Standard

This calculator is based on the IEEE STD485 Battery Sizing Procedure. Common applications are whereever protection relays and isolating devices require a DC power source. Typical Generating Stations, Substations, oil and gas plants where continouos uninterrupted power is required. These applications require the following:

• Shorter-duration, higher-current applications.
• Max current greater than 20-hr rate.
• Max current much greater than average current.

The calculations performed are based on “Recommended Practice for Sizing Lead-Acid Batteries for Stationary Applications” and “Recommended Practice for Sizing Nickel-Cadmium Batteries for Stationary Applications” IEEE standards. All the calculations in this calculator are established on conventional lead-acid or nickel-cadmium (NiCd) batteries.

EDM does not support other types of batteries, so the manufacturer’s guidance of sizing these types of battery will be required by the user.

This Battery Bank Calculator works in three easy steps:

• Step 1 - from the Battery Specifications page fill-in the required inputs.
• Step 2 - from the Quiescent Load Summary Page build your continuous load profile.
• Step 3 - from the Momentary Load Summary Page build your momentary load profile.

That's it! Your Battery Bank and Charger sizes are shown on the Battery Bank and Charger Size Page.

You do the same with the cable sizing Calculator and all cable requirement are sized. An added feature is all the protection equipment (breakers, fuses) are also calculated.

One last feature, the program produces a single line and three line CAD drawing to complete your Design!

Number of Cells

Battery banks for switchgear and control applications are made up of many cells. These cells are typically wired in series to achieve a desired voltage and may also be wired in parallel to achieve additional ampere capacity. Sizing of these battery banks, therefore, includes selecting the number and type of cells to be used.

The terminal voltage per cell varies with the battery's chemical composition. The required number of series wired cells to achieve the more common DC control voltages for switchgear control is shown in Battery Bank Information Table on the Battery Specification page. Selection of the type of cell is based on the required peak ampere output (1 min.) and total Ampere-hour (Ah) output capacity for the load and duration.

The nominal voltage of lead acid is 2 volts per cell, however when measuring the open circuit voltage, the OCV of a charged and rested battery should be 2.1V/cell. Keeping lead acid much below 2.1V/cell will cause the buildup of sulfation. While on float charge, lead acid measures about 2.25V/cell, higher during normal charge.

The nominal voltage of NiCd and NiMH are rated at 1.20V/cell; industrial, aviation and military batteries adhere to the original 1.25V. There is no difference between the 1.20V and 1.25V cell.

Load Type

IEEE Standard 485 classifies individual DC loads as continuous, non-continuous, and momentary. Typical continuous loads include lighting, continuously energized coils, and power to protective relay and communications systems.

Non-continuous loads are less common and include critical ventilation system motors and valve actuators with operating times exceeding 1 minute.

Momentary loads do not exceed 1 minute in duration and include inrush currents and circuit breaker operations.

Sizing Guidelines

Since the momentary load on a switchgear battery bank is much higher than the continuous load, the required 1-minute (peak) ampere rate typically determines the battery cell type. However the Ampere-hour rate should also be checked. The battery cell type that meets the worst-case condition between the two should be selected.

To calculate the required 1-minute ampere rate, assume the peak rate to be equal to the sum of the loads (i.e. in-rush current for all breaker charging motors, load currents for all relays and other loads, and ignore pilot lights).

Although momentary loads usually exist for much less than a minute — perhaps only a fraction of a second — it is common practice to use the full ampere value for an entire minute. Assign a required 1-minute amp peak rate equal to this peak rate divided by the ambient temperature derating factor, the battery aging factor, and a design margin as listed in the Tables on Battery Specification page.

To calculate the required Ampere-hour rate, compute the average continuous load and divide by the ambient temperature-derating factor and battery-aging factor etc., as listed in Formula section on this page. Use the manufacturer's data to select the battery cell type that meets both the 1-minute amp peak rate and Ampere-hour requirements from the Typical Battery Discharging Tables on the Battery Specification page.

Load Profiles

The first step is to gather the project loads into a load profile. Start by selecting your equipment by the categories listed below. The EDM Program will start building your load profile which will evenually determine your battery bank, charger and cabling sizes.

IEEE Standard 485 classifies individual DC loads as continuous, non-continuous, and momentary.

• Continuous (Quiescent) loads include lighting, continuously energized coils, and power to protective relay and communications systems. The Quiescent Load Profile page builds the continuous load profile allowing the user to enter the loads and EDM totaling the loads. The results are then passed on to the specific formulas for calculating loads for battery bank, charger and cabling.
• Non-continuous loads are less common and EDM includes these in the quiescent load calculations (these include critical ventilation system motors and valve actuators with operating times exceeding 1 minute).
• Momentary loads do not exceed 1 minute in duration and include inrush currents and circuit breaker operations. The Monmentary Load Profile page builds the momentary load profile allowing the user to enter the loads and with EDM totaling the loads. The results are then passed on to the specific formulas for calculating for battery bank, charger and cabling.

Formulas

Design Load: The design load is the instantaneous load for which the power conversion, distribution and protection devices should be rated, e.g. rectifiers, inverters, cables, fuses, circuit breakers, etc. The design can be calculated as follows:

• Sd=Sp*(kg)*(kd).
• Where:
• Sd is the design load apparent power (VA).
• Sp is the peak load apparent power, derived from the load profile. (Total VA).
• kg is a contingency for future load growth (%).
• kd is a design margin (%)

It is common to make considerations for future load growth (typically somewhere between 5 and 20%), to allow future loads to be supported. If no future loads are expected, then this contingency can be ignored. A design margin is used to account for any potential inaccuracies in estimating the loads, less-than-optimum operating conditions due to improper maintenance, etc. Typically, a design margin of 10% to 15% is recommended, but this may also depend on Client preferences.

Note: EDM calculates total VA, kW and Amps and uses total amps to calculate design load to accommodate Manufacturer's data. ( 1 min total discharge given in amps) as follows:

1 Minute Peak Discharge in Amps = ED/Vdc.

• Ed is the design energy demand (VA).
• Vdc is the nominal battery voltage (Vdc).

Energy Load: The design energy demand is used for sizing energy storage devices. From the load profile, the total energy (in terms of VAh) can be calculated by the following equation:

• Ed=Et*(kg)*(kd).
• Where:
• Ed is the design energy demand (VA).
• Et is the total load energy (VAh).
• kg is a contingency for future load growth (%).
• kd is a design margin (%)

Minimum Battery Capacity: The minimum battery capacity required to accommodate the design load over the specified autonomy time can be calculated as follows:

• Cmin=Ed*(ka*kt*kc)/Vdc*kdod*ke.
• Where:
• Cmin is the minimum battery capacity (Ah) .
• Ed is the design energy over the autonomy time (VA).
• Vdc is the nominal battery voltage (Vdc).
• ka is a battery ageing factor (%).
• kt s a temperature correction factor (%).
• kc is a capacity rating factor (%).
• ke is a system efficiency (%).
• kdod is the maximum depth of discharge (%).

Select a battery Ah capacity that exceeds the minimum capacity calculated above.