Toshiba VF010H05 User Manual

 

 

The current limit adjustment is factory set for 350% of the unit’s rating. 

The range of adjustment is 200% to 500%. The main function of cur-

rent limit is to cap the peak current. It may also be used to extend the 

ramping time if required. The interaction between the voltage ramp 

and the current limit will allow the soft start to ramp the motor until the 

maximum current is reached and the current limit will hold the current 

at that level. The current limit must be set high enough to allow the 

motor to reach full speed. The factory setting of 350% is a good start-

ing point.

Note:  If the motor does stall, refer to the motor manufacturer’s motor data 

for the proper cooling time.

 

Decel extends the stopping time on loads that would otherwise stop too 

quickly if allowed to coast to stop. Decel control provides smooth deceler-

ation until the load comes to a stop. Three adjustments optimize the deceleration 

curve to meet the most demanding requirements. The unit is shipped from the 

factory with the decel feature disabled.

Apply power and adjust the soft start before enabling or modifying the 

deceleration adjustments. Both acceleration and deceleration adjust-

ments should be made under normal load conditions.  

  The deceleration feature provides a slow decrease in the output voltage, 

accomplishing a gentle decrease in motor torque during the stopping 

mode. This is the OPPOSITE OF BRAKING in that it will take longer to 

come to a stop than if the starter were just turned off. The primary use 

of this function is to reduce the sudden changes in pressure that are 

associated with “Water Hammer” and slamming of check valves with 

centrifugal pumps. Decel control in pump applications is often referred to 

as 

Pump Control.

  In a pump system, liquid is being pushed uphill. The force exerted by 

gravity on the column of liquid as it goes up hill is called the “Head 

Pressure” in the system. The pump is sized to provide enough Output 

Pressure to overcome the Head Pressure and move the fluid up the 

pipe. When the pump is turned off, the Output Pressure rapidly drops 

to zero and the Head Pressure takes over to send the fluid back down 

the hill. A “Check Valve” is used somewhere in the system to prevent 

this (if necessary) by only allowing the liquid to flow in one direction. The 

kinetic energy in that moving fluid is suddenly trapped when the valve 

slams closed. Since fluids can’t compress, that energy is transformed 

into a “Shock Wave” that travels through the piping system looking for 

an outlet in which  it dissipates. The sound of that shock wave is referred 

to as “Water Hammer”. The energy in that shock wave can be extremely 

damaging to pipes, fittings, flanges, seals and mounting systems.

  By using the Soft Stop/Deceleration feature of the soft starter, the pump 

output torque is gradually and gently reduced, which slowly reduces the 

pressure in the pipe. When the Output Pressure is just slightly lower than 

the Head Pressure, the flow slowly reverses and closes the Check Valve. 

By this time there is very little energy left in the moving fluid and the