You shouldn't have too much trouble finding a suitable replacement from an
electrical jobber supplier.. Johnstone, or local independent electrical
supplies dealer.
If you have a local motor repair shop, they will know what you need by
referring to the 120VAC motor voltage and 4 HP motor rating.
Start capacitors need to be for AC usage, and are typically sized at about
500uF per HP.
The numbers on the original cap indicate that the actual value of that
series can be as low as the minimum value, or as high as the maximum value
shown.
The actual measured values (microfarad, or uF, or mfd) of start capacitors
can vary widely, as much as about 30%, especially on parts that are decades
old.
The voltage rating for start caps is generally higher than the AC line
voltage, and different manufacturers choose to use different rating numbers.
Another common marking is 377VAC.
The other source of problems in split-phase motors would be the centrifugal
switch for witching between the start and run windings.
--
WB
..........
metalworking projects
www.kwagmire.com/metal_proj.html
"dave" wrote in message
...
my ancient 4hp sears craftsman air compressor needs a starting capacitor,
I've determined (through a process of elimination). I still have the
original owners manual, and the capacitor is "part of the motor", not
shown in the parts blowup, or parts list, as a seperate orderable part.
further, the friggin' thing seems to be a 'non-standard' mfd rating, too
(it doesn't 'fall into' any capacitor size-groups of any maker's starting
cap's I can find online. matter of fact, it's not even close):
the one in it now is
110 volt, 485-580 mfd
mallory #139852-49
seems a slightly non-standard SIZE as well:
diameter: 1 13/16ths inch, and
length, overall, excluding 'spades': hair over 4 5/16ths (but clearly
under 4 3/8ths)
atttempts to locate same by the mallory part number on it entirely
unsuccessful. so (physical size and 'look' issues aside) can I "daisy
chain" two cap's and achieve the same net effect, somehow? appearance "not
an issue", I just need a working compressor. I know I can replace the cap
with a higher voltage cap, and that'd be fine (maybe even desireble) but
what about the mfd rating? if I must, is it best to go 'bigger mfd
numbers' or lesser?
thanks for tips on this, guys :-)