The key to balancing motor speed control accuracy and overload current protection thresholds in the angle grinder motherboard lies in building a coordinated "speed control - detection - protection" control system based on the main control chip. This requires precise signal conditioning to ensure stable motor speed that matches operating requirements, while also monitoring current fluctuations in real time to prevent motor damage due to overload and prevent protection mechanisms from interfering with normal speed control. During angle grinder operation, motor load often varies with material hardness and cutting force (for example, the load difference between cutting metal and wood is significant). Speed control accuracy requires stable speed output across gears, while overload protection must accurately distinguish between "normal load fluctuations" and "abnormal overload." A disconnect between these two logics can easily lead to issues such as "false protection triggering during speed control" or "delayed protection during overload." Therefore, the motherboard requires a multi-dimensional design to ensure that the two complement each other rather than conflict.
The angle grinder motherboard first establishes a balanced foundation with a high-precision current detection module, ensuring accurate capture of current fluctuations during motor operation, providing a reliable basis for speed control and protection. The motherboard embeds sampling elements (such as precision resistors and Hall sensors) in the motor power supply circuit to collect current signals in real time, convert them into electrical signals, and transmit them to the main control chip. This detection module must possess two key characteristics: First, it must have sufficient resolution to distinguish between normal motor current fluctuations during speed regulation (such as the natural current increase when switching from low to high gear) and abnormal current surges during overload (such as a sudden current surge when the motor stalls), thereby avoiding misinterpreting normal current fluctuations as overload. Second, its response speed must be adapted to the motor's characteristics, neither preventing overload protection from delayed detection due to lag nor misinterpreting the inrush current at startup as an overload due to excessive sensitivity. This ensures that the detection data truly reflects the motor's operating status, providing an accurate reference for subsequent balancing operations.
At the speed control level, the angle grinder motherboard uses fine-tuned PWM (pulse width modulation) signals, combined with gear-level-current threshold matching logic, to synchronize speed regulation accuracy with protection thresholds. Motor speed regulation is primarily achieved by changing the PWM signal duty cycle (a higher duty cycle results in a higher average voltage and faster speed). Different speed settings correspond to different motor rated currents—higher speeds require more power and result in higher rated currents; lower speeds require less power and result in lower rated currents. Therefore, the motherboard presets corresponding overload current protection thresholds for each speed setting. When switching to high speed, the protection threshold increases with the speed setting, allowing for greater current fluctuations during high-load operations (such as cutting thick metal), preventing false protection triggering during normal speed regulation due to increased load. When switching to low speed, the protection threshold decreases accordingly, preventing excessive current from exceeding the limit at low speeds due to excessive loads (such as hard-pushing cutting). This "gear-threshold linkage" ensures that speed regulation and protection are always in tune.
The angle grinder motherboard also incorporates a dynamic threshold adjustment mechanism, flexibly adjusting the protection threshold based on the motor's real-time load, further optimizing the balance. Even within the same speed setting, motor loads can fluctuate in real time (for example, due to uneven material hardness during cutting, resulting in varying loads). If the protection threshold remains fixed, issues such as false protection during sudden load increases or insufficient protection during sustained high loads can occur. The main control chip dynamically adjusts the protection threshold based on real-time load data from the current sensing module. When the load increases slowly (for example, when cutting material hardness gradually increases but without overload), the threshold is slightly raised to give the speed control system time to adjust (for example, by appropriately increasing the PWM duty cycle to maintain a stable speed), thus preventing frequent downtimes that could disrupt operation. When the load suddenly surges (for example, when the motor is momentarily stuck in the material), the threshold is quickly lowered to a safe level. If the current still exceeds the threshold, protection is immediately triggered (for example, by shutting off the motor power or reducing the speed). This approach minimizes disruption to normal speed control while ensuring timely response to actual overloads.
To prevent transient overloads from disrupting speed control accuracy, the angle grinder motherboard incorporates a "buffer time" into the overload protection to mitigate the effects of brief load surges that could disrupt the balance relationship. Angle grinders often experience transient surges during operation (such as when the motor starts up or when the motor occasionally hits a hard object while cutting). These surges cause temporary current surges. If the motherboard immediately triggers protection, it would severely impact speed control stability and operational continuity. Therefore, the motherboard incorporates a buffer timer. When the current exceeds the threshold, the motor power is not immediately cut off. Instead, the current control state is maintained while the current is continuously monitored. If the current falls back to a normal range within the buffer timer (e.g., the surge load disappears), the speed control output is maintained. If the current continues to exceed the threshold (e.g., the motor is continuously stalled), protection is triggered after the buffer timer expires. The buffer timer must be precisely tailored to the motor's characteristics, ensuring it is short enough to prevent continuous overload damage to components but long enough to filter out transient surges, ensuring that the speed control process is not disrupted by unnecessary protection.
The introduction of a speed feedback closed loop allows the angle grinder motherboard to calibrate the current protection logic based on the actual motor speed, further minimizing the potential for conflict between speed control and protection. Some angle grinder motherboards incorporate a speed feedback module (e.g., by detecting the motor's back EMF or using a small encoder) to collect the motor's actual speed in real time and compare it with the preset speed target. If the actual speed falls below the target (e.g., due to increased load causing the speed to drop), the motherboard appropriately increases the PWM duty cycle, increasing the motor current to boost speed and maintain speed accuracy. Simultaneously, the speed feedback signal calibrates the overload protection threshold. If the motor's actual speed is far below the target, but the current approaches the protection threshold, indicating that the load is nearing overload, the motherboard preemptively reduces the protection threshold's trigger sensitivity to prevent further current increases that could lead to overload. This dual closed-loop "speed-current" control ensures that maintaining speed accuracy and triggering overload protection are mutually calibrated, rather than operating independently.
The angle grinder motherboard's hardware circuit adaptation provides underlying support for balancing motor speed accuracy and overload current protection thresholds. The motherboard's power driver components (such as MOS tubes and IGBTs) must have a current-carrying capacity that matches the protection threshold. If the driver component's rated current is too low, even if the protection threshold is set appropriately, the component may be damaged when the current approaches the threshold. If the rated current is too high, this will increase costs and may force an increase in the protection threshold, affecting the protection effect. Furthermore, the motherboard's power filter circuit filters grid voltage fluctuations to prevent voltage instability from distorting the PWM speed regulation signal, which in turn causes speed fluctuations and current anomalies, thereby reducing false protection triggering due to power supply issues. Through hardware-level component selection and circuit optimization, a stable and reliable operating environment is provided for the motherboard's control logic, ensuring that the speed regulation and protection balance mechanism can be effectively implemented, rather than failing due to hardware limitations.
