ARC SUPPRESSION

When a clutch is de-energized, a reverse voltage spike is generated in the clutch coil. This reverse voltage spike can be very high and unless suppressed, can cause damage to the switch and/or coil.

There are three types of arc suppressors commonly used. Their effect on disengagement speed is as follows:

• Resistor or Varistor -- used for normal disengagement speed.
• Capacitor or Zener Diode* -- used for fast disengagement speed.
• Diode -- used for slow disengagement speed, and when arcing is to be eliminated completely.

* If Zener Diode is desired contact SEPAC Application Engineering for recommendations.

RESISTOR

On most applications, a resistor connected in parallel with the clutch coil will suffice. (See Figure 1.) The value of this resistor should be five to six times the clutch coil resistance and about 20%-25% of its wattage rating.

To eliminate the power dissipated by the resistor while the clutch is energized a varistor alone or a diode in series with the resistor may be used. (See Figure 2 and Figure 3.) These work only when the clutch is de-energized. For 90 VDC circuits, use a 1N5402 diode with a 200 PIV rating. Contact SEPAC Engineering for varistor recommendations.

CAPACITOR OR ZENER DIODE -- ARC SUPPRESSOR

For applications requiring fast clutch or brake disengagement, a capacitor or transient suppressor zener diodes should be connected in parallel with the clutch coil. (See Figure 4 and Figure 5.)

When a capacitor larger than 50 mfd. in a 24 volt circuit and 7 mfd. in a 90 volt circuit is used for an arc suppressor, a resistor should be connected in series with it (See Figure 6.) This is used to limit the capacitor charging current so that the switch or power supply will not be overloaded. The resistor should be about 12 ohms for 90 volt circuits and about 4 ohms for 24 volt circuits.

Electrolytic capacitors may be used back to back and in series to achieve the voltage rating and in parallel to achieve the capacitance rating. A simple paper condenser may be used if available in the correct rating. ANY CAPACITOR COMBINATION MUST BE BI-POLAR.

DIODE -- ARC SUPPRESSOR

If it is desirable to delay the disengagement a diode should be used. (See Figure 7.) For 90 VDC circuits, use a 1N5402 diode with a 200 PIV rating and for 24 VDC circuits, use a 1N5401 diode with a 100 PIV rating.