I am looking for a simple system to detect power outage and disconnect heavy loads from the UPS backup to maximize the longevity of the power backup.

The UPS works on a 24-V battery. The UPS switch over time is <15ms

UPS and main output voltages are 230V

Is there an off the shelf device that I can use to achieve this?

Any circuit diagrams of such a system will be helpful

Thanks in advance.

  • 7
    \$\begingroup\$ If those devices needn't be protected from power outage, why are they connected to the UPS in the first place? \$\endgroup\$
    – AJN
    Sep 12, 2020 at 2:10
  • 2
    \$\begingroup\$ UPS does not have a switch over time, this sounds like an SPS a Standby Power Supply. Many of these will have an output, like RS232 or USB, to signal to devices to shut down cleanly as there is only 20 minutes remaing as the main power source has failed. \$\endgroup\$
    – Solar Mike
    Sep 12, 2020 at 3:03
  • \$\begingroup\$ @ajn the wiring is common. (No multiple sections) \$\endgroup\$ Sep 12, 2020 at 4:14

1 Answer 1


The ideal solution would be to delink those loads from the inverter circuit. Should that be a problem, a contactor or relay, energised by the utility supply, could be used to delink them when the utility supply fails.

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In any case, it would not be possible to avoid rewiring.


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