DC Backup UPS
Application, Maintenance and Installation Manual
Revision 1
Calculation example:
2 Amps backup is required for 8 hours.
a) Multiply Amp x Hours (8 x 2 = 16). This gives 16Ahrs. Nearest size DCUPS would be 17Ahrs.
b) Look at Figure 3.1. The discharge time, in this case 8 Hrs, shows that approx. 90% of the 17Ah will be
available from a fully charged battery
c) Check: 17 * 0.9 = 16 approximately so this unit will just satisfy the load
The curve above shows the probable available Ampere-hour capacity for varying time periods over which
the battery is drained. This is fairly indicative of commercially available sealed lead acid batteries.
Figure 3.1
4
Technical description
Model 7021 and 7025 is a 12volt (nominal) DC power-supply with battery backup. An AC rectifier supplies
power to the load and doubles as a battery charger. There are 3 modes of operation:
•
AC power available. In this mode, the load is supplied from the AC rectifier. The battery is charged at a
constant voltage but with controlled current. Thermal compensation is provided to ensure that the battery
receives optimum charge.
•
AC fail condition. In this mode, the internal 12volt lead acid battery supplies the load. Battery voltage
and unbalance are monitored. Low battery is flagged as an alarm.
•
Over-current condition. In this mode, the internal battery can supply peak currents to the load for short
periods. The battery fuse limits the amount of over-current. Sustained high current will cause the fuse to
open.
Changeover from AC to DC is done electronically without break in supply to the load. In AC available
mode, the battery is charged automatically.
18/10/06
7021 and 7025_manual1.doc
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