Datasheet

PRELIMINARY
UB20.241
U–Series
24V, 20A, DC-UPS
9. BUFFER TIME
The buffer time depends on the capacity and performance of the batteries as well as the load current. The diagram
below shows typical buffer times of the standard battery modules.
Buffer time with battery module UZK24.071 min. 13’ 30” At 10A output current *)
min. 4’ 10” At 20A output current *)
typ. 16’ 53” At10A output current, see
Fig. 9-1
typ. 5’ 12” At 20A output current, see Fig. 9-1
Buffer time with battery module UZK24.121 min. 35’ 30” At 10A output current *)
min. 11’ 53” At 20A output current *)
typ. 44’ 30” At 10A output current, see
Fig. 9-1
typ. 14’ 51” At 20A output current, see Fig. 9-1
*) Minimum value includes 20% aging of the battery and a cable length of 1.5m with a cross section of 2.5mm
2
between the
battery and the DC-UPS and requires a fully charged (min. 24h) battery.
Fig. 9-1
Buffer time vs. output current with battery modules UZK24.071 and UZK24.121
270
0
2A
4A
6A
8A
10A
150 180 2100
330
30 90
360
120 240
300 390 420
Minutes
60
A
B
45
Buffer
Current
0
5A
10A
15A
20A
25 30 350
55
5 15
60
10 20 40
50 65 70
Minutes
A
B
9h
0
0,5A
1,0A
1,5A
2,0A
2,5A
5h 6h 7h0
3,0A
11h
1h 3h
12h
2h 4h 8h
10h 13h 14h
A
B
A: UB20 + 7Ah batteries (UB20 set to 22.5V)
B: UB20 + 12Ah batteries (UB20 set to 22,5V)
The battery capacity is usually specified in amp-hours (Ah) for a 20h discharging event. The battery discharge is non-
linear (due to the battery chemistry). The higher the discharging current, the lower the appropriable battery capacity.
The magnitude of the reduction depends on the discharging current as well as on the type of battery. High current
battery types can have up to 50% longer buffer times compared to regular batteries when batteries will be
discharged in less than 1 hour.
High discharging currents do not necessarily mean high power losses as the appropriable battery capacity is reduced
with such currents. When the battery begins to recharge after a discharging event, the process is completed much
faster since only the energy which was taken out of the battery needs to be “refilled”.
For this reason, the buffer time cannot be calculated using the Ah capacity value. The equation “I x t” = capacity in
Ah generally leads to incorrect results when the discharging current is higher than C20 (discharging current for 20h).
September 2012 / Rev. 1.3 DS-UB20.241-EN preliminary
All parameters are specified at an input voltage of 24V, 20A output load, 25°C ambient and after a 5 minutes run-in time
unless otherwise noted. It is assumed that the input power source can deliver a sufficient output current.
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