Induction Suppression Capacitors

Handling Inductive Loads

Handling Inductive Loads (Why It Matters)

Inductive loads are anything with a magnetic coil -motors, solenoids, transformers, mag locks, door strikes, etc. These devices generate dangerous voltage spikes when switched on and off.

ProXR Relay

Those spikes can:

Destroy relay contacts prematurely
Cause unexpected controller resets
Knock USB devices offline/li>
Damage the board’s power regulation circuitry

To prevent this, you must install an induction suppression capacitor (also called a “snubber capacitor”) across the load.

Why You Need a Capacitor

Every time an inductive device switches off, it releases a burst of high-voltage energy.
A suppression capacitor:

Absorbs these spikes before they reach your relay
Protects relay contacts from arcing
Prevents interference with the microcontroller logic
Helps maintain stable USB or serial communication

Without this capacitor, the life of your relay - and sometimes the entire controller - can be drastically reduced.

Resistive Loads Don’t Need Suppression

If you’re switching a purely resistive device, such as:

Incandescent/LED lighting
Heating elements without fans
Basic resistive appliances

…you do not need a suppression capacitor. Resistive loads don’t generate induction.

Choosing the Right Capacitor

It’s simple:
Choose a capacitor with a voltage rating equal to or higher than the voltage of the device you’re switching.

Example:

Switching a 120VAC motor → Use a capacitor rated for 120VAC or higher
Switching a 24VDC solenoid → Use a capacitor rated for 24VDC or higher

Most customers use our standard 0.1µF 250VAC capacitors because they cover a wide range of typical loads.

Easy Installation

Installing a suppression capacitor is straightforward:

Mount it as close to the relay as possible
Connect it in parallel with the inductive load
Polarity doesn’t matter—capacitors used for suppression are not polarized
Works with both AC and DC loads

That’s it. A 10-second install can prevent a $200 problem.

Don’t Share Power Supplies with Inductive Loads

Your controller must be powered by a clean, regulated power supply. Do not share the same supply with:

DC motors
High-power solenoids
Any heavy inductive device

Shared supplies create massive spikes that can permanently damage the controller.
The only exception: battery-powered systems (like automotive) where the battery naturally absorbs induction spikes.

Important Note for USB Users

USB is extremely sensitive to electrical noise. An inductive spike can cause the PC’s motherboard to drop the USB port entirely.

That means:

Your controller disappears from the OS
Your application loses communication
You must unplug and reconnect the board

Using a suppression capacitor is absolutely essential when combining USB control with inductive loads.

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