SR750HI – 750W DC UPS

No – Break ™ DC UPS for Mission Critical Applications

The New No-Break ™ DC UPS SR750HI 750W is designed to provide DC power to lead-acid batteries for critical backup applications from 12V to 48VDC. The No-Break ™ range of DC UPS systems maximise the integrity of standby battery installations, whilst optimising the life and availability of backup batteries. 

A built-in Low Voltage Disconnect (LVD) will protect the battery from over-discharge after extended periods of backup operation when AC power has failed. The standalone unit comes with a standard remote battery temperature sensor (1.7m lead) for accurate charge voltage compensation.

Our range of SRHI DC UPS 100W-750W models have relay alarms for monitoring battery status, mains, PSU failure parameters and activation of BCT (battery condition test). The new SR500HI & SR750HI models have improved their thermal reliability with two fans relocated to dissipate heat more effectively and increase life span of critical components such as capacitors, shunts, and transformers.

The unit comes with a standard input voltage of 180-264VAC but it can be easily customised to 88-132VAC for the American market. It can also be used as a DC-DC converter, for more information about this application please contact our team of engineers at


  • American Input Voltage 110 VAC ( 88 – 135 VAC)
  • Communication Port
    •  RS232 (ASCII)
    • RS485  (ASCII)
    • SNMP, webpages
  • Digital Input/Outputs: Customizable 2 digital inputs & 1 digital output
  • Internal meter
  • Battery Condition Test : Option auto test enabled on start-up
  • Mounting: 19″ Rack Mount with V/I meter available, Wall mount
  • N+1 redundancy
  • Boost Charger
  • Conformal Coating for harsh environments
  • DC Connectors:
    • Anderson plug-in style connectors

Main Features

DC Power Supply Manufactures - DC UPS
  • Separate outputs for load and battery
  • Battery detection—regular battery presence and battery circuit integrity checks
  • Ability to view power supply data remotely
  • Automatic or manually initiated battery condition testing to ensure availability of standby power
  • Battery Condition Test : Indicative test of battery autonomy at predetermined intervals (automated battery condition check, ideal for remote sites).
  • Standard remote battery temperature sensor for accurate charge voltage compensation
  • Battery deep discharge protection
  • Adjustable load
  • Power loss & battery system alarms
  • No transition switching to backup battery
  • Rugged design and construction for long life and challenging environments
  • Thermal reliability improved by using double fan cooling system
  • Serviced in New Zealand: Our highly qualified service engineers perform repairs down to component level meaning expensive total replacement costs can, in most situations, be avoided.

The No-Break ™ system is the ideal solution for:

  • Critical infrastructure systems from 100W to 750W (and above using parallel operation)
  • Applications requiring continuous on-line monitoring of battery and charger status
  • Providing cost-effective management of your battery system investment
  • Harsh environments and remote applications


  • Security Systems – Access Control
  • Industrial Processes Switching Protection
  • SCADA & Automation
  • Radio Repeaters – Remote Sites


ModelOutput (V)PSU Rated (A)Charge Limit (A)*1Recommended Load (A)Peak Load on Power Fail (A)

*Default is 100% PSU rated (A), can be customizable



Output power750W
Input Voltage180V-264VAC
88V-132VAC (on-request)
Output Voltages12V, 24V, 30V, 36V, 48V
Voltage Adj. Range85% – 120% of Vout
Fusing/ProtectionInput fuse and varistor
Battery fuse plus ECB for battery circuit
Overcurrent protectionConstant current limit under overload and short circuit conditions
IsolationInput – earth – 2.5KVdc
Output – earth – 500Vdc
Efficiency> 85%
Operating temperature-20  to 50 °C ambient at full load
OVPOver-voltage protection on output at ~130% of nominal output voltage
Humidity0 – 95% relative humidity non – condensing
CoolingFan cooled ( 2 fans)
LED IndicationGreen: Batt OK
Green: Power OK
Flash code for
Alarms RelayForm C contacts
30VDC,2A/110VDC,0.3A,125VAC, 0.5A
AUX (Activated by BCT, Fan fail/stall (toggle every 5 sec))
POWER (main fails, PSU fails)
BATTERY (batt missing , batt low, BCT fail)
Temp. CompensationTemperature sensor on 1.7m lead with adhesive pad: -4mV/ °C / cell ± 10% (customizable)
Battery Charge Current LimitCustomizable on request.
Battery MonitoringDetects for presence of battery on start up, then every 60 minutes when charge current < 200mA
Battery Circuit ProtectionElectronic circuit breaker (ECB) operates under the following conditions:
Low Battery Volts: Battery Voltage drops to 1.67V/cell
Overload: Max load must not exceed 110% of rated current. Peak loads must be connected to B+ & B– terminals. Not suitable for N+1 connection
Short Circuit:  <2ms, backed up by fuse


Optional Input Voltage88 – 132 VAC
Communication Port· RS232 (ASCII)
· RS485 (ASCII)
· Modbus RTU
· SNMP, Webpages
Digital Inputs/OutputsDigital Input (pins 1,2) / Input or Output (pin 3) / Return (pin 4)
Battery Condition Test (BCT)Option auto test enabled on start-up
Mounting· Standalone
· 19”Rack Mount . Optional V/I meter for subrack : SR-Meter
· Wall – Floor Mount Cabinet
Internal MeterInternal V/I meter displaying PSU and battery operating states and analogue
N+1 RedundancyUsing 2 charges each & output diodes
Boost ChargerCustomizable feature on request for boost charging capabilities
Conformal CoatingFor harsh environments
Temp. CompensationCustomizable temperature sensor length and voltage/DegC/cell


Item CodeDescriptionNew Model
SR750C12TFSLSystem No-Break DC UPS 12V 750WSR750HI12TFSL
SR750C12TFSUSys No-Break DC UPS110Vac>13.8Vdc 750WIt will be given a custom model number using the SR750HI
SR750C24FXLSys No-Break DC UPS 24Vdc 750W alarms, no tempco, 2 x 4way Phoenix conns,SR750HI24TFXL
SR750C24TFSLCharger DC UPS 24V 750W alarms, tempco, LVDSR750HI24TFSL
SR750C24TFSUSys No-Break 110VAC 24V 750WIt will be given a custom model number using the SR750HI
SR750C24TFXLSys No-Break DC UPS 24Vdc 750W alarms, tempco, 2 x 4way Phoenix conns,SR750HI24TFXL
SR750C24TFXL-01System No-Break  24V 750W (Phoenix connectors) Special micro manual boostIt will be given a custom model number using the SR750HI
SR750C24TFXUSys No-Break 24Vdc 750W 110Vac input (2 x 4way Phoenix conns)It will be given a custom model number using the SR750HI
SR750C30TFSLSystem No-Break 34.5V 750WSR750HI30TFSL
SR750C30TFXLSystem No-Break 34.5V 750WSR750HI30TFXL
SR750C48TFSLSystem No-Break 48V 750WSR750HI48TFSL
SR750C48TFXLSys No-Break DC UPS 48V 750WSR750HI48TFXL
SR750I12TFSL485Sys No Break 12V 750W FAN RS485 Comms InterfaceSR750HI12TFSL-485
SR750I24TFSL-LAN+No-Break DC charger 24V 750W with ethernetSR750HI24TFSL-LAN+
SR750I48TFSL-LAN+Sys No-Break DC 48V 750W with ethernet/SNMPSR750HI48TFSL-LAN+
SR750I48TFSL485Sys No Break 48V 750W FAN RS485 Comms InterfaceSR750HI48TFSL-485
SR750I48TFXL-485Sys No Break 48V 750W FAN RS485 Comms InterfaceSR750HI48TFXL-485
SR750I24TFSL485No-Break DC charger 24V 750W with RS485 communication portSR750HI24TFSL-485
SR750I48TFXL-LAN+Sys No-Break DC 48V 750W with ethernet/SNMPSR750HI48TFXL-LAN+
SR750I12TFSL-LAN+Charger -DC UPS 13.8VDC 750W with ethernet/SR750HI12TFSL-LAN+


SR – SRH Series – Downloads


  •  Why is Helios Power Solutions SR No-Break ; DC charger recommended by consultants for critical applications?

Our No-Break ™ DC chargers have been designed for industrial use and have over twenty years of proven reliable operations.  In addition, the chargers have many outstanding features such as fault alarms, LED fault alarm codes, battery detection, low voltage disconnect circuitry, automatic battery condition testing, communication options and can be connected to the battery permanently due to the precise temperature-compensated voltage control.

  • Why should we use a SR No-Break; as opposed to a normal float charger?

The No-Break ™ DC UPS  has many features which a normal float charger does not, these including:

    • Precise alarm indication for mains or DC faults
    • Overcurrent protection on the battery circuit
    • Battery presence checking
    • Temperature-compensated charging
    • Low voltage disconnect circuitry to prevent deep discharge of the battery
    • Independent charge current limit
    • Automatic battery condition testing
  • Can I use the SR No-Break DC UPS without a battery?

No, the No-Break ™DC UPS is designed to operate with a battery connected and instability may result if there is no battery connected.  If you wanted to do this then it is advisable to use a standard two-terminal DC power supply SR500HL

  • Why is the battery negative separate from the load negative in the SR No-Break DC UPS?

This is done to implement two of the features of the No-Break ™ UPS/charger.  There is an “electronic circuit breaker” fitted between the battery negative and load negative terminals to provide the battery overcurrent protection.  The separate battery circuit also allows for independent control of the charging current when required.

  • Can I connect the battery directly to the load terminals when using SR No-Break DC UPS?

No, it would nullify all the features of using the No-Break ™DC design and provide false alarm signals from the relays.  If you wanted to do this, then it is advisable to use a standard two-terminal float charger, with or without alarms.

  • When does the SR No-Break system disconnect to protect deep discharge of the battery?

At approximately 1.67 volts per 2V (nominal) cell, so for a 12V system the disconnect voltage is set at 10V.



Helios Power Solutions  has been manufacturing the SR No-Break Series (100W-750 DC UPS) for more than 40 years in Auckland – New Zealand. The No-Break ™ DC  UPS series has evolved with new technologies and most important, our customer’s feedback.

All the functionality and durability has been retained with a more modern and easier to understand range of products being developed.

Form factor and connectivity remains the same, so they will fit into the slots occupied by the old range – the legend continues!

Case Study

No Break DC UPS installed in Mount Climie to backup critical radio equipment under freezing conditions.


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