1
\$\begingroup\$

My understanding of motor run capacitors is that there is an optimal value for a paticular motor and that if it is not matched exactly, the magnetic field will vary and cause the motor to run poorly. Is this correct?

If yes, then how accurate does the capacitor size need to be? 10%? %5?

\$\endgroup\$
1
  • 1
    \$\begingroup\$ The C value increases motor current and thus torque then RPM slightly but motor temp rise increases by I^2 , while Hp=torque x RPM, so this is the tradeoff between Hp and temp rise for C value. Note that it may be not always be +5% when new as shown in answer at 105% for rated Capacitance, but allows 5% aging. A 5% tolerance cap could be 95% new. \$\endgroup\$ Feb 18 '19 at 7:19
1
\$\begingroup\$

They're typically marked +/-5% tolerance, so that should give you some idea of what is expected. Here is a (somewhat) detailed article on motor run capacitors.

When they are damaged they tend to drop in capacitance.

From a motor manufacturer, a graph that comes closer to answering your question but does not really tell you how much temperature derating you'll have to do etc.

enter image description here

For example, if the capacitor is too low and the motor stalls it may overheat because it's not cooling itself, depending on the design.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.