Electrical 12 Volt System


Eriba caravans are supplied with a 12 volt sealed lead-acid battery as part of the Eriba autonomy package, or as part of the Eriba UK Diamond Plus package, or as something the owner has added to give themselves independence from mains electrical hook-up.

This section gives advice on battery condition and charging, booster charging whilst towing, and choosing a solar panel to provide long term autonomy from mains hook up.

Battery Condition

A fully charged lead-acid battery comprises six cells, wired in series, where each cell has the potential of 2.13 volts and consequently a fully charged battery should show a no-load reading of 12.8 volts, but what most people don't realise is how little the voltage varies between fully charged and fully discharged.

Charge State
Specific Gravity

You will note that a battery goes from fully charged to 25% - which for good battery life is effectively fully discharged - and only shows a voltage difference of 0.8 volts - which is why you need a digital voltmeter to measure this change. Never let the battery discharge so much that the no-load voltage drops below 12 V.

If you see 13.8V or more, then either the battery is still connected to the charger or you are measuring too soon after charging - the battery needs to settle for 30 minutes or so.

You will achieve the best life from the battery if you always keep it above 50% charged, preventing the growth of sulfate crystals on the cell plates and eventually rendering the battery useless.

Battery Boosting

The Schaudt WA 1214-8 Booster is now a part of the Eriba autonomy kit and was a standard fitment in our Eriba Triton. This small electronics box is designed to fully charge leisure batteries from a lower voltage source. It takes the car 12V feed and raises the voltage to 14.4V, allowing the caravan battery to reach a 100% charge state and progressively drops the voltage as it senses charge completion.

Battery Charging

When using the Schaudt WA 1214-8 or maybe a full 3 stage charger, battery charging takes place in these stages: Bulk, Absorption, and Float.

Bulk Charge: The first stage of 3-stage battery charging. Current is sent to the battery at the maximum safe rate it will accept until voltage rises to near (80-90%) full charge level. Voltages at this stage are typically just less than 14 volts. There is no "correct" voltage for bulk charging, but there may be limits on the maximum current that the battery and / or wiring can take.

Absorption Charge: The second stage of 3-stage battery charging. Voltage remains constant and current gradually tapers off as internal resistance increases during charging. It is during this stage that the charger puts out maximum voltage, which is typically around 14.4 volts.

Float Charge: The third stage of 3-stage battery charging. After the battery reaches full charge, charging voltage is reduced to a lower level, typically just over 12.8 volts, to reduce gassing and prolong battery life. This is often referred to as a maintenance or trickle charge, since it's main purpose is to keep an already charged battery from discharging.

Autonomy with Solar Panels

In France, 2005, we met a Swiss couple (Fritz and Elizabeth Marti) with another Eriba Triton who had used solar panels for autonomous Summer camping for years.

They have a 44 watt Kyocera solar panel and Suntech charge controller (to prevent overcharging the battery), this allowed them to be independent of mains hook up for two weeks or more during the Summer - obviously they run the fridge on gas, and use the leisure battery for the water pump, lights at bed time, and the radio / Hi Fi.

Expect to pay around £200 for a 44 watt Kyocera solar panel, around £55 for a Suntech charge controller, and a few pounds for wires and connectors. Some web-sites offer a complete package for a reduced price, so Google for a deal, and expect to pay around £250.

Sun elevation - in the winter the sun climbs to a maximum (at noon) of 30 degrees above the horizon, 50 degrees in Spring and Autumn, and 70 degrees in Summer. These are approximate values for the whole of the UK.

Since solar panels work best pointing "flat on" to the sun - so the sunlight strikes at right angles - then you should elevate the panel to an angle of 45 degrees as a good average position.

We also looked at micro wind generators - like those on the side of motorways and yachts in harbour - but they are really expensive (£600 upwards) and need a good blow to generate power. Ideal for harbours and motorway verges, but less useful on a camping site with trees all around.


Electrical Ripple Warning

If you intend to operate sensitive electronic equipment, such as TFT panel TV, from the 12 volt supply in the caravan then you should be aware of the different qualities of this supply when running on battery or mains power.

Battery Only - obviously this is a very smooth source of 12 volt power - no precautions or advisory notes

Mains / Site Power - this appears to be a full wave rectified supply more than suitable for charging the autonomy GEL battery, operate the lights and water pump - however this supply is not regulated nor smoothed, and appears to introduce a considerable ripple on the 12 volt supply.

You may observe this ripple as extra distortion on the TV image. A project is underway to investigate ways to smooth out this ripple and consequently clean up the image.

Note that more recently, Eriba have fitted the Schaudt WA 1214-8 battery booster and charger device, and this has had the added benefit of totally removed mains induced ripple.



Updated Aug 2006


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