Many people listen to their stereo without the engine running.
This often leads to dead batteries and a vehicle that won't start. A
battery isolator will let you completely discharge one battery without
discharging the starting battery.
Different Types of Isolators:
There are 2 main types of battery isolators. The diode based type
and the relay (solenoid) type. W're only going to cover the Diode
based type.
Diode Based Isolator:
This type of isolator is basically two very high current
diodes in a heat sink. The diode based isolator has the advantage of
long life and trouble free operation but many of the diode based
isolators cause a .4 to .6 volt loss which means that the batteries
will not charge to as high a voltage as when they are connected
directly to the alternator. The diagram below shows the connection for
the diode based isolator. Some diode type isolators have a fourth
terminal which controls the current flow through the device.
Here is a typical Diode Based Isolator with fuse, and Amplifier
connection:
DUAL BATTERIES WITHOUT AN ISOLATOR
Adding a second battery without using an isolator:
Some people have good results when they add a second battery
to their system. Especially if the second battery is close to their
amplifiers. If you want to add a second battery, there are a few things
that you should know.
If the battery is inside the passenger (in a
hatchback vehicle or in a
car with a back seat that folds down), you must use a sealed battery
(i.e. Optima). If the battery is being used in the trunk of a vehicle
you can use a standard battery but you will need put the battery in a
battery box and you will need to provide proper ventillation. Proper
ventillation would mean forced air (fan) ventilation from the battery
box to the outside of the vehicle. When a standard lead acid battery
charges, it produces flammable gases which must be removed from the
vehicle to prevent a fire/explosion hazard. This is why you can
not, or SHOULD not use this kind of battery in the interior of the
vehicle .
The second battery must be fused. The fuse must be as
close to the battery as possible (just as you have on the main
battery). All
of the power for the system must flow through through the fuses (at the
batteries) to protect against electrical fires. The diagram below shows
the proper fusing and wiring. The fuse at the main battery must be
properly rated to protect wire 'A'. The fuse at the second battery must
be properly rated to protect wire 'B'.
No matter what kind of battery you use, care must be taken to assure that nothing
can come in contact with the battery's terminals. I would strongly
recommend putting the battery into a plastic battery box with a cover
that can be secured onto the box. The cover can be like the ones
used with Marine battery applications.
The ground for the second battery should be grounded to the floor pan
of the vehicle. The floor pan is the main piece of sheet metal that
forms the largest portion of most new vehicles. This will provide the
best return path for the second battery.
Both batteries should be of the same make and model. The CA and
CCA should match! Using two different kinds of batteries can
cause problems when the car is off. For example, a weak battery
can pull current from the stronger battery. However, you can
install a relay to seperate the two when the car is off.
