Re: [EVDL] Mavins motor´s bearings
Osmo S. wrote:
> I disassembled it and found out that the bearings are open ones, meant
> to be lubricated by the transmission oil. A minor detail the seller
> should mention I think.
>
> http://www.havina.fi/motor.htm
>
> The bearings have extra small inner clearance, propably because of
> the high (13000) rpm of this motor. There are sealed ones available
> with almost the same clearance, but their rpm is limited to 8500.
>
> So, my questions:
>
> What type of bearings Siemens (and other AC-) motors normally have? I
> suppose there must be sealed ones with 10000+ rpm available? Ceramic?
>
> Any problems ahead if I replace the originals with those sealed ones,
> and keep the rpm under 8500?
There are special problems with the bearings of AC motors driven by high
frequency inverters. Because the magnetic field in the rotor is
revolving, it can induce a current flow through the bearings. I.e.
current flows lengthwise through the shaft, out the bearing on one end,
back around the outside of the casing, and back in the bearing on the
other end.
With a high-current motor, the current can get quite large; enough to
damage the bearings from arcing as the balls momentarily connect and
disconnect as they move. You'll see strange wear patterns on the balls
and races, and the bearings can fail very quickly.
So, they do things like use ceramic ball bearings, add insulation
between the inner race and shaft, or between the outer race and case,
add slip rings or brushes to short out the induced current so it won't
flow through the bearing, etc.
--
Ring the bells that still can ring
Forget the perfect offering
There is a crack in everything
That's how the light gets in -- Leonard Cohen
--
Lee A. Hart, 814 8th Ave N, Sartell MN 56377, leeahart_at_earthlink.net
_______________________________________________
For subscription options, see
http://lists.sjsu.edu/mailman/listinfo/ev