What is a Soft Start?
The soft starter, using either capacitive or inductive technology, boosts low voltage DC electric power to rapidly increase the load current without an abrupt current spike.
The soft starter is used for devices that are sensitive to sudden changes in currents, notably motor loads such as refrigerators, air conditioners, and pumps. It is sometimes called a “sensitized relay” or “protective device”. When the input voltage exceeds the set point of the “sensor”, it reacts by drawing increasing amounts of power from the supply until it reaches a predetermined minimum starting level. The load current then increases to its normal operating level, maintaining the set overcurrent protection characteristics of the starter. The soft starter itself draws no additional power from the supply.
The design of the output circuit is such that when the motor reaches normal operating speeds, and the overload is removed, the internal device which was used for sensory overload is automatically de-energized by a timing mechanism. The reduced current flows through that part of the circuit that brings about an increase in generator voltage and hence, there’s a reduction in power to the load as governed by any present protective relay operation. This action also permits a rapid return to normal operation should an overload condition recur.
How does a Soft Starter work?
The soft starter monitors the motor’s electrical power level. The power monitor device is connected to the controller of the motor, which sends precisely timed pulses of current (called excitation) to the motor.
The motor responds by taking in more power to accelerate and maintain speed. The greater current draw also reduces its internal resistance and causes an electromotive force greater than that which is applied by the controller, causing it to turn off. This action makes it more difficult for a subsequent overload condition to result in transients damaging sensitive electronics and components of the motor.
The soft-start activates when a setpoint voltage is within a few volts above or below the setpoint voltage set by the overload protection relay or circuit breaker. The soft starter provides a slow, gradual acceleration of the motor. This prevents the motor from over-exciting and causing damage to itself and to the system.
A soft starter uses peak-detecting current circuits to determine when an overload condition is occurring. If a motor starts suddenly, there may be enough power flowing through it so that some electrical equipment connected to the motor may not be able to handle it (electrical equipment can be damaged by power surges or spikes). If an overload situation occurs while the motor is starting quickly, there may not be enough voltage available to trigger the overload protection mechanism in time.
What are some common applications for Soft Starters?
Soft starters are used in electrical power distribution networks to provide a time delay between the plugged-in and unplugged appliances to prevent damage caused by a sudden change in current. Soft starters are also used in power supplies and motor control circuits; they protect sensitive equipment such as semiconductor devices, computer systems, and telecommunications equipment. Soft starters may be used for slow-spinning motors that tend to overheat due to rapid changes in load resistance.
Soft starters are often used as part of a circuit breaker to prevent overcurrent transients from damaging sensitive circuits. Soft starters protect continuously-running motors such as refrigerators and air conditioners.
They can eliminate problems caused by starting motors that are too fast or too slow. These have been known to cause arc damage or fires when they start up suddenly, while other loads may not be affected. The soft starter’s inductive coil is designed to sense any overloading and turn off the motor before it starts to spin up quickly, resulting in an electrical overload for the motor and its load.
What is the advantage of using Soft Starters?
Soft starters are less expensive to operate than hard starters because the soft starter draws only a small amount of current from the electrical supply. Because soft starters do not draw significant current from the supply, they can be used in larger systems such as air conditioners and electric vehicles. Soft starters are also less complex and less dangerous to use than hard starting machines.
What are some common reasons for Soft Starts to fail?
Soft starts have undergone a variety of changes and upgrades in the past few decades, resulting in several new designs. Soft starts may be replaced if they are more than 15 years old. Older soft starters were not designed for rugged use with high-energy motors that require large amounts of current to start quickly and completely, such as those found in air conditioners, refrigerators, electric ovens, and pumps.
The soft starter was originally designed for slow-speed motors with lower amounts of current and voltage. Newer designs of soft starters accept higher starting currents from both the source as well as from the motor itself. This means that any existing soft starters can easily be damaged by today’s high-tech motors operating at higher voltage levels.
Is an improved Soft Start available?
A very recent design of soft start uses a combination of capacitive and inductive semiconductors to provide better protection capability. It can be used with very large motors, like those used in electric dryers, electric stoves, dishwashers, and other large appliances.
The innovative new design is able to sense the amount of current flowing through the motor and respond by reducing the current flow back to the supply when it senses that the motor is attempting to draw too much power from it. This new soft starter is a significant improvement over previous designs.
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