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Types of suppressors:
Passive devices.
The resistor capacitor circuit
It eliminates the power dissipation problem, as well as fast voltage rises. With a proper match between coil and resistor,
approximate capacitance value can be calculated from:
C = 0.02xT/R, where
T = operating time in milliseconds
R = coil resistance in kiloOhms
C = capacitance in microFarads
The series resistor must be between 0.5 and 1 times the coil resistance. Special consideration must be taken for the
capacitor inrush current in the case of a low resistance coil.
The record shown opposite is performed on the same relay as above. The operation time becomes:
- time to start the movement 2.3ms
- transfer time 1.2ms
The major difficulty comes from the capacitor volume. In our example of a relay with a 290
Ω coil and time delay of 8 ms, a
capacitance value of C=0.5 uF is found. This non polarized capacitor, with a voltage of 63V minimum, has a volume of about
1cm3. For 150V, this volume becomes 1.5 cm3.
Date of issue: 6/00
- 9 -
Page 2 of 4
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