How to test a generator
- May 17, 2023
Reasons to test generators
- Make sure the generator works as designed when needed. This is the only real way to check generator performance. Load testing will allow verification that the generator system will generate and maintain a full load without overheating and shutting down. Additionally, it enables testing of every system component to make sure that everything functions as intended and as designed and helps identify any potential weaknesses under controlled conditions. This allows for proactive maintenance as weaknesses are identified under controlled conditions rather than during utility outages when flaws could lead to system failure.
Loads may come from building loads but may cause business interruptions when transferred from utilities to generators. It also doesn’t allow for step-by-step load application, which allows performance to be monitored and recorded. Generally, a portable load bank is the preferred method for load-testing generator systems.
- Most generator systems are programmed to exercise regularly. Typically, there is no or minimal load during this workout period. It’s also crucial to keep track of your workout routine to make sure the generator starts and operates as intended, but it doesn’t make sure the generator is running as designed.
Most generator systems are installed and then go into automatic mode. As the generator ages, the potential for weaknesses in the system increases. Weather, bugs, and ageing are a few more possible foes that might reduce the effectiveness of generator systems. The easiest method to identify and reduce any flaws in your generator system is through a well-planned maintenance schedule that includes load testing.
- Another challenge is presented by the many installed generator systems that use diesel engines. This challenge is called wet stacking. If not addressed, wet stacking will not allow the system to operate as designed and will degrade the system’s performance. Many systems are built with some level of load redundancy or extension in mind. This means that many systems are not properly loaded to eliminate wet heaps. At a minimum, we recommend using a portable load box to load test all diesel systems for at least two hours once a year. A more extended test period may be required if the diesel system has not been load tested for more than a year. This annual test will reduce the impact of wet stacking on generator systems.
A generator system should come with a defined maintenance schedule that includes frequent load testing. Regular testing of the system will give you the best level of comfort, and when the system is required, it will perform as designed.
How to test your residential backup generator
Don’t be intimidated by a residential backup generator system. Taking regular tests is simple. Unlike portable generators, residential backup generators are connected directly to a fuel source such as propane or natural gas. The generator is then connected to the mains circuit breaker. This main utility line to your home may be located in a box outdoors, in a garage, or in a basement.
Turn off the mains circuit breaker when the main utility disconnect switch is flipped, and the incoming utility line will lose electricity, which will trigger the backup generator to start running.
Pay attention to the generator starting up and the transfer switch clicking. Transfer switches are the most common devices used to distribute electricity from an incoming utility or electricity generated throughout a house. Before the transfer switch clicks and distributes power, the generator may run for up to a minute. This is due to the transfer switch’s need to wait for stable incoming generated power.
Let your generator run for almost 10 minutes. Give warm-up and “workout ” time to your generator. This is the right time to take a walk around your home and check that the power is fully restored.
After running the test, open the main breaker and wait again for the transfer switch to click and the generator to return to standby.
Record tests and follow up when needed
Test your generator at least a few times a year, but you can test it as needed. Testing may be beneficial during hurricane season or before a major storm.
Record your tests in a notebook, so you have a record. If you encounter any problems, For a more thorough test and inspection, kindly contact a residential generator expert.
What is generator load bank testing
Testing the generator load bank is a crucial part of preventive maintenance. Generator load set testing involves the inspection and evaluation of the generator set. It verifies that all major components of the genset are in proper working order. By bringing the engine up to the proper operating temperature and pressure level, the equipment used to conduct the load bank test places an artificial load on the generator. This is especially important for backup and emergency gensets that operate infrequently and/or may not frequently be subject to heavy loads. The general rule is that if your generator is not experiencing loads above 30% of its rated kW, you should consider a load test.
Load bank testing involves starting a backup or main generator and operating it at maximum capacity for a specified period of time under artificial load. During a load bank test, data can be recorded to provide a more complete picture of the overall health of the genset. This test verifies that the generator can handle gradually increasing kW loads, can still accommodate its maximum specified load, and can operate for longer periods of time. So, in the simplest case, load bank testing is a way to verify that your backup or primary generator is still able to start and operate at maximum kW output.
Load bank testing ensures that your generator is running when needed so you can rely on it completely in an emergency. It is essential to test your generator at its maximum kilowatt (kW) output rating during load bank testing. Since many generators do not regularly run at their full power rating, it is especially important to verify that the generator can actually produce the highest horsepower possible while maintaining sufficient temperature and pressure levels to keep it running for as long as necessary.
The recommended procedure for load group testing is as follows:
- Start the generator and keep it running until the water temperature is steady.
- All manual and automatic transfer switches should be set to emergency power.
- Step load the generator using the load bank until the desired load is reached.
- Remove the load box load after testing.
- Turn all transfer switches back to their normal positions.
- Allow the generator to cool according to the manufacturer’s directions.
What is a load bank
An electrical device that is temporarily linked to the generator’s AC voltage output is called a load bank. The load is applied to the generator through a switch calibrated to produce a specific kilowatt (kW) output. This enables the tester to match the generator’s rated capacity by applying appropriate load steps.
Load bank testing ensures your generator is running when needed so you can rely on it to function properly in an emergency. The key to proper load bank testing is for your generator to operate and maintain its full kilowatt (kW) output rating. Most generators will not run at their full kW rating during a daily workout.
It is essential to verify that your generator can actually produce the highest horsepower it can possibly be asked to produce. Only with this type of testing can you verify that your equipment is functioning properly at recommended temperature and pressure levels over the full range of operating conditions.
How does load bank testing work?
When a load bank test is performed, an artificial load is placed on the generator. The kW load is raised progressively during the timed test in predetermined increments. Every time a kW load is added, the test measures and records key engine parameters, the generator’s ability to handle boost, and its ability to continue operating at the highest possible level for an extended period of time. The equipment required to complete the test includes a load box (a machine with a kW-rated size and a battery-like cable).
Putting a 100% capacity load on the generator and letting it run for a period of time will not only detect any problems in the generator, engine and cooling system; it will also fix the rings properly and eliminate buildup on the combustion chamber and valves, thereby benefiting the engine. Diesel engines, in particular, require periodic load testing to maintain performance and fuel economy.
Step 1: Check fluid levels
Check all fluid levels in the generator. Make that the oil level is appropriate, the radiator or coolant tank is full, and the tank is full if the generator is water-cooled.
Step 2: Warm up
Start the generator and give it some time to warm up to the working temperature. Keep an eye out and listen for any strange sounds or potential issues. If you find any problems, don’t continue testing until you’ve dealt with them.
Step 3: Begin connecting loads
Begin connecting loads, starting with large 220-volt loads, then add smaller 110-volt loads until each branch carries 50% of the generator’s maximum continuous rated load. Do not exceed 50% on either leg. Use a 220-volt resistive load, such as a large space heater or water heater. They simplified this step because they applied the load evenly to each leg.
Step 4: Check amperage
Check the amperage of each leg with an ammeter, check each leg’s voltage to neutral, and set the VOM to read AC voltage. For 110/220 volt single-phase generators, the voltage on each leg should be between 105 and 125 volts, and the current should be the rated power output of each leg divided by half the voltage. For example, if the voltage from each branch to neutral is a 117-volt load, and the generator is rated for 10 kW continuous, the load per branch should be 5000 divided by 117 or approximately 42 amps. The generator has failed the test and requires repair if one or both branches fall below 105 volts while fully loaded.
Step 5: Monitor the generator
Monitor the generator while maintaining this load during the test. Keep an eye out for overheating, keep an ear out for odd noises, and pay attention to the output. If there is a problem, shut down the generator quickly to minimize damage and repair the generator before it is back in service. How long the test should last depends on the type of generator. A small portable generator shouldn’t run continuously for longer than three to four hours. Contractor-grade generators should be able to run for eight hours. Continuous-duty air-cooled or water-cooled generators should run for 24 hours. Ideally, larger industrial-grade diesel generators should run at full load for about a week.
Step 6: Gradually unload your generator
After the test, gradually unload it. For five to ten minutes, turn off all loads before turning the generator off.
Wet stacking
When a diesel engine-driven generator is infrequently used or only operated under light loads, it can be prone to unburned fuel and soot buildup in the exhaust system. This is called “wet stacking”. When a wet stack occurs, the generator set can perform poorly, suffer damage, become a fire hazard, and even lead to complete failure. The generator is permitted to operate at maximum power and temperature throughout the load bank test. This will cause any wet buildup to burn off. So load bank testing actually serves two purposes:
It evaluates the generator to see if it will operate effectively and correctly at all levels and eliminates any wet buildup that may have built up inside the generator.
Benefits of load bank testing
- Verify the capability of the genset, not just routinely start it.
- Problems caught early can greatly reduce costs and prevent significant issues in the future.
- Helps avoid wet buildup and remove carbon deposits.
- Verify that the engine cooling system will operate under load.
- Make sure your genset works when you need it most.
- Tests that the genset is capable of operating at the specified peak specified kW output for the specified amount of time.
- Mitigate the effects of light loads by burning off residue that causes wet buildup.
test a generator FAQ
How often should you test your generator?
Home and business owners with backup generators don't have to worry about power outages in the event of a power outage. With an automatic backup generator, power will kick in immediately. But without proper maintenance and testing, generators may not operate as expected.
Just like a car's engine, it's useful to test the generator and have the engine run from time to time for a variety of reasons:
- By running the generator, you know it's working.
- Running the generator keeps it lubricated. If your generator has a battery (in most cases), running the generator will also charge the battery.
- Turning on the generator is also helpful to ensure the carburettor runs smoothly.
It's a good rule of thumb to test your generator a few times a year. If you can, usually every three to four months is enough. You should give it 10 to 20 minutes to run after turning it on, giving it enough time to get everything moving and oiling. You also need to ensure you run it long enough to get it to operating temperature.
Do you need a professional to test your generator?
The good news is that you may test your generator completely at home by yourself. Just turn on the generator and let it run. You should call a professional if you notice any of the following:
- Your generator will not turn on
- Your generator will not continue to run
- You notice any strange smells or sounds
- You notice any damage to the generator - which should be checked every time you do a test run - such as frayed wires or rust.
How do you test a generator that is not putting out the power?
Plug in the lights, turn on the generator switch or breaker and start the motor. Connect the battery +12 volt (red cable) to the red wire on the terminal you removed for three seconds. Remove the cord and replace the plug. The generator should now generate electricity again.
