Battery Isolator
Installing a battery isolator / dual
battery system.
Your car battery is generally quite
valuable. If you let it discharge too often it will dramatically shorten the
life of the battery. In applications where you are running electrical devices
from your car, you should install a dual battery system. This is remarkably
easy to do, requires only a few tools and can realistically be done for around
$220 to $300 depending on what tools you already have and what type of second
battery you buy.
In Australia Redarc based in South
Australia make these dual battery cut off solenoids. They cost about $118
in many automotive stores, more if you get them to fit it. I've brought one
and it performs well. I use it in reverse to the normal way of being used.
Instead of charging my deep cycle batteries from the bus altenator I charge
the bus battery from the solar panels as the bus often is stationary for long
periods of time, resulting in the bus battery going flat due to phantom loads.
It is a perfect set and forget system to ensure that even if I flatten my
deep cycle batteries, the bus battery will remain charged provided there is
good sunlight available. It does tend to run a little hot, but Redarc is coming
out with a new model that I hope to test in May that is designed to run a
lot cooler.
In addition to the isolator switch
your other main need in this system is a second battery. I would recommend
buying a deep cycle battery of at least 80 amp hours for this sort of set
up. About the maximum size deep cycle battery you would want to buy is 135
amp hours. You can go higher, but you need to ensure that deep cycle batteries
are kept well charged. More powerful deep cycle batteries take longer to charge,
so unless you are driving for hours each day, your deep cycle battery will
discharge and have a short life. Using this system of installing a battery
isolator will also mean that your deep cycle battery will be protected form
voltage fluctuations as your car starts.
How it works.
Your car alternator normally charges
one battery. You can easily install a secondary dual battery with just a couple
of cables, but this will mean that both batteries will charge at the same
time, but also discharge at the same time. When one is flat, the other is
flat. The battery isolator is like an automatic switch which will only allow
the second battery to charge after the first battery / car battery has reached
a certain voltage (normally 13.6 or 13.8 volts on a 12 volt system) indicating
that battery is charged. Then both batteries will charge until the power level
in the first battery drops below a certain point, normally 12.6 volts on a
12 volt system. At that point the automatic switch in the isolator disconnects
the two batteries. When the car battery is below 12.6 volts you can still
draw power from the secondary battery, but because hey are disconnected, you
will not draw power from the car battery. This ensures that the car battery
does not go flat. Even if the secondary battery goes flat, you can still start
your car.
The diagram below shows a basic layout
of a dual battery system. On the left we have the car battery which is charged
from the car's alternator In the middle is the isolator. On the right is the
second battery. Appliances can draw current from this second battery. The
isolator automatically acts as a switch on the positive (red) wire of the
connection, allowing current to pass from the car to the secondary battery
when the first battery is fully charged.
Some important information
and precautions.
First, a disclaimer. I am not an
electrician. I am not an auto electrician. I am not in any way qualified to
teach you this. If you are not comfortable with learning these techniques,
get a professional to install a dual battery system for you. It should take
less than an hour to do. If they quote you more than $100 for labor, go some
place else.
Second. There are some basic conventions
to 12 volt or direct current wiring. Negative wires are always black, positive
wires are always red. Don't go messing them up because if some one other than
you has to service the system they could screw up the wiring.
Next. In a dual battery system we
connect the batteries in parallel. This means we connect positive terminals
to positive wires only. We connect negative wires to negative terminals only.
This is another reason why you should use the convention of red for positive
wires and black for negative wires. You do not want to get in to a situation
like the diagram below. If you wire your positive terminals to the negative
terminals you will likely get a shower of sparks and in short time both batteries
will be flat or catch fire! Or, as shown in the diagram below you will wire
the batteries in series and end up with 24 volts in your system instead of
12.
Do NOT wire your batteries together like this!
Always do any wiring on your car
with the engine not running. 12 volts DC generally can not kill you but sparks
can hurt you and hot wires can burn you.
Always remove any metal objects like
watches, jewelry etc from your hands. These can contact wires, battery terminals
etc and form a path for the electricity. This may result in them heating up
rapidly. Metal bangles in particular can become red hot in just seconds and
melt, causing horrible burns around your wrists.
When buying the secondary battery
ask the seller if it is safe or suitable for use in a dual battery system.
Deep cycle, car or marine batteries should be okay. Dry cell (the little ones
you buy from supermarkets etc) or gel cell batteries are not safe.
Equipment.
You will need:
Equipment shown here includes wire
cutters, insulating tape, pliers, electrical cable, the battery isolator,
cable lugs and a screw driver.
Before you start.
I recommend you read all of the instructions
first and then go and follow them step by step. This will ensure you don't
make some common mistakes such as attaching lugs at the end of all cables
or cut the positive cables to sizes that don't suit. Also, remember to remove
all jewelry and watches and ensure the car is switched off and keys are NOT
in the ignition. Note that most battery isolators detect the incoming voltage
from one of the two terminals only. You MUST read your battery isolator instructions
before following the instructions below.
Step 1. Prepare cables.
Using the wire cutters, cut two red
cables to length to allow you to span the distance between the two batteries
and allow a little extra to allow you to attach the battery isolator to a
bulkhead in the car. Alternativly, if you have a heavy duty pre-wired fuse
holder, you can use that as one of the red cables. Cut a single length of
black cable to span the distance between the two negative terminals of both
batteries.
Step 2.
Trim about a centimeter of the plastic
off of the end of the cables.
Use the wire cutters to trim about
a centimeter off of the end of each cable, the positive ones as well as the
negative ones.
Step 3.
Twist the wire at the end of the
cable so that it is smooth. Note that the wire may have sharp and ragged ends
so you may want to wear gloves to do this.
Twist the cable ends.
Step 4.
Attach a wire lug to one end of both
positive cables. This should be of a type that has an eyelet large enough
to fit to the terminals of the battery isolator. Push the wire in as far as
it will go. It is okay if it comes out the far end a little.
Attach cable lug.
Step 5
Using the pliers squeese the end
of the cable lug as hard as you can. Check that the lug will not fall off
of the cable. If you do not have pliers you can usually do this by carefully
banging on the cable lug end with a hammer to achieve the same effect.
.
Squeese cable lug to achieve a
tight fit.
Step 6.
Wrap electrical tape around the end
of the cable and wire lug to ensure that there is a minimum of exposed metal
surface. Normally you should use the same colour tape as the cable, but to
make it clearer in these instructions I have used a different coloured tape.
.
Use electrical tape to cover all
of the exposed metal apart from the eyelet.
You need to prepare one end on each
of the two positive cables.
Step 7. Attach cables
to isolator.
Attach the cables to the terminals
of the battery isolator. Make sure you follow the instructions for your battery
isolator. Most battery isolators will not be damaged if you connect these
cables around the wrong way, so some trial and error can be used later on.
Connect the cables to the terminals.
At this point your set up should
be looking much like this. The battery isolator I have chosen is a Redarc
SB12 12 volt unit made in South Australia which cost me $110. Your short wire
must include an in-line fuse.
Step 8.
Wire the end of the positive cable
that is going to go to the secondary battery to the battery terminal. Your
battery terminal may look different. If you have cables going out to appliances,
lights or cigarette style sockets, wire them in to this terminal at the same
time.
Attach the end of one of the positive
wires to the battery terminal for the second battery.
Your set up will look much like
this. Instead of the short wire though you should include an in-line fuse,
as shown in my final set up.
Step 9. Wire to battery.
Wire the negative lead from the battery
isolator to the car or secondary battery. In the image below I have located
my batteries close together in a ventilated compartment, hence I have wired
the lead directly to the battery, but you could use a wire to extend this
lead and locate the isolator further away from the battery. At this time you
can also attach one end of the negative / black cable to the car battery.
Do not attach the other end yet.
Attach the negative cable from
the isolator to the negative terminal of the battery.
Step 10.
Wire up the positive cables to the
car battery and the secondary battery. In the image below I have the bus battery
on the lower left and the two 100 amp hour house batteries at the top. Note
that I have also included a cut off switch on the wall on the right so I can
disconnect the system in an emergency. I have also included two heavy duty
fuses in the set up, as shown in the Redarc instructions. These heavy duty
in-line pre-wired fuse holders cost (April 2007) about $16 and the fuse costs
about $5.50. You can get a cheaper unit on a less thick cable of about 4mm
cross section which should do the job but I like to use thick cable to ensure
minimal power loss. The cheaper one costs about $6 and will use standard car
fuses.
Also, in my set up I have four large
solar panels charging the deep cycle batteries and when these are charged
I charge up the bus battery. So the cables on my isolator are in reverse order
than they would be for a normal dual battery set up.
Connect the positive cables to
the batteries. Note that in this final set up heavy duty fuses have been wired
into position. The one on the left shows the fuse uncovered, wile the one
on the right shows how it normally is, being covered.
Step 11
Connect the negative cable ends to
the negative terminals of the secondary batteries. If there are sparks or
the smell of heat or burning at this point disconnect the negative and posative
cable and double check that you have the wiring around the right way. If you
can not figure this problem out KEEP THE WIRING DISCONNECTED AND SEEK EXPERT
HELP.
If all goes well, put your car in
neutral or park, start the engine of your car, shortly the dual battery isolator
should trip, charging the secondary battery.
The battery isolator should indicate
that the secondary battery is charging.
If you find that the isolator does
not indicate that the secondary battery is charging, wait a few minutes as
the primary car battery may still be charging. If after five minutes it still
has not tripped the isolator solenoid, you may have the wiring on the isolator
terminals around the wrong way. Turn off the car engine, remove the keys from
the ignition and then swap the wires around on the terminals of the isolator.
Start the car and try it again.
I have found that the Redarc SB12
battery isolator can run a bit hot so I have rigged up a small computer fan
running to cool mine. This model operates at 77 degrees Celsius. Redarc are
planning to bring out a new model in May of 2007 that will run cooler.
Cooling fan before final set up.
Note on the right is the ventilation fan for this battery compartment. It
sucks air from the compartment and ventilates it outside. This is for safety
reasons to avoid a hydrogen build up.
What else can I use
a battery isolator for?
The battery isolator is essentially
an automatic switch that will cut off power when the power source drops below
a certain level. On my system I have 4 large solar panels charging up the
deep cycle batteries and use the isolator to charge the bus battery as the
bus is not driven often.
You can also use a battery isolator
to protect a single battery from going flat. The isolator can be wired as
shown below. When the single battery starts to drop in voltage the isolator
will monitor the voltage until it drops to a certain point. Then it will cut
off power to the load, protecting the single battery. You may want to use
this system until you can afford a second battery.
Using a power regulator
instead.
See
here
Can I fit a secondary
power source to the system, such as a solar panel?
Yes, by all means. You will need
a power regulator for the solar panels though or you will over charge your
batteries. I would recommend researching this a lot more before wiring a solar
panel to your batteries.
The diagram below shows how I have
seen many 12 volt systems with a dual battery isolator wired up. Note that
you will need an isolator and a power regulator in both of these wiring systems
or you risk the solar panels overcharging the car battery and damaging it.
I have also seen some systems wired
up this way below.
Some stuff I left
out:
