2x Universal MZ-47R Inverter Air Conditioner Mainboard PTC Resistor Start Relay Part For Haier, Gree, Chunlan, Dongbao, Mitsubishi, Hitachi,Chigo, Colong, TCL, Lesheng, Toshiba, General, Daikin, Star, Hisense, Polka, Changhong, Panasonic, etc.

規格：

Resistance (At the R.T.  25 ): About 47 Ohm

There is the briefly introduces the roles of PTC resistors and relays in power circuits, especially how they work together to protect circuits from inrush current.

In devices like air conditioners, where a high inrush current occurs during startup, the PTC controls the current rise rate, while the relay ensures that the PTC is bypassed after normal operation begins to reduce power loss.

This combination is superior to NTC resistors because PTCs offer more durable current control, particularly for handling prolonged high inrush currents.

PTC Resistor + Relay:

• PTC: A Positive Temperature Coefficient thermistor whose resistance increases with temperature.

• During power-on, the PTC has high resistance, slowing the current flow. As the PTC heats up, its resistance rises further, and the relay replaces the PTC in the circuit, minimizing energy loss.

In some switching power supplies, such as those in inverter air conditioners, the PTC and relay are connected in parallel. The PTC’s resistance increases with temperature. But why is this design used?

This is because air conditioners, especially inverter models, require large capacitors to be charged at startup, and the compressor also draws significant startup current. This creates a substantial impact on the power supply, potentially damaging the circuit. Using a PTC helps: as its temperature rises after power-on, its resistance increases, moderating the current surge and allowing the outdoor unit’s circuit to “wake up” gradually. Once normal operation begins, the relay engages, bypassing the PTC to eliminate the high voltage drop across it. At this point, the PTC is no longer consuming power.

If an abnormality occurs during startup, such as the main relay failing to engage, the PTC’s resistance will continue to increase with rising temperature, effectively limiting the current. This behavior is similar to a fuse, though it doesn’t completely cut off the current.

Thus, air conditioners use PTCs instead of NTCs mainly because their startup inrush current is larger and lasts longer. Therefore, the control requirements for inrush current are higher in air conditioners. A PTC can “continuously” moderate the current rise, giving the main control circuit more time for a smooth startup while also providing protection in case of startup failure.