Top Reasons Portable Generator Won’t Generate

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A portable generator can be a great recreational choice for campers who appreciate “roughing it” part-time but would like reliable electricity the rest of the time. This convenient outdoor power equipment product can keep that small fridge or freezer running, allow you to charge up your phone or laptop, and keep the lights on when you need more illumination than a campfire provides.

These days, a generator can also be seen as a necessity when storms or an overtaxed power grid knock out your home’s electricity. In fact, according to a recent report, the U.S. portable generator market is booming with an expectation that 10 million units will be sold annually by 2026.

With portable generators being relied on more and more, what do you do if your generator won’t generate current? To answer that question, we should start with how a generator works.

How does a generator create electricity?

Let’s assume your portable generator has a voltage regulator and brush system, powered by a standard gasoline engine running properly with a top speed of 3750 RPM with no load applied. This generator type uses a rotor, stator, voltage regulator, and brushes to generate 120 volts of alternating current, 240 volts, or both.

The rotor is essentially a magnet that rotates inside of a conductor, such as copper coil, to create a magnetic field that induces current. The stator will often have three main copper coil windings: the excitation winding plus two voltage output windings that create the rotor’s magnetic field. The excitation winding sends voltage to the rotor through the voltage regulator and brushes. By increasing or decreasing the voltage applied to the rotor, the generator controls the voltage of the output windings.

The voltage regulator converts the voltage sent to the rotor from alternating current (AC) to direct current (DC). The regulator will monitor the output winding voltage as well. The regulator has a preset “reference” voltage that the output windings should produce. In North America, that voltage is 120 volts of alternating current at 60 Hertz. If the generator’s output voltage is too low, the regulator increases the direct current voltage being sent to the rotor to strengthen the rotor’s magnetic field. Conversely, if the output voltage is too high, the regulator will decrease the direct current output to the rotor to weaken the magnetic field.

Top 5 reasons a generator fails to provide current

Admittedly, getting your head around how a generator does what it does can require some brain power. Fortunately, the top reasons why the generator would fail to produce current are easier to understand. Here are five of them:

  1. Tripped outlet breaker – This one’s especially simple. If the outlet breaker trips, the generator will stop providing current. Switch the breaker back on to see if that solves the problem. If the breaker continues to trip, you’ll need to do some more troubleshooting. What can cause a breaker to trip? You might be using a power cord not rated to handle the current you’re trying to run through it, or the electrical system could be shorting due to water, debris, or worn insulation.
  2. Loss of residual magnetism – If you haven’t used your generator in a while, it’s likely the rotor has lost its residual magnetism which is necessary for the generator to induce current. You can try reintroducing the magnetism by performing a process called “Flashing The Field” (refer to the next section in this article to learn how to do this).
  3. Worn brushes – It’s always a good idea to inspect the generator’s brushes regularly to determine if the components are worn down or damaged. A worn brush will likely have trouble transmitting the voltage generated by the excitation winding to the rotor.
  4. Defective voltage regulator – If the brushes appear to be in good shape, the next possible culprit would be the voltage regulator. The “flashing the field” process will help determine whether the rotor has temporarily lost its residual magnetism or if the voltage regulator is defective. The good news is that the regulator is a fairly easy part to replace by the average do-it-yourselfer.
  5. Faulty rotor or stator – The rotor or stator may have failed as well, but this is not a common occurrence. You should definitely inspect the brushes and regulator first before attempting to replace the rotor or stator. You can use a multimeter to test for resistance on the rotor, if necessary, to determine if the resistance measurement is within the manufacturer’s specifications. A reading that is not within those specifications could indicate the rotor has a faulty winding.

Flashing the field

As noted above, if the generator hasn’t been used recently, the residual magnetism required to generate current may have been lost. You can try to bring this magnetism back by a process called “flashing the field”. You’ll need a 12 volt DC battery as well as two jumper leads with quarter-inch terminals or alligator clips to do this.

  • Disconnect the two wires from the brush block.
  • Connect the negative lead from the battery to the negative brush terminal furthest from the rotor bearing.
  • Connect the positive lead to the terminal closest to the rotor bearing.
  • Start the generator’s engine and allow it to run for a few seconds – to prevent shock, do not to touch the leads while the engine is running.
  • Turn off the engine and disconnect the jumper leads.
  • Reconnect the brush wires to the brush block terminals.
  • Confirm sufficient output current is being generated.

Keeping the power on with the right parts from Repair Clinic

So let’s say you’ve determined you need to replace the generator’s voltage regulator to get the equipment working properly. What’s your next step? Visit where you can purchase the exact regulator that matches your particular generator model. Simply enter the full model number of the generator in the Repair Clinic website search bar, then use the “Part Category” filter (“Alternator & Battery”) followed by the “Part Title” filter (“Voltage Regulator”) to identify the specific part you need. Repair Clinic stocks portable generator replacement parts for all the leading brand names, including Black Max, Briggs & Stratton, Cub Cadet, Generac, Homelite, Honda, Husky, Kawasaki, PowerStroke, Ryobi, Toro, Tory-bilt, and many more, but you must use the right part that matches your model for your repair to be successful.

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