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Mini-AT User Guide
Power Sharing Cable Assembly (p/n 40-2390)
Installing a Mercury Modem in a Mini-AT enclosure necessitates the sharing of a single battery pack. The
power sharing cable allows an instrument and modem to operate from a single pack by reserving the power in
a low battery for the instrument. The cable disconnects power from the modem when the battery is low.
The power sharing cable is a small electronic circuit board with two attached pigtail cables. A battery
socket is mounted on the circuit board, and the two pigtails are terminated by battery plugs. One plug
is directly connected to the socket and supplies power to the instrument. The other plug, via the circuit
board, provides switched power for the modem. Power is switched off if battery voltage drops below
a preset level (5.25 volts dc), and automatically restores if it rises above a higher level (6.40 volts dc).
The needs of the instrument dictate the battery voltage an which the modem must be disconnected.
Battery packs are affected by temperature and this complicates the process of deciding when to discon-
nect the modem. A battery nearing end of life may reach the disconnection voltage on a cold night long
before it cannot supply the modem during the day. To maximize modem availability and to prevent
nuisance shutoffs, the power sharing cable automatically restores power to the modem when battery
voltage returns to a acceptable level. To prevent a continuous cycling of power retries, a retry delay of
about six hours is incorporated. This delay is cleared, or reset to zero whenever the battery is plugged
into the cable, but can also be ended by pressing the small white push-button next to the red/black wire.
Installation
Plug the red/black pigtail connector into either of the battery sockets (J7 or J8) of the Mini-AT. Plug the white/
black pigtail connector into either modem socket (J3 or J4). Lastly, plug the power connector from the battery
pack of power supply into the power sharing cable board. At this point, you should see the modem LED's
flash during its five to ten second initialization process. If the LED's do not flash, press the white button on the
power sharing cable board. Place the power sharing cable circuit board in the instrument door to the right of
the battery pack (when viewed with the door open) and place the cables in the battery wire clip so the board
is toward the front surface of the door.
Note: The Messenger Modem does not require the Power Sharing Cable
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