Challenge #1 · motor-controls
The Chattering Contactor
A conveyor drops out at random. Nothing on the HMI. But every time it drops, you hear the contactor chattering in the panel. You've got a meter and ten minutes.
① Run your checks
② Make the call
③ Explain your reasoning optional
A strong answer covers:
- What you did: measured the coil at rest, then under load, then read the drop across TB-20 under load.
- The reason: at rest every point reads ~24V (the trap, no current = no drop), but under load the coil collapses to ~12.8V and ~11V drops across TB-20, so there's resistance in series with the coil.
- Determined outcome: a high-resistance connection at TB-20 (loose/corroded terminal) starves the coil under load and makes it chatter; fix the connection, don't swap the contactor.