On Wed, 16 Jul 2014 00:21:58 +0100, "Dave Plowman (News)"
wrote:

In article ,
Cursitor Doom wrote:
On Tue, 15 Jul 2014 15:03:43 -0700 (PDT), robgraham
wrote:


Ummmm - if it's an induction motor, which you would be able to see by
the plate on the motor showing an 'rpm', you could destroy the
controller and possibly the motor. Induction motors are mains
synchronous and don't like 'dropping out' of that with overload or low
voltage.

Is that a definitive method of identifying such a motor, then? A fixed
RPM shown on the plate?

A universal motor - the type that can be easily speed controlled, will
have brushes. Assuming no gearbox, the spindle speed will also be much
higher than an induction one. Induction motors usually around 2000 rpm -
universal 10,000+

Induction motors are usually pretty quiet - universal pretty noisy.

Well, in the mean time I've found some sellers on ebay advertising
mains motor speed controllers up to around 2kw for only around 5 quid
inc. so couldn't resist ordering one. If the motor turns out to be
unsuitable when I've had a better chance to examine it, I'll just swap
it for a better one. Can't beat 5 quid!