Do you have issues when switching DC Solenoids?

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James West, technical support engineer for Interface technology and switching devices discusses one of the technical problems he regularly gets asked about.

As a technical support engineer, I get a lot of support enquiries requesting replacement relays. Most of these application problems could be avoided by using the correct type of relay.

Solenoids are a common method of controlling valves in an automated machine. They do not have a particularly high holding current, however they are often used in high frequency switching applications and it’s this factor which will cause any associated mechanical relay to eventually fail.

DC Solenoids are an inductive load, meaning there will be an initial inrush on start-up, which when using a mechanical relay causes an ARC between the cathode and the anode during the switch from off to on. It’s this arc which, over time, will damage the relay contacts and eventually lead to relay failure.

Most relays can handle this inrush if the switching frequency is low, however if the frequency is high the mechanical life of the relay will be dramatically reduced.

Phoenix Contact has a wide range of relays that can be used to switch inductive loads. For a solenoid, an SSR (Solid State Relay) can be the perfect switching device. With no mechanical parts there is nothing to cause an arc and no contacts to damage, therefore the life of the relay will be a lot longer.

Selecting the correct SSR is very important as all solid state switching devices have maximum voltage ratings beyond which damage will occur. An over voltage spike can punch through the insulating materials used internally to protect the device and create a short circuit, so making sure you select the correct relay with the correct protective circuit is crucial.

Phoenix Contact can provide mechanical and solid state relays for all applications within automation, from very low current, high frequency data signals, to high inrush inductive loads of a motor.

Take a look at the RIFLINE relay offer in this video:

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For more information or a help in selection please call James on                01952 681700 or for a demonstration of any of the Interface range please contact Fraser Cowie on 07584 514963 or at



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