The KRC1 is cooled independently of temperature by an internal and an external fan.
This does not only make a lot of noise, but also consumes 175W apparent power.
The cooling capacity is obviously oversized for hobby use, so I
wanted to control the fan speed dependent on temperature.
Since both fans are driven by an asynchronous motor, a frequency converter was required for this purpose. I decided to use a SAKO SKI780 in the 0,75kW version. It has an integrated PID-controller with which I try to limit the temperature inside to 30°C.
The frequency inverter came with an English manual (see below), but this mainly consists of a table of about 450 parameters without detailed explanations. But with a sound technical understanding it was to be mastered. Here the parameters to be changed:
|P0-02||1||The frequency is controlled via the external connections.|
|P0-03||8||The frequency is determined by the PID controller.|
|P0-14||30Hz||To guarantee a minimum cooling capacity, I specified a minimum frequency of 30Hz.|
|PA-01||56%||This is the setpoint.|
|PA-08||0Hz||The lower the temperature, the lower the output frequency. However, the lowest frequency is for the SKI780 despite the set minimum of 30Hz not 0Hz but 50Hz with reverse direction of rotation. The parameter value of 0Hz prevents the controller from changing the direction of rotation.|
|PA-21||100%||This ensures that the motor starts in forward direction.|
With the above settings, the actual value must be present at input AI1 (see parameter PA-02). PA-01 determines the set point value. At 50% the controller would try to get 5V to input AI1, which is the case at 25°C, because the NTC has 10kOhm exactly there. 56% corresponds approximately to 30°C depending on the NTC used.
For the frequency inverter to start automatically when the mains voltage is applied, DI1 must be connected to ground (see parameter: P4-00).
The controller is parameterized as a PI controller by default (see parameters PA-05 to PA-07). Here too, everything can be left at the default values for this application.
Disclaimer of liability:
The present project requires specialist knowledge. Reproduction at your own risk and liability.