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Camper Trailer Electrics

If you mostly stay in Caravan Parks and have access to 240 V mains power, separate trailer electrics is not really necessary. If you do not have access to mains power but are willing to run your appliances on LPG, gasoline or kerosene and don't really use laptops, printers or DVDs for your entertainment, you can get by without electrics. However, if you want to make your life in the bush a bit easier and have more comforts of home with you, proper and efficient 12 V electrics is the way to go. You can run a 12 V fridge and have LED lights inside the trailer and in the annex area. With the right set up the kids can watch a DVD ever so often and you can run your laptop to keep up with emails allowing you to stay just a little bit longer or go away a bit more often.

In the higher end of the market most trailers are equipped with some kind of electrics but often the charging issue in the bush is not really thought through. Great Aussie Campers offers basic trailers without electrics (not everybody wants it) and provides customised solutions which are just right for your personal usage.

In order to determine you needs, let's at first calculate your power consumption within a 24 hrs cycle. The biggest appliance you run will be the fridge. The bigger the fridge the more power it draws. How much it will draw all depends and there are no easy answers but let's come up with a pretty rough guide: For every liter of fridge capacity the fridge will draw about an AMP (perhaps minus 10 % to 20 %). We use the 38 l Engle 2 way fridge which according to the above formula would draw somewhere between 38 AMPs to 38 - 20 % = 30 AMPs in a day. A large 80 l fridge would then draw about 80 AMPs to 64 AMPs. The upper limit will apply in particularly hot climate at particularly low fridge temperatures; the lower limit will apply in moderate temperatures at standard 4 degrees Celcius Fridge temperature.

The next appliance everybody will run are lights. I would advise against Halogen lights and fluorescent lights as they draw a fair amount of power and would recommend LED lights. A decent quality 60 to 80 LED light will perhaps draw 0.3 AMPs per hour, pretty much negligeable. If you have lights on for three sets of LED lights on for let's say 4 hours a night on average, you'll draw 3 lights times 0.3 AMPs/hour times 4 hours = 4 AMPs in an evening. Not a lot.

The next appliance you may want to run is a laptop. Good for your emails and for the DVD for the kids. Let's say your laptop draws 75 W which is about 6 AMPs at 12 V. If you run the laptop for 2 hours a day, your emails and kids a DVD every second day, you'll use another 12 AMPs.

In our example we would use in a daily cycle let's say 30 AMPs for the fridge, 4 AMPs for the lights and 12 AMPs for the laptop which is a total usage of 46 AMPs per day. Add to this another 10 to 15 % for charging / discharging losses and you need around 50 AMPs in a day.

Your 100 AMPhour battery would thus last (theoretically) two days. After that, you would either have to find mains power, go home or rough it out.

However, we have quite a nice built in charger in the tow vehicle, the alternator. In a 4 WD, the alternator will pump out about 80 AMPs in an hour which is quite respectable. The most cost efficient way to harness this power is to run a hotwire from the alternative to the towbar of the tow vehicle. The hotwire finishes with a 50 AMP Anderson plug into which you plug in a battery. When driving the alternator will charge the starter battery in the front and the auxiliary battery in the back of the vehicle. In order to avoid draining the main starter battery you should consider putting an solenoid near the alternator. This device will cut off the flow to the back of the car if the main starter battery voltage drops below acceptable levels, perhaps somehwere near 12.2 V or so. You do not need to install a solenoid (cost somewhere between $ 100 and $ 200) if you remember not to forget to disconnect the auxiliary battery once stationary. If you forget, the starter battery will eventually drain and you will be unable to start the engine. (Given that you carry recovery gear and a jumber cable and have made friends at the campground and you like an adventure this is not necessarily a drama. All by yourself in the Outback it is.)

We suggest using sealed AGM (Absorbed Glass Matt) batteries in the back of your vehicle but not standard lead acid batteries. AGM batteries are more expensive but do not emit any toxic fumes. You can therefore leave the battery in the back of the car, connected to the Anderson Plug of the hotwire. The battery is then connected to the fridge and the fridge runs during transit and the auxiiliary battery is charged during transit. Alternatively, you have the battery (or a second battery) in the camper trailer, perhaps in the front tool box or in a battery box on the side steps of the trailer and this battery is also charged during transit. A battery MUST be ventilated, even if it is an AGM battery and even if it is sealed. If the battery is not ventilated it will heat up and eventually fail. Every battery manufacturer outlines that in their manuals but not every trailer manufacturer provides ventilation of the battery.

If you are mostly touring and have moderate power needs such as 50 AMPs/24 hrs, this quite simple set up could work very well. A AGM battery accepts about a third of the total rating as charge in an hour. A 100 AMPhour battery will just charge 33 AMPs in an hour of driving. Your 50 AMP daily power need will be recovered, in this example within 1.5 hours of driving. If you go for a larger, but heavier 150 AMPhour AGM battery, the battery will accept 50 AMPs in an hour driving so that moderate touring will replenish all the energy you have consumed the previous 24 hours. If you are camping in the bush you will most likely go to the beach, the pub, the shops or just cruising around to see the sites. Just put the battery in the back of the car (with the fridge), go for a drive and come back home with a fully charged battery.

If you do not want to use the car, in our example for at least 1 to 1.5 hours a day, but want to stay put, just go fishing and not move the car, this solution is not going to work. A generator is not really going to work either. A 1000 W generator pumps out about 4 AMPs at 240 V. You should always charge your batteries with a 240 V mains charger through a generator and not through the generator 12 V outlet as this outlet has unclean, spiking voltage which will eventually fry your battery. Pumping only 4 AMPs per hour into your battery will require 12 hours of continuous generator run to charge up your battery by 50 AMPs. Most people will find this unacceptable.

Te next best solution would be to use a petrol engine driven Christie Charger. They cost about $ 1000, run on a Honda 4 stroke engine and pump out 50 AMPs (100 AMPs versions are available, too.). Running the Christie for a good hour will charge your battery. Cost and size is about the same as a 1000 W quality generator but the Christie will do the job much faster.

But perhaps you are in a National Park and running petrol driven devices is not your sense of happiness (or that of the National Parks Ranger!). In this case you'll have to consider solar energy. The green stuff! Solar panels came down enormously in price, recently, and are becoming more efficient but are still bulky, expensive and not always realiable. Even in Australia the sun does not shine all the time. A Watt of solar power will cost a bit less than $ 10 these days. So you should spend a bit less than $ 1000 for a decent 100 W solar panel including all cabling and regulators. A 100 W solar panel should in theory put out 100 W. And it does just that at 17 V to 19 V depending on the model. However, your system is a 12 V system so the effecitve power is about 20 % less than the stated power. A 100 W panel thus only provides about 80 W in real life. It will provide 80 W at peak sunshine. In order to know how many Watts the panel is going to produce in a day, we need to know the Peak Sunshine hours in Australia. Maps are available for this giving you the Peak Sunshine Hours per season all over Australia. A decent average (answering the question how long is a piece of string?) is about 7 hours a day in summer up to Townsville latitude. This will go down to about 4.5 hours in winter near Brisbane. Forget Tasmania in winter with only 2 hours of peak sunsine.

Our 100 W panel will then produce 80 W or so in real life which is 6.66 AMPs (80 W divided by 12 V) per hour or 7 times that (= 46 AMPs) per day. So our 100 W panel should in theory, most of the time, allow to run our appliances in above example. You may have to restrain yourself with the laptop during cloudy times but you should get by.

If you go for the 80 l fridge monster, freezing your fish as you go along and drawing 80 AMPs per 24 hours you will need a lot of heavy and bulky solar panels. To play it safe and have some spare energy to run a laptop you would probably need two 120 W panels. It can be done but there is a easier and probably more efficient way. Have two fridges, one 2 way 38 l fridge which you run on 12 V if in the bush. You leave this fridge in the car when you are out and about. You get another 3 way fridge (gas, 12 V and 240 V). Dometic / Chescold has been manufacturing these fridges for many years. They are very efficient on gas, cost about the same as a 2 way fridge at comparable size and can be used as fridge and freezer. You run a gas fridge on a 4.5 kg gas bottle for about 10 to 14 days. The two fridges will cost about the same as a large 80 l fridge, you get away with perhaps alternator charging for the 2 way fridge or only need a smaller 100 W solar panel.

As you see, there are so many different options. We'd love to find out what your requirements are so that we can come up with a cost effective, practical solution which works in real life in the bush. Warm beer (for Chardonnay for the Misses) is not an option!