Ndrive HP 10/20/30 User’s Manual
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4-7
Example #3:
Figure 4-7 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 4-7). 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)
: is calculated by the following formula, Power rating = ½
Watt.
Resistor (ohms) = Voltage / Load current
If the resistance of the Resistor is too low the relay contacts may fuse
together, so if the Resistor is less than 24 ohms use a 24 ohm resistor.
If the resistance of the Resistor is too high, the contacts may be damaged
due to excessive arcing, so if the Resistor is greater than 240 ohms use a
240 ohm resistor.
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 4-7.
Suppression for
AC and
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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