The Ballistic 550 Hand Wound Stator is dipped in a special motor winding epoxy and then oven-cured for several hours. Once the epoxy is cured, it prevents the wires in the stator from moving or rubbing against the laminations and other wires in extreme conditions. Preventing this unwanted contact avoids shorts in the motor coils which can lead to premature failure. The epoxy also helps transfer heat from the wires to the lamination, helping motor operation at higher power levels.
All around, the epoxy coating improves the reliability of Novak’s already high-quality stator and provides extreme vibration resistance. It also prevents rewinding of the stator.
BENEFITS OF AN EPOXY-DIPPED STATOR
Lately racers are realizing that there is tremendous value in epoxying the wound stators in brushless motors under extreme racing conditions. The following article will explain the benefits and science behind this manufacturing technique, and help you decide if purchasing a Novak epoxy-dipped wound stator is right for you and your racing style.
Benefits of Epoxy
Due to torque and vibration created by the alternating current during operation, brushless motor stator coils are subjected to very high mechanical forces under typical racing conditions. Picture it as a super-fast and very forceful tug-of-war between the coils and the magnets. This constant pulling and pushing of current through the coils causes the coils to move in sync with the drive frequency. This force increases as the load on the motor increases.
The Novak Ballistic 540 Brushless Motor - 17.5 turn has a Kt value (oz-in of torque per amp of current) of approximately 0.7 amp. During normal acceleration, the motor draws about 100 amps. This translates into 66 oz-in (or 4.1 lb-in) of torque in a Ballistic 17.5T motor—based on a 95%-efficient motor and an equal and opposite reaction of force in the coils. (For more information on this physical law, review Newton’s Third Law of Motion).
Imagine 4.1 pounds of force pushing on the motor’s coils. Over time, this movement will cause some damage to the coils. In order to improve the motor's reliability, and possibly extend its life, the stator is epoxy dipped.
Dipping them in epoxy provides the windings with an additional degree of mechanical strength, particularly in the unsupported end wind. The coils are also strengthened where they enter the slot of the stator, in order to resist the tug-of-war forces caused by the torque reaction described above.
In other words, the epoxy coating prevents coil movement caused by the changing magnetic fields created during motor operation. It is ideal to prevent the stator wires from rubbing against each other, because this vibration can eventually wear out the insulation coating, causing a short in the coil and motor failure.