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.

 

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  • http://www.facebook.com/keith.stroud.52 Keith Stroud

    what type of wire is you use for this is it tri rated

  • http://www.facebook.com/simon.m.read.5 Simon Mam Read

    Multistranded or what electricians call ‘flex’ wire can carry alot more current (amps) than the same size wire that has less individual copper strands inside it (like most electrical wires used for construction etc.).

    This is cos most of the current travels on the surface of a copper strand, and more strands = more surface area. The rough rule is flex carries the same current as non-flex that is the next size up..

    • andrewkewley

      The skin effect applies to AC wiring and not so much DC wiring…

    • Palomineo

      I understand that some wire is silver plated, and that silver is less resistant… Boat wiring is supposedly done this way to keep it from corroding and interrupting the contacts.
      Can Anybody confirm this?
      Thanks!
      Tom

  • Thom Vix

    should an electric bike with a motor hub lock-up when the battery is dead? I have a prima runner e-bike with a motor in the front hub that wont roll with the battery out or dead. is this normal or is there an electric relay that causes this. thanks thom v

    • Palomineo

      Short answer is yes if the phase wires are shorted it will lock or “cog” when you try to turn the wheel!
      Tom

  • vladimir75

    Is it possible to replace motor and install it on another wheel?

  • ScooterSquid

    Am going through this very repair right now, and am distressed at the lack of replacement wiring available. Does the author have a source for this wire; both phase and Hall? It would save me a world of headaches. Many thx!

    • greengearhead

      I reuse the old wire that was damaged so it ends up being shorter. After rewiring extend the wire on the outside if needed. The extension can be any appropriate wire like house wire from Home Depot. The wire going through the axle tube should be real Teflon coated hub motor wire.

      • Quetzalcoatlus

        Hi greengearhead, thanks for the reply,
        (Disqus is freaking out, using my old Quetzalcoatlus account instead of ScooterSquid, with no options to change it. Sorry.)

        That was a consideration, except for the nature of the malfunction. The axle’s registration plates both stripped out, causing the wiring to wrap around the axle until it went ‘Bzt! Bzt!.’
        So I’m looking at a situation where the wires inside the insulation are damaged, and I don’t know where specifically. So my hope was to run fresh leads rather than gamble. The damage point is likely at the bind at the opening anyway, which doesn’t give me enough left to solder.
        Is the real teflon-coated wire so exotic that nobody can find it? And is regular house wire such a worthy replacement? I’m dubious. The phase wires appear silvered, or tinned with something special, as another commenter noted.

        • greengearhead

          The Teflon is special because the insulation is so thin, allowing more wire in the narrow axle tube. Once the wires are replaced and you have a good 3-4″ sticking out of the axle you can easily switch to standard wire since the wire bundle does not need to pass through any narrow passages. I would go to significantly thicker cheap house wire but keep the colors the same to look neat. Color matching the heat shrink tubing used to cover the splice to the wire color also makes the house wire look very professional. If you are running hall sensors ( thin sensor wires into the hub) the sensors should be checked. They are sometimes fried after a short circuit.

  • Quetzalcoatlus

    Okay, greengearhead, you have been very helpful, thank you. But I’m still hoping to match the wire exactly, ideally from an electric-scooter-specific parts source. Re-using old wire that went “bzt!” is a gamble I prefer not to make.
    So I ask the group here at large: does anyone know of a company that sells wire specifically meant for this application?
    Many thanks.

    • brighamanimator

      Hi greengearhead, hi everyone,
      (this is Quetzalcoatlus, darn you Disqus!)
      Just fyi: I managed to find a source with THE genuine wire used in these motors. The company is Allied Wire & Cable (awcwire.com) and the wire type is MIL-W-22759. It is, as you might’ve guessed, a military-spec wire type, silver-tinned copper stranded wire and coated with teflon. They have a wide range of gauges and teflon colors. They also carry the gauge needed for the Hall sensor.
      You can order by the foot, but for gauges 28 and up (I think) there is a 10-foot minimum and the price jumps a bit. They ship out of NH, and despite my ‘chump-change’ purchase relative to their normal clientele, they were really nice & patient with me.

  • Anita Mas

    I am not mechanically inclined. It would probably be best for me to get a professional. That could either be my brother or a service.

    Anita Mas | http://www.westcoastelectricmotors.com