Battery Chargers and DC UPS Solutions

PB251A-RM Series 19" Rack Mount DC-UPS and Battery Charger

The PB251A-RM Series is a combined DC-UPS and battery charger in a 2RU 19" rack mount enclosure, designed and manufactured in Australia by Powerbox. It powers the connected load from the AC mains while charging a sealed lead acid (SLA/VRLA) battery bank. If the mains fails, the load transfers to the battery without a dip or reset, which suits ra...

Two models are available. The PB251A-12RML delivers 13.8Vdc at 20A (275W) for 12V battery systems, and the PB251A-24RML delivers 27.6Vdc at 12A (330W) for 24V systems. Output current is shared between the load and battery charging, with factory defaults of 16A load and 4A battery on the 12V model, and 10A load and 2A battery on the 24V model.

Battery management includes constant float voltage, current limited charging, a low voltage disconnect (LVD) to protect the battery from deep discharge, and auto-resetting circuit protection. A front panel digital display shows system status, and alarm relays signal DC and battery faults to remote monitoring equipment.

Natural convection cooling means there are no internal fans to maintain, and automatic over-temperature protection guards the unit in enclosed racks.

Options for the PB251A-RM include an SNMP V1 network interface with embedded webpages for remote monitoring, analogue meters, temperature compensation via an external probe, and battery charge current limits set at the factory to suit your battery. For field cabinets and enclosures, the PB251A-CM chassis mount version shares the same electrical specification. Contact Powerbox for application support or help selecting options.

Show Less

Select model number

Model:

or send a quick enquiry about this product only

PB251A-RM Series 19 inch 2RU rack mount DC-UPS and battery charger by Powerbox

Features

Trusted in Critical Applications: Widely deployed in radio communications, nurse call systems, and security/access control infrastructure, the PB251A-RM provides dependable backup DC power for mission-critical systems where continuity is essential.
True Off-Line DC-UPS Functionality: Seamlessly delivers power to connected loads from the AC mains during normal operation and automatically switches to battery backup during outages—ensuring uninterrupted operation without dips or reset events.
Compact Rack Mount Design: Housed in a 2RU 19" rack-mount enclosure, with models delivering up to 330W of output power at 13.8Vdc or 27.6Vdc, this unit fits easily into communication racks, control rooms, and centralised power cabinets.
Comprehensive Battery Management: Includes built-in battery low-voltage disconnect (LVD), constant float voltage, current limiting, and auto-resetting circuit protection. A digital display and alarm relays provide real-time system status and fault indication.
Various Options Available: Including SNMP V1 network interface for remote monitoring, analogue meters, temperature compensation, and factory-set battery charge current limits tailored to battery specifications.
Designed and Manufactured in Australia: Proudly engineered and built by Powerbox in Australia, the PB251A-RM reflects decades of local expertise and compliance with Australian standards for safety, EMC, and industrial performance.

Specifications

INPUT
Input Voltage:	190...264Vac, or 225...400Vdc
Frequency	45 to 65 Hz
Input Current:	1.4A maximum
Inrush current:	10A maximum
Line regulation:	0.2%typical

ALARMS & BATTERY FUNCTIONS
DC Ok alarm	Green LED : ON=OK voltage free change over relay contacts (32V,1A) Alarms on loss of AC mains power or failure of off-line AC/DC converter / battery charger
Charger voltage OK alarm	Green LED : ON=OK voltage free change over relay contacts (32V,1A) Alarms on battery low voltage, failure of battery fuse or battery disconnected. Alarm cancelled when fuse or battery replaced, or AC input restored
Battery low voltage disconnect(LVD)	Low voltage disconnect 10.5V for 12V battery, 21V for 24V battery, adjustable 1.6 to 2.0V / cell all models
Charger over-load protection	Auto-resetting electronic circuit breaker
Reverse polarity protection	Internal battery fuse
Battery to load voltage drop	0.2 to 0.35V typical model dependant

OUTPUT
Output Voltage	13.8Vdc, 27.6Vdc
Output Power	275W - 330W
Output Current	13.8Vdc: 20A 27.6Vdc: 12A
Load regulation	0.5% typical
Ripple & noise	100 MHz bandwidth 28mVp-p (13.8Vdc output) 55mVp-p (27.6Vdc output)
Efficiency	> 80%

ENVIRONMENT
Operating temperature	0 to 70°C ambient Derating from 40°C at 2.5%/°C
Humidity	5 to 90% relative humidity (non-condensing)
Over-temperature protection	Automatic & auto-resetting
Cooling requirement	Natural convection

MECHANICAL
Input connector	IEC60320 inlet,10A Class 1 2 meter IEC mains cord with Australian plug is supplied with each unit
Output and battery connector	PB251A-RML: M4 screw terminals
Alarm terminal	PB251A-RML: M3.5 screw terminals
Enclosure	19" Rack Mount, 2RU height, 232mm Mounting slots suitable for M6 hardware
Weight	5.5kg

STANDARDS
C-Tick	AS/NZS CISPR11 Group 1 Class A.
Safety	Complies with AS/NZS 60950, class 1, NSW Office of Fair Trading Approval N20602
EMC	Emissions comply with AS/NZS CISPR11, Group 1, Class B. Complies with ACA EMC Scheme, Safety & EMC Regulatory Compliance Marked

OPTIONAL FEATURES
Battery Charge Current	Factory set to any value within adjustment the range. For the PB251A-12RML, battery charging current limit can be set from 2A to 20.5A . For the PB251A-24RML battery charging current limit can be set from 1A to 12.5A . Battery charging current option can be specified when ordering e.g. PB251A-12RML-10 for 10A setting.
Network enabled	Option N: Internal network card in conjunction with PB251A becomes a network enabled device combining the benefits of SNMP V1, XML and embedded webpage.
Analogue meters	Option M: Load voltage, load current, battery charge and discharge.
Temperature compensation	Option T: 2.5m cable probe Option T5: 5m cable probe Float voltage set to 2.3V/cell at 25°C with compensation of 3.3mv/°C cell
Battery Capacity Test	Contact Powerbox for further information

Selection Table

MODEL NUMBER	OUTPUT VOLTAGE	LOAD CURRENT	BATTERY CURRENT LIMIT (BCL)¹	TOTAL CURRENT	OUTPUT POWER	MECHANICAL
PB251A-12RML	13.8V	16A	4A	20A	275W	19" Rack Mount
PB251A-24RML	27.6V	10A	2A	12A	330W	19" Rack Mount

Notes:

¹ Other BCL option, Battery Charging Limits, available on request. (factory set)

² Example models number, PB251A-12RML-M-10, Includes analogue meters and 10A battery charge current.

Technical Drawings

Diagram showing a mechanical outline of a rectangular unit, top view, with dimensions.

Powerbox schematic, front view, showing dimensions and battery status.

Powerbox power supply unit front panel schematic.

Rear view schematic of a PB251A-RML rackmount unit showing ports and connectors.

Electrical terminal block diagram with notes.

Powerbox monitoring webpage showing system status.

Downloads

PB251A-RM_Rev.D_08-05-17.pdf

PB251A_Installation_Manual.pdf

Warranty & Returns

Warranty periods vary by product. Please refer to the Powerbox Warranty Policy for the applicable coverage period against manufacturing defects from date of purchase. For returns and RMA requests, please visit our RMA support page or contact our support team directly.

FAQs

What output options are available in the PB251A-RM Series?

It is available in 13.8Vdc (20A) and 27.6Vdc (12A) configurations, delivering 220–330W in a 2RU 19" rack-mount enclosure.

What applications is the PB251A-RM suited to?

It is widely deployed in radio communications, nurse call systems, and security/access control infrastructure — any application requiring rack-mounted, reliable DC-UPS with battery backup in a communications or control room environment.

What optional features does the PB251A-RM support?

Options include SNMP V1 network monitoring with embedded webpages (Option -N), analogue meters for front-panel current and voltage display, temperature compensation via external probe, and factory-set battery charge current limits.

What cooling does the PB251A-RM use?

It uses natural convection cooling with automatic over-temperature protection, requiring no internal fans for quiet, maintenance-free operation in rack environments.

What safety standards does the PB251A-RM comply with?

It complies with AS/NZS60950 safety and C-Tick EMC standards and is designed and manufactured in Australia.

How does the PB251A-RM differ from the PB251A-CM?

Both share the same electrical specification. The RM is a 2RU 19" rack-mount format intended for communications racks and control rooms; the CM is a chassis-mount format for installation in field cabinets and enclosures.

Item added to your cart

PB251A-RM Series 19" Rack Mount DC-UPS and Battery Charger

Enquiry Cart

Your Details

PB251A-RM Series 19" Rack Mount DC-UPS and Battery Charger

Related Products