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cooking with excess electrical power

Cooking and heating water with electricity off-grid is usually impractical but there are exceptions. In some cases the relatively large power loads can be used without affecting house battery1) state of charge:

  • while driving2) the alternator makes a great deal of excess power. Class C RV owners often run a crock-pot while driving from site to site.
  • if a generator is being run to charge batteries cooking loads can be added
  • with lead-chemistry batteries, later in the day excess solar power is available. The actual amount of excess power will depend on what your panels+controller can put out
  • with lithium batteries, power can be consumed at any time since Li doesn't need to reach full charge.


In general DC power3) is used for warming or very slow cooking. Part of this is due to the limits of cigarette lighter outputs, typically 120w (10A x 12v). The “catch-22” is that most people don't drive their vehicle sufficient hours to do real cooking off DC.

Higher power is common with AC devices but one must have the power to run it, and to recharge the battery bank afterwards.


  • immersion (loop) heaters for DC are typically 150w. Example: RoadPro beverage heater (138w). Caveats:
    • heat only water with them; anything else baked on is extremely difficult to clean off the coils
    • carry extra fuses in case you blow the ciggy port fuse. Know where the fuses go.
    • babysit the heater while in use - if the container falls over or the heater otherwise slips out it can cause a fire.
    • unplug before removal from water to avoid overheating the element
    • have a safe place planned to set them down before heating; they will be very hot and can melt/burn surfaces after removal from the water
  • heated lunchboxes/warmers are large enough to hold hot lunches. They are typically better suited to warming precooked meals rather than cooking from scratch. They come in “lunchbox” and “suitcase” styles.
    • lunchbox - hard exterior, typically better insulated tops and higher power.
    • suitcase - soft exterior, often lightly-insulated tops and lower heating power.
  • crockpot/slow cooker typically require many hours of cooking.
  • 12v rice cookers consume about 100w. Example: Onezili recommended by Americano-with-cream
  • heated mugs can be used to keep beverages hot, or heat small amounts of water for tea, coffee. Warm canned soup, etc. Example: Wagan heated mug (12v/24w).
  • mini rice cookers. Example: mini rice cooker (12v/100w). Recommended by dannydevitosmgnmdong. See also /r/urbancarlivingcooking.

AC (inverter)

Analog cooking appliances (knobs, not electronics) run fine off inexpensive MSW inverters.

crockpot vs instant pot

There are some major ways the two differ:

  • cost - used crockpots are cheap in thrift stores
  • current - crockpots demand much less current, which may also increase the cost of wiring, batteries, and inverter, but…
  • energy use - instant pots will generally use far fewer watt-hours to took the same meal5)

also see this post

breaking the 10A barrier


Power/time saving

  • Preheating water on the dash or elsewhere
  • heating only the required amount of water
  • reducing power level after reaching a boils (ie, reduce power to simmer)
  • covering pots while heating
  • pre-soaking beans (overnight) rice (up to an hour), etc


  • use parchment paper, foil to line crocks
  • lightly oil crocks before cooking to reduce sticking
  • immersion heaters might best be used for heating plain water, as the loops can be difficult to clean


or starter battery
not idling
chassis power
new old stock
due to better insulation, temperature control, and pressure cooking
food/cooking/excess_power.txt · Last modified: 2023/05/07 18:25 by frater_secessus