DC Backup UPS
Application, Maintenance and Installation Manual
Revision 1
3
Application
Most equipment uses DC power, even if it is connected to the AC mains. Certain types of equipment used in
process control, use only 12VDC, which is usually supplied by the AC main via a transformer. The 7021 and
7025 series allows users of this type of equipment to have “no-break” power no matter what the condition of
the AC main. The use of the DC backup unit is shown below.
12VDC system supplied only from AC mains and AC UPS
12VDC system supplied by
7021 and 7025
series back-up unit
Figure 3
Figure 3 (AC only supply) shows a load, which is supported by a traditional UPS. Inrush current and power
factor of the load needs to be factored into the choice of UPS size. Getting the UPS matched to the load
(particularly in the small, price sensitive categories) is not straightforward. Then there are power spikes and
load transients to consider. A DC back-up system is a good alternative.
The 7021 and 7025 back-up system provides answers for all the above:
•
Rugged AC supply, rated to 55C ambient
•
Load transient tolerant design
3.1
Sizing of UPS
Batteries do not give their full capacity at higher loads, higher temperatures or as they age. As discharge time
gets smaller the available capacity is reduced. The main requirements are Amps required and backup time.
•
Amps:
The current required by the load in Amps.
•
Time:
The amount of time required for the power to be supplied to the load so that it can function well.
Number of hours or part there of. Use the typical, Battery Available Ahr Output chart (figure 3.1) Please
consult battery manufactures specifications as data may vary from this chart.
18/10/06
7021 and 7025_manual1.doc
Page 3 of 7
AC
UPS
System
power
supply
12VDC
load
7021 and
7025
series DC
backup
12VDC
load
