dc solid state relay application conditions

Application briefs that change the purchase, not the promise

A dc solid state relay usually switches with a MOSFET or IGBT output because there is no current zero to commute a thyristor. That single fact changes polarity rules, freewheel requirements and conduction loss relative to an AC-output cousin at the same ampere print. We translate the application into purchase fields. We do not promise that the assembled machine will meet a process result.

DC heater and solenoid circuits in OEM machines

Duty is continuous or high-cycle DC current in A, with a named voltage window in V DC. Inductive solenoids need a defined freewheel path; whether that path sits in the relay, across the coil, or in the cabinet is a specification item, not a courtesy. Reverse connection can destroy a DC output device rather than simply failing to switch.

Confirm mounting style before quoting: PCB module, panel plate or DIN rail clip. Socketed carriers help maintenance; soldered modules do not. Measure available height above the rail, because a sink that fits the catalog drawing may not fit the existing wire duct.

Battery, bus and DC-link switching in control cabinets

Duty includes interrupt of DC current without a natural zero. Ask for the output technology in writing (MOSFET or IGBT), the voltage drop at the intended current, and how the factory treats inductive energy. Isolation in Vrms stays a separate number from the load voltage.

DIN rail versus panel plate still limits the buy. A DIN body with an integral sink is a different thermal machine from a hockey-puck device on a buyer-supplied plate. Confirm enclosure ambient, airflow and whether neighbouring AC SSRs share the same heat path. NEMA enclosure type and IP rating remain two systems; do not treat them as translations.

Plant maintenance replacements

Duty is “match the existing control voltage and load polarity” plus the current the circuit actually draws, not the faded marking on the failed part. Photograph terminal layout and note AWG. If the failed unit was AC output, a DC-output substitute is a different family even when the case looks similar.

Measure or confirm before specifying: load voltage and polarity, continuous current in A, inrush, control voltage and polarity, sourcing or sinking, mounting pitch, and whether a status LED is required. Then send those fields, not a request to “make it work like the old one.”