First understand the "220V AC Cooling Fan" necessary conditions
① The control circuit of the power supply voltage, the maximum current can be supplied;
② "220V AC Cooling Fan" is the control circuit voltage and current;
③ charged circuit requires several groups, what form of contact. The selection of the relay, the general control circuit of the power supply voltage can be used as the basis for selection. "220V AC Cooling Fan" should give the relay control circuit to provide enough current, otherwise the relay is unstable.