On Thu, 30 Oct 2003 20:45:18 GMT, "tony"
wrote:

hello all

how tolerant are electric motors to capacitor ratings?
(ie, if i change the cap with a different (bigger) one?)

having trouble with an electric motor.. about 2hp (electric winch)
and it is having difficulty starting under load. but, once started
(with no load) it has alot of lifting power. (i'm not too light
and it picked me right up off the floor... only AFTER it started
spinning) ... if i load the motor (hold the cable) it just sits there
and buzzes... let it go till the cable moves, hold on, and it picks
me right up.

so, trying a little experiment, i changed the capacitor.
it has ~50uF 400V cap and i put in a ~130uF 230V cap
(its all i had around, pulled it off of a drill press)

with the new capacitor it starts fine under load. picks me
right up off the ground.

but now, when i switch directions (lowering), the motor makes
an AWEFUL sound.

i then put both caps in parallel and starting under load is fine,
but more noise. put the caps in series, wont start under load,
less (very little) noise.

so... noise and starting torque is related to the size of my capacitor.
(i'm guessing thats why its called a capacitor start)

questions:
1. can i use this motor safely just by changing to a larger
capacitor? (which size should i use)

2. why does it make that terrible noise? and only in one direction?

3. is this a sign that i just need a bigger motor? (even though once
started this 2HP is plenty strong?)

thanks!
-tony



Are you sure it's a capacitor START motor. 50 uF is about the
right size for consumer grade capacitor RUN motor. In these there is
no centrifugal switch and the capacitor is in circuit all the time.
They produce something like their rated power when up to speed but
have dead lousy starting torque.

Your terrible noise is the result of using too much run
capacitor on a motor thats very lightly loaded.

If it's this type of motor adding the 130uF starting capacitor is an
OK fix. However it needs to be brought in by a push button or a
starting relay so that it is automatically disconnected once the motor
is up to speed.


jim