NCD Articles Home Copyright © 2008, National Control Devices LLC

By Ryan Sheldon

Contact Us

Controlling Inductive Devices:

Managing Electromagnetic Interference

This video is a basic introduction to Induction and how to suppress it using Capacitors. Also read our "Induction Suppression" Article.

Perhaps the most overlooked aspect of relay control is proper handling of inductive loads.  Inductive loads can best be defined as anything with a magnetic coil, such as a motor, solenoid, or a transformer.  Controlling a inductive load using our relay controllers requires the use of induction suppression capacitors.  The purpose of this capacitor is to absorb the high voltages generated by inductive loads, blocking them from the contacts of the relay.   Without this capacitor, the lifespan of the relay will be greatly reduced.  Induction can be so severe that it electrically interferes with the microprocessor logic of our controllers, causing relay banks to shut themselves down unexpectedly. As you can see from the diagram below, a induction suppression capacitor is very easy to install.  The capacitor should be located as close to the relay controller as possible, and is connected in parallel with the load you are trying to control.  Induction suppression capacitors are NOT polarized, and may be used in both AC or DC applications.

WARNING:

THESE CAPACITORS WILL STORE DANGEROUSLY HIGH VOLTAGES FOR SHORT PERIODS OF TIME.  BEFORE HANDLING, SHORT CIRCUIT THE CAPACITOR OUTPUTS AFTER USE.

USB USERS:

UNLESS OTHERWISE NOTED, USB COMMUNICATIONS SHOULD NOT BE USED AS AN INTERFACE OPTION FOR INDUCTIVE APPLICATIONS.  THE USE OF INDUCTION SUPPRESSION CAPACITORS WILL NOT BLOCK ENOUGH INTERFERENCE FOR PROPER USB COMMUNICATIONS.  CLICK HERE FOR MORE INFORMATION.

Unlike inductive loads, resistive loads such a incandescent lights and element heaters (without a fan), do NOT require a induction suppression capacitor, and will NOT benefit from its use.

Choosing the correct induction suppression capacitor is simply a matter of choosing the maximum voltage requirement of the device you are trying to control.  Below is a list of capacitors that we offer as a convenience to our customers.

DME1P56KF

 

.56uF 100VDC / 65VAC Polyester Film Capacitor

More >>

$1.20

DME2P56KF

 

.56uF 250VDC / 160VAC Polyester Film Capacitor

More >>

$1.60

DME4P56KF

 

.56uF 400VDC / 200VAC Polyester Film Capacitor

More >>

$2.66

DME6P56KF

 

.56uF 630VDC / 250VAC Polyester Film Capacitor

More >>

$4.10