Campbell Scientific CR10 CR10 Measurement and Control - Page 196

SECTION 14. INSTALLATION AND MAINTENANCE The two leads from the charging source can be inserted into either of the CHG ports, polarity doesn't matter. A transzorb provides transient protection to the charging circuit. A sustained input voltage in excess of 40 V will cause the transzorb to limit voltage. Some solar panels are supplied with a connector, this connector must clipped otf so the two wires can be inserted into the two terminal ports. lt is recommended that these two leads be stripped and tinned. The red light (LED) on the PS12LA is on when a charging source is connected to the PS12LA CHG ports. The switch turns power on and off to the 12 V ports, battery charging still occurs when the switch is off. GAUTION: Switch the power to "off" before disconnecting or connecting the power leads to the Wiring Panel. The Wiring Panel and PSl2LA are at power ground. lf 12 V is shorted to either of these, excessive current will be drawn until the thermal fuse opens. The external port, labeled EXT, is not meant to be used with the PS12LA. The primary power source is the charging source, and the secondary power source is the internal lead acid battery. Connecting a lead acid battery to the external source is the same as connecting two lead acid batteries in parallel, causing one battery to drop voltage and the other to raise voltage. Alkaline batteries connected to the external port must have a diode in series to block charging which would cause an explosion. (The PSl2ALK battery pack has this diode.) Monitor the power supply using datalogger Instruction 10. Users are strongly advised to incorporate this instruction into their data acquisition programs to keep track of the state of the power supply. lf the system voltage level consistently decreases through time, some element(s) of the charging system has failed. InstrUbtion 10 measures the voltage at the 12 V port, not the voltage of the lead acid battery. External power sources must be disconnected from the CR10 and charging circuit in order to measure the actual lead acid battery voltage. TABLE 14.3-2. PSl2LA Battery and AC Transf ormer Specif ications Lead Acid Baftery Battery Type Yuasa NA 7-12 Float Life @ 25C 5 years typical Capacity 7.0 amp-hour Shelf Life, fullcharge Check twice yearly Charge Time (AC Source) 40 hr full charge, 20 hr 95% charge AC Transformer Input: 120 VAC,60 Hz 18 VDC @ 1.11 A max. 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 byproduct 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. Campbell Scientific makes the following recommendations: 1. A CR10 equipped with standard lead acid batteries should NEVER be used in applications requiring intrinsically safe equipment. 2. A lead acid battery should not be housed in a gastight enclosure. 14.3.3 PS512M VOLTAGE REGULATOR WITH NULL MODEM PORTS The PS512M 12 Volt Lead Acid Power Supply with Charging Regulator and Null Modem Ports is used when 5 volts is needed to power external modems besides the capabilities of the PS12LA. The PS512M supplies 5 volts to pin 1 of the 9 pin null modem pods, otherwise the capabilities and functions are identicalto the PS12LA. A common use for the PS512M is in radiotelemetry networks. The PS12LA cannot be modified to a PS512M. The maximum current drain on the 5 volt supply of the PS512M is 150 milliamps. 't4-4