High-Torque Electric String Trimmer Has A Melt-Down

String trimmers serve a real purpose in the backyard, though I think you need a Y chromosome to appreciate the subtle pleasures, as George Hackleman describes in this example of one that had an unexpected thermal incident:

I bought a $70 Black & Decker GH1000 corded electric string trimmer with a motor in the handle, and a curved shaft. I purposely bought a powerful, yet still consumer-oriented unit, with a high-amp, 120 VAC motor (it pulls 7.2 amps) as I have a lot of trimming to do.

It had so much torque, my wife actually refused to use it, leaving the weekly trimming to me. It powered through heavy grass, and I have to say that it was truly a joy to operate. I remember that when you clicked the switch, you could feel the machine twist some in your hands just like a single-speed, high-torque drill motor or a circular saw. It was certainly not a “soft start” motor.

About two months after I bought it, it seemed to slip, or jam. I didn’t worry too much as the motor sounded good, and it could be cleared. I just thought I was going into too thick a patch of grass and it was protecting itself. When it quit turning completely, I decided to take it apart.

It turns out the speed reduction from the motor was with a reduction pulley set, using a simple timing belt drive. This might be good, except it was apparently undersized for the motor. The motor pulley was aluminum and the large pulley made of some polymer. The belt had lost all its lugs, and the large pulley’s teeth had actually melted away. The motor still worked fine, and the flexible shaft was in good shape, too. I could not fix it myself, as the pulley was not made to be removed from the shaft.

I haven’t done the calculations, of course, but I expect the issue wais not the overall tensile strength of the belt, but the fact that a string trimmer is exposed to multiple starts and stops, the starting torque of the motor is high, and the load is constantly changing.

Maybe I got a bad one, but looking briefly at the reviews online, it looks like I’m not the only one who had issues though not all the problems are the same. The replacement motor and belt (since the pulley cannot be ordered separately) would have put me back another $58 plus shipping, with no reason for me to believe the new part would have done any better. All I could do was return it and will avoid this design in the future.