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 ;-) ).
> 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 ;-)
> ).
Wave you measured the current in each circuit? Are the field
windings wired properly? If you reverse one it's not going to run.
-- You can't have a sense of humor, if you have no sense.
On Thu, 9 Feb 2012 19:57:15 -0800, DaveC <inva...@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
Any chance that the angle between the brushes and the field got
changed on reassembly?
--
John Larkin, President Highland Technology Inc
www.highlandtechnology.com jlarkin at highlandtechnology dot com
Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators
> Any chance that the angle between the brushes and the field got
> changed on reassembly?
> [John Larkin]
Actually, yes. The rear casing of the motor that contains the brush holder can be mounted to the main motor frame (containing the field) at 90 degree increments. So 4 possibilities.
I reassembled the motor as I thought it was originally configured but the possibility that it's incorrect is large.
On Thu, 9 Feb 2012 21:50:32 -0800, DaveC <inva...@invalid.net> wrote:
>> Any chance that the angle between the brushes and the field got
>> changed on reassembly?
>> [John Larkin]
>Is there only one correct orientation? Or 2?
>Thanks,
>Dave
Some 'brush sets' are 180 degrees apart, and that right on the center
axis of the brush 'monolith'. Some are oriented slightly off center (but
still 180 degrees apart). Usually on a motor only meant to spin in one
direction. The result is that the brush face has the arch <sic> abraded
across it slightly off center,and may only have one 'correct'
re-installation orientation that will preclude chipping and unneeded
wear-in sessions.
> Some 'brush sets' are 180 degrees apart, and that right on the center
> axis of the brush 'monolith'. Some are oriented slightly off center (but
> still 180 degrees apart). Usually on a motor only meant to spin in one
> direction. The result is that the brush face has the arch <sic> abraded
> across it slightly off center,and may only have one 'correct'
> re-installation orientation that will preclude chipping and unneeded
> wear-in sessions.
> ["Giant Rat"]
The two brushes are mounted exactly 180 degrees apart. But the brush holder is adjustable (in rotation). I haven't touched that adjustment, so if I just get the gross orientation correct (90 degrees from current setting) all should be well.
>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
Use a battery and momentarily connect the field winding. This "magnetizes" the armature (do this with the motor un powered). You only have to do this once.
> 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
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.
> 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.
Thanks for that info.
I did not undercut mica. I presumed that since, before turning on the lathe, the motor was functioning well enough (sans bearing noise) with not-undercut mica that its purpose was not important.
What's the best way to undercut? Using an exacto or utility knife in my hands gets quickly messy...
I looked closely and eliminated any segment shorts on the commutator.
>> 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.
> Thanks for that info.
> I did not undercut mica. I presumed that since, before turning on the > lathe,
> the motor was functioning well enough (sans bearing noise) with > not-undercut
> mica that its purpose was not important.
> What's the best way to undercut? Using an exacto or utility knife in my > hands
> gets quickly messy...
> I looked closely and eliminated any segment shorts on the commutator.
> Thanks,
> Dave
Grind a tool from a hacksaw blade, mount it in the tool post, and use the carriage
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.
> 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
You didn't by any chance unwire the coupling in the field windings? If so, it sounds like you have one winding reversed. This will give you the
effect you are seeing. But you did say that you had to hunt for them and the F1 and F2 legs are on the outside?
Other possible problem is brush alignment.. if you don't have the brushes orientated so that one crosses over to the next winding while the other is lagging behind, it'll sit there and hum and some times a
spin of the rotor will start it but most likely will come to a stop.
Are you sure you have field voltage? And also, have you ohmed out the armature to make sure it isn't shorting to the rotor? It is possible you could of damaged it while it was in the lathe.
But in any case, what I've done in the past was to use a induction meter to measure the cross over point on the armature to help align the
brushes.
P.S.
May want to check to make sure you didn't over turn the commutator and also, it is very possible you had a shorted motor to start with.
Also check the field for ground shorts. YOu need to use a megga meter
for this. Or if you can get your hands on a IR bridge that will work too.
>> 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)
VWWall wrote:
> DaveC wrote:
>>> Any chance that the angle between the brushes and the field got
>>> changed on reassembly?
>>> [John Larkin
>> Is there only one correct orientation? Or 2?
> Two--one for each direction! :-) Whenever I disassemble a motor, I
> scratch a mark across the "parting line(s)". Then I know how to
> re-assemble it.
The idea is good, but there's a better way. Use a punch and put matching dimples across the 'parting lines'. Put one set on one end and two sets on the other.
> VWWall wrote:
> > DaveC wrote:
> >>> Any chance that the angle between the brushes and the field got
> >>> changed on reassembly?
> >>> [John Larkin
> >> Is there only one correct orientation? Or 2?
> > Two--one for each direction! :-) Whenever I disassemble a motor, I
> > scratch a mark across the "parting line(s)". Then I know how to
> > re-assemble it.
> The idea is good, but there's a better way. Use a punch and put matching
> dimples across the 'parting lines'. Put one set on one end and two sets
> on the other.
> mike
He now knows the importance of some sort of a mark
>> 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.
> Thanks for that info.
> I did not undercut mica. I presumed that since, before turning on the lathe,
> the motor was functioning well enough (sans bearing noise) with not-undercut
> mica that its purpose was not important.
> What's the best way to undercut? Using an exacto or utility knife in my hands
> gets quickly messy...
> I looked closely and eliminated any segment shorts on the commutator.
> Thanks,
> Dave
Using a hacksaw blade the idea is to grind off the 'set' on the teeth to a thickness that will be smaller than the commutator bar gaps.
Then it is used by having the teeth point backwards towards you, the action is then pulling rather than pushing which IMHO gives more control.
Whilst doing this try to hold the blade at an angle so that it cuts against the sides of the bars, usually you can see the material flake off when done correctly. This is important as it removes any insulation that might be on the side of the gap you are creating and then can interfere with brush contact.
While grinding the blade snap off the end and make it about 45deg away from the teeth to make it easy to get to the insulation at the connection end.
However I doubt the commy is your problem :-)
DaveC <inva...@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.
> 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)
> 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 :-)
