Aerotech SOLOIST Hardware Manual page 76

Soloist Options
4-12
Step #3 Suppression and Snubber requirements
Due to the inductive effects of the load (brake) suppression and/or snubber, components
are needed to reduce arching and prevent damage to the Brake Relay contacts.
Suppression can also reduce the electrical noise that is emitted when a circuit is turned
off. Following are three suppression circuit examples.
Example #1: Figure 4-8 is an example of a typical 24 VDC brake circuit. In that
example, the suppression component is the Varistor connected across the brake. This
method of suppression is used for systems operating at voltages up to 25 VDC and AC
systems operating at voltages up to 18 VAC. If the voltage is greater than 25 VDC or 18
VAC, one of the other methods should be used.
Example #2: Figure 4-10 is a suppression circuit that can be used for both AC and DC
systems. In this method, a resistor, capacitor and a varistor are combined and placed
across the load (see Figure 4-10). In some cases, better results are obtained by installing
the suppressor circuit across the contacts. The ratings and values for these components are
described below.
is calculated by the following formula, Watt rating = ½ Watt.
Resistor (R):
R(ohms) = Voltage / Load current
If R is less than 24 ohms use 24 ohm resistor.
If R is greater than 240 ohms use 240 ohm resistor.
If the resistance of R is too low the relay contacts may weld together.
If the resistance of R is too high the contacts may be damaged due to
excessive arching.
Capacitor (C): .1 uF, rated for AC, 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 external supply being used.
Typically, a varistor rated for a standard 120 VAC line should work.
Verify that the capacitor voltage rating is greater than the clamping
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.
Soloist Hardware Manual
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