On Jul 19, 4:07*pm, Nicholas Bodley wrote:
On Sun, 19 Jul 2009 14:18:06 -0700, Robert Macy wrote:

Does anybody have experience with the death throes of such a motor?
Robert

I do, but, it was the bearings. I don't know about the air cleaner you
mention, although Oreck advertised very heavily on radio programs I used
to listen to.

Can you turn off power and rotate the fan blades with a finger? Plainly,
they should coast.

I won't discount your hypothesis about a shorted turn, though.

A while back, I bought a very-popular Honeywell-branded three-speed
tabletop fan, a Vornado knock-off, and its bearings had run low on oil.
It has an alloy steel shaft, probably a variety of Ni Cr, and porous
bronze self-aligning bearings surrounded by oil-reservoir wicks; they
were "dry".

The motor normally ran hot, est. 125 or 150 C. I tried every lubricant I
could easily obtain except synthetic car-engine oil, and none lasted more
than maybe (at most) a week. Apparently factory lube was a high-tech
synthetic with very low volatility even when hot. I do hope that such a
lube is available in small quantities, such as 3 oz or 100 cc (probably
not equivalent, btw.)

One summer night, I had the fan on, and awoke to the odor of overheated
insulation. The bearings had "frozen" (they could still be disassembled
and cleaned), and a thermal fuse inside the windings had opened. It was
near the surface, but covered by the insulation.

I decided that it would be foolhardy to try to use the fan any more, and
put most of it out for recycling, but saved the rotor, shaft, and
bearings just for kicks. (Nice specimen for explaining commonplace tech.
to somebody who hasn't seen such things. I feel that we don't tend take
apart unwanted stuff any more, although I'm heartened by transparent
plastic housings that let us see innards. a rather-new trend).

Interesting that this fan is so popular that the dies for injection-
molding the blades have eroded badly enough to unbalance the blades
significantly. I also saved the blades, which were nicely balanced.
I have no confidence at all that if I returned one of these fans for
excessive vibration that doing so would cause them to do something about
it, other than to send me another with the same problem.

Fwiw, I was given a Nidec-Torin Alpha V square computer-type fan rated
for 240 V operation. It has advanced plain hydrodynamic (surely not
"hydrostatic"?) bearings, in which motion probably drags the oil into
narrowing cylindrical wedge-like cavities so there's no metal-to metal
contact. The lubricant (and seals) must be simply superb. Run at 120V 60
Hz, the motor has a whopping amount of induction-motor slip, but of
course it runs at cucumber temperature. I know that it will outlast me
(I'm 73), even if I last like Andres Segovia or Dan Schorr, God bless him..

I use it at night while sleeping as a very-gentle, very quiet circulator,
so that I don't re-breathe my own stale air.

After it's been running, the coast-down is so long that you'd swear that
it has ball bearings.

Btw, those 3-speed induction-motor fans have tapped windings, with taps
very carefully chosen so that the curves of motor speed and torque
correlate with fan drive torque vs. speed; both just have to be
nonlinear. Remove a fan blade, and the motor runs at all speed settings
with low slip, but different torques; you can use your fingers briefly as
a load brake if the shaft is smooth and it's a small fan. (I don't try to
slow it to half speed or so; just get an idea of running torque, or else
grip the shaft tightly enough to stall it, then switch on. Of course,
stall torque differs.)

(Slip? I do hope there's a good explanation somewhere. Try Wikipedia on
electric motors. I'm not ambitious enough just now to explain it
properly; it's the difference between synch. speed and operating speed of
a squirrel-cage induction motor, the kind you find everywhere; they run
quiet, and not especially fast.)

HTH!

=+=+=

As to the HP printer: I used to work in a very small computer store,
sales and service, run by a guy so generous-spirited I considered him to
be a "prince by [virtue of] merit". More about that, some other time.

A fellow brought in an HP inkjet of the 600 or 700 series, and its main
printhead/ink cartridge (HP lingo: "pen") carrier sliding bearing had run
dry. My boss used WD-40, against my gentle advice. Surely enough, it had
the same problem, one day later.

(Perhaps WD-40 is one of the most-misused products since 3-in-1 oil was
based on vegetable oil that polymerized into varnish, like linseed oil.)

I ran the store while he worked as a sysadmin., and called HP printer
service. They stonewalled fanatically. When I told HP he'd used WD-40, he
gave a classic "eeeeuuuuuwwww". No more info. When the p. by m. came in
at the end of the day (or else next chance) he called HP and gave them
the blazes. He had HP cert. for laser printers (he loved LJ 3's --
wonderfully built), and was therefore, in a sense, an insider, at least
regarding printers. HP, contrite, sent about four syringes of an Anderol
synthetic lubricant, and it worked marvelously.

Talk about "secret lubricants"!

Yrs trly wants to get a small quantity of grease for plastic mechanisms,
but hasn't really looked.

--
Nicabod =+= Waltham, Mass.

Thank you every one for replying!

Does anyone have a schematic for the
Oreck XL Professional Air Purifier?

Regarding bearings:

I, too, learned the hard way about the ills of WD-40. I found Singer
Sewing Machine oil to work very well and if mixed with lighter fluid
it seemed to have the same penetrating power of WD-40 [without the
varnish effect later] *and* the naptha would evaporate with time
leaving nice consistency oil.

The fan is a horizontal squirrel cage in a separate compartment from
the motor. Without power the fan can be spun by hand and takes a
great deal of time to coast to a stop. Also, spinning makes no sound.
With power [and the light grounding noise] the fan is spinning, and
has noticeable torque when the fan is stopped with my hand.

*****ARRRRG!!!!!

Nothing more valuable than experimentation! Just now I purposely
stopped the fan and could hear the grinding noise continuing. Just
for 'some reason' I touched the butt end of the motor to find it was
still turning with the fan stopped! This motor drive path has a
CLUTCH!!! to the fan [may be NOT on purpose]. The noise is the sound
the 'clutch' makes as it's slipping!

That also explains why there is only one speed. At higher speed
setting the grinding moves up a bit in pitch but the fan never speeds
up, because, again, that clutch is slipping!

This may not be a clutch by design, but rather a rubber 'alignment'
shaft. When new, the press fit kept the fan and motor locked
together, but with age and rubber deteriorating from actions of oil,
the press fit is slipping. Now to lock the fan to the motor shaft???

Thank you all.

Should I use super glue on the rubber?

Robert