Modern motorhomes have quite sophisticated electrical systems.
Often these will be both 12 volt (battery) and 230 volt (mains) and
may include the means to convert from one to the other. The whole
subject is of course somewhat ‘technical’ but I’ll
try to describe it here in relatively simple terms and will try not
to get too bogged down in the technical detail - but I will need to
use some numbers to show what’s happening.
The first thing to
understand is the entirely different scale of household and portable
electricity. Household electricity consumption is measured in Kilowatt-hours
and we use about 50 of them per day in our home. Household electricity is limitless
- the electricity company delivers however much I want. In complete
contrast my motorcaravan battery holds a finite amount of energy – a
bit less than just one kilowatt-hour in fact! It’s true that
we can re-charge it from time to time but this is a rather slow process,
we have to accept that a battery based electricity supply is somewhat
limited. In fact batteries of all kinds are the big modern
disappointment, they're always too big in size or weight but too small
in capacity. I read a 'QI fact' the other day that said all the
batteries in the world would power us all for only about ten minutes!!
Recognise the limitations and life will be easier.
The technology is very similar to that in a motorcar but with
one very important lifestyle difference. When you are in a car the
engine is running almost constantly and generating electricity to power
you need. In a motorhome your greatest electrical needs are when
you are stationary and the engine is not contributing at all.
This is potentially a real problem if you intend to stay in one place
a long time. Fortunately many motorcaravanners are inveterate
roamers! Others provide stationary power sources like solar power.
The second essential technicality to understand is the amount
of electricity consumed by different types of appliance. This
is most easily seen
by looking at the ‘power’ of the appliance in ‘watts’ -
this is almost always written on the appliance somewhere.
Typically a motorcaravan light will be 5 to 10 watts whereas a fan
heater will be 1000 to 2000 watts or even more. Heating is the most
demanding class of appliance having very high power demands, usually
far beyond anything that a 12 volt battery can deliver. As a result
most motorcaravanners rely on gas for such things. As an alternative
one can use a ‘hook-up’, a temporary connection to the
campsite’s mains electricity or even to a generator to produce
one’s own ‘mains’ electricity from the enormous energy
contained in gas, petrol or diesel. Note that not all motorhomes are
fitted with major mains electrical appliances like hobs, ovens, microwaves,
12 v batteries & charging
The heart of any portable electricity system is the battery. The battery
stores energy and turns it into 12v electricity when required. In all
but the smallest or cheapest motorcaravans this will be a separate ‘leisure
battery’, installed so that it can be charged and discharged
independently from the vehicle battery. This sensible arrangement means
you can use the living quarters electrics as much as you like and still
be able to start the ‘van when you want to!
Although any 12 volt
lead acid battery could be used anywhere in the ‘van, in practice
special types have been developed for each role. The vehicle or starter
battery is designed to give very high starting current for a few seconds
and then to be constantly charged while the engine is running. A leisure
or deep-cycle battery on the other hand is designed for long slow discharges
and occasional re-charging. Each works best and longest when doing
its designated task!
Many modern motorhomes will have two built-in
charging arrangements, one driven by the engine and one via a mains
hook-up. In our own ‘van each system charges both batteries but
this is not universally true. A control panel giving a guide to battery
condition and charge or discharge rate may also be fitted. The best
systems are adjustable for battery type and are set at a slightly lower
than optimal voltage to minimise ‘gassing’ (all conventional
lead-acid batteries produce small quantities of hydrogen and oxygen
when charging and should be vented to the exterior as a safety precaution).
There is a newer sealed battery type - a gel battery – that is
finding favour in motorhomes due to the complete absence of gassing
when charging. My own, admittedly limited, personal experiences with
gel batteries have so far all been bad with a 100% early failure rate
practice most owners will have little influence over what is provided
initially. So, the best policy is to assume that the manufacturers
have provided a suitable system but to ask about charging both on the
move and on site and then to use the systems fully to find any weaknesses
before you set off on that six-month trip to Scandinavia! It was this
process that persuaded us that we didn’t have enough battery
capacity in our latest ‘van. Battery capacity is usually described
in amp-hours – how many hours it will last giving out a set amount
of current (amps). Leisure batteries typically have ratings of 75,
90 or 110 AHrs. Naturally enough the higher rated batteries are both
larger and more expensive. We now have twin 110 AHr batteries but many
people manage quite well with a single ‘75’ and a few intrepid
types carry four or even more ‘110’s! It all depends on
your lifestyle, installed appliances, carrying capacity and how often
you are able to recharge fully.
Recharging follows a similar pattern, if you’ve
taken out 20 amp-hours you’ll need to put the same back again
when charging. In practice nothing is 100% efficient so you’ll
actually need to put back slightly more – in this case say 6
hours at 4 amps. Again in practice it is not always possible to get
the full capacity out of a battery, low temperature and high rates
of discharge both diminish capacity greatly; also for long life no
leisure battery should be discharged by more than 80% of its capacity,
preferably less than 67% (2/3). In practice the performance of a battery
is dismal once past the 67% discharge mark so you probably wouldn't
want to persevere in any case.
I should add here that there is no need to become paranoid about flat
batteries. A proper system functioning normally will allow the leisure
battery to go flat and still leave you with a fully functioning vehicle
battery. It might even pay you to deliberately flatten the motorcaravan
battery to be sure that the system really does work properly - I would
choose a non-critical time and place to do it though!
There are several different charging
systems available, the high capacity
vehicle alternator that only functions when you are on the move, a
built-in charger that only operates when ‘hooked-up’, solar
panels that are only fully effective in bright light, preferably sunlight
and small wind turbines that plainly need some wind to function. And
of course you can generate electricity with a portable ‘genny’,
many of which have a direct charger output. The noise of a genny does
however mean that there are restrictions on when and where you can
use it. The newer ‘briefcase generators’ are
much quieter but still won't make you popular with your camping neighbours!.
If we accept for the time being that all our heating will
normally be provided by gas, just what are we going to run on electricity?
Well quite a
bit in fact - lighting, music, TV & video, laptop, mobile phone,
water pump, hot air distribution, fan, and so on. Motors can be quite
heavy users if run at high speed, so blown air heating and other fans
should be run at medium or low speeds if battery capacity is
an issue. Water pumps are also heavy users but are only on for a few
at a time so are not a problem. Even showering tends to be a shorter
process than at home because there’s rather less hot water to
play with and most people use the pump just to get wet and then
again later to rinse off, rather than continuously.
Most modern motorcaravans
are well supplied with electrical gadgets so it is quite important
to remember to switch off everything that is not required at the time.
Some people are very good at this but others aren’t – us
included! To help with assessing 'demand', most appliances are rated
and labelled in watts – a
10 watt reading lamp for instance. This is not overly helpful when
been talking about volts and amps! Fortunately it is easy to work out
from knowing the other since watts is the same as volts x amps, so
for vehicle electrics all you need to know
table (see the right hand panel). Calculation does help
us to understand and illustrate the influence
of lifestyle. For example
if we sit and read with three 10 watt lights for perhaps
6 or seven hours in winter, that’s 15 or
more amp-hours taken from the battery. If we could read with
just one lamp for only three hours in summer that
would just 2.5 amp hours used. This is quite a difference when you consider
that we might only have a 75Ahr battery and should only use 1/2 or
maybe 2/3 of
that capacity anyway.
Some appliances take
a high initial current or ‘surge’ that is higher than their
official rating. Appliances like microwaves, pumps, vacuum cleaners,
etc., are well
this, while others may be particularly sensitive to voltage drops - TVs
for example. We had a particular problem in our own ‘van where
the TV would switch itself off whenever a tap was turned on and the
water pump started – this was not very popular as you might imagine!
We resolved this by putting the TV on a separate new circuit with heavier
wiring which solved the problem completely. To do this work yourself
you must understand polarity, wiring gauge, fuses and relays, otherwise
get an auto-electrician to do it for you. (We are thinking about adding
an additional technical section here to address these issues).
high demand application is cooling, not least because it often involves
heating! The mobile fridges fitted to most motorcaravans are different
to domestic ones being the absorption type. These have a heating cycle
as part of their operation, the heat is of course ducted outside so
not to negate the cooling process. These fridges can take 8 to 16
or more amps
and are usually wired so that they can only be run from 12 volts while
on the move and receiving charge from the vehicle alternator. When
stationary you are expected to run ‘3-way’ fridges on gas
or mains hook-up. It’s worth noting here that absorption fridges
are rather sensitive to ‘tilt’, about 5º is thought
to be acceptable but some manufacturers claim a greater tolerance.
Absorption fridges are favoured because they are virtually silent in
operation. More conventional compressor fridges are beginning to appear
in mobile applications now they are becoming quieter but they are still
quite expensive. The benefit is that they run on only a much lower
current draw - maybe 1 or 2 amps average, maybe less. Very few
air-conditioning units have a 12 volt option due to the very high
demands involved, typical roof mounted air conditioning units draw
anything from 35 to 55 amps average when on a 12V supply - so another
severe battery bashing application!
230V Hook-ups & appliances
A mains hook-up is available on many sites at extra charge. A special
outdoor cable with 16 Amp connectors is used to connect the ‘van
to the site mains. Numerous sites here and throughout Europe use these
standard connectors but adaptors are also available to fit the domestic
outlets found in France, Germany, UK and elsewhere. Many ‘vans
will switch over to mains automatically once plugged in but some require
you to switch on internally. Mains outlets in campervans and
motorhomes are protected
by circuit breakers or fuses in the same way as they are at home. The
more modern ‘elcb’ units are preferred due to the higher
level of protection against electric shock.
Once hooked up the 12v
leisure battery will probably be put on charge automatically and the
vehicle battery might be too, all internal mains sockets go live and
you can use electrical appliances in much the same way as you do at home.
Some motorcaravanners carry miniature ovens or microwaves to take advantage
of this. The fridge can also be switched over to mains and in some ‘vans
you’ll be able to heat water using mains too.
is not quite the same as it is at home though because there is a limit on
the amount of electricity you can use in practice - on the available
amps. There is always a limit and although top sites like those run
by the Caravan Club may offer a ‘full 16 amp’ supply you
will sometimes find you are limited to a much lower level, to 6 amps
or even to 4 amps or less on some rural sites abroad. 16 amps will
allow you to run just over 3½ Kw of appliances. Even
this relatively high level of supply limits what we can do - if
this is winter and we’re just come in from the cold wanting to
run the fan heater, put the kettle on, dry our hair and heat some food
quickly in the microwave, we can’t because the supply will trip
out (switch off) if we do! Just add up the watts to see why, 2Kw heater plus 2Kw
kettle plus 1500 watt microwave plus 1800w hair dryer = 7+Kw, more
than twice the allowed supply!! You can of course use all these items
one at a time unless you find yourself in ultra-rural France limited to 4
amps in which case you would have trouble using any of these appliances
at all since 4 amps means we'll only be able to use appliances rated
at around 1Kw (kilowatt); this is why
people buy camping irons,
etc. You might like to consider too that ‘tripping
out’ the electric supply may affect just you, but it could mean everyone connected to
your electricity post or even the whole campsite - what a way
to meet your neighbours!
Microwaves in particular cause confusion because
their description usually includes the energy output of the
unit in watts. This is actually very different to the total number
of watts consumed.
Our own domestic microwave is rated at 900w but it also has a 900w
grill; add to these the fan and the normal inefficiency in converting
electrical input into heat output and the total input is 2550w.
Even worse they are normally subject to input surges when first operated
so if needing the grill at the outset it would be wise to allow a little
over 3Kw for this particular appliance! (13 amps). This high demand
is the reason that many domestic appliances are not suitable for use
in motorcaravans. Fortunately special ‘low wattage’ versions
are made for ‘camping’.
Fridges and rooftop air-conditioning
units run well on mains hook-ups but be sure to check on the real ratings
for air-con because some have both heating and cooling built-in but
one never normally uses both together. If retro-fitting air-con it’s
worth checking that it will start and run on low power on one of the
more restricted hook-ups since they often have high start-up currents. All manner of lesser gadgets might be used
too, laptop computers, mobile phone chargers, gps systems, etc. Some
of these will run either on 230 or on 12v but normally via separate
adapters that are optional extras and most make very modest demands
on the motorcaravan battery.
Converting 12 to 230v
Conversion of mains to 12v is a fairly straightforward process via
an inbuilt battery charger giving a 12 v supply. Conversion in the
opposite direction is also possible using an inverter but this process
is somewhat problematical. Clever electronics are used to lift the
voltage and to convert the steady dc voltage of 12v systems into the
alternating waveform of mains electricity. Not all inverters are
created equal, there is a good reason why the ones 'on special' in
garages are £20 and the professionally used ones are £1000!! The process has imperfections
and so not all appliances will run satisfactorily on cheap inverters,
indeed some will fail to start, some will make strange noises and some
will burn out;
many more appliances and gadgets will now run on what are called
‘modified sine wave’ inverters but just about all will run on the more
expensive ‘pure sine wave’ devices. A particular problem is 'inductive
loads' like rechargeable toothbrushes, these will not tolerate the
cheaper inverters and damage may be done to either appliance. Inverters
are rarely fitted as standard.
more concern at a practical level is the change in amps drawn. Given
that the power of an appliance in watts will not change and that we are
stuck with the change of voltage, the only other variable is amps. Add
to that some inefficiency in the process and suddenly we're looking at a
rule of thumb that says 1Kw = 90 amps! Not only does this require
substantial wiring the size of starter cables but would also completely
flatten a normal leisure battery in less than half an hour! (the
expected usable capacity at a 90A discharge being much lower than at a
normal rate of discharge). Note too that amps as high as this are quite
capable of starting a fire if pushed through inadequate cabling. Anyone
wanting to use inverters to power high demand appliances like these
needs to make very good provision for battery reserves and for constant
re-charging via solar power, wind energy, on-board chargers and the like.
Not all is gloom and doom,
however, small inverters rated at 150w or 300w are very useful to
run laptops, mobile phones and camera battery chargers, where only
volt devices are owned and no hook-up is available. One caution is
about the newer lightweight chargers for these devices and for those
very popular electric toothbrushes, these use 'switched mode' chargers
and some are quite sensitive to the quality of electricity supplied.
They may even eventually burn out if used with the wrong inverter (check that
temperatures remain normal in use). For this reason
it is wise to have a 'pure sine wave' inverter for these appliances.
Although they are more expensive, particularly in larger sizes, it makes
sense to have one of the smaller pure sine wave devices just for those
small but expensive gadgets with the new sensitive lightweight chargers.
Smaller units also draw less current for their own purposes so it is
usually a good idea to have a small high quality inverter even if you
already have a big one for other purposes.
Relax & Enjoy it!
All this information is intended to help us understand what is going
on and where the limitations lie. It doesn’t mean that motorcaravanning
is difficult and uncomfortable but quite the reverse. Once you
accept and adapt to the limitations you can enjoy a very comfortable
relaxing time whether hooked-up on site or running on batteries
away in some
remote spot far from civilisation!