Re: pro user 850w generator opinions?

On Wed, 30 Nov 2005 16:39:28 GMT, alan@xxxxxxxxxxxxxxxxxxxxxxx (Alan)

| Hi,
| Makro are selling a petrol generator model Pro User 850w for £40
| Now I know it's not brilliant @ approx 3 amp output but surely it
| would be OK to plug into the van mains input and charge the battery /
| run small appliances etc. when on a non mains site
| Has anyone got a small genny like this or any thoughts on whether this
| sounds a good / bad idea?

Other people have given opinions, here are the *alternatives*

You can caravan without that orange cable FAQ

This FAQ is intended to give some pointers on how to caravan without
that orange cable, or at a site where hookups are not available. It
does not try to say what is best, because that will depend on your
individual circumstances, but does try to give basic information about
the methods and the advantages and disadvantages of each alternative.

For general information on batteries see:,
this is a bit US oriented, but lead acid batteries are much the same

Domestic multimeters now cost as little as £2.50 and are useful for
caravan work.

A new fully charged 110Ah Leisure Battery will last most people for a
weekend, but very few a week. For longer than a few days you will
have to recharge the battery somehow. Remember that as batteries get
older and as they have more use/misuse they will hold less charge, and
eventually need replacing.

Leisure batteries are usually *not* the no maintenance batteries
becoming common in cars. If yours allows topping up, always check
your electrolyte, and top up to marks on the body with
distilled/deionized water regularly. You should always charge your
battery(s) before you leave home, either on the bench, or by leaving
the van powered up, you should give either method several days to
fully charge. Cheap chargers make gas, so you must top up the
electrolyte. Expensive electronic chargers do not fully charge the
battery, and make less gas so need topping up less frequently.
Remember also that the electrolyte will evaporate slowly even while
the battery is unused.

There is very little power in a leisure battery so you should use it
as sparingly as practicable. You should use LPG for as many things as
possible. You should also make sure that the your electric appliances
will run off 12 Volts. High power electrical equipment is bad news. A
1000 watt heater used on its own, will run for less than 1 1/2 hours,
500 watts less than 3 hours. 250 watts some 5 hours. As a general
rule something like a TV taking 50W or 4 amps for a few hours per day
is the heaviest load practicable.

The output voltage of a battery falls slowly as a charge is used, and
eventually the 12 V equipment will stop working. TVs etc. need as
many volts as possible. Thin long wires which may be supplied by the
van manufacturer or as a D.I.Y. addition, may have a high voltage
drop. If possible add extra wiring for TV, or other electronic
equipment, of thick wires ?2 sq mm? or preferably more, and as short
runs as practicable.

You should find out how much charge you use on an average day in the
van. The maths is simple 110AH=1320wattHours. watts=12*amps,
amps=watts/12, at 12 V DC. Find how many watts/amps each appliance
uses from labels or instructions. Multiply these by the hours each is
used daily. Add daily charge used in watthours or amperehours used by
each of your appliances together to give daily charge used. You
should replace this charge averaged over 2-3 days. There are many
alternative ways of replacing this charge, the choice is yours, and
will depend on your personal circumstances. Beware especially of red
"standby" LEDs, the circuit behind them uses about 7 watts, which is a
tiny amount of power, but they are on 24 hrs, less the hours they are
used, per day. Allow 12 ampere hours or 144 watthours *each* per day,
which is a significant drain on the battery.


You can use two batteries. An extra battery can be charged in the
back of the car via a split charge relay. This battery should be
securely fastened into the car. The batteries contain Sulphuric acid
which is nasty stuff and if the battery tips over it can do a lot of
harm to the car. Also if you have a crash a battery hitting the back
of your head may cause serious injury. The tiny amounts of hydrogen
and oxygen produced, should cause no problems, in a well ventilated
car. If you use marine batteries, many of these will dump the gasses
overboard via a plastic tube. If you go out in the car and "do"
things on most days while using the van, this should give you enough
charge. If you stay on site or just drive to the local town/beach this
method will not work for you. At some sites battery charging
facilities are available. Swap the batteries daily or at slightest
sign of low voltage. Be warned however that batteries are heavy and
cumbersome to change, and this is not a method for the unfit.

You should ensure that when the van is being towed the battery is
actually being charged. There are no less than three ways in which
the van can be wired, and three ways in which the car can be wired
giving ?5? combinations, some of which do not charge the van battery
when towing. see:
If you tour continuously this will be important, but if you just tow
to a site and eventually home again you can probably ignore this


Solar cells are available specifically for vans, but are rated
pointing directly at full sun, which rarely happens in UK, but they do
give some output even on cloudy days, unfortunately the retailers do
not tell you how much. If possible point your cells due south,
slightly below the maximum local elevation of the sun. As a general
rule you will need *big* cells 25 watts or preferably more. If you
calculate charge needed as above, you can get a better estimate of the
size of cells required.


Wind generators are rated at a high wind speed which rarely happens in
an English summer, they give a lower output at lower wind speeds.
The power from a wind generator varies as the *cube* of the windspeed,
so half the wind speed gives a eighth of the power. Many caravan sites
in the countryside are surrounded by trees, which reduce wind speeds.
Other sites by the seaside are better for wind generators. As a
general rule you will need a 25Watt generator or preferably more
powerful. If you calculate charge needed as above you can get a better
estimate of the size of generator required.


Portable petrol driven generators with 240Vac output can be plugged
into your van. They however make a noise which other campers find
objectionable. These generators will also charge your battery, but how
much will depend on the generator and charger in use. Most sites
will forbid their use during the night, so you will need to use 12V
for some of the time.


Invertors which change 12Vdc to 230Vac, are commonly available.
Increase the charge calculated above by up to 20% for things run via
invertors. These should be wired directly to the equipment which uses
230VAC. Do not wire the output of the invertor to the van 230VAC
sockets, which run the charger, which runs the invertor, which runs
the charger ....
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