How to handle inductive loads



General-purpose relays are typically designed to drive resistive loads, not inductive loads.

This is why electromechanical life ratings are published for ohmic loads and not inductive loads.

Inductive loads can best be defined as anything with a magnetic coil, such as a motor, solenoid, or a transformer.

The purpose of this capacitor is to absorb the high voltages generated by inductive loads.

Unlike resistive loads, inductive loads love power, and they will do everything they can to hold on to it.

The unpleasant result of this power hunger is inductive kickback, and it has a devastating effect on the

contact life of most general-purpose relays. This is true of both ac and dc inductive loads, although

the inductive kickback is far worse with dc loads due to the constant current characteristic of dc power.

How bad is the kickback? A 24-Vdc solenoid with a current consumption as low as a quarter of an 

amp will create a negative inductive kickback of more than 300 V.

Aslo the high voltage kickbacks can easily brake the USB communication and the only way to fix it

to unplug and plug it again.


Fixing the problems


Adding a suspension capacitor could easily reduce the problems. It has to be installed as close as

possible to the Relay Board.



DME Polyester Film Capacitors are suitable for this job with capacitance around 0.47uF – 0,68uF will be satisfied.

Choose larger voltage rating than your power supply. 


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If you can't find it you can use other Metalized Polyester Film Capacitor.





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