To be able to modify and repair the Chinese KU63 e-bike motor controller I have redesigned it. The KU63 may also give insight into other Chinese motor controllers.
1. China brushless motor controller schematic
Here is the schematic of the KU63 motor controller which may also give insight into other Chinese motor controllers. Download the circuit high definition pdf file HERE. If someone finds a bug, please report!
Here I am at work:
2. KU63 motor controller facts
The KU63 motor controller is small and lightweight and well suited for 250W motors.
- BLDC motor 36V 250W
- Overcurrent 12A
- Motor HALL sensor or sensorless operation
- Battery undervoltage detection ~27.7V
- Overtemperature protection
- Brake high voltage level and low voltage level input
- Control LED inside
- Weight 200g
- X8M06-C controller IC, TQFP44 housing
- 6 power MOSFETs 2SK4145, RDS(on) 10mΩ, VDSSmax 60V, IDmax 84A
- Quiescent current off-state < 30uA
- Consume current with motor at full speed 60mA (excluding motor current)
- Switching frequency 16kHz
- Throttle voltage 1 ... 4V
3. Disabling PAS / pedal speed control
The behaviour of the KU63 is such that, without throttle, the motor power depends on the pedal speed. I don't like that, you don't have direct control over the motor power and sometimes the maximum power is not even reached. With throttle control, which I prefer, don't connect the PAS sensor and connect the green wire with the red wire at the PAS connector or connect the pin ZL with the 5V pin on the printed circuit board.
4. Speed limit
The KU63 has a speed limit connector; connect pin XS to GND to enable it. However, this is not a real speed limiter, it is just a simple voltage divider built with R77 and R87. Instead of limiting the speed, the motor power of the whole range from 0 to 25km/h is limited. So, better don't use the speed limiter. The pedelec legalisation device adds the extra speed limit functionality.
5. Pedelec legalisation device
The KU63 can be used without pedaling, which is not allowed for pedelecs. Here we need the pedelec legalisation device which can be built into the motor controller, see HERE.
6. Changing the under voltage limit
Note that the KU63 under voltage limit is only of importance if the battery has no built-in BMS. Normally, Lithium batteries have a built-in BMS which protects the battery from over discharge.
We can change the under voltage limit to another value than 27.7V by replacing R50, see for the location at the second image. It doesn't have to be necessarily a smd resistor. The new value of R50 is:
R50new = R50old * UVnew / UVold + R55 * (UVnew / UVold -1)
- R50old is the old value of R50, the value varies by product. Measure its value securely.
- R55 is 1200
- UVold is the old under voltage limit (27.7). It is preferable to measure the actual under voltage limit yourself.
- UVnew is the new under voltage limit
7. Increasing the KU63 motor current
The motor controller can deliver more power easily. By adding resistance Rtune1, the maximum motor current can be increased. Please note that the motor can be overloaded. For a maximum current increase of 50%, Rtune1 must be about 6.8kΩ and for 100% 3.3kΩ. So reducing the value of Rtune1 increases the motor current. I measured that the internal resistance of U3 pin 31 is 224Ω. A convenient way is tinning of the shunt to increase the motor current. The KU63 current limit can be increased to at least 20A, without overheating the KU63.
It turned out that the modification with Rtune1 doesn't work always. CPU pin 41 measures the motor current too; it can be necessary to add Rtune2; it has to be find out what its value should be. Probably CPU pin 41 measures the average current and CPU pin9 measures the peak current.
8. Increasing the KU63 voltage
Take the 36V version; the 24V version may be equipped with 35V elcos. For increasing the battery voltage above 36V, take these things into consideration:
- The maximum voltage of the Mosfets 2SK4145 is 60V.
- The elcos have a voltage rating of 50V or 63V.
- The resistor R1, which limits the dissipation of U1, has to be changed.
Without overhauling the whole controller, the maximum battery voltage is 43.2V, which is 12 lithium-ion cells in series. At full charge, the voltage is 12 * 4.2 = 50.4V. Just R1 has to be changed to (12*3V-14V-3V)/60mA = 270Ω / 2W.
9. Changing the power MOSFETs
Here we shall see if it is possible to reduce the losses by changing the MOSFETs.
9.1. Conduction losses
The conduction losses are caused by RDS(on). The total conduction loss is: 2 * I^2 * RDS(on). The MOSFET 2SK4145 inside the KU63, has an RDS(on) of 10mΩ. With a 36V battery, the motor current is 10A at 360W, which causes a loss of just 2W. My experience is that the KU63 barely warms up at full power. When the motor controller may still become hot, it is because of the switching losses.
9.2. Switching losses
Switching losses are caused by the simultaneous exposure of voltage and current during the switch transition. Power MOSFETs with a lower on-resistance have larger parasitic capacitances, which cause larger switching losses. So we can't simply take MOSFETs with a lower RDS(on) to reduce the losses, this may result in increased switching losses that supersede the savings in conduction loss.
10. Redusing the LM78L05 dissipation
The 5V current consumption is 50mA, which leads to a LM78L05 dissipation of 0.44W, this is close to the allowed maximum. There are known cases where the overheating of the LM78L05 caused failures. By mounting a 100Ω resistor Rdiss between the 14V and the input of U2, the LM78L05 dissipation will be reduced.
11. Fail-safe brake lever switch
The original brake switch circuit was not fail-safe. In case of a broken cable, the motor will not be turned off when braking; this is dangerous. To overcome this, modify the KU63:
- Add resistor Rbrake of 10kΩ
- Remove R54 of 2kΩ
Wire the brake switch to the SH input. During braking the brake signal SH should be 5V. In case of a broken wire, the brake signal will be 5V too; this will turn off the motor.
You can use a Hall effect sensor instead of a mechanical switch, see here.
12. Connection diagram
All connectors are replaced by smaller ones:
13. Speed up-down button thumb throttle
Instead of a rotating throttle, I use an up-down button instead. It is close to the right handlebar for easy access. The switch is connected to an Arduino computer that controls the motor controller through software. However, this solution is not public.
14. KU-63 modification board
Here is a small prototype board which contains the pedelec legalisation device, an anti spark circuit and some measurement electronics.
15. Open source smart ebike controller with the KU63
By replacing the motor controller CPU by another CPU, the software can be customized. See here how the KU63 motor controller is used as base for an open source ebike smart controller.
16. Similar KU series motor controllers
It seems that all KU series motor controllers have almost the same circuit:
- KU60 350W 6 Mosfets
- KU63 250W 6 Mosfets
- KU65 250W 6 Mosfets
- KU93 450W 9 Mosfets
- KU123 500W 12 Mosfets
- KU151 1000W 15 Mosfets
17. KU123 motor controller
The motor controllers KU123 and KU63 are roughly equal.
12 power MOSFETs STP75NF75, RDS(on) 11mΩ, VDSSmax 75V, IDmax 80A