How to Fix Field Coil Burnouts in DC Motors
Field coil failures don’t always come with sparks and smoke. Sometimes it’s a slow breakdown; other times it’s instant. Either way, repairs start with the same question: what caused the burnout? You’ll need a clear answer before you can get to work on administering a reliable fix. Here’s how.
Identify the reason the coil burned out
Not every burnout is dramatic. Sometimes it’s a smolder that cooks the insulation slowly. Other times it’s a single arc that vaporizes the winding instantly. Either way, you need to start with why. Ask yourself:
- Was the motor exposed to voltage spikes or overloads?
- Was the insulation aged, cracked, or oil-soaked?
- Did a short to ground occur upstream or internally?
- Was the ambient temperature within the motor’s rated range?
Unwind the damage completely
There’s no halfway fix for a burned field coil. Every winding needs to come out. Every trace of soot, ash, and insulation breakdown needs to be cleared. The lamination stack must be cleaned and checked for hot spots or arc marks. Leave anything behind, and you risk another burnout on restart.
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Rewind to OEM spec (or better)
Coils have a variety of characteristics, and they matter. Some coils use heavier gauge copper. Some have tighter turns per slot. Certain ones require dual-section windings or thermal class upgrades. You need to match the original build—or improve on it if failure trends call for an upgrade. Check that:
- New copper windings are tension-wound for consistency
- Slot liners and insulation are rated for high thermal endurance
- Connections are hand-soldered and torqued to spec, not left to chance
- Coils are vacuum impregnated with epoxy for maximum durability
Every detail should be dialed in to restore torque, speed, and reliability without compromise.
Balance, then test the motor under load
Field coil burnouts don’t always leave the rotor untouched. Heat and force can warp the armature, loosen components, or shift alignment. Before you power anything up, check and correct rotor shaft concentricity, bearing housing tolerances, magnetic field alignment, armature balance, and end play. Bench voltage isn’t enough. You should test DC motors under simulated field conditions — measuring speed, current draw, and torque response.
At GES, we go even further. Our experts monitor temperature rise and check brush performance during extended runs. We measure magnetic flux density and verify commutator contact patterns. And every repair comes with a service report that documents the entire process — from failure cause to final output.
Make sure all repairs go beyond the burn
Coil burnouts may seem like an isolated repair, but they need to go beyond component replacement to ensure a reliable repair. Your DC motor is a finely tuned machine and needs to be thoroughly repaired and tested before it’s redeployed. Root cause analysis, coil replacement, balancing, testing, and proper reinstallation all play a critical part in making sure your motor is ready to function at a high level once again.
