Backup power explainers
Inverter Efficiency and Backup Power Runtime
Inverter efficiency explains why a battery with 1000Wh on the label may not deliver 1000Wh to AC devices. Every conversion from battery DC to household AC uses some energy, and the inverter may consume power even when connected loads are small.
Comparison
AC inverter output
Best for: Household plug-in devices and appliances.
Tradeoff: Conversion losses and idle draw reduce available runtime.
DC output
Best for: USB-C, 12V fridges, routers with compatible DC adapters, and LED lighting.
Tradeoff: Requires correct voltage and connector compatibility.
Scheduled inverter use
Best for: Running AC only when needed to save stored energy.
Tradeoff: More manual management during an outage.
Sizing example
A 50 W load for 12 hours points to about 750-900 Wh before adding reserve and real-world losses.
A 50W AC load for 12 hours needs 600 Wh before losses. A larger capacity target accounts for inverter efficiency, idle draw, and reserve.
Decision checklist
- Identify which loads truly need AC power.
- Use DC outputs for compatible low-voltage devices when practical.
- Include inverter idle draw for small overnight loads.
- Avoid oversizing an inverter far beyond the load without checking idle consumption.
- Keep a reserve for startup surges and unplanned devices.
Planning notes
- Inverter efficiency is often highest at moderate loads, not tiny loads.
- A large inverter running a small router can waste meaningful energy overnight.
- Some power stations let users turn AC outlets off while USB or DC stays on.
- Efficiency assumptions should be conservative for outage planning.
Safety and limits
- Stay within continuous and surge ratings.
- Do not cover inverter vents or cooling fans.
- Use appliances with intact plugs and cords.
- Avoid running heat-producing loads unattended from portable backup equipment.
FAQ
What inverter efficiency should I assume?
For rough planning, many users assume about 80% to 90% usable efficiency for AC loads, with extra caution for very small loads or long runtimes.
Is DC power more efficient than AC?
Often yes, because it can avoid a DC-to-AC conversion. The device still needs the correct voltage and safe connector setup.
What is inverter idle draw?
Idle draw is the power the inverter uses just to stay on, even before the connected device load is counted.