I have just obtained a small electric motor about 100 or 150 watts on a small
tool and cutter grinder (the name plate has faded )the name on the casing is
Newream with a old Corby telephone number 0536 i assume at least 20 years old
when i switch it on it sometimes goes clockwise sometimes anticlockwise . I
sometimes have to give it a flick with my finger to get it to start,is it kaput
or just need a new capacitor.thanks
On Saturday, December 1, 2012 10:18:01 PM UTC, Graham wrote:
mall tool and cutter grinder (the name plate has faded )the name on the cas
ing is Newream with a old Corby telephone number 0536 i assume at least 20
years old when i switch it on it sometimes goes clockwise sometimes anticlo
ckwise . I sometimes have to give it a flick with my finger to get it to st
art,is it kaput or just need a new capacitor.thanks -- posted from http://w
-sometimes-oppositeway-53355-.htm using PolytechForum's Web, RSS and Social
Media Interface to uk.rec.models.engineering and other engineering groups
Try a new capacitor.
The symptoms you describe are the same as I had on my sawbench. That was cu
red by replacing the capacitor.
Single phase AC electric motors, like single cylinder steam engines,
have no inherent preferred rotation direction built into the armature,
or the piston and crankshaft. They depend on inertia to keep going in
the direction they were started in. Without a kick both can hang up at
top or bottom dead center. The engine gets its direction from valve
timing, the motor from a second winding placed at an angle to the main
one, often through electrical wizardry that makes the start winding
appear to be where it isn't, physically. The capacitor performs this
wizardry unless it's gone bad.
There is often a centrifugally-opened starting switch that deactivates
the start winding as the motor gets up to speed, since the extra
winding tends to be too thin (for cost) to survive continuous running.
this switch makes the click when the motor coasts down, like a bench
grinder. On the grinder you may see and hear the difference after the
switch closes and increases the drag that slows down the wheel.
I replaced the 3-phase motor on my lathe with a single-phase one and
rewired the switch to start it in either forward or reverse. If I
shift the switch rapidly while the motor is at full speed it just
continues in the same direction because it hasn't slowed down enough
to let the starting switch close.
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