In article ,
T i m writes:
Hi all,

I am tinkering with the idea of building a test jig and a basic bench
grinder could make the ideal platform.

Am I right in thinking you can make induction motors 'soft start'
(reduced starting torque) by the inclusion of a series resistor?

Not really enough detail about what you're trying to achieve.

Induction motors don't generally need soft start until you get up
to the sort of power where you'd use a 3-phase motor, and then you
do the soft start using a star-delta switch which starts the motor
on 240V per winding, and switches to 415V per winding when the
rotor has got up some speed. Generally, this is only done to limit
the inrush current with a stationary rotor, and not because you
want the motor to run up slowly -- induction motors tend to do
that anyway because they naturally have poor starting torque.

For an induction motor which uses a start capacitor on a single
phase supply, reducing the value of the start capacitor will
reduce the starting torque.

For any type of induction motor, a series resistor will reduce
the starting and running torque, but this isn't normally done
because...

An induction motor must normally be allowed to reach its sync
operating speed (minus the designed slip for many types).
If you don't allow an induction motor to reach the right speed,
it will generally overheat (unless it has been designed with
such a bizzare operating mode in mind). For this reason, you
generally don't want anything that limits the starting or
running torque, because this risks having the motor fail to
reach its design speed.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]