From: noel shelley (noel@shelley1722.freeserve.co.uk)
Date: Tue Oct 21 2003 - 02:03:25 PDT
Dear All ,
There are several ways to configure the starting of an
induction motor , each method has plus and minus points . Capacitor start
,induction run will give a very high starting torque but draw upto 550% of
its full load current . Split phase starting can draw upto 1100 % {yes thats
right 1100 % } of full load .
Ordinary simple fuses are unsuitable , because if they stand the start they
are to big to protect the motor ,the use of thermal cutouts of the correct
rating and proper setting are the best method normally with a contactor .
You NEED to know the full load current , the H.P. or Wattage is not good
enough . 746 W = 1 H.P. is a 100% efficiency conversion & never attained in
practice E.G. 3hp = 2.2 Kw = 18.3 A@ 120V WRONG , more likely to be about
32A in practice dependant on the type of motor.
I had a small compressor 1/4 H.P. 180 W that could not be started by a 2KvA
generator {split phase start } yet would run a 750 W drill with ease. I also
use a 3H.P. 2.2 Kw motor that starts light , on 240V full load is 17.6 A
starting
current is in excess of 60A.
HOPE this may be of help Noel
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