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10EE Monarch MG DC motor speed plateau @ 380 RPM

diblaja01

Plastic
Joined
Apr 22, 2014
Location
Grand Prairie, Tx
Hello Forum members,

I am here to humbly seek help with a 1953 10EE MG 220 volt machine of which the DC motor speed tops out around 300 -350 RPM. I will do my best to describe some of the indicators and symptoms along with what I've done thus far and hope that anyone of you can lead me to a fix. Before I get into the details I would like provide some details of my background. I've spent many years working in the digital electronics domain, diagnosing and repairing computer related boards, equipment, drives, etc. though familiar with such, I don't have any experience with motors, motor controls and control safety systems. I specially don't know anything about DC motors and generators other than what I've learned here from you all in these last weeks. Thank you.
Symptoms:
1. Turning the speed control knob the DC motor will spin up from its lowest speed to around 300 plus RPM with nothing unusual.
2. If I turn up the speed control past the ~300 RPM the sound of the MG/exciter whirling sounds as though it starts to load up and the DC motor starts to spark pretty aggressively at the commutator/brushes. The generator sparks slightly at the commutator/brushes.
3. If I push the speed control further the Forward contactor starts to chatter open and close.
4. With the spindle control in neutral and the speed control knob at slowest setting the AP relay point is closed. As I turn the speed control the AP relay contact opens.
5: The measured output of the exciter is 117Vdc when spindle control is in neutral and with E1 connected to the DC panel . It also reads 117Vdc with E2 disconnected at the terminal to the machine side.
6. The measured output the generator was 18Vdc at GA1 and GA2 with the spindle control in neutral. With GA2 disconnected at the terminal that goes to the machine side the voltage measured the same 18Vdc.
7 When the spindle control was put in forward, the voltage at GA1-GA2 started low but increased as the speed control knob was increased to where it topped out around 85 Vdc. The rheostat wiper was around the 7 o'clock position. This is the point I described above.
8. The voltage from the exciter started low but it too increased to around 80 - 85 Vdc. This is the point I described above
9. I did checked the health of the rheostats. The rheostats presented the following ohmic values:
Exciter rheostat -- full scale ~ 330 ohms,
6:30 o'clock to 12:00 o'clock < 1 ohm,
12:00 o'clock to 5:00 (max) > 1 ohm to 330 ohm.

Generator rheostat --- full scale 650 ohms.
6:30 o'clock to 12:00 o'clock 10 - 650 ohms
12:00 o'clock to 5:00 (max) 650 ohms through out.

10. I looks like the brushes in the generator are new and the exciter brushes look good. I'll have to take a better look at the DC motor brushes before I comment. I'll get some good photos of the commutators if there's any question that they could cause this problem.

11. This is also incidental but it might mean something to. When I press the start switch with the spindle control in it's forward or reverse position the MG will start. I think the MG should not start until the operator puts the spindle control in neutral. The original start and stop switches have been replaced. I also noted the original transformer for these was also removed and some wiring changes where made that lead to the heater coil section. I'm not sure if this is a contributing factor or not.
Thanks in advance for any help

James
 
The spindle motor sparking sounds like either a brush seating problem or a timing issue. If someone just popped new brushes in without using sandpaper to contour them to the commutator then you'll have sparking. Pull the brushes and see if wear pattern indicates that they're making full contact with the commutator across the sloped end of the brush. Ditto for the generator and exciter brushes.

The spindle acting up after the AP relay opens is usually caused by the failure of one of the resistors in the upper-right corner of the DC Control panel:

It sounds like someone bypassed the center-position contacts on the headstock drum switch, allowing the motor starter to close with the switch in the forward or reverse position. Here's a thread that explains how the starting circuit operates:

The little transformer in the motor starter compartment only provides power to the pilot light in the original start switch. It has nothing to do with how the starter operates.
 
Hello Cal

Thank you for your quick reply. I don't have access to the lathe until Monday when I will perform the checks you suggested. You mentioned that sparking could also be the result of a timing issue --- would this be the brushes that are out of the neutral plane position. I just learned of this and the consequences of improper adjustment. Today while I was looking at each device I was trying identify how such adjustments are made. On the exciter I was able to see the witness mark but I wasn't sure of where the hold-down screws/bolts are located to adjust the brush collar. I was unable to see how an adjustment is done on both the dc motor or the generator as presently installed. But I guess one step at a time. Anyway, thanks again.
I'll have more questions to follow.

James
 
Check the brush seating first.

On the spindle motor, the brush ring has a cross bolt that clamps the ring to the spider. The split is usually at about 45 degrees to the right or left of the 12 O'clock position, looking in from the end. Some have a neutral mark cast into the ring. Always look for factory witness marks that indicate proper timing and make your own witness marks before adjusting it, so you can tell how far you've moved it.
IMG14134.jpg

IMG14136 brush holder neutral.jpg
 
Hi Cal

Thanks for sharing the brush adjustment clamp location. I totally missed it. Today I checked the three resistors and they appear to be okay. The two 1600 ohm resitors in series measured 3200 and the one stand alone resistor measured 2K ohms. I examined the four brushes on the spindle motor and they look okay from my view. They were just about one inch in length and other than some debris built up on the edges the seem to look polished and wearing evenly with no cracks. The attached photos of the commutator are the best I could manage with the quality. The spaces between the commutator strips were filled with an oily sludge that I painstakingly scraped out. The result was disappointing in that the sparking and motor speed plateau is still there. From my previous generator/exciter findings, do those devices appear to be operating properly. Do I need to look at some more detailed analysis? I thought I read somewhere that the generator should output somewhere near 220Vdc and I've have not seen this one do so even with no load connected.
 

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The insulating plastic between the copper segments needs to be under-cut. The brushes must not touch the plastic. The natural arcing that occurs as the brush moves from one segment to the next will burn the plastic and make it conductive. The plastic can also lift the brush as it slides between segments. This also causes problems.
You can cut the plastic down with a thin bladed saw. The plastic is often a fiberglass board. The saw should remove all the plastic and even some of the copper in the slot. I use a ground down hacksaw blade for this. When generators, as opposed to alternators, were standard in cars, all auto repair shops had these generator and starter motor undercutting machines. You often see them at antique auto flea markets.
 
That commutator looks nasty. If you have tar-like stuff on the commutator(s), you need to clean that off and undercut the insulation, as suggested. Use acetone or electric contact cleaner to clean it. Don't use sandpaper on the commutator. If you still have radial black streaks on the commutator after cleaning we can talk about using a commutator conditioning stone to clean it up. Look for black bars and raised bars on the commutators.

You probably have krud on the brushes as well, so give them a good cleaning. It wouldn't hurt to re-condition and re-seat the brushes by wrapping fine (600 grit) wet-dry sand paper on the commutator, facing out, and rocking the comutator back and forth to sand the end of the brushes.

For some reason, when I initially read through your post I missed the fact that the exciter voltage is dropping out under load. That's the first thing to address; if the exciter isn't working properly, nothing else will. The exciter should be putting out about 115 VDC under all load conditions. Check the exciter's brushes and commutator, look for loose wire, etc. The variable resistor that adjusts the output of the exciter is located in either the exciter or generator's end-bell. Make sure the resistor's wiring and connections are good.
 
Hi Mr. CNC and Cal, Thank you for taking your time to help me out solve this problem. After I posted the pictures I anticipated that a commutator dressing and undercut were going to prescribed. I managed to clean much of the gooey stuff off with acetone and I scraped out some of that sludge from the undercuts only to find it is still sparking. I did take the time to check the ohmic values of the spindle motor A1 - A2 and F1 and F2 and the values were consistent to 0.1 ohm as I rotated the armature. The commutator ohmic values of the generator varied slightly from 1.5 to 2.2 ohms as I slowly turned the armature. The exact values for the spindle motor I don't have at home with me. I might have incorrectly described the exciter output the other day so I will verify that finding tomorrow and I apologize in advance if I was wrong. I found a US company -- Martindale that sells commutator service tools. If you think I should go ahead with the dressing then what size stone should I get and what grits. My thought was .75" width which I will epoxy to a stick to be worked back and forth. I think I should remove the belt drive for the spindle to lessen any chance of getting tangle up. I'm just guessing with this so I will defer to better experienced persons to see how it should be done properly. I'll report back tomorrow on some findings.

Thanks again
James
 
Another thing to check is that the wear on the copper segments is about the same all the way around. If the armature has a shorted turn, then one segment will look significantly more burned or worn, particularly at the edge.
 
... I found a US company -- Martindale that sells commutator service tools. If you think I should go ahead with the dressing then what size stone should I get and what grits. My thought was .75" width which I will epoxy to a stick to be worked back and forth. ...
I'll get with you offline about this. There's some very bad information about using commutator stones on this site. I'm working on something to straighten this out, but it's not ready yet.

Martindale is a good source for the stones, but forget about gluing the stones to a stick. That's OK for small motors, but when you get to multi-horsepower motors you can't put enough pressure on the stone to get it to work.
 
Hello Forum members,

I am here to humbly seek help with a 1953 10EE MG 220 volt machine of which the DC motor speed tops out around 300 -350 RPM. I will do my best to describe some of the indicators and symptoms along with what I've done thus far and hope that anyone of you can lead me to a fix. Before I get into the details I would like provide some details of my background. I've spent many years working in the digital electronics domain, diagnosing and repairing computer related boards, equipment, drives, etc. though familiar with such, I don't have any experience with motors, motor controls and control safety systems. I specially don't know anything about DC motors and generators other than what I've learned here from you all in these last weeks. Thank you.
Symptoms:
1. Turning the speed control knob the DC motor will spin up from its lowest speed to around 300 plus RPM with nothing unusual.
2. If I turn up the speed control past the ~300 RPM the sound of the MG/exciter whirling sounds as though it starts to load up and the DC motor starts to spark pretty aggressively at the commutator/brushes. The generator sparks slightly at the commutator/brushes.
3. If I push the speed control further the Forward contactor starts to chatter open and close.
4. With the spindle control in neutral and the speed control knob at slowest setting the AP relay point is closed. As I turn the speed control the AP relay contact opens.
5: The measured output of the exciter is 117Vdc when spindle control is in neutral and with E1 connected to the DC panel . It also reads 117Vdc with E2 disconnected at the terminal to the machine side.
6. The measured output the generator was 18Vdc at GA1 and GA2 with the spindle control in neutral. With GA2 disconnected at the terminal that goes to the machine side the voltage measured the same 18Vdc.
7 When the spindle control was put in forward, the voltage at GA1-GA2 started low but increased as the speed control knob was increased to where it topped out around 85 Vdc. The rheostat wiper was around the 7 o'clock position. This is the point I described above.
8. The voltage from the exciter started low but it too increased to around 80 - 85 Vdc. This is the point I described above
9. I did checked the health of the rheostats. The rheostats presented the following ohmic values:
Exciter rheostat -- full scale ~ 330 ohms,
6:30 o'clock to 12:00 o'clock < 1 ohm,
12:00 o'clock to 5:00 (max) > 1 ohm to 330 ohm.

Generator rheostat --- full scale 650 ohms.
6:30 o'clock to 12:00 o'clock 10 - 650 ohms
12:00 o'clock to 5:00 (max) 650 ohms through out.

10. I looks like the brushes in the generator are new and the exciter brushes look good. I'll have to take a better look at the DC motor brushes before I comment. I'll get some good photos of the commutators if there's any question that they could cause this problem.

11. This is also incidental but it might mean something to. When I press the start switch with the spindle control in it's forward or reverse position the MG will start. I think the MG should not start until the operator puts the spindle control in neutral. The original start and stop switches have been replaced. I also noted the original transformer for these was also removed and some wiring changes where made that lead to the heater coil section. I'm not sure if this is a contributing factor or not.
Thanks in advance for any help

James
James, my 10EE S/N 38043 is a DOD ordered in '52, built in '53 delivered 1/'54. Sharing your serial number would be interesting. You're in very good hands to work through everything. I suspect your lathe was also built for DOD because by this time the motor-generators were special order, most being the Works in a Drawer (WiaD). Mine also had a 2k resistor, completely shot, rather than the 1.6k. I want to drop you a non-repair email and didn't want you wondering who it was from.

Ron
 
Hello All, I apologize for my absence but I was out of town for unexpected family events. I am now back home and plan on delving into the lathes problems today. Cal, I have found in this thread "Monarch EE: Oh no, not the single phase question again.." (link) -- August 18, 2017 where you suggest a test to check the exciter and generator output voltages ---- "
The exciter will probably want some load to operate. Connect a 40 to 60 W incandescent light bulb between E1 and E2.

If you connect GF2 to E1, you put full voltage on the generator's field, which will cause the generator to put out full voltage (230 VDC) between GA2 and GS1. Best to put a 2A fuse between GF2 and E1". I want to do this check today -- at least start at this point and go forward. I also want to pick up on the discussion of the spindle motor commutator re-conditioning. Check back tonight with my findings.

James
 
Last edited by a moderator:
You need to get the exciter working properly before you worry about anything else. The post that you found isn't particularly helpful on that front. I've posted about doing resistance checks on the exciter wiring, but I don't have time to search for them right now. There's a variable resistor in either the exciter or generator end-bell that may be the culprit.

I sent you a private message about commutator conditioning. Look for the envelope icon at the top of the page.
 








 
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