What Is a Load Bank?

Testing power sources, such as uninterruptable power sources (UPS) and diesel generators, ensure that these devices will provide the required amount of power when needed. A load bank tests these power sources by developing an electrical load. Various load configurations permit testing under different conditions.

A load bank is a self-contained device that has the load elements, controls and cooling systems it needs to operate built-in. Power is delivered to a load bank, which then consumes the electrical power by applying it to a power source and either converting or dissipating the source's power output. Load banks use the energy produced to protect, support or test a power source while a "real" load or actual building load uses energy output productively.

What Is the Purpose of a Load Bank?

Load banks ensure the quality and reliability of your emergency power sources. They verify the accuracy of the generators' output capacities by creating a variety of different loads that replicate real-world use.

If you own, sell or operate generators, especially for backup power, you need to test them regularly. Without testing, you cannot be assured the generator will provide the required power when the lights go out. Many facilities require load tests of all backup power sources. Prime power generators benefit from load bank use, particularly in lightly loaded situations.

What Does a Load Bank Do?

A load bank develops an electrical load. Load banks are absolutely essential for emergency sources of power, as they verify the power source's rated output capabilities before the power source is called into actual use. A load bank should mimic the real load a power source would see during an actual use scenario. The devices usually have different levels of load, which allows critical systems to be tested under a variety of conditions.

Who Uses Load Banks?

You need this type of testing bank if you have generators or uninterruptable power sources in your business. Best practices for testing emergency power sources is regular load bank tests.

If you have diesel generators on-site, you may use a load bank to augment lightly loaded situations and keep your generator running properly. Wet stacking occurs when unburned fuel remains inside the system. The unburned diesel condenses and combines with soot in the exhaust system, leading to wet deposits on exhaust components. Left unchecked, wet stacking reduces engine efficiency until it requires a complete overhaul to restore its former power.

The best way to prevent this from occurring is to test the generator with a load bank, which enables you to complete two maintenance tasks with one action. Monthly testing is a requirement from the National Fire Prevention Association, in its Standard for Emergency and Standby Power Systems. You must test the generator at full load to maintain the minimum exhaust temperature recommended by the manufacturer. An alternative test allows you to use 30% more than the rating on the generator's nameplate for at least half an hour.

A novel use for these banks is for renewable energy sources. The Hawai'i Natural Energy Institute (HNEI) has incorporated a load bank into the power system on the island of Moloka'i. The island could not add more photovoltaic cells because it posed the threat of producing too much electricity and dropping the power produced by the island's diesel generators too low. The addition of a resistive load bank allows the island to add more solar cells because the load bank moderates the amount of power the island gets by absorbing any extra electricity produced.

Typical Load Bank Configurations

Typical Load Bank Configurations

There are four main configurations for load banks. Capacity in kilowatts (kW) and how you use the load banks will determine the best options for your business.

1. Stationary

If you have a permanent generator on-site, consider a stationary load bank that you have built into your construction. These models have power ratings up to 3,000 kW and system voltages up to 600 VAC. Stationary models are permanent solutions for regular testing and also for supplementing light loads, and typically require more space to accommodate. Safe for use outdoors and free-standing, stationary models offer the best solution for frequent testing needs.

2. Portable

If you need a more mobile option, portable banks go wherever you need them to. Portable models will fit through most doorways while still boasting 100 kW up to 1,000 kW power ratings. Portable models work best for testing lower power levels and be moved easily between sites. Portable units may weigh as little as 70 pounds and have optional cages to protect the units between uses.

3. Trailer

Trailer-mounted load banks work best for companies that require remote testing of generators on-site without purchasing separate load banks for every location that needs tests. The trailer-mounted banks tend to have larger testing capacities than portable models with power ratings up to 3,000 kW, similar to stationary models. A trailer-based load bank allows a truck to transport it easily. Low-profile models are ideal for accessing generators in parking garages or other height-restricted applications.

4. Roof or Duct-Mounted

Roof-mounted or duct-mounted models are permanently installed on the generator itself. Roof-mounted load banks are mounted such that they are cooled from the vertical generator's exhaust. These are typically up to 400 kW maximum and are ideal to supplement load and prevent wet-stacking of diesel generators. Similar duct-mounted models are resistor load banks that use the generator's radiator to help cool them and can be found as large as 1,000 kW.

5. Custom Design

For specific needs not met by other load bank designs, a customized model will serve as a solution.

What Are the Types of Load Banks?

What Components Do These Devices Include?

Load banks offer varying power factors, but resistive (1.0 pf) load banks are the most common. Inductive and capacitive load banks typically supplement resistive as testing requirements dictate.

1. Resistive

Resistive load banks are the most common type. They provide loading for prime movers and generators. The load elements simulate unity power factor loads, such as some types of heating or lighting, and resist current flow linearly. Resistive load banks turn electrical energy into heat, which must be removed from the load bank. Means of cooling include convection, water cooling or forced air. Resistive load banks use ohms are measured in ohms and watts.

2. Inductive

Inductive load banks depend on electromagnetic fields, which means that all types of motors, relays and solenoids are inductive. Inductive loads resist changes in current, so the current appears to lag behind the voltage.

Inductive load banks have two types of power: real and reactive. Real power is produced by the work the device is doing, such as a spinning motor. Reactive power is drawn to create magnetic fields. The total power consumed is a combination of reactive and real power. It's measured using volts-amps-reactive (VAR). An inductive load is usually rated at 75% of the corresponding resistive load. When taken together, the two provide a 0.8 power factor.

Inductance is measured in Henrys.

3. Capacitive

Capacitive loads resist voltage changes, making them, in many ways, the opposite of inductive loads. While current lags the voltage in inductive loads, in capacitive loads, current leads voltage (or voltage lags the current). Capacitive loads also have reactive power, like inductive loads. However, the reactive power of a capacitive load is the opposite polarity of that of an inductive load. For that reason, capacitive loads have negative VARs.

While capacitive load banks are less common than resistive or resistive-inductive, they are often used for testing powers sources connected to telecommunications and computer systems because they are better at simulating certain electronic or non-linear loads commonly used in those systems.

Capacitance is measured in Farads.

4. Resistive-Reactive

Resistive-reactive models supply both resistive and reactive loads onto the generator. These provide a more comprehensive test for the generators by creating loads that more closely mirror those encountered during typical use. 

What Components Do These Devices Include?

Load banks include several elements that allow for their optimum operation.

  • Operator Controls: Operator controls allow for manual operation during testing. You may optionally choose advanced digital controls that allow for remote operation over a network.
  • Enclosures:The surrounding enclosure for the bank protects the interior components from the elements. Enclosure designs vary based on the type of bank.
  • Cooling system: Cooling systems to allow for smaller packages by efficiently removing the heat created by the resistive load. Alternatively, the resistor model can take advantage of cooling from the generator's engine radiator.

Find Out More and the Options Available

Find more about options for load banks, including mobile and permanent solutions for your testing needs. Let us help you find the best option for your business. Contact us at Load Banks Direct today for answers to your questions or to request a quote.

Contact Load Banks Direct

125 W 34th St.
Covington, KY 41015

Toll Free Phone: 1-855-LBD-CALL
(855-523-2255)

International: 859-554-1534
Fax: 859-554-2530

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