As we stated in the previous article “Stationary UPS Sizing Calculations Part One” That Stationary UPS Sizing Calculations include:
 The UPS sizing calculations,
 Rectifier/Charger sizing calculations,
 Inverter & Static Switch sizing calculations,
 The Battery sizing calculations.
We explained the UPS sizing calculations in the above article and we explained in article “Stationary UPS Sizing Calculations Part Two”, the following calculations:
 Rectifier/Charger sizing calculations,
 Inverter & Static Switch sizing
calculations,
 The Battery sizing calculations, which
includes:
First: The Manufacturers’ methods, which
include:
 Method#1: Watts per cell method,
 Method#2: Watts per bank method,
 Method#3: Ampere per cell method.
Today, we will explain the Second methods of
Battery sizing calculations; The IEEE methods.
Second: The
IEEE Methods of Battery Sizing Calculations 
The IEEE methods include:

Method#1: IEEE
Standard 1184 Batteries for Uninterruptible Power Systems 
This method is intended to assist engineers who select and design battery systems for uninterruptible power systems (UPS) from the two main battery types:

Important Terminology 1 Equalizing charge  Nickelcadmium cells Recommended equalizing voltages range from
1.471.65 V/cell. To achieve reasonable endofdischarge voltages, the
equalizing voltage attainable in a specific application is normally
restricted by system voltage limitations to about 1.55 V/cell. Generally, equalizing is used for a fast
recharge after a discharge, and to assist in electrolyte mixing after water
addition (two rate chargers are generally recommended by the manufacturers).
Depending on the float voltage chosen, routine periodic equalizing may be
unnecessary. 2 Temperature – Nickel cadmium All batteries are affected by high
temperatures. However, nickelcadmium cells can sustain high temperatures
more easily than most other systems because the chemistry in the active
materials is relatively stable. For example, at 32 °C (90 °F) the normal life of a nickelcadmium cell
is diminished by about 20%, compared with a reduction of approximately 50%
for a leadacid cell. Moreover, a nickelcadmium battery will not
be destroyed by low temperatures or freezing. With a normal electrolyte, the
battery will operate at temperatures as low as 30 °C (86 °F) to 40 °C (104 °F); with a higher specific gravity
electrolyte, it will operate at even lower temperatures. The available
capacity is reduced at low temperatures, but at 40 °C (104 °F) a nickelcadmium battery can deliver 60%
or more of rated capacity. 3 Temperature  Lead acid Operating batteries at temperatures below 25
°C (77 °F) decreases performance. Note that temperature derating factors
(see IEEE Std 4851983) apply to the discharge rate and not the discharge
time. For example, a temperature derating factor
of 1.11 for a certain cell type at 15.6 °C (60 °F) indicates that battery performance is
approximately 10% less than at 25 °C (77 °F). If this battery can supply, say, 100 kW
for 15 min at 25 °C (77 °F), it will be capable of delivering 90 kW for 15 min at 15.6 °C (60 °F). Conversely, the battery may be able to
supply the same 100 kW load for only 10 min at 15.6 °C (60 °F), because of the decrease in battery efficiency
at higher discharge rates. The extent of this effect varies with cell
construction. 4 Battery Capacity The
amperehour (AH) capacity is the unit used in specifying the storage capacity
of a battery. While a battery that can deliver 10 A for 10 hours can be said to
have a capacity of 100 AH, that is not how the rating is determined by the
manufacturers.
A
100 AH rated battery most likely will not deliver 10 A for 10 hours. Battery
manufacturers use a standard method to determine how to rate their batteries.
Their rating is based on tests performed over 20 hours with a discharge rate of
1/20 (5%) of the expected capacity of the battery per hour. So a 100
amperehour battery is rated to provide 5 A for 20 hours. The
efficiency of a battery is different at different discharge rates. When
discharging at 5% an hour, the battery's energy is delivered more efficiently
than at higher discharge rates. To calculate the 5% discharge rate of a
battery, take the manufacturer's amperehour rating and divide it by 20.
5 Crate Crate
is a measure of the rate at which a battery is discharged relative to its maximum
capacity. 1C rate means that the discharge current will discharge the entire
battery in 1 hour; 0.1C means 10% transfer in one hour, or full transfer in
10hours; 5C means full transfer in 12 minutes, and so on.
6 State
of Health The
stateofhealth of a battery is the percentage of its capacity available when
fully charged relative to its rated capacity. For example, a battery rated at
30 AH, but only capable of delivering 24 AH when fully charged, will have a
stateofhealth of 24/30 x100 = 80%. Thus, the stateofhealth takes into
account the loss of capacity as the battery ages. 7 Voltage
Rating The
voltage rating is based on the number of cells connected in series and the
nominal voltage of each cell (2.0 V for leadacid type and 1.2 V for
nickelcadmium). Twelvevolt leadacid batteries will have six cells in series.
8 Reserve
Capacity (RC) This is
defined as the time in minutes for the battery voltage to fall to 10·5 volts
with a constant load of 25 Amps at a temperature of 25°C.
9 Cycle
Life The cycle
life of a battery is defined as the number of dischargecharge cycles the
battery can experience before it fails to meet specific performance criteria.
Cycle life is estimated for specific charge and discharge conditions. The
actual operating life of the battery is affected by the rate and depth of
cycles and by other conditions such as temperature and humidity.
10 State
of charge The
concentration (strength) of sulfuric acid within the electrolyte varies with
the state of charge. This changes the density or specific gravity of the
electrolyte, which can be measured with a hydrometer. A hydrometer is a scale
that indicates the density readings of an electrolyte.
Since
temperature also has a small effect on density, the graph below would be a more
accurate way of finding the state of charge. 
The design
steps for The IEEE 485 method Step#1: calculate Battery Total load Step#2: calculate the corrected Battery Total load Step#3: calculate the maximum number of cells Step#4: calculate the end voltage Step#5: calculate the Minimum number of cells Step#6: Cell selection Note: For each battery type, the design steps are
described in order to facilitate the selection. Noting that each design has
advantages and disadvantages, all of which should be considered when
selecting a battery. 
Case#1: for
Leadacid battery calculations 
Initial assumptions and limiting factors Battery discharge voltage range: 1.67 2.10
V/cell Battery equalizing charge range: 2.30 2.50
V/cell Step#1: calculate Battery Total load Battery Total load (W) = UPS Load (W) /
inverter efficiency Or Battery Total load (W) = UPS Load (W) +
inverter losses (W) Example#1: System size: 500 kVA at 0.80 PF, 400 kW System output voltage: 3 ph, 120/208 Vac
(not required for calculation) Inverter efficiency: 0.92 efficiency at full
load (dc input to ac output) Solution: Battery Total load (W) = 400 kW/0.92 = 435
KW Note: The very latest generation of online UPS
have inverter efficiencies of up to 97%, producing longer battery autonomies
than could previously be achieved from the same battery connected to a UPS
with a less efficient inverter. 
Step#2:
calculate the corrected Battery Total load Corrected Battery
Total load = Battery Total load × ageing factor × temperature correction
factor x design Margin Where:  Ageing factor Since the battery capacity does not remain
at its nameplate rating throughout its life, a 25% margin will be included as
an aging factor for the 435 kW.  Temperature correction factor Also, since it is expected that the
operating temperature will drop to a low of 15.6 °C (60°F), the battery capacity should be increased
by another 11% (per IEEE Std 4851983) to ensure that it will provide rated load
at reduced temperature.  Design Margin A design margin is taken into
account for any inaccuracies in the load’s estimation. Generally, a design
margin ranges between 10% and 15% is suggested. And sometimes it will be
ignored. Then, in continued example#1: Corrected Battery Total load = 435 KW * 1.25
*1.11 = 604 KW 
Step#3:
calculate the maximum number of cells In Continued example#1: It is assumed that the manufacturer
recommends an equalizing voltage of 2.40/cell. The maximum number of cells = Maximum system
voltage / Recommended equalizing V/cell Then, The maximum
number of cells = 432/2.40 = 180 cells Note: In this case no adjustment is made for the
voltage losses in the cables and cell connectors. In the final stages of
battery recharge the current drops to a point where the voltage drops are
insignificant on the large cables that have been sized for the final
discharge currents. 
Step#4:
calculate the end voltage Note: In order to take full advantage of the
battery’s usable capacity, the lowest possible endofdischarge cell voltage
should be used. This is subject to the limits imposed by the minimum
allowable system voltage and the battery manufacturer’s stated minimum cell
voltage for the discharge time in question. More important, the battery must first be
capable of being charged in accordance with the manufacturer’s recommendations
and within the maximum system voltage limit. The final
voltage per cell = Minimum battery voltage/Number of cells In Continued example#1: Allowing for the planned 2 V loss in the cables, the minimum battery voltage of 292 V is then used to calculate the final voltage per cell: The final voltage per cell = Minimum battery
voltage/Number of cells = 292/180 = 1.62 V /cell 
Step#5:
calculate the Minimum number of cells Note: In most cases, the calculated number of
cells and minimum voltage per cell would be used directly in the remainder of
the battery sizing exercise. However, in this example, it is assumed that the
battery manufacturer states a minimum discharge voltage of 1.67 V/cell for a
20 min discharge. Since the calculated minimum voltage is 1.62 V/cell and the
manufacturer’s minimum voltage is 1.67 V/cell, it is necessary to adjust the
number of cells to reflect the higher value of the minimum discharge voltage. Minimum number
of cells = Minimum battery voltage/ Minimum discharge V/cell Therefore, In Continued example#1: Minimum number of cells = Minimum battery
voltage/ Minimum discharge V/cell = 292/1.67 = 175 cells 
Step#6: Cell
selection At this point it has been determined that
the battery required is one with 175 cells that can deliver 604 kW for 20 min
and not drop below 1.67 V/cell. Each cell shall then deliver: 604 kW/175 cells = 3.45 k W/cell Now there is complete information with which
to consult the manufacturer’s performance charts and select the proper cell
for the application (20 min, 1.67 V/cell, and 3.45 kW/cell). It may be beneficial to repeat the
calculation to optimize the number of cells for a particular cell type. For example,
if there is a cell that can provide 3.40 kW/cell, it would probably be more
economical to increase the number of cells, rather than using 175 of the next
larger cell size. In this case, the new number of cells would be: 604 kW/3.40 = 178 c ells Notes:  Changing the number of cells will affect
both:
 Increasing the number of cells allows a
lower endofdischarge voltage per cell (more usable capacity) within the
lower system limit, but may result in a required equalizing voltage that is
higher than the upper system limit.  Decreasing the number of cells will not
impose any constraints on the maximum voltage limit, but will result in a
higher endofdischarge voltage per cell (less available capacity).  In this particular example, it is already
known that 180 cells can be accommodated within the upper system voltage
limit. At the lower voltage limit, the use of 178 cells would allow
discharging to 1.64 V/cell, but would fail to meet the battery manufacturer’s
stated minimum of 1.67 V/cell.  Battery selection, then, is a process of finding
the best fit between the maximum charge voltage and the minimum operating
point of the UPS that will allow the maximum use of the available battery
capacity. 
Case#2: for Nickelcadmium
battery calculations 
Initial assumptions and limiting factors Battery equalizing voltage 1.52 V/cell Battery discharge voltage 1.00  1.10 V/cell Step#1:
calculate Battery Total load As in example#1 
Step#2:
calculate the corrected Battery Total load Since the design life (assumed to be 15
years) is well within the life expectancy of vented nickelcadmium batteries,
a 10% margin will be included as an aging factor for the 435 kW. Typically, temperature factors are used in
nickelcadmium battery sizing only when there is a considerable deviation
from room temperature. In this example, the 15.6 °C (60°F) minimum temperature typically would give
rise to a capacity reduction of only 3% or so. This figure would generally be
incorporated into the overall battery sizing margins to give a combined figure
for both aging and low temperature operation. Then, Corrected Battery
Total load = Battery Total load × ageing factor × temperature correction
factor x design Margin Corrected
Battery Total load = 435 kW x 1.10 = 479 kW 
Step#3:
calculate the maximum number of cells Selection of number of cells (cell type) and
end voltage point The most economical battery choice results
from using the lowest endofdischarge voltage and the largest possible
number of cells that will satisfy the manufacturer’s recommendations. The
first step in the battery calculation is to ensure that the battery can be
properly charged. For this example, it is assumed that the manufacturer recommends a minimum equalizing voltage of 1.52 V/cell. The maximum number of cells is therefore: The maximum number of cells = Maximum system
voltage / Recommended equalizing V/cell The maximum
number of cells = 432/1.52 = 284 cells 
Step#4:
calculate the end voltage Note: In this case no adjustment is made for
voltage losses in the battery cables and cell connectors. In the final stages
of battery recharge the current drops to a point where the voltage drops are
insignificant on the large cables that have been sized for the final
discharge currents. Allowing for the planned 2 V loss in the
cables, the minimum battery voltage of 292 V is then used to calculate the final
voltage per cell: The final voltage
per cell = Minimum battery voltage/Number of cells Then, The final voltage per cell = 292/284 = 1.03
V/cell 
Step#5:
calculate the Minimum number of cells Minimum number
of cells = Minimum battery voltage/ Minimum discharge V/cell Then, Minimum number of cells = 292/1.1 = 266
cells 
Step#6: Cell
selection At this point it has been determined that
the battery required is one with 284 cells that can deliver 479 kW for 20 min
and not drop below 1.03 V/cell. Minimum discharge V/cell = 479/284 = 1.69 k W/cell Now there is complete information with which
to consult the manufacturer’s performance charts and select the proper cell
for the application. When using tabular data, it may be necessary to
interpolate between published values. For instance, in the example the cell type required is one that will supply 1.69 kW/cell for20 min to a final voltage of 1.03 V/cell. In this case it would probably be necessary to interpolate between values given for a final voltage of 1.05 V/cell and 1.00 V/cell. Since most manufacturers offer high, medium, and low rate cell ranges, it may be advisable to determine cell sizes for two or more of the ranges. The most economical option meeting the above parameters can then be chosen. Battery selection then, is a process of finding the best fit between the maximum charge voltage and the minimum operating point of the UPS that will allow the maximum use of the available battery capacity. 
Method#2: IEEE
485 Lead Acid Batteries for Stationary Applications 
This
standard details methods for defining the dc loads and for sizing a leadacid
battery to supply those loads in full float operation The IEEE 485 design method
has the five steps as follows: Step#1: develop the overall connected load list that the battery
requires to supply Step#2: Develop a load profile Step#3: Calculating the Design Load & Energy
Demand Design Load Step#4: Choose the type of
battery and determine the cell characteristics Step#5: On the basis of design
loads, calculate the desired Amperehour (Ah) battery capacity 
Step#1: develop the overall connected
load list that the battery requires to supply The first step is the determination of the total connected loads
that the battery needs to supply and making a load list. This is mostly
particular to the battery application like UPS system or solar PV system. For
this purpose, Loads are classified as:
Calculating the Consumed Load ( VA ) Here, we can calculate the consumed apparent power of the loads
in terms of VoltAmpere. For every single load, we can compute the VA using
the following formula: S=Pcosϕ×η Where S, load consumed apparent power (VA) P, load consumed active power (W) η, load efficiency (pu) cosϕ, load power factor (pu) 
Step#2: Develop a load profile The load profile is developed from the load list that
demonstrates the load’s distribution over the
period of time. The standard recommends a
duty cycle be drawn showing the anticipated loads (in Ampere or power) for
the required duration of battery backup time and take in Consideration the following:
Figure1: Duty Cycle Diagram There are two various methods to develop load profiles:
Note: Both methods use the same first three general steps with some
minor differences. 1 the 24 Hour Method This method exhibits the average instantaneous loads over a period
of 24 hours and it is primarily utilized in solar PV system applications. In the 24 hour profile method, the associated time period
is represented in tens of "ON" and "OFF" times. These are
the times in the day (in hours and minutes) that the load is expected to be
switched on and then later turned off. For loads that operate continuously,
the ON and OFF time would be 0:00 and 23:59 respectively. A load item may
need to be entered in twice if it is expected to start and stop more than
once a day. 2 the Autonomy Method This method is primarily utilized in backup power applications
such as battery systems in UPS. This method exhibits the average
instantaneous loads over an autonomy (backup) time, which is the time period
(the number of hours) in which the load
needs to be supported during a power supply interruption The “Autonomy method” for constructing load profile is typically
used for AC UPS system & batteries. And we get
it either from:
Sometimes
a single autonomy time is used for entire UPS load, which obviously makes the
construction of the load profile easier to compute. Some loads may only be required to ride through brief
interruptions or have enough autonomy to shut down safely, while some
critical systems may need to operate for as long as possible (up to several
days) How to develop he load profile using Autonomy
Method? The load profile in the Autonomy Method is developed
by heaping “energy rectangles” on top of one another. In this energy
rectangle, height represents the
load (VA) and the width represents the autonomy time (backup time) whereas
the rectangle area represents the total load’s energy.
The load profile is produced by heaping the broadest rectangles first. Example#2: Let’s assume the loads given in the following table are based on
the Autonomy (Backup) Method: For example of drawing the load profile for
every load, the Digital CrossConnect Section will be a rectangle of width 4
(hours) and height of 200 (VA). The load profile is produced by heaping the
broadest rectangles first so the telecom section will be the first
represented load Figure2: Load
Profile for the Battery Sizing Example 
Step#3: calculating the Design Load & Energy Demand
Design
Load First: the Design Load The design load is the one for which all the system devices
should be rated such as fuses, breakers, cables, inverters, rectifiers. The
design load can be computed using the following equation: Sdes=Speak(1+kcont)(1+kdm) Where: Sdes, design load in VA Speak, peak load in VA kcont, contingency factor for load growth (%) kdm, design margin (%) Notes:
Example#3: Let’s assume that the peak load apparent power is 640 VA.
Considering a future growth of 10 % and a design margin 10%, the total design
load is: Sdes=Speak(1+kcont)(1+kdm)=640×(1+0.1)(1+0.1)=774.4VA Second: the Energy Demand The design energy requirement (VAh) is utilized for energy
storage devices sizing. The total design energy can be calculated by
computing the area under the load profile curve. The total design energy
requirement can be computed using the following equation: Ede=Etle(1+kcont)(1+kdm) Where: Ede, total design energy required (VAh) Etle, total load energy (area under the load profile) in VAh kcont, contingency factor for load growth (%) kdm, design margin (%) Example#2 continued: From table 1 above, the total load energy is 2,680VAh.
Considering a future growth of 10 % and a design margin 10%, the total design
energy required is: Ede=2680×(1+0.1)(1+0.1)=3243VAh 
Step#4: Choose the type of battery and determine the cell
characteristics The following step is the selection of the type of battery (e.g.
Leadacid or nickelcadmium). While choosing the battery type, the following
elements should be considered as per IEEE guidance:
Next is to determine the battery cell characteristics which are
generally provided in manufacturer’s data sheet. The primary cell
characteristics that should be considered are:
Battery’s AmpereHour capacities are provided by the battery
manufacturer on the basis of various EODVs. For leadacid type batteries, an
EODV is principally based on an EODV value that prohibits cell damage by
overdischarge. Generally, EODV ranging between 1.750V and 1.80Vis utilized
per cell when discharging time is longer than 1 hour. For short discharging
time (<15 minutes), an EODV of about 1.66V per cell may be utilized
without cell damage. Total Number of
Cells The number of cells required for a particular voltage rating is
presented below: But, the number of cells required can be determined more
precisely in order to match with the load tolerance more accurately. The
number of battery cells expected to be linked in series fashion must fall
between the two limits (Nmin & Nmax) which are given below: The number of cells in a battery is computed to match the minimum and maximum voltage tolerances of the load. As a minimum, the battery at its EODV must be within the minimum voltage range of the load. Meanwhile, as a maximum, the battery at float voltage (or boost voltage) needs to be within the maximum voltage range of the load. The cell charging voltage depends on the type of charge cycle that is being used, e.g. float, boost, equalizing, etc, and the maximum value should be chosen. The number of battery cells required to be
connected in series must fall between the two following limits: Nmin = Vdc*(1+Vmax) / Vc Nmax = Vdc*(1Vmin) / Veod Where: Nmin = minimum number of battery
cells Nmax = maximum number of battery
cells Vdc = nominal battery voltage
(V) Vmin = minimum load voltage
tolerance (%) Vmax = maximum load voltage
tolerance (%) Veod = cell end of discharge
voltage (V) Vc = cell charging voltage (V) Choose the required number of cells within these two limits
(although choosing cell numbers in the middle of minimum and maximum values
would be most suited). Example#3: The minimum and maximum load
voltage tolerances are Vmin = 10% and Vmax = 10%, respectively. For the
battery, nominal voltage is Vdc = 120V, endofdischarge voltage is Veod =
1.8V/cell, and the cell charging voltage is Vc = 2.05V/cell. Then, Nmax = 120(1+0.1) / 2.05 Nmax = 64.4 or 64 cells Nmin = 120(10.1) / 1.8 Nmin = 60 cells Use 62 cells in series (number
of cells between 60 and 64). Another method for calculating Number of Cells and Cell
Voltage The number of cells is estimated based on the maximum battery
voltage and float charge voltage: Number of cells = maximum
voltage / float charge voltage The
minimum battery voltage is the minimum system voltage (including voltage
drops across cables). Given the minimum cell voltage the minimum cell
voltage is given by: Minimum cell voltage (V/cell) =
minimum battery voltage / number of cells 
Step#5: calculate the Desired AmpereHour (Ah) Battery Capacity The battery capacity desired to accommodate the total designed
load over the determined back up (autonomy) time can be calculated using the
following formula: Cminimum= Ede(kaf×ktcf×kcrt) /( Vdc×kmdod×kse) Where: Ede,
total designed energy over back up time (VAh) kaf,
Battery Aging Factor (%) ktcf,
Temperature Correction Factor (%) kcrt,
Capacity Rating Factor (%) Vdc,
Battery Voltage (Nominal) kmdod,
Maximum depth of Discharge (%) kse,
System Efficiency (%) Choose a battery capacity (AmpereHour) that surpasses the
minimum capacity calculated using the above battery sizing formula. An explanation of the various elements:  Aging Factor: It actually represents the reduction in battery performance with
the passage of time. To ensure the battery can meet the design requirements
throughout its life the standard suggestions the initial capacity should be
125% of the design capacity.  Temperature correction factor: The battery cells capacity is generally provided for a
standardized temperature which is 25^{o}C and if it varies, the
battery cells capacity will vary as follows: Temperature decreases, the battery cells capacity decreases And vise verse as the temperature increases, the
battery cells capacity increases So, a correction factor is needed to implement and this
correction factor we can get it from the below table.
Temperature correction factor Table  Capacity rating factor This factor accounts for voltage reduction during the discharge
of the battery. In Leadacid batteries, a voltage dip occurs in the early
phases of battery discharge followed by certain recovery. There
are two ways of expressing capacity: Term R_{t} The term R_{t} is
the number of amperes each plate can supply for t minutes, at 25^{o}C to a defined minimum cell voltage. Ct = Rt Term K_{t} The term K_{t} is the ratio of amperehour
capacity, at a standard time rate, at 25^{o}C and to a
defined minimum voltage which can be delivered for t minutes. Ct = 1/Kt R_{t} is not equal to 1/K_{t} because
each factor is expressed in different units.  System efficiency It accounts for battery losses (coulombic efficiency) as well as
power electronics losses (such as charger and inverter).  Design Margin It accounts for unexpected circumstances (increased loads, poor maintenance,
recent discharge, etc.) it is common to allow a design margin of 10% to 15%.  Depth of discharge (DOD) Consider shallow DOD (max 20% recommended)
and occasional deeper DOD (max 80%) Example#4: calculate for the minimum
battery capacity using the given energy demand of 4020 VAh, battery
aging factor (kaf) = 25%, temperature correction factor at 30 deg C (ktcf) = 0.956, capacity rating factor (kcrt) = 10% and depth of discharge (kmdod) = 80%, system efficiency (kse) = 95% Cminimum = Ede(kaf×ktcf×kcrt) /( Vdc×kmdod×kse) Cminimum = [4020 VAh X (1.25 X 0.956 X 1.1)] / (120 V X 0.8
X0.95) Cminimum = 57.94 Ah Use a VRLA battery with a 60 Ah
capacity. 
Example#5: Battery Sizing Calculation Steps#1 and #2: Collect All the Connected
Loads and Develop a Load Profile In this particular example, we will apply the same loads and
load curve provided in the Load Profile Calculation Example.
The load profile for this case is demonstrated in the figure below. Step#3: calculating the Design Load &
Energy Demand Design Load From the load profile, the following parameters were computed: Total Design Energy Demand = E_{de} = 3,245 Vah Step#4: Choose
the type of battery and determine the cell characteristics For this particular example, a vented leadacid battery has been
chosen. We assumed the following values in order to calculate number of
cells required: Vdc=120V Vload,min=10 Vload,max=20 Veodv=1.80V/cell Vcharging=2.25V/cell Maximum number of cells required to be connected in series: Nmaximum=Vdc(1+Vload,max)/Vcharging=120×(1+0.2)/2.25=64 Cells Minimum number of cells required to be connected in series: Nminimum=Vdc(1−Vload,min)/Veodv=120×(1−0.1)/1.80=60 Cells The number of cells chosen for this example is 62 cells which is
in between the maximum and minimum limits. Step#5: calculate the Desired AmpereHour
(Ah) Battery Capacity We assumed the following values in order to compute the
battery capacity: Ede=3245 VAh kaf=0.30 ktcf=0.96 kcrt=0.12 Vdc, Battery Voltage (Nominal) kmdod=0.75 kse = 1 Using the above mentioned parameters, we can compute the minimum
battery capacity as: Cminimum=Ede(kaf×ktcf×kcrt)/Vdc×kmdod×kse Cminimum=3245×(1.30×0.96×1.12)/(120×0.75x1)=50.4 Ah Choose
a battery capacity (AmpereHour) that surpasses the minimum capacity computed
using the above formula. 
Very important Note
Mixing different battery sizes or types in a system is generally
not recommended due to variations in voltage, capacity, and
charging/discharging characteristics. It is best to use batteries of the same
type, capacity, and age to maintain optimal performance and balance within
the system.

In the
next Article, we will explain the following:
 UPS Backup time calculation
 Selection and sizing of UPS protective devices (CBs or Fuses)
 Selection and sizing of UPS Cables
 Sizing a generator set for UPS system
 UPS room ventilation calculation
So, please
keep following.
Subject Of Pervious Article 
Article 
Applicable Standards for UPS Systems
1Voltage range, 2No. of phases, 3 Mobility, 4 Technological design, 
Classification and Types of UPS – Part One 
5 Physical Size/capacity, 6 Form factor/ configurations: 6.1 “N” System
Configuration 
Classification and Types of UPS – Part Two 
6.2 “N+1” System
Configuration, which includes:
6.3 Parallel Redundant with Dual Bus Configuration (N+1 or 1+1) 
Classification and Types of UPS – Part Three 
6.4 Parallel Redundant with STS Configuration
6.5 System plus System 2(N+1), 2N+2, [(N+1) + (N+1)], and 2N 
Classification and Types of UPS – Part Four 
7 According to UPS Topology 7.1 Offline or Standby UPS, 7.2 Line Interactive UPS, 7.3 StandbyFerro UPS, 7.4 Online Double Conversion UPS, 7.5 The Delta Conversion OnLine UPS. 
Classification and Types of
UPS – Part Five 
8 According to UPS Distribution
Architecture 8.1 Centralized UPS Configuration, 8.2 Distributed (Decentralized) UPS Configuration, 8.2.1 Distributed UPSZonewise Configuration 8.3 Hybrid UPS Configuration. Conventional (Monolithic) Vs Modular
UPS System:

Classification and Types of UPS – Part Six 
Three Basic Configurations Of Mains And Bypass For A UPS System:
9According to Use of transformers with the UPS

Classification and Types of
UPS – Part Seven 
Transformer Arrangements in Practical UPS Systems: 1Transformer options for the “single mains” configuration 2Transformer Options for the “Dual Mains” Configuration 
Classification and Types of UPS – Part Eight 
3
Transformer options for “single mains without bypass” 

Components of Online Double Conversion UPS: 1 Rectifier, 2 Inverter, 3 Energy Storage system: 3.1 Battery 
Components of Online Double Conversion UPS– Part One

3.1.1 Battery
Configurations
3.1.2
Battery Size and Location 3.1.3
Battery Transition Boxes 3.1.4
Battery Monitoring 3.2
Energy Storage System – Flywheel 3.3
Energy Storage system – Super Capacitors 3.4
Hydrogen Fuel Cells 4 Static
switch Earthing
Principles of UPS Systems 
Components of Online Double Conversion UPS – Part Two 
Evaluation Criteria for Selecting an UPS: Step#1:
Determining the need for an UPS, Step#2:
Determining the purpose(s) of the UPS, Step#3:
Determining the power requirements, Step#4:
Selecting the type of UPS, Step#5:
Determining if the safety of the selected UPS is acceptable, Step#6:
Determining if the availability of the selected UPS is acceptable, Step#7:
Determining if the selected UPS is maintainable, and Step#8: Determining if the selected UPS is affordable. 
Evaluation Criteria for Selecting an UPSPart One

Example:
Selecting an Uninterruptible Power Supply (UPS) UPS
System Ratings and Service Conditions First:
from IEC 601464 Second:
according to American standards 
Evaluation Criteria for Selecting an UPSPart Two 
The
UPS sizing calculations steps: Step#1:
List All the UPS Loads Step#2: List for Each Equipment/Load, the Voltage,
Number of Phases, and Frequency Step#3: List the KVA for Each Equipment/Load Step#4: Determine The UPS Voltage, Number Of Phases,
and Frequency. Step#5: Segregate the Loads (NonMotor Loads &
Motor Loads) Step#6: Determining Load Power Factor and KW Demand Step#7: Determining Load Inrush Current/KVA. Step#8: Determine Loads’ Sequence of Operation Step#9: Apply the Derating Factors (If Any) Step#10: Calculate the Design UPS Load KVA 
Stationary UPS Sizing Calculations – Part One

2
Rectifier/Charger Sizing Calculations 3
Inverter sizing calculations & Static Switch Sizing 4
The Battery sizing calculations First:
The Manufacturers’ methods, which include:

Stationary
UPS Sizing Calculations – Part Two 
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