AC inverters

see also:

• 12V batteries and battery boxes
• cooking options when camping
• photography and camping main index page

• if you wish to use 240V appliances whilst camping off-grid on unpowered sites, you will need a AC inverter as well as a battery power source
• some power “stations” come with an AC inverter as well as a battery and charger
• if you only have a battery +/- battery box, you will need an inverter if you wish to run 240V appliances
• inverters should be well ventilated and wiring should be heavy gauge to manage the high DC input current

• in general, a pure sine wave inverter is a safer option for computer and other electronic appliances but they are more expensive
• pure sine wave inverters:
  • more efficient - usually 90% compared with 70-80% for modified sine wave
  • compatible with all electronics and much less interference and buzzing with audio
  • extends appliance life by providing more stable power
  • better performance with inductive loads like microwaves and air conditioners
• modified sine wave inverters:
  • usually use a square wave instead of a sine wave
  • may damage sensitive electronics including computers
  • tends to cause interference and buzzing with audio
  • can cause issues with variable speed power tools and some medical equipment such as CPAP devices
  • less efficient with inductive loads, potentially consuming up to 30% more power
  • use only with basic, less sensitive appliances

• the more powerful the inverter, the more expensive, heavy (~1kg per 500W max power) and bulky it is
• when doing calculations, be mindful that inverters are not 100% efficient and they do lose some power through heat loss and fan
• maximum continuous power is reduced as temperature increases - can almost drop to a half if the inverter hits 65degC compared to standard 25degC
• also they will consume power even in zero load - this tends to be ~12W for a 1000W inverter and 20-30W for a 2400W inverter
• industrial quality inverters such as those from Victron will be much larger and weigh 10-30kg depending upon power (1000-4000W respectively)
• running high current draw appliances will also drain your battery fast and your battery needs to be able to be capable of these high discharge rates
• the rating for AC inverters is for their max. continuous current at 25degC, most allow a brief surge current of twice this

• induction cook top
  • a single cook top could potentially cook a steak or most meals using about 500-600W and would need at least a 1000W inverter (preferably 1500W)
  • most are rated at around 1200W but could be run at a lower output such as 500W if you don't have a more powerful inverter
• microwave ovens
  • these generally run at 1000-1200W on full power so you would need a 1500W-2000W inverter
• air conditioners for a caravan
  • two main sizings:
    • 2 to 2.5 kw (suitable for vans up to 5 metres in length)
    • 3kw plus (suitable for vans up to 7 metres in length)
  • you will probably need to run a petrol generator for prolonged use on hot days

• NB. a standard Anderson plus is only rated at 50A (ie. 600W) so you will generally be directly wiring the AC inverter to the battery terminals using a heavy duty cable
• many of these are rated only for working temperatures between 0-40degC
• pure sine wave inverters are generally 90% efficient (expensive, heavy industrial ones such as Victron tend to be 94% efficient)
• some have remote controls to turn on/off
• some have UPS function with a brief Battery Supply & AC Main Transfer Time of < 50msec and a 240V AC input so the inverter only kicks in when the AC input ceases
  • eg. Renogy 1000W 12V to 230V/240V Pure Sine Wave Inverter (with UPS Function) $AU242
• they generally have protections such as:
  • Low Voltage Shutdown: 10VDC
  • High Voltage Shutdown: 16.3VDC
• higher power ones generally have two AC outlets while lower output ones usually only have one AC outlet

• these combine an AC inverter and a lithium or lead battery charger
• examples:
  • Renogy 2000W 12V Pure Sine Wave Inverter Charger w/ LCD
    • 510 x 285 x 193 mm; 23.2kg; $AU835
    • not sure the advantage of such a unit given the size, weight and price.

• a LiFePO4 battery is recommended as it can drain to zero without damage as would occur with lead acid batteries (plus they are much lighter, allow greater discharge rates and last longer)
• running an induction cooktop at 600W to cook a steak is likely to require ~10 minutes at 600W (2 minutes to achieve 240degC) which equates to at least 10Ah of a 12V battery consumed (600W at 12V = 1Ah per minute)
• most would supplement the battery with solar charging or a petrol generator