On Tue, 6 Aug 2002, Roman Black wrote:

>Hi Peter, maybe "constant current supply" is a little
>too literal, I meant that the motors are very low turns
>and attention to CORRECT current needs to be a function
>of PWM current limiting etc, ie deliberate, rather than
>just connecting a power supply which will cause the
>symptoms he saw, of 40x the specified current.
>
>Most of the VCR 3-coil flatmotors I have here have
>only a handful of turns on each of the 3 coils, they
>are almost short circuit to measure.

Yes but they also have a buck regulator built in or somewhere out of sight
that supplies them with voltage on demand (under servo control).

>So by "constant current supply" I meant a "current-controlled
>supply that only allows a fraction of the current that
>would flow it it was turned on constantly". ;o)

Ok, I just through I'd remind that a brushless PM motor behaves like its
brushed counterpart and the voltage sets the RPM and the current sets the
torque. So current limiting is what you want to prevent shorting the
supply, the control is done in voltage (excepting where torque control is
required).

Peter

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