Velleman-Kit K2649, Illustrated Assembly Manual

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The setting of the hysteresis does not depend on the set temperature. Do not set the minimum hysteresis
right from the beginning: in this case the regulation is most precise, however it could happen that the heating
gets switched on and off much too fast and too often (e.g. when the thermostat is located near the radiator).
This is not too healthy for the heating installation and/or relay, and too much energy is consumed. Therefore
start with RV4 in the middle position, and then search the ideal position for your application.
Suppressing inductive loads :
Should the operation of the thermostat get disturbed by the switching of inductive loads (even if the switched
power is not so high), then this is due to the sparks produced in the relay. In most cases this can be reme-
died by putting a VDR (e.g. VDR300) over the contacts. Moreover a series connection of a 100 ohm resistor
with a 47 or 100nF/400V capacitor can be placed in parallel with the VDR in order to further reduce the
sparks (see Fig. 8.0).
100 ohm / 0,5W
100nF/400V
VDR
(VDR300) MAINS
LOAD
FIG. 8.0
Use