To calculate how long a 27 Watt cooling fan will run on a 30000 mAh power bank

 To calculate how long a 27 Watt cooling fan will run on a 30000 mAh power bank, you can use the following formula:

Time (hours) = Battery Capacity (mAh) / Device Power (mAh)

First, you need to convert the power bank's capacity from mAh to Wh (Watt-hours) because the fan's power is given in Watts.

Battery Capacity (Wh) = Battery Capacity (mAh) / 1000 * Battery Voltage

Assuming the power bank voltage is around 3.7V (common for lithium-ion batteries), you can calculate the Wh as follows:

Battery Capacity (Wh) = 30000 mAh / 1000 * 3.7V = 111 Wh

Now you can calculate the runtime of the fan:

Time (hours) = 111 Wh / 27 Watts ≈ 4.11 hours

So, the power bank will take approximately 4.11 hours to go from 100% to 0% when powering the 27 Watt cooling fan continuously. Keep in mind that this is a theoretical estimate, and actual runtime may vary depending on factors like the efficiency of the power bank and the fan.