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UK Caravanning (uk.rec.caravanning) A forum for the discussion of caravanning undertaken by residents of the United Kingdom, whether in the UK or abroad. It encourages the interchange of views on the merits of models of caravan, makes of tow car, accessories, caravan sites, caravan clubs, and other related topics. The term caravan is to include trailer vans, motor caravans and trailer tents.

12v - 230v inverters



 
 
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  #1 (permalink)  
Old February 13th 07, 07:23 AM posted to uk.rec.caravanning
Classic Car Man
external usenet poster
 
Posts: 13
Default 12v - 230v inverters

I'm about to buy an inverter to run a few things when away from the mains -
radio, laptop, portable tv - nothing too heavy. The fridge etc will still
run on gas so no drain from the van.

Question?
If the item (TV) is rated at 100w, how long should a good 12v spare 65amp/h
car battery last?

Basically, what is the formula to work out how the kids can watch TV on a
single charge?

Regards


Ads
  #2 (permalink)  
Old February 13th 07, 07:50 AM posted to uk.rec.caravanning
Dave Fawthrop
external usenet poster
 
Posts: 1,831
Default 12v - 230v inverters

On Tue, 13 Feb 2007 08:23:42 -0000, "Classic Car Man"
wrote:

|!I'm about to buy an inverter to run a few things when away from the mains -
|!radio, laptop, portable tv - nothing too heavy. The fridge etc will still
|!run on gas so no drain from the van.
|!
|!Question?
|!If the item (TV) is rated at 100w, how long should a good 12v spare 65amp/h
|!car battery last?

See FAQ Below.

|!
|!Basically, what is the formula to work out how the kids can watch TV on a
|!single charge?

I have every electronic thing in my van which runs on 12V. They are rather
more expensive than 230/240V ones, but IME this is well worth the expense.

Beware the cheap invertors produce a square wave (modified sine wave), not
a true sine wave, check that your TV etc will work on the inverter you
choose.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~~~~~

You can caravan without that orange cable FAQ
---------------------------------------------
updated 23/07/06

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: http://www.batteryfaq.org,
this is a bit US oriented, but lead acid batteries are much the same
worldwide.

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

Charge
------

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, water heating, heating, cooking, fridge etc. 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.

Car
---

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: http://www.volvoclub.org.uk/towbar_electrics.htm.
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
method.

Site chargers.
--------------

Some sites particularly CC CLs advertize charging facilities for
batteries, usually in some sort of barn or outhouse. If you carry a
spare battery, this can work very well, a single battery only charging
during the day it is less convenient. Humping a leisure battery around
requires some strength, and is not for the unfit.

Solar
-----

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. A charge controller is a good idea. 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.
The Australians with all their sun fit 80 watt solar panels or larger.
If you calculate charge needed as above, you can get a better estimate
of the size of cells required.

Wind
----

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. A charge controller is
a good idea. 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.

Generators
----------

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
---------

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 ....

--
Dave Fawthrop dave hyphenologist co uk
20,000 free e-books at Project Gutenberg! http://www.gutenberg.org
For Yorkshire Dialect go to www.hyphenologist.co.uk/songs/
http://www.gutenberg.org/author/John_Hartley
http://www.gutenberg.org/author/F_W_Moorman
  #3 (permalink)  
Old February 13th 07, 10:45 AM posted to uk.rec.caravanning
Andy R
external usenet poster
 
Posts: 821
Default 12v - 230v inverters


"Classic Car Man" wrote in message
...
I'm about to buy an inverter to run a few things when away from the
mains -
radio, laptop, portable tv - nothing too heavy. The fridge etc will still
run on gas so no drain from the van.

Question?
If the item (TV) is rated at 100w, how long should a good 12v spare
65amp/h
car battery last?

Basically, what is the formula to work out how the kids can watch TV on a
single charge?


amps=watts/volts

therefore 100watts is just over 8 amps at 12v plus a bit for inverter
inefficiency, say 10 amp max

if your battery is in good nick and well charged you should get around 5
hours out of it before the inverter trips out due to low voltage although
there should still be enough power in it to run 12v lights for some time
longer.

Rgds

Andy R


  #4 (permalink)  
Old February 13th 07, 03:19 PM posted to uk.rec.caravanning
Harry Bloomfield
external usenet poster
 
Posts: 582
Default 12v - 230v inverters

Classic Car Man formulated the question :
I'm about to buy an inverter to run a few things when away from the mains -
radio, laptop, portable tv - nothing too heavy. The fridge etc will still
run on gas so no drain from the van.


Question?
If the item (TV) is rated at 100w, how long should a good 12v spare 65amp/h
car battery last?


Basically, what is the formula to work out how the kids can watch TV on a
single charge?


100w -call it 120w allowing for inverter losses/inefficiency. 120w/12v
= 10amps. 65amp hour/10 = 6.5 hours to completely flat at that rate,
but expect the voltage to start to die off some while before then and
the inverter to shut down say around 5 hours max.

It is not good for the battery life to completely discharge it, so aim
for no more than 3 hours use from a full charge assuming the battery is
new and a good one. More sensible would be an LCD screen TV which runs
directly from 12v, basically much more efficient and no need for the
voltage conversion.

--

Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk


  #5 (permalink)  
Old February 13th 07, 09:52 PM posted to uk.rec.caravanning
Terry
external usenet poster
 
Posts: 72
Default 12v - 230v inverters

On Feb 13, 5:23 am, "Classic Car Man" [email protected]
spam.freeserve.co.uk wrote:
I'm about to buy an inverter to run a few things when away from the mains -
radio, laptop, portable tv - nothing too heavy. The fridge etc will still
run on gas so no drain from the van.

Question?
If the item (TV) is rated at 100w, how long should a good 12v spare 65amp/h
car battery last?

..
Probably something of the order of 5 to 6 hours, provided the battery
is in good condition and at 'normal', not cold, temperature.

At 12 volts the battery will have to supply at least 100/12 = 8.3
amps.
Dividing the 8.3 into 65 = approx 7.8 hours.

However no inverter will not be 100% efficient in converting from 12
to 230 volts.

Allowing for inverter inefficiency, (which depends on the type of
inverter and what the conversion efficiency is at any particular level
of load); but assuming its conversion efficiency is, say, 90%; then
8.3/0.9 = 9.2 amps from the battery.

That's probably about the same as leaving all the lights of car on at
the same time?

So, 65/9.2 = probably at best 7 hours! Provided also there are no
other 'Gameboy' or other devices also plugged in!

Then battery will then need a complete recharge which will require
some 120% of it's rated capacity to be pumped back into it. A 65
amp.hr battery will therefore require 65 x 1.2 = 80 amp hours
recharge.

Using a 10 amp AC mains operated charger (which is a fairly
substantial sized one) it will take about 10 hours to recharge the
battery. If a battery is continually drained and recharged, like that,
night after night don't expect it last more than a season or two.

 



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