Hi,
When my inverter/charger is putting out more than 40 amps, then the fan comes on, especially if warm in the basement. If less than 40 amps, normally the fan stays off. My inverter is a Trace M1512 with a 70 amp max charger rate.
If you have a shorted cell, or dry battery, or something wrong with a battery, then your charger might be putting out near max amps for a while. If the battery voltage is less than 11.9 when you start charging, then normally it will go to the maximum output, even if the battery is otherwise in great condition. Max output normally means the fan should be on.
On a hot day, say 90F near the charger, then the fan might run at only 50% of it's max output, until it cools down a bit.
Fred.
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