Load profile for this example
is the design AC load current (full load) (A) is the selected UPS rating (kVA)
is the nominal output voltage (line-to-line voltage for a three phase UPS) (Vac) Select the next standard inverter rating that exceeds the design AC load current.
Like the inverter, the static switch must be rated to continuously supply the UPS loads. Therefore, the static AC load current (as above for the inverter sizing).
Step 1 and 2: Collect the AC UPS Loads and Construct Load Profile
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Vac)
Like the inverter, the static switch must be rated to continuously supply the UPS loads. Therefore, the static AC load current (as above for the inverter sizing).
Step 1 and 2: Collect the AC UPS Loads and Construct Load Profile
For this example, we shall use the same loads and load profile detailed in the
example. The load profile is shown in the figure right and the following quantities were calculated:
Design load Sd= 768 VA
Design energy demand E
Step 3: Battery Sizing
For this example, we shall use the same battery sizes calculated in the
example. The selected number of cells in series is 62 cells and the minimum battery capacity is 44.4 Ah. A battery capacity of 50 Ah is selected.
Step 4: UPS Sizing
Overall Sizing
Given the design load of 768 VA, then a 1 kVA UPS would be appropriate.
Rectifier Sizing
Given a nominal dc link voltage of 120Vdc, the design DC load current is:
A
Suppose the minimum battery recharge time is 2 hours and a recharge efficiency factor of 1.1 is used. The maximum battery charging current is:
A
Therefore the total minimum DC rectifier / charger current is:
A A DC rectifier rating of 40A is selected.
For this example, we shall use the same loads and load profile detailed in the Energy Load Profile Calculation example. The load profile is shown in the figure right and the following quantities were calculated:
Ed= 3,216 VAh
For this example, we shall use the same battery sizes calculated in the Battery Sizing Calculation
xample. The selected number of cells in series is 62 cells and the minimum battery capacity is 44.4 Ah. A
Given the design load of 768 VA, then a 1 kVA UPS would be appropriate.
Given a nominal dc link voltage of 120Vdc, the design DC load current is:
Suppose the minimum battery recharge time is 2 hours and a recharge efficiency factor of 1.1 is used. The maximum battery charging current is:
e total minimum DC rectifier / charger current is:
A A DC rectifier rating of 40A is selected.
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example. The load profile is shown in the figure right and the following quantities were calculated:
Battery Sizing Calculationworked xample. The selected number of cells in series is 62 cells and the minimum battery capacity is 44.4 Ah. A
Suppose the minimum battery recharge time is 2 hours and a recharge efficiency factor of 1.1 is used. The
Inverter and Static Switch Sizing
Suppose the nominal output voltage is 240Vac. The design AC load current is:
A An inverter and static switch rating of
Template
A professional, fully customizable Excel spreadsheet template of the AC UPS calculation can be Lulu.
The template is based on the calculation procedure described in this page and includes the following features:
Load schedule and automatic load profile generation
Battery sizing
UPS component sizing (e.g. r
UPS Configuration
Suppose the nominal output voltage is 240Vac. The design AC load current is:
An inverter and static switch rating of 5A is selected.
A professional, fully customizable Excel spreadsheet template of the AC UPS calculation can be
The template is based on the calculation procedure described in this page and includes the following features:
Load schedule and automatic load profile generation UPS component sizing (e.g. rectifier, inverter, etc)
Screenshots from AC UPS Template
Load Profile
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A professional, fully customizable Excel spreadsheet template of the AC UPS calculation can be purchased from
The template is based on the calculation procedure described in this page and includes the following features:
Battery Sizing
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Computer Software
Preliminary sizing is normally done manually. Notwithstanding this, many AC UPS manufacturers provide sizing tools as part of their service package (for example, see the APC online UPS selector tool).
What next?
Using the results of the UPS sizing calculation, the approximate dimensions of the batteries and UPS cabinet can be estimated based on typical vendor information. This will assist in developing the equipment / room layouts.
Preliminary budget pricing can also be estimated based on the calculation results.
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Battery Sizing
Contents
1 Introduction
o 1.1 Why do the calculation?
o 1.2 When to do the calculation?
2 Calculation Methodology
o 2.1 Step 1: Collect the battery loads
o 2.2 Step 2: Construct the Load Profile
o 2.3 Step 3: Select Battery Type
o 2.4 Step 4: Number of Cells in Series
o 2.5 Step 5: Determine Battery Capacity
3 Worked Example
o 3.1 Step 1 and 2: Collect Battery Loads and Construct Load Profile
o 3.2 Step 3: Select Battery Type
o 3.3 Step 4: Number of Cells in Series
o 3.4 Step 5: Determine Battery Capacity
4 Computer Software
5 What Next?
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Introduction
Stationary batteries on a rack (courtesy of Power Battery)
This article looks at the sizing of batteries for stationary applications (i.e. they don't move). Batteries are used in many applications such as AC and DC uninterruptible power supply (UPS) systems, solar power systems, telecommunications, emergency lighting, etc. Whatever the application, batteries are seen as a mature, proven technology for storing electrical energy. In addition to storage, batteries are also used as a means for providing voltage support for weak power systems (e.g. at the end of small, long transmission lines).
Why do the calculation?
Sizing a stationary battery is important to ensure that the loads being supplied or the power system being
supported are adequately catered for by the battery for the period of time (i.e. autonomy) for which it is designed.
Improper battery sizing can lead to poor autonomy times, permanent damage to battery cells from over-discharge, low load voltages, etc.
When to do the calculation?
The calculation can typically be started when the following information is known:
Battery loads that need to be supported
Nominal battery voltage
Autonomy time(s)
Calculation Methodology
The calculation is based on a mixture of normal industry practice and technical standards IEEE Std 485 (1997, R2003)"Recommended Practice for Sizing Lead-Acid Batteries for Stationary Applications" and IEEE Std 1115 (2000, R2005)"Recommended Practice for Sizing Nickel-Cadmium Batteries for Stationary Applications". The calculation is based on the ampere-hour method for sizing battery capacity (rather than sizing by positive plates).
The focus of this calculation is on standard lead
specific supplier information for other types of batteries (e.g. lithium
that the design of the battery charger is beyond the scope of this calculation.
There are five main steps in this calculation:
1) Collect the loads that the battery needs to support
2) Construct a load profile and calculate the design energy (VAh) 3) Select the battery type and dete
4) Select the number of battery cells to be connected in series 5) Calculate the required Ampere