If it is a truck generator, although it is nominally 24V on the nameplate, its output voltage is around 28V because it is used to charge the vehicle battery .
If this type of generator cannot reach 28V during operation, there are two situations:
1. The vehicle battery loses too much power and generator output voltage during initial charging. Pulled down by the battery to 24V. This situation should be normal. Continue charging and the voltage will slowly increase.
2. Automatic voltage regulator failure.
Use a multimeter to measure. The battery voltage measured before starting is usually 24 V. After starting, the voltage increases significantly to 26-28 V, which proves that the generator is producing electricity.
Never use a fire to check if the generator is producing electricity. The generators of aToday they all use integrated circuit regulators. A fire will damage the generator regulator.