Managing Without MainsIf you are a regular rallier or a lover of CL's and remote sites you will have been faced with the problems of managing without mains charging. With a good battery and careful management 3 - 4 days should not be a problem during the lighter months. But what if you want to stay longer or caravan outside the main season? In this article we examine ways of maintaining your 12-volt supply for extended periods. |
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Employing a Second Battery
The simplest way of lasting longer is to carry a second battery and to swap to it when the first one goes flat.. This may be all you need to stay the course. Both batteries can then be recharged when you get home or to the next site with mains electricity.
The problem arises when a second battery is not enough. You need some means of keeping your main battery topped up or of re-charging the second one. Fortunately there are a number of other options.
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A second battery can be bought quite cheaply or you could splash out and get one of the carbon fibre types as shown here. They are claimed to be resistant to sulphation and are guaranteed for 5 years. |
Charging with your towcar
Your towcar's charging system is an obvious first port of call. All you need to do is to provide a secure mounting for your battery and connect to the split-charge relay (the output of this goes to pin 2 on the 12S socket on older towcars, or to pin 6 on vehicles with the latest single relay wiring). If you have two batteries you can have one on work and the other one charging in the car as you drive round. The secret is not to let either battery get too flat (no less than about 12.3 volts or nearing the bottom of the green arc on your caravan's meter) so that the car's charge will be readily accepted. If you do charge a second battery via the wiring to pin 6 please remember to disconnect it before plugging in the caravan to the car's 12S socket. If you don't then the battery could be flattened by the caravan's fridge.
Using Solar Power
Even in a climate like that of the UK solar power can produce useful energy. What's more with the latest solar panels the sun does not even have to be shining for useful power to be produced.
Beware that there are two types of solar panel on the market - polycrystalline and monocrystalline. The former have been around longer and have a uniform dark appearance. The latter are constructed from discrete cells, each one a complete silicon wafer or half wafer. Monocrystalline panels are dearer but give a higher output for a given area.
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Solar panels come in two types polycrystalline (left) and monocrstalline (right). The panel on the right is made up of half wafers and is rated at 50 watts. See text. |
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For decent results though you will need a panel with a rating of about 40 watts. This will have an active area of 3.5 to 5 square feet (0.325 - 0.500sq m). depending on its type. Ideally you need to keep the panel pointing at right angles to the brightest point in the sky but failing this just aim for south with an elevation of about 60 degrees (UK).
Most panels come with blocking diodes to prevent the battery discharging through them at night when they produce no power. Larger panels (say greater than 15watts) need a charge controller to prevent the battery from being over-charged. Charge controllers normally eliminate the need for a separate blocking diode. A 40 watt monocrystallline panel will cost around £250 complete with charge controller.
The advantages of solar power are that it is totally 'green' producing no noise or other pollution. The disadvantages are that no power is produced at night and outputs are lowest during the winter months when you may need most power. Larger panels can be quite bulky and heavy.
Wind Power
Most small wind generators are designed for use in yachts and other small boats where there are normally few obstructions to slow the wind. Nevertheless they can be ideal for caravanners as they can produce useful power all the year round as well as at night. An entry level one such as the one shown above left can produce up to 48 watts of power in a 36-knot wind although this reduces to just 8 watts in a more typical 12-knot (14 mph) wind. It weighs 5kg (11lb) and costs about £300. The one on the right can produce 24 watts in a 12-knot wind but is considerably more expensive and needs a 2.5 inch diameter pole mount.
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Here are two popular makes of wind generator. The smaller one on the left has a diameter of 580mm (about 23") whereas the one on the right has a diameter of 910 mm (about 6"). This increase in diameter makes it much more powerful - see text |  |
The majority of small wind turbines are pole mounting so you will need adequate space for the pole and its guy ropes. With the smallest systems you may be able to secure the pole by means of the jockey wheel clamp but you may still need guy ropes to prevent overloading the clamp mounting and caravan chassis. Wind generators also normally require a charge regulator (see pic below).
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| Above right is the output graph for the popular Rutland 503 generator shown above left. The 503 has a blade diameter of 510mm (20") and can be mounted on a 1.5" diameter pole. Overcharging is prevented by the use of a regulator (centre). | ||
When looking at wind generators remember that the power produced (within the design limits) will be proportional to the square of the radius and the cube of the windspeed. In simple terms this means that a 3-foot diameter generator can produce more than twice the power of a 2-foot diameter one at the same wind speed. Also a 15 mph wind can produce more than 3 times the power of a 10 mph wind for a given generator. Indeed high wind speeds can cause larger generators to run hot so it is important that some kind of thermal protection is built in.
Engine Driven Generators
Generators have the advantage of producing instant power whatever the weather but even the quietest still produce some noise. If you have nearby neighbours you may become very unpopular very quickly. That is why they are banned on Swift weekend rallies.
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If you're going to buy a generator for caravan use make sure it's an ultra quiet one such as the model shown here. |
Beware that switch-mode power supply/chargers such as those found in most UK caravans can be damaged if operated from a generator. The reason is that some generators are not well regulated and can produce abnormal voltages and frequencies, especially on start up. Never use the output of a generator until it has settled down to a steady tone. If you need to connect sensitive loads such as your caravan's charger or a computer then try to give the generator a small but steady load first e.g. by switching the caravan's two mains lights (if fitted). For battery charging most generators have a 12-volt output for this purpose so you needn't risk the caravan's charger at all.
A good quality low noise 1000 watt (max) generator will set you back about £650 and weigh about 14 kg (31 lb) in running order.
Combined Systems
There are systems which combine two or more power sources to give better performance over a wide range of conditions. The most popular are those that combine solar and wind energy via a common charge regulator. A test of such a system (Rutland 503 wind generator plus 20w solar panel) by the Caravan Club gave excellent results over a 5-day period in early spring..
Conclusions
If you're going to be motoring for an average of an hour or more each day then the simplest way of maintaining your 12-volt supply is to use a second battery charged from your towcar via the split charge relay.
If you're not going to be using your car so much then a combination of wind and solar power should work very well. Alternatively you can use either in isolation as long as you are aware of the limitations.
If you have no close neighbours then a generator could be the ideal solution. You can have power whenever you want and at 230-volts into the bargain.
Useful Links
Internal
back to where you left the "Understanding Your Caravan Battery" article
Related article, No Hook up - No Problem!
External
www.unlimited-power.co.uk
www.solarcentury.co.uk
www.marlec.co.uk
www.powermate.com
www.honda.co.uk/energy/GenHome.jsp