Highly sensitive single-phase AC motor forward and reverse control circuit

When controlling the forward and reverse rotation of micro motors or washing machine motors, phase-splitting capacitors are often used to split single-phase current into two-phase current. There are generally two ways to use single-phase capacitors to control the forward and reverse operation of motors: one is to swap the ends of any of the main and auxiliary windings when the motor is disconnected from the power supply; the other is to connect the capacitor connected in series to the main winding to the auxiliary winding when the motor stops.

The single-phase AC motor forward and reverse control circuit introduced below uses two solid-state relays SSR1 and SSR2. As a new type of contactless switch, it can replace electromagnetic relays and drive current valves, single-phase and three-phase AC induction motors, etc. Solid-state relays (SSR) have the advantages of low noise, no sparks, high sensitivity, high operating frequency, and long service life.

The working principle is shown in the figure: close the automatic power switch ZD of the motor D, the power is supplied, and the motor D is in a stationary state. Close the switch S, the AC 220V is stepped down to AC 10V by the transformer B, and then rectified by the diodes D1~D4 bridge full-wave, filtered by capacitors C1 and C2, and stabilized by 7805, and the output +5V power is supplied to the motor control circuit. At the same time, the time relay SJ is energized and attracted, its normally open contact SJ-3 is closed, and the normally closed contact SJ-2 is disconnected. After the normally closed contact SJ-3 is closed, the AC solid-state relay SSR1 foot ① obtains +5V electricity and conducts, the AC load terminals ③ and ④ of SSR1 are turned on, the main winding of the motor D is connected to the 220V AC power supply, and the secondary winding and capacitor C are connected in series to the 220V AC power supply, and the motor D rotates in the positive direction. The time relay SJ starts to delay, and when the delay reaches the set time of SJ, the delay contact SJ-1 of the time relay is disconnected. SJ loses power and releases, its normally open and normally closed contacts are reset, the solid-state relay SSR1's ① foot loses DC power and is disconnected, the AC output terminals ③ and ④ of SSR1 are also disconnected, and the motor D stops rotating. At the same time, because the normally closed contact SJ-2 of the time relay SJ is reset and closed, the AC solid-state relay SSR2's ① foot obtains positive power and the SSR2's ① and ② feet are turned on, and the AC load terminals ③ and ④ are also turned on, so that the auxiliary winding of the motor D is connected to the AC 220V power supply, and the main winding and capacitor C are connected in series to the AC 220V power supply, and the motor D rotates in the opposite direction. The time relay SJ starts to delay, and when the delay reaches the set time, its normally closed delay contact returns to its position. SJ-1 closes and connects the time relay SJ, SJ is energized and attracted, and the voltage causes the motor D to change its rotation direction.

Component selection: Time relay SJ can be selected with a product with a normally closed contact (SJ-1) that delays power off after power on and a normally open contact (SJ-3) that delays power on after power off, and a normally closed contact (SJ-2) that does not delay power on. AC solid-state relays SSR1 and SSR2 can be selected according to the motor capacity, such as SSR220V5A or SSR220V10A. Other components such as automatic switch ZD, switch S, etc. can be selected according to the usual practice.