Campbell Scientific CR7 Measurement and Control System - Manual (Page 148)

SECTION 14. INSTALLATION
14-4
Regulated solar panels (e.g., MSX18R) limit
voltage to approximately 14V. The CR7
Solar Panel input requires 15-25 VDC to
charge.
14.2.3 EXTERNAL BATTERY CONNECTION
An external battery may be used to supplement
the internal lead acid batteries of the CR7. The
ground and +12 leads are connected to the
appropriate "EXT BATT" terminals.
The recommended procedure for connecting
the CR7 to an external battery is to make all
required ground lead connections before
connecting the battery. Accidental shorting can
be prevented by insulating one of the power
leads until cable routing is completed. When
disconnecting a battery, remove the positive
lead before disconnecting the ground lead.
Power for operating the CR7 may also be
provided by connecting the power leads from an
external 12V battery to the 2 terminals located
on the left side of the I/O Module CPU card.
This is a quick and convenient method of
connecting an alternate power supply to the
CR7 if it is necessary to disconnect or replace
the CR7s internal lead acid batteries. However,
the primary purpose of the terminals on the I/O
Module is to provide access to 12V for powering
external devices such as sensors.
Reverse polarity protection is NOT provided
on these terminals and CR7 damage will
occur if external power is connected with
reverse polarity.
If an external power supply is connected to the
I/O Module terminals the CR7 remains
powered-up even when the power switch is off.
The external supply must be removed to power
the CR7 down.
CSI recommends using 22 AWG lead wires or
larger when connecting an external battery to
the CR7.
14.2.4 CONNECTING TO VEHICLE POWER
SUPPLY
When the starting motor of a motor vehicle with
a 12 Volt electrical system is engaged, the
voltage drops considerably below the nominal
12 volts. If the CR7 were connected directly to
the vehicle power supply, the CR7 batteries
would be pulled down as well, causing the CR7
to "bomb" any time the vehicle was started. To
avoid this problem, a diode (i.e., 1N4001) and a
3 ohm 5 watt resistor must be placed in series
in the positive lead going to the EXTERNAL
BATTERY terminal. The diode allows the
vehicle to power the CR7 without the CR7
attempting to power the vehicle (diode installed
with bar end toward datalogger). To reduce the
potential for ground reference errors in
measurements, the ground lead should be 16
AWG or larger.
FIGURE 14.2-1. Connecting Vehicle Power
Supply to CR7
14.2.5 SAFETY PRECAUTIONS
There are inherent hazards associated with the
use of sealed lead acid batteries. Under normal
operation, lead acid batteries generate a small
amount of hydrogen gas. This gaseous by-
product is generally insignificant because the
hydrogen dissipates naturally before build up to
an explosive level (4%) occurs. However, if the
batteries are shorted or overcharging takes
place, hydrogen gas may be generated at a rate
sufficient to create a hazard. Because the
potential for excessive hydrogen build up does
exist, CSI makes the following
recommendations:
1. A CR7 equipped with standard lead acid
batteries should NEVER be used in
environments requiring INTRINSICALLY
SAFE EQUIPMENT.
2. When attaching an external battery to the
CR7, insulate the bare lead ends to protect
against accidental shorting while routing the
power leads.