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solid state relay misfiring

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venuselectronics

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hi

we have developed atemperature control panel, earlier panel was working nicely, but when we placed servo motor controller inside panel, ssr gets turned on without control voltage ,our ssr is not potted , is it turning on with noise of servo drive or humidty in environment i dont understand

whether potting will solve problem

venus electronics
 

See and post the results, by disconnecting the Primary (LED) side. See wether the SSR still conducts when the LED side is left open. If yes, your SSR is leaky coz it just cannot conduct without a pulse from the optocoupler from the primary side. EMI's from the servo coil may too affect the working, while diodes like 1N5408 across coil terminals will solve the problem.
Cheers
 

Two things can trigger SCRs and Triacs (it will be one or the other inside the SSR), they are current through to opto interface and very rapid changes in the main terminal voltage. You only want the opto interface to control it. Do as @pranam77 suggests, disconnect the control side of the SSR and see if it still does it. If it still misfires it is because the servo is creating spikes on the supply and these are causing the SSR to fire by itself. If it is the spikes, try connecting a snubber across the SSR main terminals. Try 100 Ohms resistor and 100nF capacitor in series across the terminals. Note that the capacitor must withstand the highest peak voltage.

Brian.
 

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