Fairbanks H90-3052-D Fairbanks Scales - Manual (Page 12)

50144 Rev. 4
4.5. Theory of Operation
The charger first determines the actual
voltage of the current charge on the battery
pack. A microcontroller puts out a PWM
signal to open and close a transistor,
allowing the current to flow to the battery
pack. The voltage level of the battery pack
determines how much current is pushed into
the pack, and this determines its STATE
for the microcontroller.
STATE ONE indicates no battery is
detected, or the charge on the battery
pack is below 0.1V, and the battery pack
is defective. The charger displays a solid
RED led and the charger allows no
current to flow.
STATE TWO is when the battery voltage
is between 0.1V and 3.6V. The pack is
considered damaged. The charger will
attempt a charge. A RED LED will flash,
indicating there may be a problem with
the charger or battery pack. The charger
will shut down after 16 hours if the
battery pack has not reach a value
higher than 3.6V. This shut down timer
allows the charger to fix severely
discharged packs, but does not emit
enough power to damage the charger.
Current flow depends on the battery pack
and charger used.
STATE THREE is the charging state, and a
YELLOW LED. The battery pack is between 3.6V
and 7.2V. The full amount of current the charger
can supply is pushed into the battery pack. If the
charger has not reached a full charge state after
sixteen (16) hours, the power turns off. When the
battery is faulty, the YELLOW LED is illuminated
steady with a flashing RED LED.
STATE FOUR is when the battery reaches a “fully
charged voltage” (about 7.2V), it continues a trickle
charge with a solid GREEN LED. The charger then
maintains the charge on the battery pack. This
mode will be held indefinably, as long as the
charge on the battery pack remains between 6.6V
and 7.2V.
STATE FIVE is when the battery’s voltage drops
while in the charger. Upon doing so, It will reenters a
charging state. If the battery voltage rises above
7.2V, the charger enters an “Over-charged State”.
The charger then stops supplying current to the
battery and waits for the voltage to drain back down to
the 7.2V. This state displays a GREEN LED with a
flashing RED LED, indicating a possible fault with the
battery pack.
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