Caution: Any
electrical work or maintenance of battery chargers or
inverters must be carried out by qualified personnel.
Always switch off any AC power supply and disconnect the
battery before any maintenance is carried out and let the
electrician know if there is an inverter.
Always comply with battery manufacturer’s
safety instructions and ensure the required system voltage
does not exceed the product’s capacity. Protective devices
such as fuses, circuit breakers and safety switches are
required to meet relevant safety standards.
There are
several ways to obtain power to charge or maintain the
charge of your RV batteries
Tow VehicleAlternator
– as you are driving your vehicle, with a
caravan, 5th wheeler, travel trailer or camper
trailer under tow, the wiring from the tow vehicle can be
linked to the RV for the vehicle to charge the RV
batteries. Heavy duty cables are run from the tow vehicle’s
alternator to the tow bar where there will be a connector
such as an Anderson plug. Heavy duty wiring will also be
run from the RV batteries along the ‘A’ frame or draw bar
with another Anderson plug which connects to the one from
the tow vehicle.
RV three way refrigerators as they are
commonly known (12V/LPG gas/240V) run on 12V power sourced
from the vehicle alternator whilst the RV is under tow then
on LPG gas or mains power when on site.
The
ability to charge an in-house battery in your caravan from a vehicle
alternator will be limited to any spare capacity of the alternator
left over from what the vehicle needs to run itself and any portable
chest refrigerator you may have in the vehicle itself . You should
seek specialist advice if you want to have a set-up to do this as
there are a lot of factors that come into play such as a specialty
alternator, the cabling, the type of battery, the type of vehicle
you have and how long you drive each day.
Generators–
generators convert mechanical energy into electrical
energy so when a generator is plugged into your RV
you are able to run 240V appliances as well as the
lighting. Generators can also be used to charge
deep-cycle batteries if batteries have been
installed in the RV. Obviously, you must have fuel
to run the generator.
Generators can be portable or located in
built-in compartments in RVs, such as those in
larger motorhomes.
The generators used for charging
batteries must be capable of supplying a ‘constant’
power supply and also be capable of supply for the
AH size of the charger. To avoid any variation to
constant power make sure you have filled your
generator with fuel before charging the batteries
because as it begins to get low on fuel the output
is likely to fluctuate. The Victron Energy user
manual for the Phoenix MultiPlus charger states – ‘The
rating of the generator should be 75% or higher
compared to the VA rating of the MultiPlus Compact.
(for eg: a genset of at least 1500 VA will be
required to operate in parallel with a Multi Compact
12/2000/80’.
The
downside of using a generator is the noise, the ongoing cost of fuel
and disturbing the serenity of fellow campers so please be
considerate.
If
you want to use a generator to run 240V appliances such as a micro
wave oven or air conditioner you may need to turn off the RV battery
charger as it is likely to cause an overload on the generator unless
the generator is suitable sized to run the battery charger and
appliance(s) at once.
To
charge a deep cycle battery in your 4WD using a generator you will
need a suitable mains powered charger. Look into a 3 stage charger
for this purpose.
Battery Chargers
All batteries will slowly discharge over time so a
battery charger is required to recharge them. Wikipedia defines a
battery charger as ‘a device used to put energy into a secondary
cell or rechargeable battery by forcing an electric current through
it’.
For
three or four stage chargers you will hear terms such as
‘bulk’ or ‘boost’, ‘absorption’, ‘float’ and ‘storage’
phases.
Boost phase
= is the first stage of the charging process. Essentially it
is the stage where the charger puts in as much current it is
capable of and as the battery storage voltage increases the
charge rate decreases until the battery is about 75% full.
Absorption phase
= this is the second stage of the charging process where the
charge going in is reduced to about half of the ‘boost’ rate
or a constant rate for several hours (unless a heavy load is
drawn and it will then cycle back to the ‘boost’ stage).
Float phase
= at this stage the battery charge is decreased again to
about 97% of charge.
Storage phase
= or ‘maintenance’ stage is where there is constant voltage
to maintain the battery at full capacity whilst maintaining
any DC operating loads.
Digital battery monitors can be installed to enable
you to monitor the level of charge in your batteries.
There are various types of battery chargers for
various types of application. There are those battery chargers
designed for lead acid batteries, sealed lead cell and others for
AGM gel cell batteries and the charging
output depends on the battery manufacturer’s recommendation. The
Xantrex TRUECHARGE2 battery charger has setting for flooded, gel,
AGM or lead-calcium batteries and is generator compatible.
Battery chargers range from the simple charger that
supplies constant DC current to the battery and this type often take
a long time to charge with a risk of over-charging the battery. Then
there are time based chargers which really are simple chargers with
a timer, configured for a particular battery, and then left to
charge but these types of battery chargers still run a risk of
over-charging. Other battery charges use a pulse width modulation
or pulse technology where a DC pulse is fed into the batteries but
it is not recommended to leave AGM or Gel battery types connected to
the charger for extended period of time.
The new ‘smart battery chargers’ are designed to
recharge multiple battery banks simultaneously, they are designed to
know when to stop the charge to avoid battery cell damage and
provide good charging performance from inconsistent line voltage.
For example, the Xantrex TrueCharge 20+ and the 40+ or the Xantrex
TRUECHARGE2 are micro-processor controlled battery chargers with a
20 amp or 40 amp continuous duty multi-stage charger which is ideal
for deep-cycle RV batteries. The TrueCharge can be left permanently
attached to the batteries for a ‘set and forget’ operation.
Then
there is the Victron Phoenix Multi/ MultiPlus Inverter/ Charger
which is a 3000 watt true sine wave inverter and charger in the one
unit. The Power Assist feature ‘..will
make sure that insufficient shore or generator power is immediately
compensated for by power from the battery. When the load reduces,
the spare power is used to recharge the battery. Note: minimum shore
current 2 A or generator capacity 2 kW required per MultiPlus’.
Suitably rated fuses or circuit breakers must be
fitted close to the battery to protect the wiring and minimise the
risk of fire. When a circuit breaker is tripped it can prevent
destruction from an overloaded circuit and may prevent a fire
occurring.
Charging Time
The time it takes to
charge a battery or batteries depends on several
things:-
1.
the size of the battery charger
2.
(CAP = capacity) - the battery capacity in amp hours (Ah)
3.
(DOD = depth of discharge in %) how deeply the battery is discharged
and
4.
(CC = charge current) the rated current output of the charger in
amperes
and an approximate charging time calculation may be:-
CAP x DOD
CC x 80
For example:-
Xantrex’s user manual has a calculation table and
let’s say you have a Xantrex TrueCharge 40 and –
- one battery with a rated capacity of 120 Ah (CAP)
and it is 50% discharged (DOD) then the approximate charging time
with a TrueCharge 40 would be:-
120 x 50
= 1.875 or say 2 hours 40 x 80
- a battery bank of say 4 batteries in parallel with
the rated capacity of 120 Ah each and the battery bank is discharged
50% then the approximate charging time would be:-
(4 x 120) x 50% = 7.5 hours
40 x 80
The above calculation however, is a rough guide only
as a ‘bulk’ or ‘boost’ charge will go to 75% after which a charger
will back off and the next phase will take longer at a lower current
until ‘float’ phase which could take 12-24 hours to do a full top
up. It does however, indicate that charging batteries may take
considerable time.
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If
you want to use a generator to run 240V appliances such as a micro
wave oven or air conditioner you may need to turn off the RV battery
charger as it is likely to cause an overload on the generator unless
the generator is suitable sized to run the battery charger and
appliance(s) at once. 
Then
there is the Victron Phoenix Multi/ MultiPlus Inverter/ Charger
which is a 3000 watt true sine wave inverter and charger in the one
unit. The Power Assist feature ‘..
