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Ndrive HL User’s Manual
4-8 www.aerotech.com
Example #3:
Figure 4-8 is a suppression circuit that can be used for both AC and DC
circuits. In this method, a resistor, capacitor and a varistor are used across
the load (see Figure 4-8). In some cases, better results are obtained by
installing the suppression devices across the relay contacts. The ratings
and values for these components are described below.
Resistor (R)
: calculated by the following formula, Power rating = ½
Watt.
Resistor (ohms) = Voltage / Load current
If the Resistor is less than 24 ohms use 24 ohm resistor.
If the Resistor is greater than 240 ohms use 240 ohm resistor.
If the resistance of the Resistor is too low the relay contacts may fuse
together.
If the resistance of the Resistor is too high, the contacts may be damaged
due to excessive arching.
Capacitor (C)
: .1 uF, rated for AC circuits and a voltage rating of not
less than 250 Volts. If the voltage rating of the capacitor
is too low, the Varistor may not be able to protect it and it
may fail.
Varistor (V)
: Rated for the maximum voltage of the users power
supply, Typically, a varistor rated for a standard 120
VAC line should work well. Verify that the capacitor
voltage rating is greater than the clamp voltage of the
varistor. If the voltage rating of the varistor is too low, it
may conduct during normal operation and overheat. If the
voltage rating of the varistor is too high, it may not
protect the capacitor (C) against over-voltage conditions.
Figure 4-8.
RC Suppression for DC Brake Systems
The user may reconfigure the connections for the brake,
such that the positive supply lead is switched by the relay
instead of the supply common.
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