DC motor problems

[Salmon Egg]

In article
<0001HW.CB59D59B00710F2AB01029BF@news.eternal-september.org>,
DaveC <invalid@invalid.net> wrote:

A 1/2(?) horsepower 2-brush DC motor was having bearing issues so I
disassembled it and replaced the ball bearings, turned down the commutator on
a lathe, and installed new original equipment brushes. A good clean-up was
done as there was much grease and carbon dust inside.

Now when I apple power it just growls. If I turn it by hand with power
applied it will turn 1 or 2 revolutions then stop. Before disassembly the
motor ran as expected.

The field and armature are separately terminated at the outside of the motor
and wired to a motor speed control PCB.

The commutator segments are well-separated. I put an ohm meter on the brush
terminals and turned the motor slowly. I see 10 ohms across the armature with
each commutator position (each brush contacts 3 segments). The field measures
1000 ohms. I thought that a bit high, so I found where the 2 separate field
windings are connected (in series) and measured each winding separately: each
is approximately 500 ohms.

There is no mechanical reason the motor should not spin at speed. By hand, it
turns freely and there is no interference between the armature and field
laminations(?).

The motor is rated at 180 volts DC, 1.5 amps. There are 2 separate field
windings (wired in series) and the commutator has 36 segments.

I've had this motor apart several times but still can't find a reason it's
not operating like it should.

Any suggestions would be greatly appreciated (and the sooner the better ;-)
).

Thanks,
Dave

There is a device called a "growler" that has been used for decades to
detect winding problems in dc motors. It is useful, because the low
winding resistances in dc motors makes it difficult to detect some
flaws.The growler counts on induction to discover winding flaws. I
suggest yuou look up growler and put one together.

--

Sam

Conservatives are against Darwinism but for natural selection.
Liberals are for Darwinism but totally against any selection.

 

[daestrom]

On 2/9/2012 22:57 PM, DaveC wrote:

A 1/2(?) horsepower 2-brush DC motor was having bearing issues so I
disassembled it and replaced the ball bearings, turned down the commutator on
a lathe, and installed new original equipment brushes. A good clean-up was
done as there was much grease and carbon dust inside.

snip

Thanks,
Dave

A growling sound without turning can be a couple of things.

First, check that commutator bars aren't shorted. If you turned it on a
lathe or something, you should have then cleaned/undercut the slots
between the bars. This cleans out any copper that would short them and
it lowers the mica between the bars so it doesn't interfere with the
brushes sliding across the tops of the bars. If you didn't, take the
rotor out and clean the slots with a thin saw blade or tool that will
just fit in the slot. Don't use a triangular file, that will bevel the
edges of the bars and cause other problems (more sparking/burning at the
brush edge). But a lot of shorting between bars usually just keeps it
from turning at all, it doesn't 'growl' much, the shorts just trip the
supply breaker.

Next, if it has only two sets of brushes, this thing probably has just
two field poles in the stator. If you disconnected the wiring between
each pole, it is critical that you reconnect them together correctly.
If they end up so that both are creating a north pole towards the center
of the machine (or south pole), then the torque created from current in
the rotor windings will just cancel out and it will sit and buzz/growl.
With the rotor removed, connect a small battery (D flashlight cell
would work) to the winding and slowly move a compass near each pole,
noting which end of the compass needle points to the pole. The two
poles should be opposite polarity.

If the brushes are re-installed 90 degrees from where they should be,
that too will cause the symptoms you describe. If you didn't match mark
these before dis-assembly, well experience is a great teacher, isn't it
. Move them 90 degrees and try again. If it rotates the wrong way,
swap either the field wires, the armature wires.

Lastly, a damaged winding that shorts across several coils will do this,
but since it worked before you took it apart, you would have to have
bashed the windings with a hammer or something to damage them like this.

This doesn't sound like it's really big enough of a DC motor to have
commutating poles or a series field winding, so I won't bother with
those issues (suffice to say, getting those straightened out takes more)

Good Luck,

daestrom

 

[daestrom]

On 2/10/2012 19:36 PM, Martin Riddle wrote:

"DaveC"<invalid@invalid.net> wrote in message
news:0001HW.CB5AA7FE00A25E80B01029BF@news.eternal-september.org...
Grind a tool from a hacksaw blade, mount it in the tool post, and use
the
carriage
[Rick]

So, just a sharp knife point thing?

Thanks,
Dave


I was going to mention cleaning between the communicators. Use a round
cutter, to scoop all the surface crap out.
Some also bevel the edges of the communicators so they don't tear up the
brushes. For small motors a ball point pen is usually used ( that should
give you an idea)

Some folks advise against beveling the edge of the bars. It doesn't
really help the brush slid onto the bar. But it does widen the gap and
reduce the surface area for brush-bar contact. This can increase brush
sparking/burning.

On large machines, GE and WE always advise cleaning the slots but
keeping perfectly straight bar edges.

Using a knife wouldn't be my first choice, it's too easy to actually
carve off some of the copper. Someone mentioned a custom ground blade
to fit the slot, and that's best. Just wide enough to get all the mica
and not leave a thin sliver on either side, but not so wide that it cuts
away any copper from the bars. That's what we did in the Navy's motor
rewind shop (lot's of DC motors of various sizes on submarines


daestrom

 

[The Ghost In The Machine]

BOOWAHAHAHAHA !

YOU GUYS ARE AWESUM...KEEP UP THE GOOD WORK.

AND DO NOT...I REPEAT..DO NOT OPEN ANYTHING WHEN YOU CAN JUST LUBE IT.

NICE DESIGN GRID STROMDAE...MAKES ME WANT TO RELOCATE.
BOOWAHAHAHAHA !

TGITM

 

[Fred Abse]

On Fri, 10 Feb 2012 14:38:32 -0800, The Ghost In The Machine wrote:

YOU SHOULD HAVE LEFT IT ALONE....NEXT TIME JUST FLUSH IT OUT WITH
SILICONE LUBRICANT.

There's a recipe for disaster. Watch the commutator ringfire.

Motors that size generally have sealed, pre-lubricated bearings. You can't
replace those without dismantling. Read the OP about "bearing issues".

Silicone lubricants should not be used in such applications, anyway.

--
"For a successful technology, reality must take precedence
over public relations, for nature cannot be fooled."
(Richard Feynman)

 

[Fred Abse]

On Sat, 25 Feb 2012 13:08:33 -0500, daestrom wrote:

A growling sound without turning can be a couple of things.

Dave posted that he'd solved the problem, 15 days ago.

Brushgear wrongly aligned on reassembly.

--
"For a successful technology, reality must take precedence
over public relations, for nature cannot be fooled."
(Richard Feynman)

 

[The Ghost In The Machine]

<==<<< CARRY ON >>>==>

TGITM

 

[David J]

I would suspect that the replacement brushes are a little short or that the
spring force on the brushes is too weak. I used to go as far as slightly
contouring the brushes to the commutator to make max contact (and reduce
arcing).

David_J

"DaveC" <invalid@invalid.net> wrote in message
news:0001HW.CB59D59B00710F2AB01029BF@news.eternal-september.org...

A 1/2(?) horsepower 2-brush DC motor was having bearing issues so I
disassembled it and replaced the ball bearings, turned down the commutator
on
a lathe, and installed new original equipment brushes. A good clean-up was
done as there was much grease and carbon dust inside.

Now when I apple power it just growls. If I turn it by hand with power
applied it will turn 1 or 2 revolutions then stop. Before disassembly the
motor ran as expected.

The field and armature are separately terminated at the outside of the
motor
and wired to a motor speed control PCB.

The commutator segments are well-separated. I put an ohm meter on the
brush
terminals and turned the motor slowly. I see 10 ohms across the armature
with
each commutator position (each brush contacts 3 segments). The field
measures
1000 ohms. I thought that a bit high, so I found where the 2 separate
field
windings are connected (in series) and measured each winding separately:
each
is approximately 500 ohms.

There is no mechanical reason the motor should not spin at speed. By hand,
it
turns freely and there is no interference between the armature and field
laminations(?).

The motor is rated at 180 volts DC, 1.5 amps. There are 2 separate field
windings (wired in series) and the commutator has 36 segments.

I've had this motor apart several times but still can't find a reason it's
not operating like it should.

Any suggestions would be greatly appreciated (and the sooner the better
;-)
).

Thanks,
Dave

 

[Fred Abse]

On Thu, 01 Mar 2012 19:36:35 -0500, David J wrote:

I would suspect that the replacement brushes are a little short or that the
spring force on the brushes is too weak. I used to go as far as slightly
contouring the brushes to the commutator to make max contact (and reduce
arcing).

Wossgoinon?

This was satisfactorily resolved ages ago.

Read the thread.

--
"For a successful technology, reality must take precedence
over public relations, for nature cannot be fooled."
(Richard Feynman)

 

[Oppie]

"nesesu" <neil_sutcliffe@telus.net> wrote in message
news:d90681d5-c8db-4f05-80cd-62848f00608b@tj4g2000pbc.googlegroups.com...

On Feb 9, 7:57 pm, DaveC <inva...@invalid.net> wrote:

After you turned the commutator, did you undercut the mica between the
commutator segments? It is critical that the insulation be below the
surface of the copper to ensure good contact between the brushes and
the copper. If there is still sufficient undercutting [you only
skimmed the surface of the comm] then be sure that there is no copper
shorting between commutator bars. The copper often 'smears' a bit when
being turned and will bridge the gaps here and there. A "pole growler"
will show up any such shorts.

Neil S.

Been there, did that...
My wife's grandmother was the only person I've ever known that wore out an
old Electrolux vacuum cleaner. When the motor was disassembled, there was a
noticeable groove in the commutator. Put it on a lathe and turned it down in
very small steps, finishing off with very fine grit on a wet cloth to smooth
to a near mirror finish. Complete by removing any copper flash that wound up
in the gaps between commutators.

Be careful not to cut too much at a time as the torque drag might twist the
commutator on the shaft. Also watch that you don't get too close to where
the wires are attached to the commutator.

Everything was marked on disassembly to get the orientation correct on
reassembly. If all is right, applying a DC to the motor will cause a
rotation speed equal to the speed when the polarity is reversed. If the
fields aren't aligned to the commutator, it will run faster in one
direction.

With new brushes, worked at least another ten years and Grandma was very
happy.

 

[Michael A. Terrell]

Oppie wrote:

"nesesu" <neil_sutcliffe@telus.net> wrote in message
news:d90681d5-c8db-4f05-80cd-62848f00608b@tj4g2000pbc.googlegroups.com...
On Feb 9, 7:57 pm, DaveC <inva...@invalid.net> wrote:

After you turned the commutator, did you undercut the mica between the
commutator segments? It is critical that the insulation be below the
surface of the copper to ensure good contact between the brushes and
the copper. If there is still sufficient undercutting [you only
skimmed the surface of the comm] then be sure that there is no copper
shorting between commutator bars. The copper often 'smears' a bit when
being turned and will bridge the gaps here and there. A "pole growler"
will show up any such shorts.

Neil S.


Been there, did that...
My wife's grandmother was the only person I've ever known that wore out an
old Electrolux vacuum cleaner. When the motor was disassembled, there was a
noticeable groove in the commutator. Put it on a lathe and turned it down in
very small steps, finishing off with very fine grit on a wet cloth to smooth
to a near mirror finish. Complete by removing any copper flash that wound up
in the gaps between commutators.

I used to turn down commutators on lots of vacuum cleaner motors
without taking them apart. I would run them on a variable DC supply and
use a hard ink eraser, with it running. Some were so bad that I had to
hit the worst spots with emery paper, but I didn't have a lathe and it
worked.


--
You can't have a sense of humor, if you have no sense.

 

[Fred Abse]

On Fri, 02 Mar 2012 21:48:04 -0500, Oppie wrote:

Be careful not to cut too much at a time as the torque drag might twist
the commutator on the shaft. Also watch that you don't get too close to
where the wires are attached to the commutator.

You need high speed (~200 ft/min) and a *very* sharp tool. Commutators
are a bitch to machine to a decent finish without ripping the segments off..

Cheap commutators sometimes have very thin segments, maybe .025" thick.

--
"For a successful technology, reality must take precedence
over public relations, for nature cannot be fooled."
(Richard Feynman)

 

[Oppie]

"Fred Abse" <excretatauris@invalid.invalid> wrote in message
newsan.2012.03.03.08.57.32.240466@invalid.invalid...

On Fri, 02 Mar 2012 21:48:04 -0500, Oppie wrote:

Be careful not to cut too much at a time as the torque drag might twist
the commutator on the shaft. Also watch that you don't get too close to
where the wires are attached to the commutator.

You need high speed (~200 ft/min) and a *very* sharp tool. Commutators
are a bitch to machine to a decent finish without ripping the segments
off..

Cheap commutators sometimes have very thin segments, maybe .025" thick.

When in doubt I use as close to a zero rake as possible to avoid pulling out

the copper bars. Most of the motors I've worked on are pretty old and they
didn't skimp on the thickness of the copper. I would use a pointed cutting
tool and a really slow feed rate to get minimum cutting forces. Last pass
would be with a more rounded tool just to smooth it out and finally the fine
grit to polish it out.

 

[Baron]

Michael A. Terrell Inscribed thus:

Oppie wrote:

"nesesu" <neil_sutcliffe@telus.net> wrote in message

news:d90681d5-c8db-4f05-80cd-62848f00608b@tj4g2000pbc.googlegroups.com...
On Feb 9, 7:57 pm, DaveC <inva...@invalid.net> wrote:

After you turned the commutator, did you undercut the mica between
the commutator segments? It is critical that the insulation be
below the surface of the copper to ensure good contact between the
brushes and the copper. If there is still sufficient undercutting
[you only skimmed the surface of the comm] then be sure that there
is no copper shorting between commutator bars. The copper often
'smears' a bit when being turned and will bridge the gaps here and
there. A "pole growler" will show up any such shorts.

Neil S.


Been there, did that...
My wife's grandmother was the only person I've ever known that wore
out an old Electrolux vacuum cleaner. When the motor was
disassembled, there was a noticeable groove in the commutator. Put it
on a lathe and turned it down in very small steps, finishing off with
very fine grit on a wet cloth to smooth to a near mirror finish.
Complete by removing any copper flash that wound up in the gaps
between commutators.


I used to turn down commutators on lots of vacuum cleaner motors
without taking them apart. I would run them on a variable DC supply
and
use a hard ink eraser, with it running. Some were so bad that I had
to hit the worst spots with emery paper, but I didn't have a lathe and
it worked.

I've done that with a lolly stick and fine glass paper, then I
discovered the abrasive sticks made just for this purpose.

--
Best Regards:
Baron.

 

[Michael A. Terrell]

Baron wrote:

I've done that with a lolly stick and fine glass paper, then I
discovered the abrasive sticks made just for this purpose.

This was 30 years ago. No internet, and no industrial suppliers in
town.


--
You can't have a sense of humor, if you have no sense.

 

[Baron]

Michael A. Terrell Inscribed thus:

Baron wrote:

I've done that with a lolly stick and fine glass paper, then I
discovered the abrasive sticks made just for this purpose.


This was 30 years ago. No internet, and no industrial suppliers in
town.

Similar time frame. Maybe 40...
It was "Hoover" that provided the abrasive stick. The idea was to use
them to quieten down particularly sparky motors. Even though they had
noise suppression capacitors and chokes on the motors they could cause
TV picture break up. People did complain about it as well. I'd being
using the lolly stick for some time before then to smooth the comm.
I'm of the opinion that poor manufacture of some armature left the comm
slightly off centre causing the brushes to bounce and thus arc more
than they normally would.

--
Best Regards:
Baron.

 

[Michael A. Terrell]

Baron wrote:

Michael A. Terrell Inscribed thus:


Baron wrote:

I've done that with a lolly stick and fine glass paper, then I
discovered the abrasive sticks made just for this purpose.


This was 30 years ago. No internet, and no industrial suppliers in
town.


Similar time frame. Maybe 40...
It was "Hoover" that provided the abrasive stick. The idea was to use
them to quieten down particularly sparky motors. Even though they had
noise suppression capacitors and chokes on the motors they could cause
TV picture break up. People did complain about it as well. I'd being
using the lolly stick for some time before then to smooth the comm.
I'm of the opinion that poor manufacture of some armature left the comm
slightly off centre causing the brushes to bounce and thus arc more
than they normally would.

A lot of those motors had the air flow over the commutator, and it
would get dirt or sand in it when people didn't put the bag in right, or
would use it till the bag was full, and ripped. I wasn't working on the
vacuums, just the motors so the only parts I saw were new bushes &
bearings. A neighbor was in the used vacuum cleaner business and would
give me half a van load of bad motors at a time, then buy back any that
I fixed.


--
You can't have a sense of humor, if you have no sense.

 

[Baron]

Michael A. Terrell Inscribed thus:

Baron wrote:

Michael A. Terrell Inscribed thus:


Baron wrote:

I've done that with a lolly stick and fine glass paper, then I
discovered the abrasive sticks made just for this purpose.


This was 30 years ago. No internet, and no industrial suppliers
in
town.


Similar time frame. Maybe 40...
It was "Hoover" that provided the abrasive stick. The idea was to
use
them to quieten down particularly sparky motors. Even though they
had noise suppression capacitors and chokes on the motors they could
cause
TV picture break up. People did complain about it as well. I'd
being using the lolly stick for some time before then to smooth the
comm. I'm of the opinion that poor manufacture of some armature left
the comm slightly off centre causing the brushes to bounce and thus
arc more than they normally would.


A lot of those motors had the air flow over the commutator, and it
would get dirt or sand in it when people didn't put the bag in right,
or
would use it till the bag was full, and ripped. I wasn't working on
the vacuums, just the motors so the only parts I saw were new bushes &
bearings. A neighbor was in the used vacuum cleaner business and
would give me half a van load of bad motors at a time, then buy back
any that I fixed.

That sounds like a nice little earner. ;-)

--
Best Regards:
Baron.

 

[Michael A. Terrell]

Baron wrote:

Michael A. Terrell Inscribed thus:

A lot of those motors had the air flow over the commutator, and it
would get dirt or sand in it when people didn't put the bag in right,
or would use it till the bag was full, and ripped. I wasn't working
would use it till the bag was full, and ripped. I wasn't working on
the vacuums, just the motors so the only parts I saw were new bushes &
bearings. A neighbor was in the used vacuum cleaner business and
would give me half a van load of bad motors at a time, then buy back
any that I fixed.


That sounds like a nice little earner. ;-)

$10 to $20 for common motors, and $50 for Rainbow/Rexaire. He would
stop by in a panic, telling me what he needed. I'd tell him to give me
an hour to dig through my good motors and would try to find one. Then i
would dig out what he needed, and fix it. A lot had dmagaed fans from
metal or glass being picked up, so it was a five minute job to remove
them and a set of good ones from a burnt out motor, polish the armature
and put it all together. then the scrap metal went into bins for the
scrapyard. I got really good with a wood chisel & various punches to
remove the copper from the old motors. The segments were easy to
remove, with a pipe wrench. Clamp the armature in a vise, and give a
twist with the wrench. it was kind of like taking corn off a cob. ;-)

Sometimes I would strip 100 bad motors at a time, for the good parts
just to make room.


--
You can't have a sense of humor, if you have no sense.

 

[Baron]

Michael A. Terrell Inscribed thus:

Baron wrote:

Michael A. Terrell Inscribed thus:

A lot of those motors had the air flow over the commutator, and
it
would get dirt or sand in it when people didn't put the bag in
right,
or would use it till the bag was full, and ripped. I wasn't
working
would use it till the bag was full, and ripped. I wasn't working
on the vacuums, just the motors so the only parts I saw were new
bushes &
bearings. A neighbor was in the used vacuum cleaner business and
would give me half a van load of bad motors at a time, then buy
back any that I fixed.


That sounds like a nice little earner. ;-)


$10 to $20 for common motors, and $50 for Rainbow/Rexaire. He
would stop by in a panic, telling me what he needed. I'd tell him
to give me an hour to dig through my good motors and would try to
find one. Then i would dig out what he needed, and fix it. A lot
had dmagaed fans from metal or glass being picked up, so it was a
five minute job to remove them and a set of good ones from a burnt
out motor, polish the armature and put it all together. then the
scrap metal went into bins for the scrapyard. I got really good
with a wood chisel & various punches to remove the copper from the
old motors. The segments were easy to remove, with a pipe wrench.
Clamp the armature in a vise, and give a twist with the wrench. it
was kind of like taking corn off a cob. ;-)

Sometimes I would strip 100 bad motors at a time, for the good
parts just to make room.

A very profitable exercise nowadays with the price of copper being so
high. I just wish the thieves would stop stealing the iron grates and
aluminum road signs. A whole load of them have vanished overnight.
Not to mention the theft of copper wiring from the railway system.

Next door neighbor came round today and asked if I knew that water from
the kitchen sink was pouring out of the wall and onto the yard !!! The
swine had pinched the two meters of lead drain pipe between the wall
and grate,

--
Best Regards:
Baron.