Wednesday, Aug 18, 2021 at 08:54
Hi Bob,
Firstly let me state that I am not an Auto. elec. or a 12 volt expert, just someone who has been camping in both tent and caravans for more than 50 years.
If you a seriously looking at Off
Grid camping, forget about heaters, electric blankets and most other electrical appliances, they just draw too much power from batteries. Yes you can get your vehicle set up with enough batteries and charging capacity, but it will be very expensive.
You can get 12 volt kettles, but they take a very long time to boil, better off using an LPG stove. As for electric blankets, a good sleeping bag with the appropriate rating and a good “thermal” blanket should be sufficient for most people. Even high country campers in the snow do not use electric blankets. However, if you must, you need to consider the continuous power consumption on your
battery.
As for sizing your
battery and charging system, you need to look at all the electrical appliances that you want to run, and total up their power consumption in amps, and the number of hours you want to run them, this will help you decide how large a
battery/batteries you will need. You state that you have not yet got a 12 volt fridge, when sizing your
battery system, it would be prudent to factor the fridge into your equation so that you do not have to add additional batteries later on. IMHO, Lithium Iron Phosphate (LiFePo4) batteries with the appropriate charging system is the way to go. They are lighter, can discharge to a deeper State of Charge (SOC) without affecting their longevity, and will recharge faster with the appropriate charger.
Next as for charging these batteries, a good rule of thumb is that for every
battery Amp, you need double the watts of solar capacity. That is, for 100 AmpHr of batteries, you need 200 watts of solar capacity. Of course, solar only works during the day, and for maximum efficiency, in full sun at the appropriate angle to the sun.
A good DC/DC charger with a high amperage output (greater than 30 amps) and solar controller should keep your batteries topped up from your car or sun. You need to remember that your charging system needs to be large enough to top up your batteries while they are still discharging.
You have not indicated if you have a ute with a canopy set up, or a wagon, or a
sedan. Depending on your vehicle, this may limit what size
battery system you can install. An 80 Ltr. compressor fridge/freezer will draw around 4 amps per hour when cycling. So if you factor that the fridge will cycle for about 16 hours per day, depending on ambient conditions and how often you open it, 16 x 4 = 44 amps per day. Worst case scenario if the fridge was to cycle continuously, that would equate to 96 amps for 24 hours. So, you would need at least a100 AmpHr
battery just for the fridge, without anything else running. These numbers will vary depending upon a number of different factors. Size and make of fridge, ambient conditions, enclosed space etc.
In the back of my wagon, I have a 60 Ltr Engel fridge, with a 40 amp DC/DC charger and a 100 AmpHr LiFePo4
battery. I carry a 290 watt folding solar blanket for when I am stationary. In my caravan, I have a 190 Ltr compressor fridge, 200 AmpHr of LiFePo4 batteries with 390 watts of fixed roof mounted solar panels. I mainly
camp off
grid, sometimes sitting stationary for several weeks at a time.
I hope this info has been helpful.
EDIT, I do not have an inverter. I have just read Allans response and
John’s blog. Very good info there.
Macca.
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