Greenworks CSB412

I received a pair of “underperforming” Greenworks CSB412 chainsaws for evaluation.  The CSB412 has a 20" bar and is rated at 3.4 kW.  This is equivalent to 4.5 horsepower.  It claims an unloaded chain speed of 82 ft/s (25 m/s).

I did a fairly extensive write-up on the CSB410, so in this section I'll just highlight some differences between it and the CSB412.

Theory

I used an optical tachometer and measured a motor speed of 12,670 RPM unloaded (no chain) @ 78.6 volts.  So it's probably rated to run at 13k RPM. 

It has a 7-tooth sprocket and uses a chain with a 0.325" (8.255 mm) pitch.  That calculates to the rated 25 meters per second at 13k RPM. 

The saw comes with a 4.0 Ah battery which has an energy capacity of 288 watts.  Assuming a full 80-volt charge, the current draw would be 42.5 amps (prior to accounting for any losses in the controller itself).  The high-capacity battery is not just to increase run-time, it also provides the higher current required for increased power capability. 

Using a clamp-on DC ammeter, I measured a draw of about 4 amps to just run the motor (no chain installed).  At the time, the battery was at 76 volts.  So the saw requires about 300 watts to “do nothing”.  Put another way, we could expect a new 4.0 Ah battery to “idle” a chainless saw for less than an hour.

 Theoretically, operating at the rated power of 3.4 kW, this battery would be depleted in less than 0.085 hours (5 minutes).  And probably much sooner in practice. 

Motor

The motor is marked “Globe 71405 T030101B-00”.   It is not part of Allied Motion's Globe Line of BLDC motors.

Physically, it uses an outer rotor that has an OD of 80 mm.  It exhibits 18 detent (cogging) positions.  There's an 83 mm ID shroud that surrounds the motor to keep it cleaner.  This motor required substantially more effort to rotate it by hand than a CSB410 motor.  At first, I thought the chain brake was partially on, but it was not. 

I counted 9 slots (winding coils) through the ventilation openings.  This number must be evenly divisible by three for any 3-phase motor.  With 9 slots, the permissible number of poles (magnets) could be 2, 4, 6, 8, 10, 12 or 14.  The number would likely be at the lower end of the range due to space constraints.  I have not disassembled the motor to count them. 

Electrically, the phase-to-phase resistance is 66 milliohms.  Inductance when measured at 1 kHz was 115 uH in the quadrature axis (rotor at a detent position) and 87 uH in the direct axis (rotor in-between detent positions).

The motor uses three Hall-effect sensors for position feedback to the controller.  

The NTC thermistor measures 40.3k ohms at 65 degrees F.

More to Come...