Replacing the magnets in a generator (specifically the permanent magnets found in many smaller alternators and brushless generators) is a detailed mechanical task that requires patience and safety awareness.
Here is a comprehensive guide on how to do it.
High Risk of Pinching/Crushing: The rotor has an extremely powerful magnetic field. It can snap into place with tremendous force, easily crushing fingers or hands. Handle with extreme care.
Demagnetization: Striking or dropping a permanent magnet can cause it to lose its magnetic field (demagnetize). Handle the old and new magnets gently.
Personal Protective Equipment (PPE): Always wear safety glasses to protect your eyes from metal shards or epoxy, and heavy-duty work gloves to protect your hands.
Replacement Magnets: Ensure they are an exact match for your generator model (size, shape, and strength).
Workbench with a Vise: To securely hold the rotor.
Puller Set (Gear Puller): Often essential for removing the old rotor from the shaft.
Heat Gun: A propane torch can work but is riskier (can demagnetize magnets or damage metal properties if overheated).
Dead-Blow Hammer or Mallet: To gently tap components loose.
Screwdrivers, Wrenches, Sockets: To disassemble the generator.
High-Temperature Epoxy (e.g., J-B Weld): For securing the new magnets.
Isopropyl Alcohol : For cleaning the rotor surface.
Marker or Punch: For marking orientation.
Wooden Blocks or Non-Marring Shims: To protect the magnets and rotor.
Disconnect and Secure the Generator: Disconnect the spark plug wire on gas engines or disconnect all battery cables on diesel models. Ensure the generator cannot accidentally start.
Gain Access to the Rotor: This typically involves:
Removing the generator housing/shroud.
Removing the cooling fan and any air guides.
Unbolting and carefully removing the stator (the stationary coil assembly) from the engine block/rotor. Note the placement of any shims.
Remove the Rotor Assembly: The rotor is usually pressed onto the crankshaft and held with a key and a nut.
Use the correct socket to remove the large nut on the end of the shaft.
Use a gear puller to carefully pull the rotor off the shaft. Do NOT hammer on the shaft end or the magnets themselves, as this can damage the engine's bearings and demagnetize the magnets.
Secure the Rotor: Once removed, clamp the rotor securely in a vise. Use soft jaws or wooden blocks to protect it. The shaft should be pointing up.
Mark Magnet Polarity (CRITICAL STEP): Before removing anything, take pictures and use a marker to clearly indicate the North (N) and South (S) pole of each magnet. The alternating polarity (N-S-N-S) is crucial for generating electricity. Getting this wrong will render the rotor useless.
Apply Heat: Use a heat gun to gently heat the area around one magnet. The goal is to soften the epoxy adhesive holding it in place. Avoid excessive, concentrated heat which can demagnetize the other magnets.
Pry the Magnet Out:
Place a wooden shim or block against the magnet.
Use a mallet to gently tap the shim and work the magnet loose.
You can also try to slide a flat-head screwdriver between the magnet and the rotor, using the shim to protect the metal.
Work slowly and carefully around the magnet until it pops free.
Repeat: Repeat the process for all magnets that need replacement.
Thoroughly Clean the Slots: Use a wire brush or sandpaper to remove all old epoxy and debris from the magnet slots on the rotor. Finish by wiping the area down with isopropyl alcohol. It must be perfectly clean and dry for the new epoxy to bond.
Test Fit the New Magnets: Without any epoxy, ensure the new magnets fit perfectly into the slots.
Apply Epoxy:
Mix your high-temperature epoxy according to the instructions.
Apply a generous, even layer to the bottom and sides of the magnet slot.
Also, apply a thin layer to the back of the new magnet.
Insert the Magnets with Correct Polarity:
This is the most critical step. Refer to your markings and photos.
Carefully place each magnet into its slot, ensuring the polarity alternates (N-S-N-S) exactly as the old ones were.
The powerful magnetic forces will try to snap them into place. Use wooden blocks to carefully guide them and prevent your fingers from being caught.
Let Epoxy Cure: Follow the epoxy manufacturer's instructions for full curing time (usually 24 hours). Do not disturb the rotor during this time.
Reinstall the Rotor: Once the epoxy is fully cured, carefully slide the rotor back onto the engine's crankshaft, aligning the Woodruff key with its keyway.
Reassemble in Reverse Order: Reinstall the nut, washer, stator, cooling fan, and housing. Ensure all wiring connections are secure.
Test the Generator: Start the generator and check its output voltage and frequency with a multimeter. It should be within the specified range (e.g., 120V / 60Hz). If the output is low or nonexistent, double-check your magnet polarity.
Consider hiring a professional generator repair technician if:
You are not comfortable with heavy mechanical work.
You lack the proper tools (especially the gear puller).
The generator is very large or expensive.
You are unsure about identifying and maintaining correct magnet polarity.
This is a complex repair, but with meticulous attention to detail—especially regarding polarity and safety—it can be done successfully.
Replacing the magnets in a generator (specifically the permanent magnets found in many smaller alternators and brushless generators) is a detailed mechanical task that requires patience and safety awareness.
Here is a comprehensive guide on how to do it.
High Risk of Pinching/Crushing: The rotor has an extremely powerful magnetic field. It can snap into place with tremendous force, easily crushing fingers or hands. Handle with extreme care.
Demagnetization: Striking or dropping a permanent magnet can cause it to lose its magnetic field (demagnetize). Handle the old and new magnets gently.
Personal Protective Equipment (PPE): Always wear safety glasses to protect your eyes from metal shards or epoxy, and heavy-duty work gloves to protect your hands.
Replacement Magnets: Ensure they are an exact match for your generator model (size, shape, and strength).
Workbench with a Vise: To securely hold the rotor.
Puller Set (Gear Puller): Often essential for removing the old rotor from the shaft.
Heat Gun: A propane torch can work but is riskier (can demagnetize magnets or damage metal properties if overheated).
Dead-Blow Hammer or Mallet: To gently tap components loose.
Screwdrivers, Wrenches, Sockets: To disassemble the generator.
High-Temperature Epoxy (e.g., J-B Weld): For securing the new magnets.
Isopropyl Alcohol : For cleaning the rotor surface.
Marker or Punch: For marking orientation.
Wooden Blocks or Non-Marring Shims: To protect the magnets and rotor.
Disconnect and Secure the Generator: Disconnect the spark plug wire on gas engines or disconnect all battery cables on diesel models. Ensure the generator cannot accidentally start.
Gain Access to the Rotor: This typically involves:
Removing the generator housing/shroud.
Removing the cooling fan and any air guides.
Unbolting and carefully removing the stator (the stationary coil assembly) from the engine block/rotor. Note the placement of any shims.
Remove the Rotor Assembly: The rotor is usually pressed onto the crankshaft and held with a key and a nut.
Use the correct socket to remove the large nut on the end of the shaft.
Use a gear puller to carefully pull the rotor off the shaft. Do NOT hammer on the shaft end or the magnets themselves, as this can damage the engine's bearings and demagnetize the magnets.
Secure the Rotor: Once removed, clamp the rotor securely in a vise. Use soft jaws or wooden blocks to protect it. The shaft should be pointing up.
Mark Magnet Polarity (CRITICAL STEP): Before removing anything, take pictures and use a marker to clearly indicate the North (N) and South (S) pole of each magnet. The alternating polarity (N-S-N-S) is crucial for generating electricity. Getting this wrong will render the rotor useless.
Apply Heat: Use a heat gun to gently heat the area around one magnet. The goal is to soften the epoxy adhesive holding it in place. Avoid excessive, concentrated heat which can demagnetize the other magnets.
Pry the Magnet Out:
Place a wooden shim or block against the magnet.
Use a mallet to gently tap the shim and work the magnet loose.
You can also try to slide a flat-head screwdriver between the magnet and the rotor, using the shim to protect the metal.
Work slowly and carefully around the magnet until it pops free.
Repeat: Repeat the process for all magnets that need replacement.
Thoroughly Clean the Slots: Use a wire brush or sandpaper to remove all old epoxy and debris from the magnet slots on the rotor. Finish by wiping the area down with isopropyl alcohol. It must be perfectly clean and dry for the new epoxy to bond.
Test Fit the New Magnets: Without any epoxy, ensure the new magnets fit perfectly into the slots.
Apply Epoxy:
Mix your high-temperature epoxy according to the instructions.
Apply a generous, even layer to the bottom and sides of the magnet slot.
Also, apply a thin layer to the back of the new magnet.
Insert the Magnets with Correct Polarity:
This is the most critical step. Refer to your markings and photos.
Carefully place each magnet into its slot, ensuring the polarity alternates (N-S-N-S) exactly as the old ones were.
The powerful magnetic forces will try to snap them into place. Use wooden blocks to carefully guide them and prevent your fingers from being caught.
Let Epoxy Cure: Follow the epoxy manufacturer's instructions for full curing time (usually 24 hours). Do not disturb the rotor during this time.
Reinstall the Rotor: Once the epoxy is fully cured, carefully slide the rotor back onto the engine's crankshaft, aligning the Woodruff key with its keyway.
Reassemble in Reverse Order: Reinstall the nut, washer, stator, cooling fan, and housing. Ensure all wiring connections are secure.
Test the Generator: Start the generator and check its output voltage and frequency with a multimeter. It should be within the specified range (e.g., 120V / 60Hz). If the output is low or nonexistent, double-check your magnet polarity.
Consider hiring a professional generator repair technician if:
You are not comfortable with heavy mechanical work.
You lack the proper tools (especially the gear puller).
The generator is very large or expensive.
You are unsure about identifying and maintaining correct magnet polarity.
This is a complex repair, but with meticulous attention to detail—especially regarding polarity and safety—it can be done successfully.
