Electronic – Are both of the SSRs broken or am I doing something wrong

acsolid-state-relay

I have one side of a 125VAC panel-mount indicator connected to the AC load points of a solid state relay. The control points are hooked to a microcontroller with a basic program that switches the indicator on and off depending on characters that arrive on the UART.

The problem is that even when no voltage is applied to the control points, the indicator light still glows dimly. When I engage the control points, the indicator lights up brightly.

At first I thought the SSR had failed, so I ordered another one from a completely different company, but it's doing the exact same thing. Is it just a coincidence that I got two broken SSRs in a row from different manufacturers or (more likely) am I doing something wrong?

EDIT: Here are the SSRs I've tried.

  1. ECE ESR5102401000 24-240VAC/10A 3-32VDC
  2. SHZHE SSR-25DA 24-380VAC/25A 3-32VDC

Best Answer

You don't have enough of a load on the output of the SSR.

Most SSRs contain a snubber network that consists of a resistor and capacitor in series and then connected in parallel with the output terminals of the SSR. The capacitor allows some leakage current to flow.

This leakage current is enough to illuminate neon lamps and will even cause some 120 Vac strobe lights to flash periodically. Connecting a small incandescent lamp (5 Watt Christmas bulb) across your load terminals is usually enough to swamp out that leakage current.

Note: the snubber network is required for the triac inside the SSR to not false-trigger when certain conditions are just right. But the snubber does introduce its own set of problems.