充电完成后，控制电路通过继电器的触点或晶闸管将电阻短路，完成变频器的上电过程。如果变频器的交流输入电源频繁通断，或者旁路接触器的触点接触不良或晶闸管的导通阻值变大，反复充电或充电时间过长都会导致充电电阻烧坏。因此在替换充电电阻前，必须找出原因，才能再将变频器投入使用。
After charging, the control circuit shortens the resistance through the contact of the relay or the thyristor to complete the power on process of the inverter. If the AC input power of the frequency converter is frequently turned on or off, or the contact of the bypass contactor is poor, or the on resistance of the thyristor becomes large, repeated charging or too long charging time will cause the charging resistance to burn out. Therefore, before replacing the charging resistor, the reason must be found out before putting the inverter into use.
但有的变频器在启动期间CPU是有一个电压检测和降频动作的，如果接触器线圈引线端子松动造成接触不良，接触器未能吸合，启动时的较大电流在充电电阻上形成较大的压降，主回路直流电压的急剧跌落为电压检测电路所侦测，CPU会做出降频指令，在空载或轻载时，检测电路将欠压故障“及时上报”，CPU马上停机保护。电阻来不及烧掉，变频器已经停机保护。
However, some frequency converters have a voltage detection and frequency reduction action during startup. If the lead terminal of the contactor coil is loose, resulting in poor contact and the contactor fails to close, the large current during startup will form a large voltage drop on the charging resistance. The sharp drop of the DC voltage of the main circuit is detected by the voltage detection circuit, and the CPU will make frequency reduction instruction when it is no-load or light load The detection circuit will "report the undervoltage fault in time", and the CPU will shut down immediately for protection. The resistance is too late to burn out. The frequency converter has been shut down for protection.