Quote:
Originally Posted by redpoint5
Does measuring alternator output reliably tell you accessory draw? I used battery draw only since I know it's reliable and will only output what is being consumed. With an alternator, you don't know if it's feeding the battery, or supplying a load.
I suppose if you take a baseline measurement with the car running, you can subtract it from whatever the reading is when an accessory is turned on. Still unsure of accuracy since alternators can vary output depending on the load it senses and bump up voltages.
I've got a decent DC clamp meter that goes up to 400A that I use to measure starter draw.
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I would say it would be accurate, presuming the amp meter is accurate of coarse. A healthy, fully charged battery will draw almost no current, usually well under 1 amp.
But if you want the most accurate measurement possible, I would suggest fully charging the battery either by running the engine or using an external charger, check the amp draw of the battery with the engine running by clamping the meter around one of the battery cables, allow the amp draw to stabilize, and then subtract the small amount of current the battery is drawing from the measurement.
In my opinion, that would be a better way of checking the draw of accessories because they will be running on their normal voltage. Resistive loads such as incandescent lighting and heating elements will draw more current the higher the voltage, while capacitive loads (like computers and some LED light bulbs) will actually draw more currant when provided a lower voltage because they are designed to maintain a specific output.