12 Volt System
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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.
- 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.
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.
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.
Only - obviously this is a very smooth source of 12 volt
power - no precautions or advisory notes
/ 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.