MFJ-249B Instruction Manual
HF/VHF SWR Analyzer
4
NiCd Batteries
If NiCd AA batteries are used, the jumper for the J5 header labeled
CHARGER
must be placed from the center pin to the pin labeled
ON.
The
CHARGER OFF
mode is the factory default.
The internal battery pack is not automatically disconnected, considering the possibility of using
10 AA rechargeable NiCd batteries.
The MFJ-249B has a NiCd battery's charger. The unit uses a 20 - 30 mA continuous trickle
charging current supply. This rate is enough to maintain a fully charged battery and low enough
to permit continuous charging while keeping cell temperature and internal cell pressure at a safe
level. The minimum supply voltage necessary to charge 1.25V AA NiCd batteries with that
current rate is 15V. The MFJ-1315 is able to provide that voltage when the power is OFF. With
power ON it is able to supply more than 13V at the maximum power required. The charger, if
enabled, is active while the power of the unit is ON or OFF.
WARNING:
Do not use external power supplies with less than 13V, if NiCds are already
installed in the unit. This could discharge the batteries to the voltage supplied.
It is recommended to charge the batteries with the power OFF, establishing periods according to
the hour capacity of the battery (C). NiCds, like all batteries, self-discharge. They have a
relatively high self discharge rate of about 1% per day at room temperature. The purpose of
trickle charging is to replace the charge that is draining off.
Power Saving Mode
The unit has a battery saving mode set up by default. This mode can be disabled by pressing the
MODE
push button before the initial messages are displayed. If the battery saving mode is
disabled the message “Power Saving OFF” will be displayed while holding the
MODE
push
button.
The battery saving mode is to extend the life of the batteries. If there is not any
MODE
operation or any 50 kHz frequency variation during 180 seconds, the unit will go into the power
saving mode. This mode will be indicated with a blinking
SLP
text over the display right corner.
By pressing either the
MODE
or
GATE
button the unit will be back to regular operation.
