Smart Cabinet Integration: Leveraging DC-OK Relay Contacts and Signal Outputs for Remote Power Diagnostics

A power supply that only delivers volts is blind. A supply with a DC-OK relay contact tells your cabinet exactly when output is healthy, when it has dropped out, and when it is about to fail. By wiring that dry contact to a PLC, BMS, or IoT gateway, you turn a rack of DIN-rail units into an observable, remotely diagnosable system—cutting truck rolls and catching faults before they cascade. HENGWEI DIN-rail families (HDR, MDR, NDR) carry DC-OK and alarm contacts ready for this integration.

Bottom Line

• DC-OK is a dry relay contact that closes only when the output is within spec.
• Wire it to a PLC/BMS input to get remote “supply healthy / fault” status with zero extra sensors.
• Pair DC-OK with the alarm/output contact for early-warning before a hard dropout.
• HENGWEI HDR/MDR/NDR DIN-rail units expose these contacts for cabinet-level diagnostics.

What Is a DC-OK Signal and Why Cabinets Need It

A DC-OK (sometimes labeled “DC OK” or “Power Good”) contact is a galvanically isolated relay inside the supply. It energizes when the DC output is present and within tolerance, and de-energizes the moment the output falls out of range—overload, input loss, or overtemperature. To the rest of your system it is a simple binary: healthy or not. That one bit removes the guesswork from remote sites.

From Blind to Observable

Without DC-OK, a field technician finds out a supply died only when the load stops working. With DC-OK polled by the cabinet controller, the SCADA screen shows a red flag the instant a unit drops, and you dispatch to a known fault instead of a symptom. At scale—hundreds of cabinets—this is the difference between reactive firefighting and scheduled maintenance.

Related HENGWEI Products

Wiring DC-OK Relay Contacts to Your BMS/PLC

The contact is normally a dry (voltage-free) pair: common (C), normally-open (NO), normally-closed (NC). Connect C and NO to a PLC digital input with the PLC’s own 24 V sense. When the supply is good, the contact closes and the input reads high; on fault it opens and the input drops—your logic fires an alarm. Because the contact is isolated, it never exposes your 24 V bus to the AC side.

HENGWEI DIN-Rail Units with DC-OK

Both the HDR 150 W and MDR 100 W DIN-rail supplies are built for rail mounting in control panels and expose the DC-OK / alarm contact. Mount them on a standard 35 mm DIN rail, land the contact on your controller, and the cabinet becomes self-reporting.

Alarm and Redundancy Strategies

Integration Example: A Distributed Cabinet Network

Picture 50 roadside cabinets, each with two DIN-rail supplies feeding a controller and radios. Wire each DC-OK to the cabinet PLC; the PLC reports status over the existing cellular link. A single dashboard now shows every supply’s health. When one DC-OK opens, you get a ticket with the cabinet ID—no truck roll to “figure out what died.” Add the alarm contact and you often catch the degradation a week early.

Commissioning Checklist

• Verify contact continuity with the supply powered and unpowered (should close / open).
• Confirm isolation: no DC bus voltage on the contact terminals.
• Map each contact to a labeled PLC address in your SCADA.
• Test by pulling input AC—DC-OK must drop within the spec response time.

FAQ — DC-OK Integration

Frequently Asked Questions

Q: Is the DC-OK contact powered or dry?

A: It is a dry (voltage-free) relay contact, isolated from both the AC input and the DC output. You supply the sense voltage from your PLC.

Q: Can I run DC-OK and an alarm together?

A: Yes. Use DC-OK for healthy/fault and the alarm contact for early warning, then act on either in your controller logic.

Q: Do HENGWEI DIN-rail supplies support this?

A: The HDR, MDR, and NDR rail families expose DC-OK / alarm contacts for cabinet diagnostics—check the specific model sheet for contact ratings.