What do you do to power your RV when you have no mains power supply? How to calculate the
battery size to run lights and compressor refrigerator in my RV?
Caravans, 5th wheeler caravans, camper
trailers, motorhomes and campervans can all obtain their
power from a mains/shore supply. We all love to camp in
national parks, bush camps or remote places where mains
power may not be available but we would still like to have
lighting in our RV or even be able charge our mobile phone,
watch TV or a DVD or use a laptop computer. But what do you
do to power your RV when you have no mains power supply?
For bush/independent camping or ‘free
camping’, as it is sometimes known, some RV’s are wired so
the lighting and any 12V compressor refrigerator will be
powered directly from the power stored in the battery in
your RV. The battery or battery bank (multiple batteries
connected to increase the available capacity) is then topped
up by the battery charger when connected to mains power,
running a generator or by solar panels.
Note:
This article has not been written
by an electrician, battery or solar expert & should not
be considered a replacement for specialist advice. The
articles are provided for informative purposes only.
Always seek professional advice for any
battery or solar problems. While great care has been
made in the creation of these articles, we cannot
guarantee the accuracy or omissions on these pages. If
in any doubt whatsoever, seek professional advice.
Power usage
Firstly,
you need to consider what electrical appliances you expect to run
from the battery storage system and calculate how much power (Amp
hours or Ah) is required to run all the items over a 24 hour period.
The period you decide on is dependent on how much charging capacity
you have to restore the power used from your batteries. After you
have made that calculation, you then factor in about a 20-25% safety
margin. This calculation will assist in deciding what amount of amp
hour battery bank capacity (or battery size) you require to meet
your power needs.
There
are a number of calculators available on the web to help you
calculate the minimum battery size and solar panels you require to
meet your power needs and Bainbridge Technologies website has an
excellent one.
Some
calculators show the amount of power expressed as Watts. If this is
the case, divide the wattage by the system voltage and this then
gives you the current capacity in amp hours (Ah). For example, an
estimated usage would be roughly –
- 90
Ah battery could supply 1 amp for 90 hours, or 9 amps for 10 hours,
or 5 amps for 18 hours
- 120
Ah battery could supply 1 amp for 120 hours, or 9 amps for about 13
hours or 5 amps for about 24 hours
An
example of a calculation table of battery usage for a 12V system may
be:-
Electrical Equipment
Power Consumption (or Watts)
Current (Amperes)
12V
Hours used each day
Total Ah per day
Compressor fridge/freezer
#
60W
5
18
90
Interior lights
2 x 8w fluros *
16W
1.3
3
4
Recessed exterior light – fluro
21W
1.75
2
3.5
LCD TV
60W
5
3
15
Lemair Washing
Machine via Inverter
270W (on spin)
22.5
1
22.5
Xantrex 1800
Inverter
1 A (idle)
5 A
Water pumps
(ShurFlo Extreme)
10 (max)
0.5
5
Bose SoundDock
30.7W
2.56
2
5.2
Computer and phone chargers
2.0
3
6.00
Fan «
0.19
4
0.76
Total
156.96
Add 20% safety margin
31.39
Total Ah needed
188.35 ◊
#
Vitrifrigo 230ltr - the refrigerator cycles. This is average Ah per
day and this could change depending on how long the compressor is
actually running.
*
Little Lunar fluro 0.75 amps x 2. LED lighting would use less power
«
Bora 12V fan Model 748CA – 0.19 amperes on high
◊ As it
shortens battery life to discharge the batteries below 50% then you
would not want to discharge the batteries below that point too many
times (see battery manufacturer’s charge/discharge curves), so based
on the above calculations, roughly your power requirement would be
188.35 x 2 = 376.7 Ah of battery capacity. Of course, the
other options are to limit your power usage by not running some
appliances as long or as often as shown above or don’t use
appliances which have a large power consumption.
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Firstly,
you need to consider what electrical appliances you expect to run
from the battery storage system and calculate how much power (Amp
hours or Ah) is required to run all the items over a 24 hour period.
The period you decide on is dependent on how much charging capacity
you have to restore the power used from your batteries. After you
have made that calculation, you then factor in about a 20-25% safety
margin. This calculation will assist in deciding what amount of amp
hour battery bank capacity (or battery size) you require to meet
your power needs. 
