Checking Whether SSR Off Leakage Keeps a Small Load Active

A solid state relay in its commanded off state can still pass a small current. With a sensitive or high impedance load, that current may produce a substantial voltage or prevent release. Determine whether the observation is expected leakage, an input command problem, or an actual output failure.

Separate input and output leakage

The Omron explanation of SSR turnoff problems distinguishes leakage in the drive circuit from leakage through the output path. Input leakage can keep the relay commanded on, while output leakage can affect the load even after the input is genuinely inactive.

Measure the voltage and current at the relay input and compare them with the specified release conditions. Do not rely only on the processor output state or a software command.

Characterize the actual load response

Read the SSR’s maximum off-state leakage under relevant voltage and temperature conditions. Compare it with the load’s release current or operating threshold, including any internal rectifier or storage capacitor.

For illustration, a hypothetical 100 microampere leakage flowing into a 100 kilohm resistive load can produce 10 V while enough source voltage is available. A high measured voltage therefore does not by itself establish a low impedance short through the relay.

Use an appropriate measurement load

Document the meter input resistance because the instrument becomes part of the circuit. Compare the observed voltage with the expected leakage and load relationship. Use a controlled method appropriate to the circuit’s voltage and energy rather than introducing an arbitrary short as a diagnostic.

If the load stores charge, observe voltage over time. Intermittent charging and discharge can cause blinking or repeated partial activation even when average leakage appears small.

Evaluate a supported correction

A suitable parallel load or a relay technology with lower leakage may address the requirement. Calculate continuous dissipation and verify component ratings before adding a bleeder. Check the selected manufacturer’s guidance for the specific SSR and load.

Repeat the off-state test at relevant supply and temperature conditions and after normal operation. Verify that the load reliably releases and that the correction does not create unacceptable standby consumption.

Save input state, output leakage conditions, instrument loading, load behavior, and the final correction. A satisfactory result distinguishes harmless residual voltage from unwanted functional activation. It also prevents a small-load compatibility problem from being mislabeled as a permanently shorted SSR or hidden by a measurement that changes the load enough to make the symptom disappear.