![]() ![]() Let’s begin by adding a couple of time-delay relay coils, one in parallel with each motor contactor coil. What we might like to have is some kind of a time-delay function in this motor control system to prevent such a premature startup from happening. If the fan was still coasting forward and the “Reverse” pushbutton was pressed, the motor would struggle to overcome that inertia of the large fan as it tried to begin turning in reverse, drawing excessive current and potentially reducing the life of the motor, drive mechanisms, and fan. This could be problematic if an operator were to try to reverse the motor direction without waiting for the fan to stop turning. If our hypothetical motor turned a mechanical load with a lot of momentum, such as a large air fan, the motor might continue to coast for a substantial amount of time after the stop button had been pressed. Let’s consider another practical aspect of our motor control scheme before we quit adding to it. The “Stop” switch, having normally-closed contacts, will conduct power to either forward or reverse circuits when released. Now, if either forward or reverse circuits are latched, they may be “unlatched” by momentarily pressing the “Stop” pushbutton, which will open either forward or reverse circuit, de-energizing the energized contactor, and returning the seal-in contact to its normal (open) state.
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