DC motor troubleshooting

The Gorton 2-28 milling machine that I put in my shop recently, works great, with one exception: its power feed for the X axis is not
working.
The way it is supposed to work is via a DC motor, controlled by a simple DC drive. The DC motor has a field winding.
The problem is that the motor does not run.
The DC drive does supply voltage to both F1-F2 and A1-A2. I interpret those as field and motor windings. F2 and A2 are connected together and voltage between that point and F1 or A1 is 50 volts.
I opened the motor up. When opened, I tested voltage between brushes and found out that there is 0 volts between brushes, or brushes and armature.
How can I interpret this finding and what is the usual cause of such behaviour.
The motor was really dirty inside, I washed it in a parts washer, but have not yet reassembled, since I could not find the problem.
Thanks
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Sounds like one of the flex wires connecting the carbon part of the brush to the brush holder is open. Or the connection between A1 or A2 and the brush holder is open. Art
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brush

the

Yup.
There's not much can go wrong there, Ig. Check the voltage between the inlet terminal for A1 or A2 and its corresponding brush holder.
If there's anything more than a nuisance couple of volts, you've got a break between the A1 or A2 terminal and its corresponding brush.
LLoyd
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Makes sense, great idea
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wrote:

e.

You might check to see if the brushes are worn so much that they do not quite contact the armature.
Dan
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How would that result in zero voltage between the brushes themselves or between their guides/housings?
Yes, worn brushes would cause the symptom. But he's already reported a troubleshooting symptom that indicates that would not be the problem.
LLoyd
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On 2013-05-12, Lloyd E. Sponenburgh <lloydspinsidemindspring.com> wrote:

Right. No voltage between brushes.
Additionally, the armature is worn quite a bit. This mill, it seems, has this design that the power feed motor runs all the time, and is engaged and disengaged with a mechanical gear, it does not really turn off.
i
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Armatures don't wear, Ig, unless the bearings are so bad that it's been rubbing on the field steel.
COMMUTATORS wear. If they're made of thick enough copper, they can be trued up and undercut like new. If not, you toss it.
Lloyd
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On May 11, 9:31pm, "Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote:

I kind of assumed that Iggy would have also checked the voltage between A1 and both of the brushes and between A2 and both of the brushes while he had the meter in his hands. If he did and did not find the problem, then his readings do not make sense and something was mismeasured. So time to recheck what he thinks he knows. There is always the possibility that there are two problems , which makes it a bit harder to figure out what is happening.
Besides he needs to check the brushes for excessive wear while he has it apart.
Dan
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On Sat, 11 May 2013 17:50:58 -0500, Ignoramus9202

Sounds like your armature is burned out.
--
"You guess the truth hurts?

Really?
  Click to see the full signature.
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On Sat, 11 May 2013 17:50:58 -0500, Ignoramus9202

F1and F2 Field A1 and A2 armature. Unhook all wires and check continuity across f1 and f2 a1 and a2. Both should have very low resistance. If your getting 50 volts in and out then sounds like your missing the negative from the drive.
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Is the motor fed voltage from the drive with two or four wires?
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Three wires from the drive, connecting to four wires to the motor.
i
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On Sun, 12 May 2013 08:22:58 -0500, Ignoramus5857

???? Guess I can't help you then. Most dc motors I work on require either two or four power leads. Waiting to see what you find.
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Didn't read the post? It HAS two windings, and four leads. Two to field, two to armature.
It just _happens_ that the field and armature power supplies share a common. That does just occasionally happen in electrical stuff -- that two supplies might share a common ground... even bipolar supplies are usually ground-referenced.
Lloyd
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On Sun, 12 May 2013 19:47:19 -0500, "Lloyd E. Sponenburgh"

Lloyd, I did read his post, several times in fact. I did not fire a volley, one shot only, trying to hit the target.....
I am not trying to cause problems here, just trying to help where I think I can as I do have experience in things DC albeit in the forklift trade.
If I'm reading it correctly his motor sounds like any other dc motor that is not a permanent magnet motor. It has a field winding F1 F2 and an armature with a commutator that brushs ride on A1 A2.
The fact that it only has three leads is what confuses me.
Either way supply voltage out the controller + or - will enter the armature go through the fields and then back to the controller causing the armature to rotate. Pulse Width Modulation will control the speed and torque of said motor.
If by any chance this is a separately excited motor, the field cables are normally smaller then the armature cables. The fields and armature would each be supplied voltage via the controller which would to my knowledge take four motor leads. Seeing as this has ( THREE ) motor leads with one connected to both A2 and F2 the other two must go to A1 and F1. The single wire to A2 F2 would be the positive in, according to Iggy 50 volts and the other two would be would be pulsed negatve from the controller but since Iggy said it was a SIMPLE DC DRIVE I didn't think it was that kind of motor.
The fact that he has fifty volts at A2 F2 out to A1 and also F1 would suggest that the motor is ok.
My thoughts are that the drive is bad. To test the motor I would hook up a car battery to it, POSITVE lead to A1 NEGATIVE lead to F1 Install a jumper to connect A2 and F2 together and will turn one direction, reverse the power cables on A1 and F1 and it will turn the other direction although slower then at 50 volts.
Is the X and Y travel on this thing fed through one or separate controller? That would seem to be a good way of checking where the problem lies
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You are assuming it is a series traction motor - which would be useless on a feed screw because it has no speed regulation. This is almost CERTAINLY a shunt motor - with variable field current to control the speed - quite accurately in fact - independent of load. Your fork lift experience is helpfull as far as it goes, but it doesn't go far enough.

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On Mon, 13 May 2013 21:20:13 -0400, snipped-for-privacy@snyder.on.ca wrote:

You are correct, I was assuming and know better. Thank you

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No, I think you mis-read that. He said there was 50V across the field, and ALSO 50V across the armature.
It's entirely possible for a drive to supply a steady-state voltage to the field, and vary the armature voltage -- even to the point of inverting the polarity of that second one.
Not all DC drives are "simple". I have a golf cart (personally) that accepts DC from the battery into the (electronic) drive, and supplies +-V (plus OR minus polarity) to the motor armature at full battery voltage (without relays), and pulse-width-modulates the field at a single polarity.
That provides both directions and variable speed without switches or relays... from a 'single' 36V storage battery.
LLoyd
LLoyd
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On Mon, 13 May 2013 20:22:23 -0500, "Lloyd E. Sponenburgh"

He said there was 50V across the field, and ALSO 50V across the armature.
Shit I should have read it one more time, I missed across.... open circuit.... Sorry

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