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HOW TO REWIND A 7.5 kVA

1. Coil Winding

This refers to the process of removing the old burnt coils and replacing them with new ones.

Steps:

• Open the alternator/motor carefully and remove the old coils from the stator slots.
• Take measurements before removing them: coil size, number of turns, wire gauge, and slot arrangement.
• Prepare your winding machine or hand-winding jig.
• Wind new coils based on the exact number of turns you measured earlier.
• Maintain tight and even winding to avoid vibrations and overheating.

2. Copper Gauge

This is the thickness of the wire used for winding.

Why it matters:

• Using thinner wire than the original causes overheating and low output.
• Using thicker wire may not fit into the stator slots.

For 7.5 kVA alternators/motors:

• Most 7.5 kVA units use 1.0 mm – 1.2 mm copper wire (but always confirm the original gauge).
• Measure the old wire with a micrometer before buying new copper.

3. Insulation Class

This protects the winding from heat, moisture, friction, and electrical breakdown.

Important insulation materials:

• Slot liners
• Wedge papers
• Glass tape / Cotton tape
• Varnish (Class F or Class H)

Steps:

• Insert slot liners in all stator slots before placing coils.
• Tape the coil joints with high-temperature tape.
• After winding and assembling, varnish and bake the stator in an oven to harden the insulation.

4. Turns per Coil

This determines the voltage output of the 7.5 kVA machine.

Steps:

• Count the number of turns per coil before removing the old winding.
• Record the number of turns for each phase (if it’s 3-phase).
• Ensure that all coils in the same phase have equal turns for proper voltage balancing.

Wrong turns cause:

• Low voltage
• High current
• Coil heating
• Vibration

5. Stator Rewinding

This is the final assembly of the coils into the machine.

Steps:

1. Arrange the coils according to the winding diagram (e.g., ABC ABC for 3-phase).
2. Insert the coils into the stator slots carefully.
3. Use wooden mallets to avoid damaging the wire.
4. After slotting all coils, insert slot wedges to lock them firmly.
5. Make all phase connections (star or delta depending on the design).
6. Varnish and bake the winding.
7. Reassemble the rotor and test for:
   • Continuity
   • Insulation resistance (Megger test)
   • No-load voltage
   • Load performance

SUMMARY (Simple)

Rewinding a 7.5 kVA is mainly about:

• Removing old coils
• Using the correct wire gauge
• Following the exact turns per coil
• Ensuring proper insulation
• Reassembling correctly inside the stator