Bunk Ledger markBunk Ledger

Free tool

Sleeper Cab Power Planner

Add a night of cab loads, from a 12V fridge to a CPAP, and see whether the battery and inverter cover the hours the engine is off.

Bunk Ledger editors

Each load has its own hours. The engine-off box is a reminder of the break. It does not override the load hours.

DC. Dometic lab average is the default.

CPAP feed

Inverter. 65 W is a planning figure.

DC. About 10 W at 12 V.

DC. 1 A is a planning figure.

DC. About 15 W at 12 V.

Inverter. Off unless you check it. 900 W is a planning figure.

Battery voltage

The result is read-only. Change the inputs, or start over.

How this night is added up

Each 12 V load is current times hours. Multiply by the system voltage and you have watt-hours taken straight from the battery. A 24 V selection halves the 12 V current, on the assumption the device uses the same power. Confirm that in the manual.

Each inverter load is watts times hours, then divided by efficiency, because the inverter wastes some of the battery as heat. Add the 12 V watt-hours and the inverter watt-hours. That is the night you typed. Compare it with amp-hours × voltage × the depth of discharge you picked.

If the battery has energy left, the page calls it a surplus. If the night is larger, it calls it a shortfall and looks for the next battery size on a short list: 100, 200, 300, 400, 600 Ah. The inverter suggestion uses only the AC loads, at 125% of their watts added together, because those loads can be on at the same time. A 12 V fridge does not size the inverter.

The single-job versions of the same math are the inverter runtime calculator and the fridge overnight calculator. Related notes: 12V fridges, inverters, CPAP in a sleeper, and shore power.