Those of us who live in mobile dwellings are as entitled to all the conveniences of home appliances as anyone who lives in a bricks and mortar home. If I read another example of someone lecturing along the lines of "if you need a (insert appliance), you shouldn't be on the road," I'll hunt them down and demonstrate exactly how one inserts an appliance, namely a stick blender.
In saying that, at the end of the day, we must realise the extent of our limitations in terms of electrical power, when living off grid.
The kettle and toaster question comes up perpetually in groups and forums. It's like a revolving door. The average kettle consumes 1,800W, as much as many air conditioners, yet people are always asking if there are 12v versions available. The same goes for toasters.
Anything designed to generate a lot of heat over a short period of time, is always going to consume a hell of a lot of power. That power needs to come from somewhere. In off grid 12v systems that's always going to be the battery bank.
In every identical online thread, some genius always comes up with the same solution to running powerful appliances off grid! "Get an inverter."
Whilst inverters do indeed convert 12v DC to 240v AC power, they don't pluck power from out of thin air. It still has to come from the battery.
Let's refer back to Ohm's Power Law and do some simple sums.
I (Current in Amps) = P (Power in Watts) / E (Electromotive force in Volts)
In the case of an average kettle: 1,800W / 12v = 150A
Yes! The kettle would draw 150 Amps from your 12v supply.
Now let's throw an inverter into the equation. The general rule of thumb is to substitute the value of 12 representing EMF in volts, with 10, in order to allow for typical inverter inefficiency. This of course varies slightly between inverters, but it gives us a very good estimation.
The equation therefor becomes 1,800W / 10 = 180A
That's huge! That means that a kettle could drain a 180 Amp hour battery in 1 hour. Take into consideration that most deep cycle batteries should only be discharged to 50% depth. it would actually discharge a 180Ah battery to a point of being unusable, in 30 minutes.
The kettle and inverter would in fact be consuming 3Ah per minute. That means it would discharge a 100Ah battery to the recommended safe Depth of Discharge in 17 minutes.
A combined ten minutes of boiling a 1,800W kettle each day, would consume a whopping 30 Amp hours from a battery bank.
Using an electric kettle or toaster would require a significant battery bank, a fair sized solar array and a very powerful inverter. That's one hell of an expense when one considers how easy it is to put a kettle on a gas ring or a couple of slices of bread under a gas grill.
Back to inverters. Inverters supply potentially lethal 240v AC electricity from a 12v system that isn't earthed. In the case of caravans and RVs, inside a metal box. There are a lot of cheap Chinese OEM manufactured inverters for sale on ebay, but would you want trust your life and the lives of your family members to one. An el cheapo 2,000W inverter could cost as little as $300 from ebay, but if you want something that offers trusted safety features and reliable power, you're looking at more like $2,000! Throw in extra solar panels and an extra 100Ah in your battery bank, we're talking about a bloody expensive cup of tea!
It's probably important to note here that good quality inverters in the 600W to 1,000W range, are significantly more affordable than a 2,000W plus inverter. Using appliances that consume under 1,000W is significantly more manageable and affordable. However one must still pay close attention to power consumption and recharging.
But wait there's more!!!! No, there's no steak knives.
The serious current draw takes place between the inverter and the battery. Just yesterday, someone asked in a camping group, how they might power their 1,000W blender, off grid. What was the first suggestion posted as a reply? "Get an inverter and plug it into your cigarette lighter!"
Thankfully, if someone did attempt something so insane, chances are the car cigarette lighter fuse would shit itself instantly and prevent a potential fire. But be aware! I have known blade fuses to melt and fuse 'in contact!' That means there's something very wrong in the circuit, but instead of breaking that circuit, the fuse literally fuses together. It's not common, but it happens.
An inverter that consumes significant power, requires cables with a significant internal surface area between the battery and the inverter, even if the cable run is very short. That connection also requires a breaker that's able to handle the current that the inverter draws. That's quite a breaker and they don't come cheap. Without the correct cable gauge and a breaker, the cable between the battery and the inverter will very quickly melt down and start a fire.
So the moral of the story is, if you want to power an appliance that consumes a lot of power, you're going to need to have a lot of power available in order to power it. Inverters don't just suck power out of thin air. Quite the contrary. They draw current from your battery. The bigger the appliance, the bigger the inverter you'll require. The bigger the inverter, the more it'll cost and the the bigger the battery bank that you'll require. The bigger the battery bank, the bigger the solar array required to charge it.
Whilst most things are possible; do you really want to spend in excess of $2,500 on a heavy, space inefficient 12v setup, in order to avoid sticking a kettle on a gas stove or some bread under the grill?
Everyone is entitled to have whatever appliances they want, but everyone must also ensure that said appliances comply to the laws of physics and don't burn down their car, caravan or motorhome.
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