15
Fig. 14 Example of closing time
(2) Difference between AC and DC operations
The closing time of AC operated contactor and the double coil type DC operated one is short, and that of the direct
input type DC operated one is long. This is because the former flow a large current at closing and perform attraction
with a strong force, and after closing, the large current is changed to a small current. The releasing time of DC
operated contactor is longer than that of AC operated one.
2-3-3 Suppression of Coil Surge Voltage
Generally, in the semi-conductor circuits, an external noise generated near them may cause an unexpected malfunc-
tion. When operating the contactor, especially when cutting off the exciting current of coil, the coil generates a
sharp surge voltage with the result that the peak voltage may reach higher than 4kV and the frequency, higher than
5kHz. This is radiated as noise to the outside, and it is difficult to prevent such noise even if a protective element is
placed in the semiconductor circuit. Therefore, it is necessary to take measures against occurrence of noise from the
coil. Connect coil surge absorber including condenser and resistor in series to the coil of the contactor in parallel.
Then, the noise generated from the coil when cutting off the exciting current can be reduced Coil surge absorber is
shown on catalogue page 42 and 43.
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