Do you have a generator that keeps tripping?
Overloaded generators are one of the most common causes of generator failures during power outages. If your generator is overloaded, it can trip and stop providing power to your home or business. This can be very frustrating and can cause a lot of damage.
This article will discuss what causes generators to overload and some ways to fix an overloaded generator. We hope this information helps you keep your family or business safe and powered up during an emergency.
Read our article on how to fix an overloaded generator today!
Why should you avoid overloading?
All electrical equipment, machines, and conductors like transformers, motors, generators, cables, panels, etc., are designed to carry a particular amount of current, translated into the equipment’s rated load capacity, at their nominal voltage.
If you exceed this current value, you are said to be causing an overload condition. Circuit breakers in the respective feeders are designed and set to sense this overload situation and disconnect the power to the downstream electrical appliances.
Let us consider that the ambient temperature considered while designing a portable generator is 30°C. Let the maximum temperature that the winding insulation can withstand under continuous operation be 90°C.
If you exceed this temperature, the insulation deteriorates and will eventually fail if frequently exposed to high temperatures. The rate of deterioration depends on the temperatures it is subjected to (beyond 90°C) and the duration.
The current that causes a 60°C rise in the conductor temperature (from 30°C to 90°C) is the rated current for the generator, subject to deration if other constraints are also available. Any current in excess of this value will cause a generator overload. A prolonged engine overload will cause the insulation to fail and may cause a short circuit or a ground fault (whereby the ground fault current flows from the frame of the generator to the ground connection).
However, the generator is able to withstand the overload for short periods of time, like at the time of starting a motor. This is where the starting wattage comes into play. However, as the overload current increases, the duration for which a generator can withstand this overload decreases. So the overload current is inversely related to the duration it takes to reach the maximum continuous temperature that the insulation can withstand.
Running the gasoline generators in overloaded conditions is particularly risky and may lead to fire or explosion once the gasoline heats up.
What Causes Generators To Overload?
With all this background, let us explore the reasons that can cause an overload on your portable generators.
loading your generator above its rated wattage.
The main reason behind overloading your generator in most cases is the connection of too many appliances, thereby exceeding the rated running watts of the generator. There could be various reasons causing this, like
- You have not evaluated your power requirements during a power outage, and your generator does not have enough wattage rating to feed the connected loads.
- You may have considered only the running watts during the evaluation without properly evaluating the starting current when an electric motor starts.
- You have considered the running and starting watts correctly but have not considered the actual loading on each of your internal house wiring circuits. And an imbalance exists between the circuits of your house.
- Let us understand this with an example. Suppose, with the previous generator sizing method, you arrived at a running watts requirement of 6000W with all your appliances plugged in. But, in reality, the two circuits of your house wiring, L1 and L2, carry a current of 20A and 30A. To feed 30A, you require the generator running watts to be 30 x 240 = 7200W, else the circuit breaker connected to this outlet will trip. If your loads were balanced, with 25A in both circuits, you could have easily fed 25 x 240 = 6000W.
- With your current circuit loading, you have three options (a) rebalance your loads, (b) go for a larger generator, or (c) use another generator in parallel if your previous generator supports it. Anyway, it is always recommended to keep a margin of 10% to 20% while sizing any generator.
- Your generator trips when you switch on your air conditioner. You may not have again sized the generator correctly based on actual data from the air conditioner manufacturers’ catalogs. See the detailed sizing procedure in our detailed article on the subject.
Short in the winding
An inter-turn short in the generator windings can impact the capacity of the alternator, particularly the rotor. This short will reduce the resistance of the rotor winding, increase the rotor current, cause an imbalance in the rotating magnetic field, and may result in vibrations due to differences in currents in the two poles.
Depending on the number of turns shorted and their location, you may require higher field current than earlier, resulting in higher operating temperatures and much lower efficiency.
Short in the wiring
There may be electrical problems with your wiring and cables, ranging from wrong connections to a short circuit or a ground fault, resulting in excess current manifesting as an overload.
Short in your appliances or equipment
In the same way, short or mechanical issues, particularly in bigger appliances, will require more power from the portable generator and cause its overloading.
Another generator in parallel operation tripped.
If you are using two or more portable generators in parallel, and one of them trips due to any issue, the circuit breaker of another generator will trip on overload.
If you face low rpm, insufficient power due to a lean mixture caused by air leaks, or your generator is slowing down under load, it indicates mechanical issues within the generator. There can also be external issues, like high ambient temperatures, no free space around the generator to dissipate its heat, operating electrical or air conditioning equipment near to the generator, and discharging their heat. All these issues must be investigated if everything listed in the sections above is fine.
How to know if the generator is overloaded
As highlighted above, generators are designed to withstand a temporary overload for a short period of time. However, the sustained overload will impact the performance and long-term health of the machine, manifesting itself in many ways as below:
Generator keeps tripping
As stated in all the articles on the net, most modern generators have the main circuit breaker and individual circuit breakers for each outlet. If they are not holding, you may start your troubleshooting by disconnecting the largest load and switching the generator back. If it still trips, you should progressively disconnect the heavy loads. The process will eliminate the faulty equipment or tell you the load the generator can withstand.
If the problem still persists, check for the short circuit or ground faults in the power cords, outlets, plugs, etc.
Indications on the Generator Control Panel
A green output light indicates the normal operation in most generators. Many inverter generator models have an overload indicator light to alert you if your generator is overloaded. This overload warning light is usually red in color and is located on the front panel. The generator will stop feeding power after a few seconds. In some sets, the green light flashes before the red line come on to give you time to switch off some loads and avoid dropping out of the generator.
A drop in power output
The conditions like a drop in power output, insufficient power, or generator slowing down under the load conditions may be due to
- Reduction in the capacity of the generator caused by inter-turn short in rotor winding,
- Insufficient power is generated due to the lean mixture caused by air leakage to the carburetor or a reduced fuel flow.
- The generator is slowing down on load due to stator and rotor winding issues.
An extremely noisy generator fan
Suppose any of the conditions listed above causes an overload on the generator. In that case, the fan will try to put extra effort into lowering the temperatures, resulting in a very noisy operation.
Weird noises coming out from the generator
The active power delivery or the “kWs” of any generator depends on the throttle and, in turn, on the engine rpm. Whereas the reactive power depends on the rotor excitation and controls the voltage output.
When the generator is overloaded, the voltage drops, requiring the automatic voltage regulator to increase the field excitation. The increased rotor current will also heat the rotor windings. To deliver more kilowatts, the engine has to run at higher rpm.
The situation is further aggravated if there are inter-turn shorts in the rotor winding, particularly in older generators, which may lead to vibrations due to an imbalance between poles. Such a situation sometimes results in a strange noise from the generator, which is a clear sign of an overload.
The generator overheated and won’t start.
Many generators have high-temperature sensors that will shut down the generator within a few minutes and won’t allow them to start again till the temperatures have reduced to normal limits. As explained earlier, an overload will result in a higher load current that will overheat the generator. The following factors will further aggravate the situation:
- The generator is designed for a particular ambient temperature, and the difference between this ambient and insulation withstand temperature is the permitted temperature rise. If the ambient temperatures are high, the value of permitted temperature rise reduces. You can only apply reduced loads due to the constrained temperature rise value. This is known as the deration of the machine. If you apply the rated loads with a high ambient temperature, your generator will overheat.
- You need to ensure that your generator is placed in an open area with adequate air to cool it and nothing is around it to obstruct the heat dissipation, as the difference between heat generated and heat dissipated will result in a temperature rise.
- There must be no other electrical or air conditioning equipment that may cause an increase in the heat load in the surrounding area.
Black Soot in the exhaust
Black soot in the exhaust usually indicates incomplete combustion due to rich fuel or lack of air. Just the presence of the soot does not indicate an overload. However, soot formation during an overload can happen, if the engine is consuming more fuel, but there is a lack of air to support the combustion.
This is why running your generator set in an open area that can provide adequate air for combustion and discharge of the exhaust is recommended. This extra amount of air will also cool your generator.
Increased smoke generation does indicate an overload.
Ways To Fix an Overloaded Generator
We have discussed various reasons that may cause an overload on the generator and the ways to troubleshoot them above. Let us summarize in easy steps.
- Start by turning off your generator and disconnecting all the appliances.
- Press the overload reset button and restart the generator.
- If the overload light disappears, you can connect your loads to troubleshoot. If the light is still on, you may have to go in for professional help, as there may be an internal fault.
- By now, you would have figured out if you are putting an additional load on the generator above its rating.
- Start loading your generator by connecting your appliances one by one, keeping the largest load disconnected. If everything works fine, you may have to revisit your sizing calculations or redistribute your loads among various circuits.
- If the generator again trips out on overload, you might have to reduce the load further and repeat the process.
- If the tripping continues, it is time to check the outlets, cords, appliances, etc., as discussed earlier, until you can locate the fault and rectify it.
This article looked at what can cause generators to overload and ways to fix an overloaded generator. We also discussed how to know if your generator is overloaded and what you should do if it is. Please let me know in the comments section below if you have any questions or would like more information. I will be happy to help out in whatever way I can. Thanks for reading!