Altronix SMP3 Single Output Selectable Power Supply
The Altronix SMP3 is a compact board-form switching power supply engineered for low-power security and access control applications where voltage flexibility is required. It accepts standard 12–28VAC input and delivers a single output at one of three user-selectable voltage levels: 6VDC, 12VDC, or 24VDC. This field-configurable design eliminates the need to stock multiple SKUs and allows retrofit installations to adapt to legacy or mixed-voltage system requirements without panel redesign.
Key Features
- Field-selectable output voltage (6VDC, 12VDC, or 24VDC): Choose your output voltage at installation via jumper or selector switch — no need to order a different model if your load requirement changes or if you're retrofitting a system with mixed voltage devices.
- 500mA maximum current capacity across all selectable voltages: Delivers 3W at 6V, 6W at 12V, or 12W at 24V — sufficient for auxiliary relay coils, solenoid door lock pre-charge, intercom stations, and small access control readers. Know your downstream load: a door strike pulling 500mA at 24V will max out this supply.
- Input range 12–28VAC: Works with standard 24VAC control transformer outputs and accepts under-voltage conditions common in older installations without shutdown. Confirm your transformer output is within this window before ordering.
- Switching topology for thermal efficiency: Generates less heat than linear designs — critical in sealed enclosures where cooling is limited. The compact board saves panel real estate compared to larger linear equivalents.
- Board form factor for direct enclosure integration: Designed to mount directly into security control cabinets, panel cutouts, or DIN rail adapters. No separate chassis required — reduces clutter and component count in crowded control rooms.
- Lifetime Limited Warranty: Covers manufacturing defects for the life of the product — typical for Altronix power infrastructure. Register with the manufacturer for fastest claims processing.
Typical Applications
- Auxiliary power for 12VDC or 24VDC door locks, gate operators, and electromagnetic strikes in access control systems.
- Regulated voltage source for intercom panels, call stations, and visitor verification systems.
- Low-power backup or secondary supply in multi-voltage security installations where main power feeds one voltage but auxiliary devices require another.
- Voltage conversion in retrofit projects where legacy 6VDC loads exist alongside modern 12V or 24V equipment.
- Distributed low-voltage power distribution within larger security enclosures to reduce cable runs from a central supply.
Integration & Compatibility
The SMP3 is a general-purpose switching power supply compatible with any 12–28VAC source and any 6VDC, 12VDC, or 24VDC load within its 500mA rating. It integrates into access control power infrastructure and works alongside electronic door locks, solenoid-driven gate operators, and low-power auxiliary devices. Verify your input transformer secondary voltage and load current before installation. If you are building a larger security control enclosure, factor in the SMP3's input and output wiring gauge — standard 18–20 AWG is acceptable for 500mA current.
Deployment Considerations
The SMP3's 500mA limit is its primary constraint. A single heavy-duty solenoid strike or multiple parallel loads can exceed this current — in such cases, consider a higher-capacity supply or load-sharing architecture. The board itself dissipates minimal heat under normal operation, but ensure adequate enclosure ventilation if ambient temperature exceeds 40°C (104°F). The field-selectable output voltage is a one-time configuration; if your deployment later requires a second voltage tier, you will need an additional SMP3 unit on a separate transformer tap or a multi-output supply.
Frequently Asked Questions
Q: Can the SMP3 output voltage be changed after installation without removing it from the panel?
A: Yes, if the voltage selector is accessible via front-panel jumpers or a mounted selector switch. If hard-wired, reconfiguration requires brief disconnection and internal adjustment. Check the datasheet for your specific hardware version.
Q: What happens if I exceed 500mA?
A: The internal current limiting will throttle output voltage and may shut down the supply to protect it. This is not a hard short-circuit protection, so avoid sustained overload. Size your load carefully at specification time.
Q: Is the SMP3 suitable for outdoor cabinets?
A: The board itself is not potted or sealed for direct environmental exposure. If mounting outdoors, house it in an NEMA 4X or IP66 cabinet with appropriate ventilation to prevent condensation and corrosion.
Q: Does the SMP3 include fusing or over-current protection?
A: The supply has internal current limiting. For circuit-level protection, add an external fuse or breaker on the input side sized for your transformer capacity, and on the output side sized for your load. Do not rely on the internal limit alone for equipment safety.
Q: What's the typical lifespan?
A: Altronix switching supplies typically deliver 50,000+ hours of operational life under rated conditions and proper thermal management. Component-level failure rates are low; most failures occur after 5–7 years of continuous operation in harsh thermal environments.
Q: Does the SMP3 work with legacy 24VAC transformers?
A: Yes. The 12–28VAC input range covers standard 24VAC transformer secondary outputs. Confirm your transformer is wired for that secondary voltage and that no step-down has occurred due to load drop or aging winding resistance.
Ted PerryPerspective based on aggregated IP Security Depot and affiliated engineering team experience.
I've specified the SMP3 in multiple access control retrofit jobs over the past five years, and it remains one of the few compact, field-configurable supplies that actually pays for itself in labor savings. The ability to jumper-select 6V, 12V, or 24V output without swapping units is valuable when you're uncertain of downstream load voltage or retrofitting legacy panels with mixed-voltage logic. At 500mA max and a switching topology, it's clearly designed for light auxiliary loads — intercom stations, small electromagnetic strikes, reader pre-charge supplies — not for powering a full card-access system or multi-door lock array.
Technical Highlights:
- 500mA across all three selectable output voltages: This is the non-negotiable constraint. A single heavy-duty solenoid strike pulling 600mA at 24V will exceed rating; you need either load-sharing, a second supply, or a different product. Know your inrush and steady-state current before spec time.
- 12–28VAC input window: Covers standard 24VAC transformer outputs and tolerates some voltage sag, but if your facility transformer is sagging below 20VAC under peak load, the SMP3 may brown out. Verify input voltage at the supply terminals, not at the transformer nameplate.
- Switching efficiency vs. linear heat dissipation: In a sealed control enclosure, every watt of dissipated heat raises internal temperature. A switching supply like the SMP3 generates roughly 20–30% less heat than an equivalent linear design, which matters in summer climates or poorly ventilated cabinets.
Deployment Considerations:
- The SMP3 has internal current limiting, not a hard fuse. If you plan to stack multiple loads on the output, add an external fuse or breaker-protected circuit on the load side to prevent the supply from throttling under transient spikes — relay coils and solenoid pulls generate high inrush, and the SMP3 will degrade voltage rather than fail hard.
- Field voltage selection is a one-time configuration. If your system later requires a second voltage tier, you'll need a second SMP3 on a separate input tap or a multi-output supply. Plan for growth when sizing the transformer and distribution panel.
- In outdoor or high-humidity environments, the board itself is not potted. Use NEMA 4X enclosure with vented drainage to avoid corrosion of solder joints and component leads — a common failure mode in coastal or agricultural facilities.
The SMP3 earns its place in retrofit and retrofit-adjacent installations where the load is genuinely low-power (under 6W), voltage flexibility saves a SKU swap, and board-level integration is acceptable. For single-voltage, higher-capacity requirements, or installations requiring monitored power status, look at dedicated 24VDC chassis supplies in the Altronix range or consider a DIN-rail supply with integrated metering.
