I have a 9" Craftsman (Sears) drill press that just smoked the motor
capacitor. I call Sears about a replacement and they want to sell me
the whole motor (of course). I'm trying to replace just the
capacitor but I don't know if it's a run or start. Here's what
labeled on the cap:
16mF +/- 5%
Wenling Star &Fire Capacitors Factory
The model of the drill is 137.219090 if that helps
How can I determine if it's a run or start cap?
If there's only one capacitor it will be a "run" one.
It would be highly unusual for a small drill press to have a motor with
a "start" capacitor, but there really isn't any difference between a
"run" and a "start" capacitor, the term comes from the application, not
You'll be able to purchase a 16 mfd 250VAC motor capacitor at lots of
places. Getting one the correct size and shape will be the more
I seem to recall that start caps are smaller and less expensive and rated
for less ripple current than run caps. For instance, Grainger's 4CU61 and
2GU30 caps have similar values and voltage ratings, but the 4CU61 costs
$8.26 vs $15.12, and it's only rated for 20 3-second starts per hour, ie
a 2% vs 100% duty cycle.
YOU GOT A POINT THERE JUDGE! *
I'll stand corrected on the ripple current rating thing, which seems to
If the OP really can't find the value he needsk he could get one of
these monsters which comes with jumpering instructions to replace
anything from a 12.5 to a 67.5 mfd capacitor, but it might be bigger
than the motor itself. <G>
I'm betting the OP's motor has a cylindrical paper covered cap under a
sheet metal "hump" on it's side.
* From "Bad Man's Ballad" - Kingston Trio - ca 1960
I wouldn't expect to see a capacitor-start motor in a drill press.
Drill presses start up under no load (except some friction from the
bearings and belts) so they don't need much starting torque. A
capacitor-run motor provides a positive starting direction and better
running torque than a split-phase motor, without any need for a starting
switch or starting relay.
I have a Sears drill press with a capacitor-run motor. One bench
grinder is also capacitor-run.
Besides, starting capacitors are often in the range of hundreds of uF,
while run capacitors are usually tens of uF.
I'm having a tough time locating a replacement locally. The only two
places that I'm aware in the area are Grainger and Johnstone Supply
and neither seem to have any 250VAC or 16mf. Are you aware of any
online sources? My Google searches have so far yielded no luck.
On Wed, 18 Apr 2007 12:49:21 -0400, "John Grabowski"
I prefer the phone book myself, but sometimes it confuses me, like, Is
there still a Business to Business Yellow pages and would this
category be in that one.
There is also in the US yp.yahoo.com which is a lot like the yellow
pages, but when I was trying to find the major electric motor repair
store in Baltimore, that I've been to, it didn't seem to come up in
Probably not necessary here, but if one can find the right kind of
store somewhere else, the Electric Motor Repair in Baltimore, even if
they are not a mail order store, if you pay them extra they'll often
be glad to put what you need in a box and ship it to you. "Extra"
might not even be that much. They have boxes, tape, pens, and they get
deliveries all the time via ups etc.
For example, not electric motors but Eliot's Hardware in Dallas isn't
mail order, or at least wasn't 14 years ago, but they'll still mail
things out if one asks. I think they charged, for an envelope of
shelf pins, 32 cents to ship them. That was the cost of the stamp.
No other shipping or handling charge. A great store.
No normal electric motor has a 16 MF start capacitor. And, most run
capacitors are 370 volt. You can replace it with a 16 MF 370 volt run
capacitor. They are available at W.W. Graingers or Johnstone. Or, why not
try Sears parts?
I've used both Mouser & MCM for years for electronic items. Good sources.
Also I bet the 21ufd cap here would work:
This is the kind of thing that in most areas is easier to obtain through the
No, these are "different same" items.
Both are typically electrolytics which are compact but lossy. The start
type is rated for a low duty cycle so they can be made very compact and
very lossy (i.e., cheap). The run type must be physically bigger and more
expensive for the same capacitance to make it less lossy, so that it
doesn't overheat in a 100 percent duty cycle.
Weren't they past the phlogiston and ether theory when you studied EE?
Start vs run types vary in the real component of their impedance, which is
reflected in the resistive component of the lumped element model. This is
usually explained in dumbed-down terms of "ripple" for the non-engineer.
No, I don't think Richard is a hack. He was right to pounce on me over
I stand corrected. I either never learned or never thought about the
operating requirement differences for "start" and "run" capacitors, but
it now seems obvious, especially since supply houses list them for one
or the other purpose.
Though, if push came to shove I'm sure one could use a run capacitor of
the correct capacitance rating to do a start capacitor's job, but not
the other way around, huh?
Jeff (Looking forward to attending his 50th MIT class reunion in less
than two weeks. <G>)
Probably. The run capacitor would be too large to fit the space
provided for a start capacitor of the same voltage and capacitance
rating, but it ought to work fine electrically. The start capacitor
used as a run capacitor would soon overheat.
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