Electric Pruning Shears

Overview

Electric pruning shears deliver the cutting force of pneumatic tools without air-line hassles or the fuel/exhaust of gasoline chainsaws. A rechargeable lithium battery powers a compact Electric Motor, whose output is geared down and converted into either a reciprocating or rotating Blade Assembly. The operator squeezes a Trigger Switch to run the motor; releasing it stops the blade (or allows coasting, depending on type). A single charge typically enables 30–60 minutes of continuous cutting on branches up to 20 mm diameter.

Compared to hand pruners, the motor removes user fatigue during repetitive work. Compared to chainsaws, the straight shear cuts cleanly without crushing bark. Compared to pneumatic shears, there is no compressor or hose tether.

How it works

The Lithium Battery Pack stores chemical energy in lithium-ion cells (typically 18650 or 21700 form factors), each producing approximately 3.7 V nominal. Cells are wired in series (e.g., five cells for 18.5 V) or mixed series–parallel configurations to achieve the target pack voltage (18–36 V) and capacity (1.5–4 Ah). A BMS Board monitors individual cell voltage and temperature, preventing overcharge, deep discharge, and thermal runaway.

When the user squeezes the Trigger Switch, a Switch Contact closes, completing a circuit through the MOSFET on the Control Circuit Board. The MOSFET gate is energized, turning it fully on and allowing battery current to flow to the Electric Motor. Motor speed is modulated by pulse-width modulation (PWM): the microcontroller varies the on/off ratio of the MOSFET 1000+ times per second, effectively controlling average current and motor speed.

The motor's Motor Rotor and Stator Assembly interact magnetically, spinning the shaft at high speed (typically 5000–10,000 RPM). The Gearbox Assembly reduces this through a Gear Set to the Output Shaft, which drives either an oscillating or continuous-rotation blade mechanism.

In oscillating designs (reciprocating shears), a crankshaft or cam converts the output shaft rotation into back-and-forth motion of the Upper Cutting Blade. The Lower Blade / Anvil remains stationary (or counter-oscillates slightly), creating a scissor-like motion at 1200–2000 cycles per minute. With each cycle, the sharp edge of the upper blade shears the branch against the anvil of the lower blade.

In rotary designs (less common), the blade disc rotates continuously, with multiple blade edges passing the stationary anvil to create a rapid series of cuts. Either design cuts cleanly through green wood and dormant canes.

The Return Spring returns the blade(s) to the open position after each cut. When the trigger is released, the MOSFET turns off, motor current ceases, and the blade coasts to a stop (friction and spring action stop the motion quickly, usually within 1–2 seconds).

Excess current (e.g., jamming the blade against a hard knot in wood) causes the current to rise. The Control Circuit Board can sense this and limit PWM to prevent motor burnout. A manual Safety Lock prevents accidental trigger depression while the shears are slung across the operator's body.