Altronix MAXFIT3FD 12V/24V 6A Dual-Voltage Power Supply with Fire Alarm Disconnect and Battery Backup
Overview
The Altronix MAXFIT3FD is a commercial-grade, dual-voltage power supply and distribution assembly built for access control and surveillance installations that must integrate with fire alarm systems and survive an AC outage. Running on 120VAC at 3.5A input, it delivers up to 6A of regulated DC output at either 12VDC or 24VDC — the two voltages that cover the vast majority of electronic locks, door controllers, cameras, and relay modules deployed in commercial security. The MAXFIT3FD ships as a complete assembly: two ACM8CB power distribution modules and a BC750 enclosure are included, so you're not sourcing components separately and hoping they fit.
For installations governed by NFPA 72 or local fire codes, the integrated fire alarm disconnect supervision is the spec that matters most. Both latching and non-latching configurations are supported, giving the AHJ what they need regardless of local interpretation. The EOL supervision uses a 10K resistor — a detail wiring crews need before they pull wire, not after.
Key Features
- Dual-Voltage Output — 12VDC or 24VDC @ 6A: A single unit covers both 12V and 24V device ecosystems. Configuring for 24V doubles the effective wire run length for the same conductor gauge — useful in large-floor or multi-zone installs where IR drop is a real concern.
- Fire Alarm Disconnect Supervision (Latching/Non-Latching): The MAXFIT3FD supports both latching and non-latching fire alarm disconnect modes, letting you match the requirement of the authority having jurisdiction without modifying hardware. This is the field-inspection checkpoint most integrators get caught on — it's handled here at the factory level.
- Form C Contacts for AC Failure and Battery Supervision: Separate Form C dry contacts report AC loss and battery fault conditions to your panel or monitoring head-end independently. You get granular alarm differentiation — AC fail versus low battery — without adding external relays.
- Battery Backup for Up to Four 12AH/12VDC SLA Batteries: The MAXFIT3FD supports up to four 12AH sealed lead acid or gel-type batteries, giving you meaningful standby capacity for multi-hour outage scenarios. Battery fusing is at 10A/32V — sized to protect the battery leads without nuisance tripping under peak load.
- Low DC Power Shutdown — 71–73% for 12V, 70–75% for 24V: The unit shuts down before deep-discharging the battery bank. Sealed lead acid batteries permanently lose capacity when discharged below roughly 10.5V; this threshold protects the investment in your battery bank and avoids a post-outage service call to replace batteries that were killed by over-discharge.
- Auxiliary 1A Unswitched Output: A separate 1A power-limited auxiliary output — unswitched and always live — powers ancillary devices like readers, REX sensors, or door position switches that must remain powered regardless of the main output state.
- 5A/250V Input Fusing: Protects the transformer and downstream circuitry from upstream fault conditions. Replaceable at the unit level — no board-level repair required for an over-current event.
- Operating Range 0°C to 49°C (32°F to 120°F): Covers typical IT closet and electrical room environments. The 49°C ceiling is worth checking against your mechanical room peak ambient before installation — most commercial MERs run well under this, but a poorly ventilated riser closet in a hot climate can approach it.
- Includes Two ACM8CB Modules and BC750 Enclosure: The complete assembly eliminates the compatibility question. The BC750 enclosure provides the physical housing and mounting surface; the ACM8CB modules handle power distribution and fusing for the downstream device runs.
Integration and Compatibility
The MAXFIT3FD is designed for integration into fire-alarm-supervised access control and video surveillance power distribution architectures. The dual Form C contact outputs — one for AC failure, one for battery — connect directly to supervised input zones on most commercial panels. The fire alarm disconnect function removes power from the access control output when a fire condition is declared, supporting fail-safe (power-to-lock) door hardware configurations as required by most life safety codes.
Battery compatibility is limited to sealed lead acid or gel-type 12VDC batteries — do not use AGM batteries rated differently or lithium chemistries, as the charge profile will not match. Up to four 12AH units may be connected; larger AH ratings are not addressed in the evidence and should be confirmed with Altronix directly before specifying.
For power supply planning across a multi-door project, review the Altronix product line to find output-matched assemblies for different channel counts and enclosure sizes. If your project involves high-current electric strikes or mag-locks on multiple doors, pair this unit with appropriate access control hardware verified for 12V or 24V operation. For camera-dense deployments also requiring power distribution, consider whether a dedicated PoE switch better serves the camera side while this unit handles the access control loads.
Frequently Asked Questions
Q: Can the MAXFIT3FD output both 12VDC and 24VDC simultaneously?
A: No. The unit is configured for either 12VDC or 24VDC output — not both at the same time. Select the voltage at installation based on your device requirements.
Q: How many batteries can the MAXFIT3FD support, and what type are required?
A: The MAXFIT3FD supports up to four 12AH/12VDC batteries. Only sealed lead acid (SLA) or gel-type batteries are compatible — the charge profile is matched to these chemistries.
Q: Does the MAXFIT3FD support fire alarm disconnect, and is it latching or non-latching?
A: Yes. The MAXFIT3FD includes fire alarm disconnect supervision with support for both latching and non-latching configurations, allowing the installer to match the requirement of the local authority having jurisdiction.
Q: What is the EOL resistor value for the MAXFIT3FD supervision loop?
A: The end-of-line (EOL) resistor value is 10K ohm.
Q: What do the Form C contacts on the MAXFIT3FD supervise?
A: There are two sets of Form C contacts — one monitors for AC power failure, and a separate set monitors battery condition. These connect to supervised panel zones to report each fault type independently.
Q: What is the operating temperature range of the MAXFIT3FD?
A: The MAXFIT3FD operates from 0°C to 49°C (32°F to 120°F). Verify that your enclosure location — particularly mechanical or riser closets — stays within this range under peak summer ambient conditions.
The detail I focus on first with the MAXFIT3FD is the dual Form C contact output architecture — separate supervised contacts for AC failure and battery condition. On a typical commercial access control job, your panel only has so many supervised zones, and getting granular fault differentiation without adding relay boards saves both panel zones and field labor. That spec, combined with the fire alarm disconnect supporting both latching and non-latching modes, is what makes this unit appropriate for fire-code-governed installations rather than just a generic power supply.
Technical Highlights:
- 6A @ 12V or 24VDC output: At 24V, you can run longer home-run wire distances before IR drop becomes a problem — relevant on large-floor commercial deployments with doors spread across 300+ foot runs on 18 AWG.
- Up to four 12AH SLA batteries supported: Four 12AH batteries at 12VDC gives you meaningful standby time for a 6A-loaded system — roughly 2+ hours depending on actual load, which meets most code-required minimum standby durations for access control.
- Low DC shutdown at 71–73% (12V) / 70–75% (24V): The unit cuts off before the battery bank drops to a damaging depth-of-discharge. SLA batteries that get repeatedly discharged below ~50% capacity lose significant cycle life — this threshold is set conservatively enough to protect them.
Deployment Considerations:
- The latching vs. non-latching fire alarm disconnect setting must be confirmed with the AHJ before rough-in. Some jurisdictions require latching (the output stays off until manually reset after a fire event); others accept non-latching. Getting this wrong means a failed inspection.
- The 49°C operating ceiling is the watchout on this unit. Riser closets in southern climates, or any enclosure mounted near HVAC exhaust, can exceed this — budget for ventilation or a larger enclosure with more thermal mass if ambient temps are a concern at your site.
The MAXFIT3FD is the right spec for multi-door commercial access control projects where the panel, doors, and power distribution all need to live in a single enclosure and fire alarm integration is a code requirement — not an option. It is not the right call for a simple single-door installation where you don't need fire supervision, battery backup, or distribution modules; a smaller single-output unit will do that job more economically.
