Melted phase wires on QS 260 5000W

dominik h

10 kW
Jul 24, 2021
I just installed a Fardriver ND72680 in my scooter and during the test rides I melted my phase wires.

The little controller realy made 680A peak phase current and little over 490Asinus (measured with a calibrated true RMS current clamp). I drove uphill with 23kW drawn from the battery, measuring around 310Adc with a voltage sag around only 3V. The battery 21S5P with a total 100Ah , power pouch with 8C constant discharge can still do more, but the BMS is limited to 350A for max 5 minutes.

I expected things like this to happen, but I did not know with which controller this could happen, so I'm glad I did not install the ND96850 or the ND721800 I also have setting in the garage, they might have melted the wires much faster.

The phase wires from my QS60V500835 (5000W) only melted under the swingarm.
At the controller and through the motor axle they where ok. I checked the temperatures during my testdrive every minute by hand at the controller and in front of the axle, underneath the swingarm I did not check the temperatures.

Now I opened it up and had a look at it and compared it to the erider / Masini Extremo 8kw motor, i also have.
The one with more copper inside is the 5kW QS 60V Motor.
The other is the erider 72V 8kW motor.
Both are 260mm motors, the 5kW has 40mm magnets and 7x22mm gaps and AWG6 13,3mm² phase wires, the 8kw has 45mm magnets and 7x15mm gaps and 2x6mm² phase wire per phase.

For what is the circular winding on both sides of the 5kw motor.
The 8kw does not have this winding at all.

And why did the phase wires only melt at the steel swingarm?

Did I build an induction heater?

I always thought the motor axle is the weak or hot spot.

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Under the swingarm

In front of the axle , they where not melted but one insulation was drwan back

The wires inside the axle are ok

I will repair the 5kw QS motor, as there is nothing burned inside.

I have already bought new phase wires from Lapp, Ölflex Heat 205°C (400F), they have the slightly bigger diameter than the original phase wires.
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The wires going through the axle can dissipate some heat to the surrounding axle. On the swing arm, they must have been insulated and the heat built up. Fatter wires will help, right up to where the go into the axle. If you can press the wires against the swing arm, they might be able to dissipate some heat to the metal swing arm.
After failing to get the new wires throug the axle, I found out that the original phase wires are AWG6 13,3mm². The new ones are 16mm² .
So I had to get rid of the protective hose inside the axle. Now capton tape has to do the job.

Inside the axle was a lot of dirt, as it was sealed only on the inner side of the motor.

I even tried to get coper stripes through the axle, but bending them 90degrees will be no noch job.


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The new AWG5 16mm² phase wires are through the axle, a temp sensor is added.
The motor is already installed and the scooter is running again.
The hardest work was to get the bearing over the new and thicker wires.
I insulated the phase wires through the axle with two layers Kapton tape, it was not possible to get a protection sleeve over the wires.


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That is some good melting. Makes me scared for my QS260 50H motor. So you weren't running a temp sensor before? How hot does the motor get when you ride?
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During a normal ride on flat roads the motor stays between 60-90C .
But uphill was already a problem with the Sabvoton SVMC72150 , even with that controller I got 180C at the phase wires.
I did not have a temp sensor before. The motor is 10years old, and was driven 7 years 22000km with a controller that had a maximum of 5kw. Afterwards I did ride it 2 years 10000km with the sabvoton with up to 14kw, my Saboton made 175Adc.
Now I aded a temp sensor and have set the controller to max 220Adc. I tuned it to around 18kw up to 65kph and from there to top speed with falling power down to 11kw at 103kph. This is to not burn the motor during short uphill rides.

The controller can force the motor to run 115kph ond even more but with 18kW at 115kph and much weakening field the motor temp rises very fast. So I set it to a little lower max speed, now it only uses weakening field when the battery is at a low SOC.
My scooter has a dry weight of 180kg. On a bike this should be no big problem, if you do not permanently drive at full speed.

When I set the controller max dc current to 300A the motor heats in 3 zero to topspeed runs up to 140C.
So I personaly think 23kW for peroids of more than 30 seconds is to much for this 260 motor.
Now I have separated the wires, and if it still is nececary I will ad spacers to the metal swingarm. I used 205C wire, and
I also added a 125-150A charge terminal for my fast charger, i hope the QS10 plug will survive it.


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