Generators aren't "magnetized" in the traditional sense. Instead, they rely on a small residual magnetic field in the rotor to induce an initial voltage. This voltage then powers the field windings, creating a stronger electromagnet that allows the generator to produce its full output.
Remagnetizing a generator, often called flashing the field, involves applying a small DC voltage to the field windings. This re-establishes the residual magnetism necessary for the generator to begin producing electricity. You can use a 12-volt battery or a battery charger. Ensure correct polarity is observed, connecting positive to positive and negative to negative, usually for a few seconds. This process is crucial for self-excited generators that have lost their initial magnetic field.
Generators can lose their residual magnetism due to several factors. Extended periods of disuse, short circuits, or even simply sitting idle for too long can demagnetize the field. Vibrations, extreme temperatures, or improper shutdown procedures might also contribute. Additionally, if the generator has been subjected to an overload or a fault condition, it can sometimes disrupt the delicate magnetic field, necessitating a re-flashing procedure to restore normal operation.
A dead battery itself doesn't directly demagnetize a generator. However, if the generator relies on the battery for initial excitation (which many do), a dead battery would prevent it from getting the initial voltage needed to build up its magnetic field. So, while not a direct cause of demagnetization, a dead battery can certainly prevent a generator from starting to produce power, making it seem like a magnetism issue.
Yes, it is generally safe to flash a generator with a car battery, provided you follow the correct procedure. A 12-volt car battery provides the necessary DC voltage. Always ensure you connect the positive terminal of the battery to the positive field terminal of the generator and the negative to negative. Connect for only a few seconds. Incorrect polarity or prolonged connection can potentially damage the generator's voltage regulator or windings.
A generator should only be remagnetized when it fails to produce power due to a loss of residual magnetism. There's no fixed schedule for remagnetization. If your generator is working correctly, there's no need to flash the field. It's a troubleshooting step, not routine maintenance. If you find yourself frequently needing to remagnetize, it might indicate a deeper issue with the generator or its voltage regulator.
The primary sign that a generator needs remagnetizing is that it starts and runs, but produces no electrical output. You might hear the engine running smoothly, but your voltage meter will read zero, or significantly below its rated output. There will be no power at the outlets. This indicates a lack of the initial magnetic field required to induce voltage. It's a common issue after long storage periods.
No, a generator cannot self-excite after completely losing its residual magnetism. Self-exciting generators rely on that small, inherent magnetic field to begin the voltage generation process. Without it, there's no initial current to build up the full magnetic field. Therefore, manual flashing of the field is necessary to re-establish this crucial starting point, allowing the generator to then build up its own excitation.
The size of the generator doesn't fundamentally change the remagnetization process, but it might influence the duration or the specific terminals used. The principle remains the same: applying a DC voltage to the field windings. Larger generators might have more robust field windings or different terminal configurations, but the core method of flashing the field with a DC source, like a 12-volt battery, is consistent across various sizes and types of generators.
Residual magnetism is absolutely crucial for a self-excited generator. It's the small, inherent magnetic field remaining in the generator's iron core even when it's not operating. This tiny magnetic field is what allows the rotating armature to induce a very small initial voltage. This initial voltage then feeds back into the field windings, strengthening the magnetic field, which in turn induces more voltage, creating a self-sustaining build-up of power.
While the core principle of applying DC voltage to the field windings is universal, there are slight variations in method. The most common is using a 12-volt battery or battery charger. Some technicians might use a drill battery pack. The key is ensuring the correct polarity and applying the voltage for a very brief period, typically a few seconds. Some modern generators might have specific procedures outlined in their manuals, but the underlying electrical principle remains consistent.