Battery Electric Chainsaws

Battery electric chainsaws seem to be a natural area of interest for anyone who rides an electric trials bike.  They are perfect for building sections and maintaining trails.  Advantages are: much quieter operation, minimal vibration, no pull-starting, and no fumes.

They won't completely replace my ICE chainsaw, which is still the go-to choice for big jobs.  But being mindful of their limitations, they are extremely convenient for a wide variety of tasks.

The biggest disadvantage is that they are considered throwaway items with zero availability of electrical parts. 

B+D LP1000

My first encounter with an electric “chainsaw” was the corded Black+Decker LP1000 Alligator.  You can see how it got the nickname Alligator in the photo below.  It works a bit like a pair of scissors.

It was rated at 4.5 amps.  Running on 120 VAC puts it in the neighborhood of 540 watts (3/4 horsepower).

It's the safest type of saw I can imagine that uses a chain.  My wife loved it for cleaning up deadfall in the yard.  It worked fabulously well, but the cord was a nuisance.

Our next acquisition was a battery-powered Alligator, the B+D LLP120.  It uses a small 20-volt, 1.5 Ah Li-ion pack which provides surprisingly-long runtime.  But best of all, it can be carried in a backpack for trail maintenance while riding a trials bike.  This was far superior to the bow saw I had been using for such tasks.

Most chainsaws have an incontinence problem — some bar oil leaks out regardless of orientation when it's stored.  So, depending on your point of view, the lack of an oil reservoir may be a plus or minus.  You are supposed to drip oil into a small hole every 10 minutes or so.  This is not convenient while working out on the trail, so I do it every battery swap.  I suppose 10 minutes of actual cutting time is about as long as a battery lasts, but it really depends on the age of the tree.  Green wood cuts easily, as does rotten wood, but anything in-between takes a lot more time to cut.

My first real electric chainsaw was a Greenworks CS80L01 with a 16" bar.  You can see it in the header photo.  There's no mention of it being brushless, so I assume it has brushes (never had it apart to check).  It's rated 1.8 kW and works well.  It's also uncomplicated and very light, so you can easily hike with it.  My only negative comment is that it lacks any type of soft-start capability.  There's a bit of a delay after pulling the trigger, and then it roars to life at full speed.  

Honestly, I expect the low-tech brushed motor is going to have better long-term reliability than the newer brushless models simply because there are fewer electronic parts to fail.

Representative Greenworks Chainsaw Electrical Components

The photo below shows the electrical components found in a Greenworks CSB404 chainsaw.  I chose it for illustration because it's simple and representative of other brushless-motor chainsaws.  It was also e-waste due to shorted MOSFETs in the motor controller.

• Motor Controller & Relay: The motor controller is the brain of the system.  It's often just called a controller.  Engineers frequently refer to it as an “inverter” because it makes the AC required by the motor out of the DC supplied by the battery.  The large black cube on the controller is an electromechanical relay that switches the high-current path for the motor.  The relay may be located elsewhere in different saws.  Additionally, an unswitched low-current path is also present to run the controller itself.  The large silver area is a heatsink for the power MOSFETs (semiconductor switches) that drive the motor.  

• Motor: The motor is the brushless DC type (abbreviated BLDC).  Its three phase-windings are the heavy yellow/black/red wires.  These wires were originally soldered directly to the controller.  I installed terminal lugs so I could test the controller and motor separately.  Newer saws have a removable connector there instead of direct soldering.  There is also a 6-wire ribbon cable.  This connects three Hall-effect sensors (for rotor position) and a single NTC thermistor (for motor temperature) to the controller.  Some saws run a “sensorless” rotor position algorithm in the controller.  This trades a decrease in component count for an increase in firmware complexity.  

• Battery Box: In addition to the red (positive) and black (negative) wires, a blue wire allows communication between the battery and the controller.

• Trigger/Throttle: This 5-wire device has two parts: a push button switch to actuate the saw and a potentiometer to regulate motor/chain speed.

• Chain-Brake Switch: This 3-wire lever-action microswitch serves as a safety device.  It only allows the motor to run when the chain-brake handle is in the proper position.