Inductive Rated Relay Controllers

You may have noticed, we are making our inductive series controllers with RED circuit boards.  A Red circuit board means that a inductive rated relay driver is employed by the controller.  If the controller has a on-board computer interface, you can bet is is isolated in some way.  In addition, a Red circuit board is a quick way for you to know that extra engineering has gone into the design of this controller, and it should be safe in applications where our standard series controllers should not be used.  In particular, when controlling high voltage 120VAC-250VAC motors, solenoids, valves, or in applications where the controller must be install near a high power RF source, such as a radio transmitter, or in other high EMI locations.

Inductive rated relay boards also offer additional filtering not found on our other controllers, as well as a full star layout, routing everything back to the power supply terminals on the board.

All Inductive Rated relay controllers are ProXR compliant, meaning they all support our standard ProXR command set.  In addition, they offer your choice of a 8-Channel A/D Converter or a UXP Expansion Port.  All ProXR series controllers offer a standard XR Expansion Port for adding additional relays.

Below we highlight the most important design characteristics of our inductive rated relay controllers.  We still recommend the use of external capacitors to improve relay life.  Please see our Induction Suppression page for complete details.



Dual Circuit Design:

All USB Inductive Rated Relay Controllers offer a Dual Circuit Architecture.  The primary interface circuit is shown in Black and White.  This portion of the circuit is galvanically isolated from the rest of the relay controller using a 8-pin galvanic isolator, designed specifically for high-speed data transfer.  There is no possible way inductive spikes can ever reach your computer using this galvanic isolation barrier.  This is especially important when controlling highly inductive loads.  When the USB connector is plugged into the controller, the 3 LEDs (shown at the top of the B&W portion) will flash during USB connection.  The controller still requires a External power supply to power the rest of the circuit.

Redesigned Driver Stage:

The Inductive Rated relay controllers also benefit from a newly re-designed driver stage.  This driver is designed to improve EMI isolation and noise immunity between the logic and drive circuitry.  Additional filtering components have been added to the design to route all transient induction directly back to the power supply at it source, using a PCB that has been routed with a Star configuration. 

No USB Powered Relay Controllers?

Proceed with Caution if you are looking for such a device.  The truth is, you may be risking your motherboard.

We have had plenty of time to study the effects of inductive loads, and how it affects a computer interface, logic, and driver components.  A mechanical relay controller should NEVER be powered from the USB Bus (the only exception being small reed relays).

How Relays Kill Motherboards:

One of the most overlooked design flaws we have seen among our competitors is that they do NOT account for the USB specification.  The USB Specification EXPLICITLY states that you CANNOT place surges on the USB bus.  This isn't a problem if you are controlling a couple of relays.  But it's a HUGE concern if you activate several relays at one time.  What you have done is just surged the USB bus, risking damage to your motherboard.  So if you do find a mechanical relay controller that is USB bus powered, you need to ask a lot of questions before you make your purchase.

How Relay Loads Kills Motherboards:

If you think relays are 100% isolated from the coil, think again!  It is possible for inductive spikes to be inducted onto the coil, especially when switching inductive AC loads (such as motors) in the 120-250VAC region.  We have seen all kinds of spikes that you don't want anywhere NEAR your motherboard.  The fact is, a relay controller needs isolation, particularly on the fragile USB bus.  True isolation requires two power supplies.  And to effectively isolate the USB bus, you would have to use a isolated DC/DC converter.  These aren't cheap, so there is no way you are going to find a properly designed mechanical relay controller powered from the USB bus for a reasonable price.

How it Can Be Safe:

This is not to say we will NEVER create a USB Bus powered relay controller.  It is safe to control a few small mechanical relays powered from the USB bus without damage, but you CANNOT use these relays for inductive applications, such as controlling motors, coils, or anything else that moves.  A few relays that do NOT surge the port beyond specification, controlling resistive loads is acceptable if no USB isolation is available.