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6 Common Setting Parameters Available On Most Of The Softstarters
6 Common Setting Parameters Available On Most Of The Softstarters (photo credit: ABB)

Softstarter parameters

This technical article includes a short description of six common setting parameters available on most of the softstarters. Other settings may be available depending on the type of softstarter and manufacturer.

The setting can be done either by adjusting potentiometers, changing dip switches, using a key pad, a computer or similar and 

  1. Start ramp
  2. Stop ramp
  3. Initial voltage
  4. Current limit
  5. Step down voltage
  6. Adjustable rated motor

1. Start ramp

Start ramp is the time from were the softstarter start its ramp (initial voltage) until full voltage is reached. The ramp time should not be too long, as this will only result in unnecessary heating of the motor and a risk of the overload relay to trip.

If the motor is unloaded the start time for the motor will probably become shorter than the set ramp time, and if the motor is heavily loaded, the start time will probably become longer.

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2. Stop ramp

Stop ramp is used when a soft stopping of the motor is required, for example a pump or a conveyor belt. The stop ramp is the time from full voltage until stop voltage (initial voltage) is reached.

If the ramp time is set to zero the stop will be like a direct stop.
Diagram showing start ramp, stop ramp and initial voltage
Figure 1 – Diagram showing start ramp, stop ramp and initial voltage

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3. Initial voltage

Sometimes named pedestrian voltage or torque, this is the point from where the softstarter starts or stops its ramps. The torque of the motor will drop with the square of the voltage and if the voltage is set too low, for example 20 %, the starting torque will become 0.22 = 0.04 = 4 % only, and the motor will not start from the very beginning.

Therefore it is very important to find a level that is just high enough to make the motor take off directly to avoid unnecessary heating.

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4. Current limit

Current limit can be used in applications where a limited starting current is required, or at a heavy-duty start when it is difficult to achieve a perfect start with the setting of the initial voltage and the start ramp only.

When the current limit is reached, the softstarter will temporarily stop increasing the voltage until the current drops below the set limit, and then continues ramping up to full voltage.

Note that this feature is not available on all softstarters!

Current limit function in softstarter use
Figure 2 – Current limit function in softstarter use

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5. Step down voltage

Step down voltage gives a special type of stop ramp. It is possible to adjust the voltage to drop to a level where the speed of the motor starts to reduce immediately at the stop command.

For low loaded motors the speed will not reduce until a very low voltage is reached, but using the step down voltage function can eliminate this phenomenon and is especially useful for stopping pumps!
Curve showing the step down voltage function of a softstarter
Figure 3 – Curve showing the step down voltage function of a softstarter

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6. Adjustable rated motor

Adjustable rated motor current makes it possible to set the motor rated current on the softstarter for the used motor. This setting may affect other values as well, such as the trip level of the electronic overload relay, the level of the current limit function and so on.

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Reference // Softstarter Handbook by ABB

About Author //

author-pic

Edvard Csanyi

Edvard - Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV high power busbar trunking (<6300A) in power substations, buildings and industry fascilities. Designing of LV/MV switchgears.Professional in AutoCAD programming and web-design.Present on

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