Hi, Chris, you need a non-polarized cap to handle ac without
deteriorating (the juice will evaporate on the reverse cycle in a
polarized standard electrolytic). However, there's an easy fix:
Use two back-to-back electrolytics in the 100-150 microfarad range,
each with a diode across it so it won't experience back voltage.
Connect the negative sides of the electrolytics together, and connect
the diodes so that the "bar" is at the positive end of each cap (I
always have to think about which way it goes, but you want no current
to flow through the diode when the voltage at the positive end of the
cap is positive).
Also, motor caps are special nonpolarized units, but you can get them
at a motor supply outfit for a lot less. They gradually wear out as
the juice inside dries up, so they are a standard replacement item.
Cheers de Dave, W6NL
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