Below are several single-button start-stop motor control circuit diagrams I found. For each diagram I performed drawing analysis and wired the actual components (the KA and KM in the drawings were replaced with SIMENS 3TF4022 contactors, installed horizontally). The control circuit diagrams do not show circuit breakers, thermal relays, or similar components.
Circuit 1
This is a classic circuit with clear structure and reasonable layout. Both the circuit analysis and the actual wiring worked without erroneous operations. Single-button start-stop circuits are often considered only academically interesting, but they can be practical. Consider this engineering requirement: a gas pressure tank and two system supply solenoid valves KV1 and KV2. When tank pressure reaches the preset level the first time, solenoid valve KV1 energizes to supply system 1; when it reaches the preset level the second time, KV2 energizes to supply system 2; when it reaches the pressure the third time, KV1 energizes again, and so on in a cycle. The above circuit can meet this requirement with only minor changes to component symbols.
KA is a relay. KM1 and KM2 control solenoid valves KV1 and KV2, respectively.
Circuit 2
This is actually a PLC ladder diagram; converted into a circuit diagram it becomes:
Theoretical analysis of this diagram can appear problematic (after KM picks up, pressing SB again causes KM to release briefly and then pick up again). However, the actual wiring worked reliably: pressing the button 100 times produced no erroneous operations. When slowly pressing the small plastic projection on the "contactor" KA1 by hand, KM releases briefly and then picks up again, matching the observed behavior. The PLC wiring also showed no errors after repeated testing (a Jia Hua PLC was used). This ladder diagram is suitable for PLCs where the I/O point count determines cost.
Circuit 3
Both circuit analysis and actual wiring are valid; no erroneous operations were observed. This is an interesting circuit: pressing SB does not actuate KM, but releasing SB immediately energizes KM; pressing SB again does not actuate KM, and releasing SB immediately de-energizes KM. Its applications are essentially the same as the first circuit.
