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B AT T E R Y M A N A G E M E N T
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Specifications subject to change. See bluesea.com for current information.
Back Cove Yachts installs the SI-ACR as original equipment aboard their yachts,
including the Back Cove 37.
Automatic Charging Relay Operation
1.
ACR relay is open and batteries are isolated. Voltage begins to rise slowly
after engine starts or battery charger is turned on.
2.
When voltage rises to COMBINE voltage 13.0V
in this example
,
ACR relay closes, connecting and charging both batteries.
3.
When engine stops or battery charger is turned off, voltage rapidly
begins falling.
4.
When voltage falls to ISOLATE voltage 12.75 in this example
ACR relay opens, isolating batteries while discharging.
Automatic Charging Relay vs. Battery Isolator
Battery Isolator
.6V Drop - Batteries Under Charged
Automatic Charging Relay
A lower voltage drop replacement for battery isolators
.05V Drop - Batteries Fully Charged
Automatic Charging Relays Explained
In a boat or vehicle with two battery banks, it is useful to be able to
charge both banks while underway. Charge management devices allow
two battery banks to be charged from a single source, such as an
alternator, but keep batteries isolated when not charging. If one battery
becomes depleted, there will be a charged bank available for
emergency starting.
There are two main types of charge management devices
used on boats:
Automatic Charging Relays (ACR
)
use a relay combined with a voltage
sensing circuit. When a charge is being applied to a battery and the
voltage rises over 13V DC, the relay closes and combines the two
batteries. When the charge is taken away or the load on the battery is
greater than the charging input causing the voltage to drop to 12.75V
DC, the relay opens and isolates the two batteries.
Battery Isolators
are one-way electrical check valves that allow current
to flow to, but not from, the battery. Their disadvantage is that they use
diodes, which cause a voltage drop that consumes charging energy,
creates heat, and causes batteries to be undercharged.
Although alternators with external voltage sensing can correct for
undercharging, voltage drop and heat remain a problem.
Zero Drop Isolators
have more recently been developed to address the
voltage drop issue of the traditional isolator but have had limited market
acceptance due to the higher price than either of the other two options
mentioned above.
An ACR passes the current from one battery to the other
An isolator splits the current
TECH
tip
by BLUE SEA SYSTEMS
Engine
Alternator
Battery 1
Battery 2
Engine
Alternator
Battery 1
Battery 2
Intro to Automatic Charging Relays