PowerSafe V Product Guide new - EnerSys

Battery Sizing
Battery capacity is affected by the discharge rate, end
voltage, temperature and age.
Battery sizing calculations should include factors for
temperature and loss of capacity over life. A battery usually
is determined to have reached end of life when its capacity
has fallen to 80% of its rated capacity.
Strings of the same SBS batteries can be connected in
parallel to obtain higher capacities.
Telecom Applications
In general, telecom applications are a constant power or
constant current load for a specified period, to a specified
end voltage. The appropriate battery model can be selected
by referring to the Discharge Tables.
EXAMPLE 1
The following information is needed:
■ Nominal system voltage
■ Minimum system voltage
■ Load (constant current or constant power)
■ Backup time
■ Temperature range
A nominal 48V system requires a constant current of 9 Amps
for 4 hours to a minimum of 42V at a minimum operating
temperature of 20°C/68°F.
Step 1. Number of cells = nominal system voltage divided
by nominal cell voltage:
48V/ 2V = 24 cells
Step 2. Cell end voltage = minimum system voltage divided
by the number of cells:
42V/ 24 cells = 1.75 volts per cell
Step 3. Correct load for temperature and ageing:
Temperature factor = 1/Factor from Temperature
Correction Chart = 1/0.978 = 1.022
Ageing factor = 100/80 = 1.25
9 amps x temperature factor x ageing factor =
9 amps x 1.022 x 1.25 = 11.5 Amps
www.enersysinc.com
Step 4. Refer to the constant current discharge table for an
end voltage of 1.75 Vpc, and in the 4 hour column
find the model that will provide the load current.
In this example an SBS60 will provide 11.7 amps/
4 Hrs/1.75Vpc SBS60 is a 12V six cell monobloc,
so 4 blocs are required for a 48V battery.
UPS Applications
In general, UPS systems are rated in kVA, (kilo Volt
Amperes). This is a multiplication of the output voltage in
Kilo Volts and output current in amperes. The kVA rating is
always an AC rating. The kVA rating may be converted to kW
by simply multiplying the kVA by the Power Factor (PF).
kW Rating of UPS = (kVA of UPS) x (PF of UPS)
kW Rating of UPS Battery = kVA x PF
Inverter Efficiency
EXAMPLE 2
This first example covers a basic sizing procedure with no
power factor or efficiency involvement. This procedure
details only the fundamental steps required.
In an example such as this the following information is
needed as a minimum requirement:
(i) system kilowatts
(ii) required autonomy (run time)
(iii) minimum DC voltage
(iv) maximum DC voltage
If the load is given in kVA, then the PF and inverter efficiency
values must also be known.
Therefore, for a UPS requiring the following autonomy,
Battery kW Rating: 10
Battery nominal voltage: 120
Battery end voltage: 1.67 Vpc
Battery run time: 10 minutes
Publication No: EN-SBS-PG-001 February 2003
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