We do a complete replacement of the electric bike wiring — the whole process, including the controller wiring


Hello friends!

With the rise in demand for e-bikes, there are many craftsmen offering electrification services for bicycles. However, these services are not always of sufficient quality.

After purchasing an electric bike from one of these private traders, its owner quickly noticed a discrepancy between the actual range and the declared one — the bike traveled 40 km in assistance mode, and about 20. On the throttle stick, about 20. Although the seller voiced the values of 60 and 30 km. It was problematic to return the bike to the seller right away due to the remoteness — it was purchased in another city.

By the beginning of the next season, the bike stopped working altogether — the throttle stick sometimes worked, then not. The owner’s attempts to figure it out on his own did not lead to anything.

As it turned out, the problem was in poor-quality electrical wiring, namely, in the contacts oxidized during the winter.

Briefly about the bike itself: this is a folding Stels with a Bafang engine. The 48 volt battery is installed in a bag on the trunk. By the way, its real capacity turned out to be 9.8 Ah, and the declared one was 16 Ah.

The KT-LCD3 display was damaged in transit and the owner plans to replace it himself. On the left on the steering wheel there are buttons for turning on the light and signal.

On the right handlebar there is a trigger-type throttle and a display control panel. The brake levers have built-in sensors — buttons.

There is already a connector on the motor cable, this will simplify the task a little, since you do not have to solder the connector to the motor itself.

The controller is designed to work with voltages of 36 V and 48 V, and for a maximum current of 25 A.


Controller model KT36 / 48ZWSRM-SLS02G. Pay attention to how many wires are coming out of it. On the one hand, it is convenient when assembling on a table. On the other hand, when using a bicycle, these connectors must be hidden somewhere, as they are susceptible to corrosion and subsequent loss of contact due to vibration.

Remove the cover — here you can see the thick phase wires going to the engine (blue, green and yellow) and the incoming power wires (red and black). At the point where the wires enter the seal on the inside of the controller, a little hot glue is applied, which, in theory, should fix the wires from being pulled out, but here it is rather for show, and can be easily removed with tweezers.

Having previously discharged the capacitors by closing the controller power contacts, we begin to unscrew the screws on the side wall — they press the power transistors to the case, thereby ensuring their cooling.

We remove the controller board from the case. This version uses 9 power transistors — 3 for each motor phase.

We sketch in a notebook all the wires included in the controller board — this will help when soldering new cables.


Now you can safely solder the wires and clean the holes with a solder suction. The only thing I decided to keep was the DC-DC converter for powering the headlight (right).

It is not used in this case, since the headlight is connected in parallel with the controller’s power supply and is turned on with a button on the steering wheel. But it doesn’t make much sense to delete it either — suddenly someone decides to use it.

We solder the new wires in accordance with the entries in the notebook, and put nylon ties on them near the sealing gum to protect them from being pulled out.


The second is the XT60 power connector. It had to be unsoldered and then re-soldered in order to put on a protective glass-reinforced tube, and on top — heat shrinkage.

The third is a 3-pin Julet for connecting the PAS sensor (pedal assist) and the fourth is the Bafang motor cable.


We apply hot melt glue on all sides of the wires inside the controller for additional fixation and sealing. We return the board to the case and fix the controller on the bike.

To minimize the number of wires, we will use an integration cable with Julet connectors. On the one hand, it connects to the controller, and on the other, it has a connector for the display (5-pin green), brake sensors, throttle sticks (3-pin yellow) and headlights (4-pin blue).

We connect it to the controller and lay it along the frame to the steering wheel. Now you can push off from the end position of the connectors and determine the lengths of the wires to the controls on the steering wheel.

Remove the cover on the throttle and see the Hall sensor. Wires go to it: red — plus, black — minus and green — signal.

We unsolder the wires and replace the cable with Julet. The white wire became the signal. We fix it with hot glue for reliability and close the lid.

A push-button sensor is installed on the brake levers. When you press the knob, two contacts are closed, and in theory, a 2-pin connector would be sufficient. But since we have a 3-pin connector on the integration cable, we will use the corresponding mating connector.

The white wire is the signal wire and the black wire is ground, or GND. When these two wires are closed, the controller «understands» that the brake is pressed and turns off the motor.

The third wire (red) is simply insulated and will not be used. It is required when Hall sensors are installed on the brakes.

After soldering the wires, we put hot glue on them, put on a heat-shrinkable tube on top and heat with a hairdryer. The glue displaces air and a reliable tight connection is obtained, which excludes corrosion and subsequent destruction of the contacts.

Let’s take a look at how the LED headlight with integrated signal was connected. A connector with a black and yellow wire was connected to the controller, and inside it — directly to the battery power. In this case, both long wires went from the steering wheel to the controller.

I could not resist and decided to look inside the headlight. Black wire is ground, red is signal (beep) and green is light.

Inside the remote control, everything is quite simple — two buttons: a red one with a latch to turn on the headlight and a green one without latching for a signal.

We unsolder the old wires from the buttons and solder the new ones. From the blue 4-pin Julet connector, which will be connected to the integration cable, take two wires — red and black. It is battery powered.

We shorten the wire to the headlight, since it is located on the plug, which is much closer than the controller. Agree, there are fewer wires, and this will affect the appearance. We fix the wires with hot glue and close the cover of the remote control.

We shorten the wire from the PAS sensor installed in the carriage assembly and solder a 3-pin Julet to it, which will connect directly to the controller.

The controller is fixed to the frame with polycarbonate clamps. We lay the wires and fix them with nylon ties.

The number of wires on the frame has been noticeably reduced, and there is no longer a huge bundle of connectors at the exit from the controller.

What are the benefits of the bike with the new wiring?

First, it is, of course, a reduced number of wires. Secondly, there is no bundle of connectors near the controller. Thirdly, reliable moisture protection of the connections, thanks to which the bike will last a long time.

And what is no less important — the ability to quickly replace components in case of damage and failure.

The work was carried out in the workshop

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