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Discussion Starter #1
[EVDL] Mavins motor´s bearings

I know Victor and others on this list warned about these motors, but
I wanted to check if they are usable, so I bought one last spring.

I disassembled it and found out that the bearings are open ones, ment
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 (13 000) 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 10 000+ rpm available? Ceramic?

Any problems ahead if I replace the originals with those sealed ones,
and keep the rpm under 8500?

As far as I can tell, the tranny/differential oil was ment to run
freely inside the motor, also around the rotor. Is that possible?
What if there is air instead of oil (should the distance between the
rotor and the stator be different etc)?

kyseleepi taas,
Osmo

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Discussion Starter #2
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

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Discussion Starter #3
Re: [EVDL] Mavins motor´s bearings

> As far as I can tell, the tranny/differential oil was ment to run
> freely inside the motor, also around the rotor. Is that possible?
> What if there is air instead of oil (should the distance between the
> rotor and the stator be different etc)?

This is the motor used in my Ranger EVs, which is directly mated to
the rear axle. They use an aerospace "Tribolube" instead of normal
gear oil, so I guess this is what you engineers call
"application-specific". No wonder mavin got them cheap: once Ford
stopped making the electric Rangers, there was no use for such an
odd-ball motor - they probably still have enough in stock for repairs
for the next decade, considering how few of them are on the road. The
only people who would find this motor cost-effective would already
have a Ranger EV drive train to begin with.

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Discussion Starter #4
Re: [EVDL] Mavins motor´s bearings

Hi,

The original post along with others have not been
making it thru to me. Don't know what's up with that.

Lee,

WRT bearing currents or induced shaft voltage in
inverter fed induction motors; this occurrence is rare
and unpredictable. Did the original application have
means to deal with this? Do Siemens, AC Propulsion,
or the EV1 motors? I think not. I doubt it would be
a problem here.

Osmo,

Nice looking motor. I don't know how you'll couple to
it. But my opinions to your questions. I have used
precision ball bearings in high speed induction
motors. With drip oil lube. You can get by with
sealed grease lubed bearings, even at higher speed.
You'll just have some higher drag and shorter bearing
life. But it probably would be acceptable for a
battery EV. What type of bearing is on the other end
of your motor?

Jeff M



--- Lee Hart <[email protected]> wrote:

> 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



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Discussion Starter #5
Re: [EVDL] Mavins motor´s bearings

> battery EV. What type of bearing is on the other end
> of your motor?

Jeff,

good to hear your experiences. So I will replace the originals with
the sealed ones. There is some difference in the clearance though:
the original (C4H) has a 0.040 - 0.051 mm clearance while the sealed
one (C4) has 0.030 - 0.051 mm. I suppose that is ok.

The two bearings are identical. The original tranny/differential oil
was ment to lubricate both.

Any good tips how to get the work done easily? Should I cool the
rotor in a fridge first, then heat the bearing before pulling it off?

Osmo


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