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Discharging

 
(1) Discharge Current and Discharge Cut-Off Voltage
Recommended cut-off voltages for 6V and 12V batteries consistent with discharge rates, are given in the figure below. With smaller discharging currents, the active materials in the battery can work effectively. As a result, the discharge cut-off voltages are set to the higher side to control overdischarge. For larger discharge currents, on the contrary, cut-off voltages are set to the lower side.

Discharge Capactiy vs. Cut-Off Voltage

 
(2) Discharge Temperature
(a) Control the ambient temperature during discharge within 5F to 122F
(-15C to 50C) for the reason described below.

(b) Batteries operate on the electrochemical reaction that converts chemical energy to electric energy. The electrochemical reaction is reduced as the temperature lowers. Therefore, available discharge capacity is greatly reduced at temperatures as low as 5F(-15C). For the high temperature side, on the other hand, the discharge temperature should not exceed 122F
(50C ) in order to prevent deformation of resin mateirals that house the battery or deterioration of service life.
 
(3) Effect of Temperature on Discharge Characteristics
Available discharge capacity of the battery varies with ambient temperature and discharge current as shown in the figure below.

Discharge Capactiy by Temperature and by Discharge Current

 
(4) Discharge Current
Discharge capacity of batteries is expressed by the 20 hour rate(rated capacity). Select the cattery for the specific equipment so that the discharge current during use of the equipment falls between 1/20 of the 20 hour rate value and 3 times that (1/20 CA to 3 CA); Discharging beyond this range may result in a remarkable decrease of discharge capacity or reduction in the number of times of repeatable discharge.When discharging the battery beyond the said range, please consult TEMPEST in advance.

For some types of SLA batteries with built-in thermostats, the discarge current may be auotmatically cut off by these thermostats when above 4A at the room temperature of 104F (40C). Therefore, the maximum discharge current value should be the smaller of either 4A or 2CA.

 
(5) Depth of Discharging
Depth of discharging is the state of discharge of batteries expressed by the ratio of amount of capacity discharged to the rated capacity.
 


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