Battery
isolators are a necessary part of high-reliability multi-battery
systems. They're used to isolate batteries so a failure
of one battery won't bring down the battery network.
Several inherent problems are associated with multi-battery
isolation systems.
One problem is
the insertion loss from a component introduced directly
into the power path. The full load current must pass
through this device (traditionally a silicon or Schottky
rectifier), resulting in the associated power loss of
load current multiplied by the voltage drop across the
device. This is a substantial amount of power simply
being thrown away.
A
second problem:
in addition to decreasing the efficiency of the system,
this power loss generates heat, LOTS OF HEAT,
which is typically addressed by heat-sinking the isolation
diode(s) via three to six pounds of aluminum extrusion.
Third
problem
is that as the battery level drops, the voltage-drop
becomes more and more significant with respect to providing
adequate operating voltage for high power accessories.
The
traditional silicon rectifier package is what most of
us think of when we hear the term "battery isolator."
The package is usually a square or rectangular chunk
of extruded aluminum, anodized a pretty color, and contains
several threaded studs for connecting batteries and
alternator. At higher current, these isolators can drop
in excess of one full volt and in doing so, get viciously
hot. Because they get hot, manufacturers suggest mounting
the device vertically for greater air flow and heat
dissipation purposes which also makes installation troublesome
at best. Due to the voltage drop, these packages are
usually alternator specific based upon the type of regulator
used. The voltage-drop across the isolator throws the
regulator's "sense" off, thus causing over
or under-charging situations . Consequently, the regulator's
"sense" terminal must be jumped across the
isolator in an effort to compensate for the voltage
drop.
Similar
packaging is offered using Schottky diodes instead of
silicon diodes. The Schottky diode package is more efficient,
but still suffers from dramatic voltage drop (approximately
.6v) creating power loss and heat dissipation issues.
With the more efficient Schottky package, one derives
somewhat better efficiency at a premium price for marginally
better performance.
To
clarify and put things in perspective, the traditional
silicon diode package drops 1 vDC and the Schottky diode
package drops .6 vDC. True, the Schottky diode package
is 40-50% more efficient than the silicon diode package.
THE POWER-GATE diode package has
a max voltage drop of .05 vDC, over 1000% more efficient
than the Schottky package. And the kicker....that
rating is at 300 amps! When it comes to efficiency,
POWERGATE has no equal.
Mechanical
solenoids
(often called relays or contactors) are often used to
isolate, or disconnect batteries. Using a mechanical
solenoid to make or break (connect or disconnect) high
current is a common practice (think car starter solenoid),
and it's no coincidence that starter solenoids have
the highest failure rate of any automotive component.
Here's why: every time the contactor makes or breaks
current, electrical arcing takes place (think small
lightning bolt). Over time, this arcing causes the smooth
contact-points to become pitted which progressively
becomes a high-resistance connection. As we all know,
high-resistance equals heat, and heat is what kills
products. Using a solenoid for a high-current multi-battery
isolation system is the technical equivalent of rubbing
two sticks together; yeah...it'll work...but there's
got to be a more efficient way.
The
POWER-GATE line of products strike the perfect balance
of quality, durability, and efficiency by melding the
world of mechanical design with solid-state electronics.
Selecting POWER-GATE over traditional isolation and
switching devices can make the difference between a
robust, reliable system, and one that experiences untimely
failures. POWER-GATE is the perfect switch and the clear
choice for high current DC switching and isolation applications.
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