Thread: Woodfast 410

You are right that DC has been used in locomotives for its low rpm torque, but that is in comparison to the combustion engine and I've read information indicating that this system is being replaced with AC due to advances in drives and their lowering cost. Torque in a DC motor gets rather complicated and relies heavily on the build of the motor because to retain torque at low speeds (low voltages) the current must increase (power = voltage times current). And an increase in current pushes heat limitations in the motor windings. More on that here: Torque and speed of a DC motor - Wikipedia, the free encyclopedia . Nobody's really wrong in the discussion. It has more to do with keeping up with technology and market advances. It used to be that a DC controller was simpler and less expensive than AC, but a DC motor costs much more than the AC equivalent. Now the DC controller is still simpler, but costs similar, if not more than, the AC controller and AC motors still cost less. There is also increased efficiency in the AC systems.

Personally, I find the biggest vote towards AC in the comparison of response to load changes. Every DC system I've interacted with has not impressed me in this regard, but AC systems with well-designed drives handle this very well. As woodturners, we dive in and out of cuts all the time and on my older DC system the speed would slow at the introduction of an aggressive cut and when I backed off the speed would surge till it settled out. This was especially dangerous if I had an out-of-balance piece on the lathe, had selected the fastest speed that felt safe, and was near the piece as its speed surged beyond. Admittedly this wasn't the best of DC systems, but those characteristics are common in some magnitude.

Pardon my longwindedness. Hope it's helpful

Originally Posted by Barden Koenig

Pardon my longwindedness. Hope it's helpful

Very helpful, thanks

My knowledge on electric motor control systems (which was never comprehensive) is at least 25 years out of date, so I appreciate the info.