Hub motor repair and upgrade
One common issue with hub motors is broken or shorted wires at the point where the wires exit the motor axle. If the wires are tugged or twisted the sharp edges of the hub motor axle can cut through the wire insulation or completely sever the wires. Most hub motors employ hall sensors to tell the controller the motor position. Hall sensors are easily burnt out if the signal wires short to power or ground. The motor shown below stopped functioning after the wires were damaged. A quick test showed that the hall sensors were burnt out. (Testing Hall sensors article to come)
The wire harness exiting a typical hub motor look like this. Five thin wires that connect to the sensors and three thick wires that connect to the phase windings. The phase wires shown here are thick enough for reliable use with a 20-25 amp controller.
If the sensors were still functioning after the wires were damaged it would have been possible to simply repair the wires and continue using the stock 20 amp sensored controller that was installed on this ebike. Testing the hall sensors showed that the sensors were burnt out. Replacing burnt out hall sensors is time consuming intricate work and is not recommended. Another option once sensors are burnt out is to replace the controller with a sensorless controller. A sensorless controller is in the $200 range and will allow the motor to be used without sensors and allow for higher than stock power output.
Wether you are repairing existing wires for use with the stock controller or upgrading to thicker phase wires for use with a higher powered sensorless controller; the motor must be opened, the wires going through the axle removed and replaced.
Warning disassembling a hub motor is dangerous if you are unsure how to reassemble the motor components safely. During reassembly the motor halves will suddenly slam together due to magnetic attraction and possibly sever your finger tips.
See hub motor assembly /disassembly article to come or reference other sources if you have not opened a hub motor before.
Most motors will suffer a shortened life span and overall reduced reliability when the controller power is significantly increased , such is the price you pay for high performance.
40 amp Sensorless controller
Once the motor is disassembled cut the wires leaving at least an inch of wire connected to the phase windings.
Cut the hall sensor wires. If you are repairing a motor to be used with a sensored controller these wires must be replaced with similar gauge wires. If you are switching to sensorless operation these wies are no longer needed.
The passage through the hollow axle is very narrow. If you are not using sensors it is possible to use thicker phase wires since the sensor wires will no longer be taking space in the axle tube. Thicker phase wires allow for a higher powered controller to be used with out melting the thin stock phase wires ( a common issue after controller upgrade)
Pull new wires through the axle tube. Be careful not to cut the insulation on the edge of the hole at the base of the axle.
Remove the old phase wires from the phase windings using a soldering iron. keep track of which color went to which winding.
Solder or crimp the new phase wires to the phase windings. Keep the colors the same to aid in reconnecting later. One alternative to thicker phase wires is to use two strands of stock thickness wire. Reuse the fiber insulation that the manufacturer used to cover the solder joints.
Once the three phase wire connections are complete zip tie the wires down to the stator.
Reinstall the stator into the rotor.
This step is dangerous. The stator will fly into the rotor with tremendous force due to magnetic attraction Keep you fingers clear!
Repaired and upgraded motor ready to be reinstalled on an ebike.
Double strands of wire have been run to the phase coils. This motor will be run at almost double the wattage with upgraded phase wires and upgraded controller.