8fun bafang SWXH motor doesn't work, after bike fall down

[gari1981]

Hello to all.

I'm new on this forum. I have ebike for only one week, first time in my life.

It's Milan Fassi bike, with 8fun bafang SWXH hub motor, 36V battery.

It is pedalec bike, without throttle control.
It have pedal sensor, and 3+3 wires that goes in motor. 3 thick ones for phases of the motor, and 3 thin ones (not 5).

I have one problem with the bike, after fall down. Motor doesn't want to start.

Symptoms are next:
- motor doesn't start when you turn the pedals
- battery voltage is 38V, at the output wires (red and black)
- display is on
- speed indicator is showing 0.0 km/h when you driving (before that he was showing the actual speed, even you dont turn the pedals, and motor is off)

I checked the voltages on the wires:
- supply voltage on pedal sensor (between red and black wire) is 85mV
- voltage between blue and black wire on pedal sensor is 85mV, constantly, even you put the sensor near the magnet, or put it far from it
- supply voltage on motor sensor (between red and black wire) is also 85mV
- voltage between blue and black wire on motor sensor is also 85mV, constantly, even you turn the motor
- voltage on both brake sensors are 25mV, and goes to 0V if you press any of the two brakes

Does anybody can recognize this symptoms, or have reference voltages for supply the sensors, and expected sensor output.

Thank you for your help.

 

[Rassy]

For starters, it sounds like your speed pick-up might be out of line. Check to see that the magnet on the spokes lines up properly with the pick=up sensor which is normally on either the front fork or rear chain stay. Perhaps your controller doesn't kick in when it thinks you are going 0 km/h.

Edit: And at the same time check that the wire from the speed pick-up to the controller or display unit was not damaged.

 

[gari1981]

I have the doubt that, fall down of the bike generated some soldering brakes on the circuit board in the controler.

I think that the sensor inside motor generate the signal for speed measurement.

I need somebody who knows what is reference voltages that supplies sensors, in the motor and on the middle shaft.
I looked at alixpress for some sensors, and it says that it should be supplied with 5V. I measured 85mV.

One interesting thing is that when I bend the electronic board in the controler, the supply voltages of the sensors goes up to 300mV.

For me, on the first sight, it seems that the sensors are not supplied well.

 

[gari1981]

I analysed again. Signal that is coming from motor, thin blue wire, goes directly to display, just passing the controller.

I understood this is sensorless motor, just have speed indicator, that is shown on display.

That is the purpose of 3 thin wires, that comes into the motor.

My understanding is that with fall down of the bike, I loosed supply on both sensors, one in the motor that gives speed signal, and another one in the pedals, that start the hub motor.

Inside controller, I saw that red wires that supplies both sensors are shorted and in current situation it gives 85mV. On aliexpress I saw that it should be 5V.

I need somebody to confirm me the supply voltage of the sensor, to try to give the external supply to the sensors, in order not to burn them.

 

[Rassy]

OK, sorry, not familiar with this model. Sounds like you have found that the controller is faulty. I would probably just replace the controller, figuring if that fixes the problem, great. If it doesn't fix the problem, then you have a spare controller on the shelf for future use when needed, and you have determined that the controller is not the problem.

Good luck with getting it all sorted out.

 

[d8veh]

Sometimes, when you fall off an e-bike, it damages the motor wire where it comes out of the axle. Did you check that? Is the motor difficult to turn backwards?

The speed sensor and pedal sensor both work on 5v. You must have a short on one of the 5v wires somewhere, which will pull them all down. My guess is that the short is at the axle.

Unplug the three thin motor wires if possible to see if the 5v returns on the pedal sensor, which should make the motor work, though the controller might keep going to sleep without a speed sensor. If that's so, you can use a cycle computer sensor on the wheel instead of the motor one.

 

[gari1981]

I cut the 5V wires that comes out the controller, and put external supply, for both pedal and motor sensors.

Both sensors started working, and display started showing the speed, and pedal sensor started blinking (LED diode inside) when you turn the pedals.

I also put 5V on brakes, but motor doesnt want to start.

I measured the voltage on the phases wires that come out controller and goes to motor, and it showes voltage 0V.
Sound like controller doesnt give a power to motor at all.

I'm trying to find new controller on aliexpress that can work in sensorless mode, and trying to find to replace with stronger one, above 20A max current (actual one is with 12A maximum current).

 

[d8veh]

I think there might be an easy solution. Disconnect the brakes to see if it works. You've probably broken a brake switch. Disconnect one at a time to see which one. You only need one brake switch.

 

[gari1981]

After further analyse of the problem, and understanding purpose of each wire, I found that there is 0V on ignition blue wire that comes from display to controller.
After examining aliexpress site I understood that on this type of controller, controller expect 36V on blue ignition wire to start working, and give the voltage to all sensor and the motor.

I shorted this wire to battery 36V supply, and everything alived. Sensors started working, motor started run. But everything working even display is off. You can shutdown the sensors, only with battery power off.

After that, I was curious why display is not giving this 36V on blue wire, even it is turned on.

I opened the display, and inspect the board, and found that one leg of the transistor inside, unsolder it self, because of the bike fall down.
I soldered it again on the board, turned on the display and it gave 36V on blue wire.

I returned wiring in the controller to standard wireing and everything started working, as it was new.

With fall-down of the bike and one leg of the transistor unsoldered, shutted down complete electronics on the ebike, just display worked.

So with almost of one week analysing, learning, using youtube, forums, alixpress I understood next.
This configuration of the bike, with no hall sensor in the motor works like this.

In the motor, it have 6 wires, 3 for the motor phases, 3 for the speed sensor inside the motor.
3 wires for the speed sensors are red, black and blue. Black is ground, Red should have at least 5V to supply the sensor, and the blue one gives a speed signal that goes directly to the display (just passing the controller)

Pedal sensor, also have 3 wires red, black and blue. Black is ground, Red should have at least 5V to supply the sensor, and the blue one gives a signal for motor to start and impact the how much power the controller gives to the motor. It have led diode, and if you rotate the pedals, led have to blink (not to be constantly turned on, or not constantly turned off). So it have to power off, power on, power off, power on, when you rotate the middle shaft.

Display have 5 wires, red, black and blue, green, yellow. Red should have at least 36V to supply the display. When display is off, on blue on you should have 0V. When you turn it one, it should give 36V and start the controller (breakdown in my case).
Green wire is giving the controller the level of assistance you want. My have 3 level of assistance, so 3 discreete level of voltage, whan you are pressing the display from 1, to 2, to 3.
Yellow wire is directly connected to motor signal, just passing the controller, as I mentioned.

Excepet what I mentioned, controller have 3 wires that supplies the motor (blue, green, yellow), 2 wires for battery supply (red and black).
Also 2 x 2 wires for the breaks, that shutdowns the motor if it's pressed.

So that's it. If you have some experience using electrics, and voltmeter, you can repair it by yourself, or even find what's wrong and order it from aliexpress.