.

Once the battery has been recharged after starting then most of the alternator power is available.

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