Mean Well MDR-40-12 DIN Rail Power Supply

Name: Mean Well MDR-40-12 DIN Rail Power Supply | Seven Star LLC
Brand: Mean Well
SKU: MDR-40-12

Compact 12 V DIN rail supply with a DC OK relay contact

The Mean Well MDR-40-12 is a 40 W industrial DIN rail power supply with a 12 V DC output rated at 3.33 A. The MDR-40 series is a small-format Mean Well family with a 40 mm wide housing, free-air convection cooling and a relay contact that reports the state of the DC output.

It accepts 85 to 264 VAC (120 to 370 VDC) and returns 85% typical efficiency at 12 V. Protection covers short circuit, overload and overvoltage. In an overload the output enters constant current limiting between 105% and 150% of rated power and recovers automatically. No-load power consumption is below 0.75 W, and every unit receives a full-load burn-in.

Technical specifications

Parameter	Specification
Manufacturer / series	Mean Well, MDR-40
Model	MDR-40-12
Nominal output	12 V DC / 3.33 A
Output power	40 W
Adjustment	12 to 15 V
Ripple and noise	120 mVp-p
Output tolerance	+/-1.0%
Line and load regulation	+/-1.0% / +/-1.0%
AC/DC input range	85 to 264 VAC; 120 to 370 VDC
Efficiency	85%
Input current	1.1 A at 115 VAC; 0.7 A at 230 VAC
Inrush current	Cold start 30 A at 115 VAC; 60 A at 230 VAC
Hold-up time	50 ms at 230 VAC; 20 ms at 115 VAC
Overload response	105 to 150%, constant current limiting, automatic recovery
OVP	15.6 to 18 V, shut down; re-power to recover
DC OK signal	Relay contact, 30 V / 1 A resistive (max.)
Operating temperature	-20 to +70 C, with derating curve
Hazardous location listing	Class I, Div. 2, Groups A, B, C, D, T4 (per datasheet)
Isolation test voltage	Input-output 3 kVAC; input-FG 2 kVAC; output-FG 0.5 kVAC
Dimensions	40 x 90 x 100 mm
Net weight	0.3 kg

What the DC OK relay is for

Many small DIN rail supplies offer only an indicator light. The MDR-40 series adds a relay contact rated at 30 V and 1 A resistive, which can feed a PLC input or an alarm circuit when the 12 V rail drops. Wire it as a normally supervised signal so that a failed supply is detected before sensors and communication modules start misbehaving. The relay is a signal contact, not a power output.

Typical uses and selection

Mean Well lists industrial automation machinery, industrial control equipment, mechanical and electrical equipment, and electronic instruments as applications. A 12 V, 3.33 A rail suits network switches, I/O gateways, small HMI panels, LED indicators and low-voltage sensors. Total up the load current and leave headroom; the 3.33 A rating is continuous, and the output voltage can be raised to 15 V with the potentiometer if cable drop needs compensating. Clip the supply on TS-35/7.5 or TS-35/15 rail and keep ventilation space around it, because cooling is by natural convection. If the cabinet needs 24 V instead, the same series is offered as MDR-40-24. Label the DC OK terminals clearly in the panel drawing so that maintenance staff can find the alarm contact without opening the datasheet.

Documents and quotation

Use the attached MDR-40 datasheet to check the mounting drawing, derating curve and terminal data before ordering. When requesting a price for MDR-40-12, include how many units you need, the incoming supply, the continuous and peak load, the temperature around the unit and certifications you must meet. See also Power Modules.

Mean Well power supply families

The catalogue covers DIN rail power supplies from 15 W to several hundred watts in single-phase and three-phase versions, enclosed chassis supplies with fan or convection cooling, medical-standard supplies, DIN rail DC-DC converters and many other formats. Each series has a datasheet that lists all output voltages, derating curves and approvals. The standard catalogue format suits machine builders, panel builders and maintenance teams that need a documented, replaceable supply rather than a custom design.

Frequently Asked Questions