25A SIP Solid State Relay Question
Your datasheet tells us that this is a "25A SIP Solid State Relay With Paired SCR Output, Integral Heatsink". This sounds as though it is a pair of back to back thyristors and will behave rather like a triac. Thyristors and triacs work well on AC circuits but are not much use in DC circuits unless the DC is rectified mains with no smoothing.



Figure 1. Triacs (or thyristors in this case) once switched on remain on until the current through them falls below the hold-on value. With a steady DC supply this never happens. Image source.







simulate this circuit &ndash; Schematic created using CircuitLab

Figure 2. AC test circuit.

Try repeating your test will a small transformer - say 12 V or so - and a couple of back-to-back LEDs with current limiting resistor.