PMU-27V155WCBA Power supply Delta Electronics PMU 155 W 27.6 V

PMU-27V155WCBA is a 151 W DC-UPS (uninterruptible DC power supply) from Delta Electronics with a built-in charger. Output 27.6 V DC (adjustable 24–28 V), load current up to 4.0 A plus 1.5 A for battery charging. Single-phase input 90–132 / 180–264 V AC, panel mounting, M3.5 terminal block. In normal mode the unit powers the 24 V load and charges the battery; on a mains sag it switches to the battery with no break, keeping the controller from rebooting. The "B" suffix denotes the build WITHOUT the signal-monitoring board (no AC OK / DC OK / Battery Low).

This is the 27.6 V model for a 24 V SLA battery (or 2×12 V in series).

Typical applications:

• 24 V cabinets with PLCs and operator panels where uninterrupted power is critical
• Security, telemetry and communication systems that must stay active through dips
• Nodes that must finish a process cleanly when the 220 V fails

Note: WCBA has no signal board; if you need AC OK / DC OK / Battery Low signals, choose WCCA. The battery is NOT included — an external 24 V SLA battery and a 30 A fuse in the B+ path are required.

Delta PMU-155W — DC-UPS power supply with integrated charger for the control cabinet

The Delta PMU-155W series is not an ordinary power supply but a compact DC-UPS (uninterruptible DC power supply) with a built-in battery charger. A single unit combines three functions: a regulated 151 W AC/DC converter, a charger for an external sealed lead-acid (SLA) battery, and a zero-break backup module. While the ~220 V mains is present, the PMU feeds the load from the rectifier and simultaneously trickle-charges the buffer battery; the instant the voltage disappears, the supply switches to the battery with no break at the output (zero switch-over time). The controller on your installation never even "sees" the mains outage.

How it works, and why 13.8 / 27.6 V instead of 12 / 24

The key thing to understand: 13.8 V and 27.6 V are the working output voltage of the unit, while the 12 V and 24 V in the datasheet are only the nominal rating of the battery you connect to it. The elevated voltage is required precisely to charge the SLA battery correctly in CC-CV mode (constant current — constant voltage): through the B+ terminal the unit keeps the battery in buffer mode and automatically switches to it when the mains fails. The charging current is set by a potentiometer (factory default 1.5 A). A built-in monitoring circuit provides AC OK, DC OK and Battery Low signals, a green LED indicates output presence, and a red LED warns of reversed battery polarity. On board you also get protection against overvoltage, overload, over-temperature, short circuit, deep discharge and reverse battery polarity.

IMPORTANT: the battery is NOT included

The PMU ships without a battery (batteries not included). To get backup operation you need an external SLA battery (sealed lead-acid): 12 V for the PMU-13V155W model, or 24 V (a single 24 V unit or two 12 V in series) for the PMU-27V155W. Supported capacities are 3.3 / 7 / 12 / 15 Ah; backup time depends on capacity and load (for example, a 24 V / 15 Ah battery gives roughly 2 h 30 min at light current, and tens of minutes at full load). An external fuse must be fitted in the B+ path (30 A / 80 V, automotive FK3 type) to protect the wiring between the battery and the unit.

Series ratings (from the Delta datasheet)

Typical applications

• Security systems: access control, intrusion and fire alarms, automatic doors — anywhere power must never drop.
• Industrial controllers and PLCs: holding control through sags and short mains outages so the system does not reboot.
• Emergency and critical power: nodes that must finish a cycle correctly, save state, or shut down in an orderly way when the 220 V fails.

Our take

The PMU-155W is a sensible choice when you need reliable backup on the DC side rather than a bulky 230 V online UPS. All protections and IEC/EN/UL 62368-1 certification are already on board, with MTBF over 700,000 hours. Just keep the main point in mind: the unit is bought separately from the battery, so budget an SLA battery of the right capacity into your project too. If you are unsure which variant (13.8 or 27.6 V) and what battery capacity to choose for your load and required backup time, contact us — we will size it by current.