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
Reply to
Ignoramus9202
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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
Reply to
Artemus
"Artemus" fired this volley in news:kmmj0j$8a5$1 @dont-email.me:
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
Reply to
Lloyd E. Sponenburgh
e.
You might check to see if the brushes are worn so much that they do not quite contact the armature.
Dan
Reply to
dcaster
" snipped-for-privacy@krl.org" fired this volley in news:4ed26075- snipped-for-privacy@w15g2000vbn.googlegroups.com:
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
Reply to
Lloyd E. Sponenburgh
Sounds like your armature is burned out.
Reply to
Gunner Asch
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.
Reply to
jeff
Makes sense, great idea
Reply to
Ignoramus9202
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
Reply to
Ignoramus9202
Check the armature. (My VOM has a beeper mode which speeds things up in cases like this.) Opposite commutators usually connected by a winding (180 degrees apart when the brushes are set in that position.) Also verify that none of the commutators are shorted to the shaft, then verify that the commutator is connected to the wire it's supposedly soldered to. Sometimes the brush can wear off the solder and lose a connection, but that just ends in a motor which won't start in certain positions. Verify that each brush and its connector are actually intact. Some had carbon rather than wire inside and it can degrade.
Logically, as you usually do. :)
Sometimes it's just dirty and cleaning/reassembly fixes it. Do the individual tests. If you find nothing, assemble and try again. I've brought home dozens of "broken" or "burned out" electrical products which had a grain of sand between working and not working. I've made hundreds (if not thousands) of dollars reselling the working product.
Reply to
Larry Jaques
Ignoramus9202 fired this volley in news:lbudnSi2zvZmYBPMnZ2dnUVZ snipped-for-privacy@giganews.com:
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
Reply to
Lloyd E. Sponenburgh
Yep. I will post updates when I am done figuring it out. Thanks
i
Reply to
Ignoramus9202
It would be worthwhile to include more details in your posts, as you've been criticised for previously.. so days later someone may realize what it is your talking about.
This drive got a name, p/n, or voltage marked on it? Someone may have a schematic/wiring diagram or other useful info for a similar drive if you would give details.
It appears that a voltage is present for the field (but it may not be the correct voltage). The motor also needs an armature voltage A1-A2.
The armature voltage isn't getting to the armature. Failed drive circuitry. Switch device open. Half-assed previous repair/anything. The armature voltage is the one that's controlled by the circuit.. any of the components associated with the motor speed could have failed. I've read more than a couple of times that speed pots had failed in a certain table drive.. Enco maybe. There may be some info and/or a schematic in the dropbox archives.
It may be that the drive motor runs all the time because it failed before and some motor monkey found a way to make it run.
You've seen considerable wear present, but you'll likely spend hours trying to make the old drive work, possibly poorly or only briefly, then hold out for another used drive for cheap. Possibly you were thinking you'd get an old machine that you'd be able to use for years without ever spending a dime on it.
The machine probably didn't cost much but if you aren't willing to spend some money on it, you probably just dragged it back to scrap it.
Plan B.. put a handwheel on the feedscrew.. which is a good plan, that may even dissuade the operator from walking away from an operating machine.
Reply to
Wild_Bill
Is the motor fed voltage from the drive with two or four wires?
Reply to
jeff
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
Reply to
dcaster
Ignoramus9202 fired this volley in news:f_KdnXyf86GQihLMnZ2dnUVZ snipped-for-privacy@giganews.com:
Ig, It's somewhere near worthless and a waste of time to post any details until you get it solved.
Ig, it's apparent that some folks refuse to read your first post, wanting instead to make the problem fit their solution. However, three people all suggested the same, useful thing.
Ig... those who suggested checking continuity between the "A", leads and the brush holders shouldn't have had to make that suggestion. That check should have been a natural part of your protocol to begin with, as soon as you saw power to the A leads, but none on the brushes themselves. (just a small finger-wagging )
LLoyd
Reply to
Lloyd E. Sponenburgh
Three wires from the drive, connecting to four wires to the motor.
i
Reply to
Ignoramus5857
You are right. I decided to take the stator off and wash it before proceeding, due to it being extremely dirty.
i
Reply to
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.
Reply to
jeff
jeff fired this volley in news: snipped-for-privacy@4ax.com:
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
Reply to
Lloyd E. Sponenburgh

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