Alternator cycles as needed?

white94rx · February 15, 2019

Just got my 2019 last week. I've noticed something odd about the voltmeter in the cluster. It seems to hover around 12 most of the time, and then cycles up to 14 every 20 seconds or so, but only stays there maybe 3-5 seconds. I measured directly on the battery with a DVOM, and confirmed 12.3 ish normal, and then goes up to 14, and then back down.

Is this normal? Some type of energy savings for fuel economy? Does it cycle on and off based on load and only charge when needed? I did turn on everything I could to load the system, and it stayed longer in the 13.5-14 range. I never saw anything below 12.3. And start/stop is always off.

Maybe as the battery ages, the alternator will have more on time than off time, but this is something I've never seen, even on a BMW (I'm a BMW tech by day). We have smart alternators that decrease output (amperage), but they don't lower the voltage. So this truck is either doing this on purpose, or something is wrong with the alternator. Anyone else's truck do this?

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OnTheReel · February 15, 2019

Yeah, the alternator will turn on and off as needed. Usually for a few minutes after you start the truck it will recharge and then disengage based on load demands. The same type of system was used on the previous generation and I think even the ones before that. Theoretically saves fuel although I can’t imagine it being much. I just let it do it’s thing as I never had a problem with the last truck’s battery.

white94rx · February 16, 2019

Thanks for the response. I've noticed today that if I'm coasting, it almost always charges. So that's probably efficient dynamics as BMW would call it.

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