UPS for Security Cameras, NVRs and DVRs: Keep Recording When the Power Is Cut

The point of a UPS on a camera system

Most equipment goes on a UPS so it can ride through a flicker or shut down cleanly. A camera system has a different job: keep recording while the power is out. An outage is exactly when the system is most likely to matter, whether that is a storm when nobody is home or an intruder who flips the main breaker or cuts the service drop before entering. A system that goes dark with the lights records nothing useful.

That changes the design target. A computer UPS is judged by whether it can hold the load for 5 to 15 minutes. A camera UPS is judged by how many hours of recording it delivers at night, when the cameras draw the most.

Map what has to stay powered

Camera systems come in four broad shapes, and each has a different backup list.

Cameras scattered around a building on Wi-Fi with individual adapters are the hardest to back up, because each outlet would need its own UPS. A wired PoE system is the easiest: one switch, one UPS, every camera covered.

What the equipment draws

PoE cameras

A typical fixed dome or bullet camera draws roughly 4 to 8 W in daylight. At night, infrared LEDs switch on and add about 1 to 3 W, sometimes more for long-range IR. White-light "color night" cameras with spotlights, PTZ cameras with motors, and outdoor units with heaters or blowers can draw 15 to 60 W or more and may need 802.3at or 802.3bt ports. Use the manufacturer's maximum power figure for the camera when budgeting, then measure.

The PoE switch (or the PoE ports built into the NVR) adds its own base load plus conversion losses, often 10 to 15% of the PoE power it delivers.

NVRs and DVRs

A small 4 or 8 channel recorder with one or two hard drives typically draws 15 to 40 W running, excluding PoE. Each 3.5-inch hard drive can draw roughly 20 to 25 W for a few seconds while it spins up, so a four-drive recorder briefly pulls noticeably more at power-on. That surge matters when the system restarts after an outage, not while it is running on battery.

Analog systems

Analog and HD-analog cameras usually run on 12 V DC from a central supply or distribution box, about 2 to 6 W each with IR. Put that supply on the UPS along with the DVR. If cameras use individual plug-in adapters spread around the house, the cameras far from the UPS will go dark.

Worked example: 8 PoE cameras, NVR and remote alerts

An 8-camera system, measured at night:

Goal: two hours of recording with alerts.

With about 90% inverter efficiency, the battery must supply 256 / 0.9 = 284 Wh. Lead-acid batteries discharged over about two hours typically deliver around 80% of their rated capacity, so the nominal battery needed is roughly 284 / 0.8 = 356 Wh.

A typical 1500 VA tower with two 12 V 9 Ah batteries has 2 x 12 x 9 = 216 Wh nominal:

To reach two hours you need a model that accepts an external battery pack, or a larger UPS with more internal battery. The inverter rating is not the constraint here: 128 W is under 15% of a 900 W unit. You are buying battery, not watts. Try different targets in the runtime calculator.

Stretching the same battery

• Prioritize cameras. If the PoE switch allows per-port power control or scheduling, you can script turning off low-value cameras on battery. Keeping the 4 cameras covering entrances (about 31 W with losses) instead of 8 cuts the load to about 96 W and stretches runtime to roughly 216 x 0.8 x 0.9 / 96 = 1.6 hours.
• Lower recording settings. This saves storage, not much power. Camera draw depends mostly on the sensor, encoder and IR, not bitrate.
• Separate the internet gear. A DC mini UPS on the modem and router frees the main battery for recording (see UPS for modem and router).

Setup and recording integrity

1. Put everything on battery outlets. Surge-only outlets on consumer units do nothing in an outage.
2. Hide and secure the UPS with the recorder. A locked cabinet or a closet away from the electrical panel. An intruder who finds the NVR can take the footage with it, so enable cloud or off-site clip backup if your system supports it.
3. Configure shutdown, if the recorder supports it. Some NVRs and video management software can receive a UPS signal (USB, or network tools such as NUT) and shut down cleanly near the end of runtime; many consumer NVRs cannot. If yours cannot, the UPS's low-battery cutoff will drop power abruptly, which risks losing the clip being written. That is still far better than losing power at minute zero.
4. Set up power alerts. A camera system that emails you when it goes on battery tells you something is wrong at the property. Some NVRs alert on camera loss; the UPS's own software or Home Assistant monitoring can alert on the power event itself.
5. Test at night. Switch off the breaker, confirm every camera keeps recording and that you receive alerts, then check the footage covers the gap.

Common mistakes

• Backing up the NVR but not the PoE switch, or the DVR but not the 12 V camera supply. The recorder records black screens.
• Sizing from the daytime reading and discovering at night that runtime is shorter.
• Treating PoE budget as consumption. A 120 W budget switch feeding six 5 W cameras is drawing around 35 to 45 W, not 120 W.
• Placing the UPS in a hot garage or attic. Heat shortens lead-acid battery life sharply; a battery rated for several years at 77°F (25°C) may last far less in a space that regularly reaches 95°F (35°C) or more. See UPS battery lifespan.
• Never replacing the battery. The system will report everything fine until the outage reveals 10 minutes of runtime where you expected an hour.

When a UPS is the wrong tool

For a handful of cameras at a remote site that loses power for days, a UPS is the wrong tool. A 12 V or 24 V lithium battery system with solar charging, feeding a DC PoE injector or a low-power recorder, avoids the inverter overhead and can run for days. For a home with only battery cameras, skip the big UPS and put a small one (or a DC mini UPS) on the hub and router. And for commercial intrusion alarms, the alarm panel has its own standby battery requirements set by codes and standards such as NFPA 72 and NFPA 731 and the monitoring company; do not substitute a UPS for the panel's specified battery.