Permanent magnet DC (BLDC) motors in the hubs of the wheels are the heart of any modern electric vehicle. Over time, under the influence of high currents, overheating or mechanical damage, the insulation of the windings can collapse, leading to short circuits and failure of the device. winding-wheel, which allows not only to restore efficiency, but also to improve the specifications of traction.
The process of restoring windings requires high accuracy, specialized tools and an understanding of the physics of electromagnetic processes. An error in the number of turns or connection circuitry can lead to instantaneous failure of the controller or reduce the efficiency of the engine to critical values. In this article, we will discuss the process in detail, starting from dismantling to final assembly of the unit.
Diagnosis of malfunctions and preparation for repair
Before starting disassembly, you need to make sure exactly the nature of the malfunction. Often the symptoms indicating burnt-out windings can be caused by damage to the Hall sensors or a wedge of bearings. The primary diagnosis is carried out using a multimeter: you need to call the phase wires for short circuit between yourself and the body. If the resistance between phases tends to zero or is significantly different from the norm (usually these are Ohm's lobes), and the insulation is broken into the body, then wheel-drive It needs rewinding.
It's also important to visually assess the condition of the magnets on the rotor, so if they're overheated, their magnetic force may have weakened, which would require replacing them or remagnetizing them, and you'll need a clean, well-lit workplace to work, because the fine parts and wire are easily lost.
Prepare the following set of tools: a set of wrenches and heads, a bearing removable (or device for knocking out shafts), a hammer, pliers, cutters, a high-power soldering iron, a thermophene and a multimeter. You will also need to purchase an enamel wire (winding wire) of the right diameter, insulating materials (press pan, varnish) and chemical solvents for cleaning.
⚠️ Warning: Before starting any work, be sure to turn off the battery. Residual voltage in the controller capacitors can be dangerous, although when working with the motor itself, the risk is minimal, the safety of power chains is a priority.
Take a picture of the circuitry (phases and sensors) before they are soldered off. Color markings may vary from manufacturer to manufacturer, and the confused phases will cause the motor to twitch.
Disassembly of the wheel motor and retrieval of the stator
The disassembly process depends on the design of the engine, but most models have a similar architecture: first, the wheel is removed from the frame, the brake disc or drum is removed, and the spokes or axle are removed if the design requires it, then you need to disconnect the cable channel and carefully remove the sensor wires and phases from the housing.
The most difficult step is to separate the rotor (the outer part with magnets) and the stator (the inner fixed part with windings). Magnets create a powerful attraction, so separation often requires special removers or a method of neatly knocking out the shaft. When using a hammer, you need to act through soft stretchers (copper, aluminum, wood) so as not to damage the threads or seating of the bearings.
After successfully splitting the halves, the stator is removed from the rotor housing, and you can see the burnt windings at this stage, you have to cut the copper wire off one side of the stator teeth, so you don't want to damage the metal core itself, and then you pull the wire out on the opposite side, and you have to count the number of turns on one tooth, because that's a key parameter for calculating the new winding.
- 🔧 Remove the terminal box lid and unfurl the phase wires.
- 🔧 Dismant the axle and bearing units if they interfere with access.
- 🔧 Use a removable or neat impacts to separate the rotor and stator.
- 🔧 Clean the insides of old insulation and dirt before starting the winding.
Calculation of parameters and selection of winding wire
The quality of the rewind directly depends on the correct choice of the diameter of the wire and the number of turns. Diameter of wire It determines the current load, and therefore the torque and the heating. If you take a wire thinner than the original, the engine will overheat; if thicker, there may be no space in the winding window, or inductance changes, which affects the operation of the controller.
Turn count affects the KV (revvs per volt) of the engine. Increased turns reduces KV, increasing torque at low speeds, but reduces top speed. Reducing turns backfires. For urban electric bikes, the balance between traction and speed is often sought, so deviation from factory parameters should be justified.
When calculating, consider the window filling rate. Copper should occupy the maximum possible volume, but the wire should lie tight and smooth. Using wire in heat-resistant insulation (for example, PET-155 or higher) will prolong the life of the engine at high loads.
Smoothness, balancing
| Parameter | Motor impact | Recommendation |
|---|---|---|
| Diameter of wire | Maximum current, heating, efficiency | Use the original or the nearest larger standard |
| Number of turns | Speed (KV) and torque | Strictly calculated for the desired voltage |
| Winding circuit | Observe factory order (star/triangle) | |
| Quality of insulation | Protection against KZ and breakdown | Use lacquer and cushioning materials |
Formula for calculating the length of the wire
For one tooth, the length is equal (Perimeter of the tooth + reserve for the frontal parts) * Number of turns. The reserve for the frontal parts is usually 30-40% of the perimeter of the tooth.
Manual coil technology
Winding is the most time-consuming process. To make things easier, homemade or industrial winding machines are used to allow the wire to be laid evenly. Before starting work, insulating gaskets made of pressespan or similar heat-resistant material are installed on the stator teeth, and they must completely cover the metal, preventing breakage on the body.
The winding process requires constant stretching of the wire. Too little stretching will lead to a loose coil that will vibrate and damage, too strong can break the enamel. The turns are stacked in rows, trying not to cross the wire chaotically. It is desirable to smear each layer with a thin layer of glue or lacquer for fixation, although this is done after all the work is completed.
It is important to follow the winding pattern (usually 9N12P or 12N14P for popular motors). The winding direction (clockwise or counterclockwise) must alternate through the tooth or group of teeth according to phasing. An error in the direction of winding even on one tooth will cause the engine to fail.
☑️ Checklist before winding
⚠️ Attention: When winding, monitor the integrity of the lacquer insulation of the wire. Any microscopic tear can cause an interturn circuit that will only appear under load and lead to re-repair.
Lacquer and winding drying
Once the winding and soldering of the terminals is complete, the coils must be soaked in a special electrical varnish, which serves three purposes: fixing the turns (so that they do not vibrate or rub), improving heat sink (copper better gives heat through the varnish to the stator), and protecting against moisture and dust.
They use polyester or epoxy-based varnishes with a high melting point, and they put the stator in a bath of varnish or pour it over with a brush until the air bubbles stop coming out, and then the excess drains off and the stator is sent to dry.
Drying is done in an oven or a special oven at a temperature specified by the varnish manufacturer (usually 100-150°C) for several hours. Undried varnish will remain sticky and fail to perform its function, and overheating can destroy the wire enamel.
Once cooled, the insulation resistance must be checked with a megaohmmeter, it must be high (megohmmeters), which ensures that there is no breakage, and only after successful testing can assembly begin.
High-quality impregnation and drying increase the life of the motor wheel by 2-3 times, preventing the destruction of the windings from vibration and overheating.
Assembly and initial start of the engine
The assembly is reversed. The stator is carefully inserted into the rotor. When the halves are joined, the magnets will be strongly attracted, so you need to control the gap and not pinch the wires. The axial nuts are tightened at the recommended moment, often using a thread lock, because vibrations during operation can weaken the attachment.
The first run is better done on weight, fixing the wheel in the frame or on the stand, so that in case of errors it does not create an emergency. controller Smoothly increase your speed while listening to the sound of the engine. A steady hum without jerking, clicking or vibration indicates a successful rewind.
After the initial break-in (10-15 minutes of operation at medium currents), it is recommended to re-check the tightening of contacts and the absence of local overheating of the body. If all parameters are normal, the motor wheel is ready for installation on the vehicle and active operation.
- 🚀 Carefully combine the slits and seats of the rotor and stator.
- 🚀 Tighten the axle at the right moment using a dynamometer key.
- 🚀 Check the free rotation of the wheel with your hand before applying power.
- 🚀 Conduct a test run at low currents under temperature control.
Frequently Asked Questions (FAQ)
Can the motor wheel be rewinded with a wire of a different diameter?
Yes, it can, but it will change the specifications of the engine. A larger diameter wire will allow more current to pass (increase power and torque), but reduce the number of turns that will fit in the window, which may require a change in circuitry or reduce efficiency.
How long does it take to rewind the wheel motor at home?
For a beginner, this process can take from 2 to 5 days, including time to disassemble, clean, wind (the longest stage), soldering, impregnation and drying. An experienced craftsman can cope in 1-2 days.
Do I need to change the magnets when rewinding?
Not necessarily, unless they've lost their properties. Check the magnets: if they hold a steel plate with the same force as the new ones, they can be left behind, but if the motor burns out from overheating, the magnets can demagnetize, and then they must be replaced.
Which is the best way to use for smearing?
It is optimal to use specialized varnishes for electric motors, for example, KO-916, ML-92 or their modern imported counterparts. They have high heat resistance and good adhesion to copper and insulating materials.