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RVS-DX, Digital Soft Starter Instruction Manual—4/01/04
5-4
Initial Voltage
The initial voltage determines the motor’s initial torque setting (the torque is directly proportional to
the square of the voltage). The initial voltage can be set from 10 to 50%. The initial voltage also
affects the inrush current and mechanical shock. An initial voltage setting that is too high may cause
mechanical shock and a high inrush current. An initial voltage setting that is too low may result in a
prolonged period of time before the motor begins to turn.
Generally, this setting should cause the motor to begin turning immediately after the start signal,
while minimizing mechanical shock and inrush current.
Current Limit
The current limit feature sets the highest current level that will reach the motor during the starting
process. The current limit may be set from 100 to 400%. Once the present current limit value is
reached the voltage will level off and only continue ramping up once the current is below the limit
again.
If the current limit is set too high, there will be a greater current draw from the main power and a
faster acceleration. If the current limit is set too low, the motor may be unable to reach full speed (the
starter may trip on maximum start time).
Generally the setting should be high enough to start the motor without stalling.
Acceleration Time
The acceleration time determines the motor’s voltage ramp up time from initial to full voltage. The
acceleration time can be set from 1 to 30 seconds.
The time it takes the motor to reach full speed may not necessarily be the same as the acceleration
time. The following situations may override the acceleration time setting.
1. Since current limit overrides acceleration time, setting the current limit low will extend the
acceleration time (but never to exceed maximum start time).
2. When the motor reaches full speed prior to reaching nominal voltage, acceleration time is
overridden and voltage quickly ramps up to nominal. (This situation is common with lightly
loaded motors.)
3. Using curves (1, 2, or 3) will prevent a quick acceleration time.
Generally this setting should be the minimum acceptable time.
Maximum Start Time
The maximum start time is the maximum allowable time from start signal to end of acceleration. If
the voltage does not reach nominal during this time period, the RVS-DX will trip, and the LCD
display will read “LONG START TIME”. The maximum start time is settable from 1 to 30 seconds.