What stays on when the power goes out

Inverters, batteries and wiring diagrams — with real specs, schematics and consumption figures. From a 10 W router to a 12 kW house.

Find your system Plan the panels All articles

How a backup power system works

The grid powers the house directly, and the inverter sends spare capacity into the battery.

Incoming 3.4 kW

To house 1.8 kW

Battery 72 %

Runtime 8 h

Start from your own situation

Inverter power and battery capacity follow the load, not the other way around. Find the row closest to yours.

3–12 kW Detached house Well pump, boiler, fridge, sometimes an electric stove. A 48 V hybrid inverter with headroom for solar panels is the most common choice. Hybrid inverters

0.05–0.5 kW Apartment, bare minimum Router, lights, laptop, chargers. A mini battery and a small UPS are enough — you can build it yourself in an evening. Mini batteries and UPS

1–3 kW Whole apartment Fridge, internet, lighting, TV. A low-voltage 12–48 V system with an inverter up to 3 kW. 12–48 V systems

15–100 kW Workshop, business Three-phase load and machinery. High-voltage 48–800 V packs, where cable losses and protection matter. 48–800 V systems

How a lithium iron phosphate battery charges

LiFePO4 charging runs in sequence, and each stage takes a different amount of time — which is why “charged in an hour” and “fully charged” are not the same thing.

1
Constant current

The charger holds a set current while cell voltage rises on its own. This is where most of the capacity is gained — roughly up to 90%.

0 → 90%most of the time
2
Constant voltage

Voltage is held near 3.55–3.65 V per cell and the current tapers off. This stage collects the remainder, but noticeably slower than the first.

90 → 100%current tapers
3
Balancing

The BMS evens the cells out against each other. Skipping it is costly: cells that drift apart in voltage eat into the capacity of the whole pack.

BMS at workhours

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