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3 phase motors


#1

G’day; There is a current thread (pun intended) on revitalising
certain machines with the use of 3 phase motors instead of the
usual 2 phase type. There is yet another possibility to take
into consideration here. It is not possible to control the
speed of the 2 phase motors in common use which are called
’squirrel cage’ motors. But it is possible to have speed
control over some of the three phase industrial motors. For
instance, many professional wood turners I know have installed 3
phase motors up to 5 hp on their lathes, because on turning very
large and heavy pieces of wood complete and rapid speed control
without loss of power is necessary. I suggest that anyone
considering the use of heavy duty motors and perhaps needing
speed change might like to think in terms of 3 phase rapid,
infinite speed change. This of course is only worth while with
power requirements above 1 horse power. There are plenty of light
AC 2 phase motors available capable of being speed controlled -
the familiar jeweller’s flex drive and sewing machines are
obvious examples, but even with modern electronic control
systems, a certain loss of power is inevitable at low speeds. Not
necessary for many practices used in jewellery, but it is a
possibility you should be aware of. Ample advice for an ohm
workshop perhaps with a high frequency of use that could
transform your work. Cheers, John Burgess