How this is worked out
- Camera load is cameras × current per camera × supply voltage. A 12 V dome with IR on draws about 0.5 A; without IR, about half that.
- A safety margin is added to the SMPS so it is not run at its limit — 1.25 is the usual allowance, and it covers the surge when IR cuts in at dusk.
- The UPS VA rating is the watts divided by the power factor. Indian inverter-type UPS units are usually quoted around 0.6–0.7.
- Battery Ah = watts × backup hours ÷ (battery volts × inverter efficiency). The efficiency allows for what the inverter itself wastes.
- Allow for the recorder, the switch and the monitor if they also have to stay up. A monitor is often the biggest single load — leave it out if nobody watches during a power cut.
An estimate for planning, not a design document. Site conditions change the answer — send it to us and we will confirm it free of charge.