Re: [CAD_CAM_EDM_DRO] chopper?

Tim wrote:

> A chopper stepper driver is one that controls the current to the
> windings by monitoring the current and rapidly switching the current on
> and off (chopping).

Close, but not quite correct. You can't change the current in an inductor
instantaneously. (getting close to that is how a car's spark coil works.)
A chopper drive changes the voltage on the windings almost instantaneously,
dissipating minimal (lost) power that way.

> This allows them to run a much higher voltage than
> the motor is rated for and the high voltage helps to overcome the
> inductance of a stepper to allow better torque at a higher rpm. The
> alternative is to balance the drive voltage with power resistors to keep
> the current within the limits of the motor rating. Not as efficient and
> worse it will require that you use a power supply that is pretty near to
> what the motor voltage is rated.

And, if the original poster of this question hasn't worked with large
L-R stepper drivers, the resistors are HUGE - hundreds of watts,
and throw off a vast amount of heat.

Jon