"220V Cooling Fan" can save some power when the speed is reduced. Starting and stopping is associated with the fan before starting requires a certain starting voltage. After the fan operation, once the fan voltage down to stop voltage, the fan will stop running. Starting voltage is generally cvoltage, in the absence of speed monitoring, determine the fan is running or stopped in two ways: The first is to ensure that both ends of the fan voltage is always greater than the starting voltage, and can set the voltage greater than the rated voltage of 60%, in order to reduce the fan voltage control range. The second is to use the "220V Cooling Fan" with tachometer by the micro controller to monitor the tachometer. Before the fan does not start or stop using the software can understand their state, but this approach will increase the complexity of the design of hardware and software resources.