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Saving the 5HP Kinamatic DC Motor

rabler

Cast Iron
Joined
May 25, 2020
Location
Rural S.W. Indiana
I've gone the long way around to saving the DC motor on my 10EE rebuild. As I've posted earlier, it came with a Danfuss controller that wasn't delivering full RPM range. I completely gutted those electronics and started over. Ebay for a Parker 514c-32 and 507. Decided I wanted lots of features like the original factory setup, anti-plugging, full field braking, etc, so I built a digital controller to manage the two Parker units. That interface is all working (on a test bench) to control the motor. I'll need to tune the Parker's to get good performance, and I haven't wired up all the current/voltage/rpm/interlock monitoring circuits yet but those are relatively easy compared to getting the control algorithm right.

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At this point it looks like the DC motor needs some attention before spending more time on the controllers.


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Debating the merit of pulling the motor apart and replacing the bearings. Not totally obvious that is necessary but it seems prudent.
Also, this motor looks to have 2 brushes, reading back through lots of threads it seems like the 3HP typically had 4. Am I totally missing something?

1) New brushes (order from Monarch)
2) Stone commutator
3) replace bearings (?)
4) time brushes

If I pull the motor apart to replace the bearings, should I consider slightly grooving the mica on the commutator?

Right now the motor arcs quite a bit in reverse and sometimes in forward. It will sometimes hang on startup if the brushes are in a bad spot. And it is rough at low RPM. I'd rather get all of that cleaned up and running nicely. Doesn't make sense to me to try to get the drive controller tuned to a motor in poor shape.

I suspect I have close to $2k into the electronics at this point. The Parker units weren't cheap even used, plus I had a couple of small circuit boards printed for the digital interface. Going with a VFD and a 7.5 or 10HP motor would have been more straightforward and probably less confusing if I ever tried to resell this thing (very unlikely), but I'm far enough along to keep pursuing this path.

I currently have the apron apart on the bench, so I'm swapping between these. I'll probably want to finish the apron before digging into the motor, especially if I pull it apart for new bearings. Too many loose parts on one project machine otherwise. Not to mention the other project machines.
 
Hate to tell you but the comm is too far gone just to stone, tear the unit down and turn and undercut the comm, replace the bearings and do a good cleaning. You can buy brushes from any motor repair shop at a better price than monarch it would think. I am surprised that the motor only has 2 brushes but all you have holders for.Also you do know about field weaking, without it you will still have a top speed of 1100 rpm..Phil
 
Phil
Thanks for the evaluation, I’ll go for the full teardown.
I do have the Parker 507 set up as a separate DC drive for the field so that it will do field weakening. My initial motivation for the digital control front end was to coordinate field weakening, braking, etc, all with one knob. I’m not a fan of the dual potentiometer approach.
 
Yeah, that comm looks bad. Maybe it is the camera / reflection / lighting, but I wonder if it is too far gone to be undercut? Hopefully there is a lot of meat on there yet. One way to find out, get it apart and on a lathe and cleaned up. I think one of the concerns is loose comm bars if things have gone too far awry.
 
You also need to full field the motor for braking, (elsr)controls get a little tricky with the dc motor. I have 2 10ee,s one is dc the other will be ac vfd drive...Phil
 
You also need to full field the motor for braking, (elsr)controls get a little tricky with the dc motor. I have 2 10ee,s one is dc the other will be ac vfd drive...Phil

Are you re-using the reduction gear on your VFD/AC drive 10EE? That's the route I'd go if I had to do this again. This strategy will mean it'll run from single phase 220V (as would an oversize VFD). I do have an RPC but that is in a different building than the 10EE for now. I'm planning a 2400 sq ft shop to be built this summer. I'm hoping building materials come down a bit in price by then, but perhaps that is more wishful thinking.

I hope the DC motor isn't beyond saving given the $$ and time invested, but I'll jump in and find out, and go from there.

Yes, this machine has an ELSR. State machine implementation in the microcontroller, IDLE (power down field and armature), BRAKING (full field current if slowly to less than 1000rpm), STARTUP (full field up to 1000rpm for speeds faster than that), RUN, with a bunch of transition states and delays. Basically two DC power supplies, one for the field and one for the armature. Each supply has an analog input (0-10V for the field, -10 to 10 for the armature to cover reverse) plus a "RUN" input, so the microcontroller is programmed to handle those appropriately for each state. For now there are some arbitrary delays for spinup/braking type things, but I plan on a hall effect RPM sensor, and a low speed sensor on the gearbox. Also an interlock circuit for the spindle lock. Not fully debugged yet, first need a smooth running DC motor and then assemble it all in the lathe.

To further make things interesting, I'm setting it up with two independent speeds, nominally one forward and one reverse, but either can be set in the full range of -3500 to 3500 RPM via the ELSR knob. Simulating the ELSR switches via the two loose silver switches sitting on the bench. The 100 and -100 on the display represent the two speed setpoints, 100 and -100 being the poweron defaults. The large aluminum knob turns an encoder that changes the current speed. Letters represent Stop/Go, Forward/Reverse, and Powerup (the state the controller thinks the lathe is in). E-stop and square power switch on the left directly control the main power contactor. LEDs for main power, power to motor, and CPU fault. Round buttons (I happened to have red and green but they're not power related buttons) are for a few menu items settable on the display, for example to change the power on default RPM.

All still in progress getting all the details worked out, but at this point the DC motor needs to be overhauled before more effort is put in.

Most of the circuit board electronics are for isolation, RF noise resistance, and surge suppression. The black panel fits in the 10EE original on/off panel position.



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Yeah, that comm looks bad. Maybe it is the camera / reflection / lighting, but I wonder if it is too far gone to be undercut? Hopefully there is a lot of meat on there yet. One way to find out, get it apart and on a lathe and cleaned up. I think one of the concerns is loose comm bars if things have gone too far awry.

The step on the commutator is maybe .005-.010 at the left edge of where the brushes are tracking. The white commutators are lighting effect, but it runs poorly. I'll get it apart and turn it in the CK then relieve the mica, hope for the best. Just need to put the 10EE apron back together first.
 
Yes, after the first 10ee with dc drive the vfd looks easy and cheaper, I think the dc drive will work better at low speeds and the elsr might work better to...Phil
 
I agree with the others about recutting the commutator. I like to install the commutator end bearing and chuck the other end, then hold the bearing in a steady rest set just tight enough to hold the outer race from rotating. Not too much because it will distort the race. That way the commutator will run dead true with the bearing. You can undercut it with a hack saw blade. Use the end that cuts on pull. A used one is fine because you work with the end that is not used. Grind the set out and an angle on the end so it is easy to get all the way up the slot. A little tape on the rest of the blade will reduce damage to your hands. You can take the burrs off with some 400 grit sandpaper. Never mind the follks who tell old wives tales about grit embedment. Just make sure to blow all the dust out of the slots. wrap a strip of the 400 grit around the commutator and rock it back and forth to seat the brushes.

I have one of those motors that came off a 10EE a dealer parted out. The owner must have not owned an oil can because the parts I saw were worn beyond reasonable salvage but the motor either had been replaced or overhauled because the commutator looks new. You are correct that the 3 hp Reliance motor had four brushes while the GE only has two. The four brush motor running on clean DC is exceptionally smooth. I maintain a modular with the 5 hp motor but the thyratron drive is too jerky at low speeds to evaluate the motor performance. It could be that Monarch knew the drive would be rough at low speeds so the motor didn't matter that much. I put Scissio solid state thyratron replacements in it, which work very well, but they have a sharper firing characteristic that at low speeds in direct drive looks like it is driven by a ratchet. Of course, switching to back gear moves the problem mostly off the work envelope.

Make sure the motor is running right before reinstalling because you only want to have to do it once. At one point, the lathe was doing funny things with relays flapping for no apparent reason. I could only see the upper brush on the motor and it looked good, so I looked elsewhere for the problem. After drawing blanks everywhere else, I finally wedged a camera down next to the lower brush and found that it was worn out. Changing that brush in situ is a screaming PIA. Changing one brush must have made the lathe run so my predecessor didn't bother with the other. We had to lift the motor off its mounts and pull it a few inches out of the housing to reach the brush but that cured the problem.

If you are going to run a GE motor on a clean DC, I would like to hear the results.

Bill
 
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I agree with the others about recutting the commutator. I like to install the commutator end bearing and chuck the other end, then hold the bearing in a steady rest set just tight enough to hold the outer race from rotating. Not too much because it will distort the race. That way the commutator will run dead true with the bearing. You can undercut it with a hack saw blade. Use the end that cuts on pull. A used one is fine because you work with the end that is not used. Grind the set out and an angle on the end so it is easy to get all the way up the slot. A little tape on the rest of the blade will reduce damage to your hands. You can take the burrs off with some 400 grit sandpaper. Never mind the follks who tell old wives tales about grit embedment. Just make sure to blow all the dust out of the slots. wrap a strip of the 400 grit around the commutator and rock it back and forth to seat the brushes.

I have one of those motors that came off a 10EE a dealer parted out. The owner must have not owned an oil can because the parts I saw were worn beyond reasonable salvage but the motor either had been replaced or overhauled because the commutator looks new. You are correct that the 3 hp Reliance motor had four brushes while the GE only has two. The four brush motor running on clean DC is exceptionally smooth. I maintain a modular with the 5 hp motor but the thyratron drive is too jerky at low speeds to evaluate the motor performance. It could be that Monarch knew the drive would be rough at low speeds so the motor didn't matter that much. I put Scissio solid state thyratron replacements in it, which work very well, but they have a sharper firing characteristic that at low speeds in direct drive looks like it is driven by a ratchet. Of course, switching to back gear moves the problem mostly off the work envelope.

Make sure the motor is running right before reinstalling because you only want to have to do it once. At one point, the lathe was doing funny things with relays flapping for no apparent reason. I could only see the upper brush on the motor and it looked good, so I looked elsewhere for the problem. After drawing blanks everywhere else, I finally wedged a camera down next to the lower brush and found that it was worn out. Changing that brush in situ is a screaming PIA. Changing one brush must have made the lathe run so my predecessor didn't bother with the other. We had to lift the motor off its mounts and pull it a few inches out of the housing to reach the brush but that cured the problem.

If you are going to run a GE motor on a clean DC, I would like to hear the results.

Bill

Bill
Thanks for the advise on how to proceed with the commutator. The idea of the holding the bearing in a steady rest makes a lot of sense. I'll let everyone know how this turns out. Not sure the Parker qualifies as "clean DC" as my understanding is that it is basically an unfiltered switcher. I'll put a scope on it when I get the motor overhauled. I have a small arsenal of differential chokes and film capacitors that I may mess with a bit to smooth things out and reduce EMI if all goes well with the mechanical part of the motor overhaul.
 
I said that the output of thyratrons was pulses, but the SCRs have even more harmonic content and by firing more consistently make the pulsation even more apparent. An inductor is the way to go since a capacitor filter requires ones that can carry heavy currents in and out. As the saying goes, ask me how I know. I boiled them running unloaded. A diode clamping the input side of the inductor to common would also help by giving it to work against and not make it waste energy generating negative spikes.

There is some to be said for just a 3 phase Variac and full wave bridge. I have a plating supply I built using three transformers in delta and three in wye, giving 12 peaks per cycle with no filtering needed. 3 phase Variacs don't come in a box of Cracker Jack, but they really simplify things.

Bill
 
When I was working at a rewind shop I recut many comms. Using a razor sharp tool and slower rpm gave me the best results. I also had to hand cut the mica with a short handled hack saw blade or used a comm cutting saw. Be very careful not to nick the copper bars, if you can't stone out a scratch i would suggest taking a few more light cutting passes and re stone it (soft stone bar). We never used a steady, just a 3 jaw and a rotating center in the tailstock. Try not to get finger grease on the comm after you recondition it. I always wrapped the comm in stator insulation paper and taped it up until it was time to install.

Most of the old motors I rebuilt also needed the end bells resleeved and machined back to bearing tol. size.
 
I said that the output of thyratrons was pulses, but the SCRs have even more harmonic content and by firing more consistently make the pulsation even more apparent. An inductor is the way to go since a capacitor filter requires ones that can carry heavy currents in and out. As the saying goes, ask me how I know. I boiled them running unloaded. A diode clamping the input side of the inductor to common would also help by giving it to work against and not make it waste energy generating negative spikes.

Bill

Reversing the motor requires reversing armature polarity, which is done internal to the Parker DC drive controller, not via external contactors. Wouldn’t that rule out a clamping diode?
 
Very impressive on the electronics. I have the Parker setup with 2 pots. My ELSR had spdt switches and I thought those were the only ones available, so I had a number of relays to get proper reversing and full field braking when running in field weakening. Everetteng happened to mention his switches were dpdt. Bought some of those and was able to get rid of the relays, now I have proper ELSR function and full field breaking using just the micro switches no matter what position the pots are in.

I don’t know about the GE, but the small frame Reliance had plenty of commutator bar to turn and clean up.

Motor musings, WiaD motor
 
My Sheldon came without a motor because it was originally intended to be a demo with a variable drive but they went out of the manual lathe business and soon, all business. I installed a 15 hp DC motor and feed it with a three phase Variac and three transformers that originally powered heaters in the Monsanto St. Peters gallium arsenide ovens and a full wave three phase rectifier set. The motor get six sine wave peaks per cycle, close to pure DC. The Variacs are motor driven with "up' and "down" buttons on the control panel and speed changing is similar to a Hardinge HVLH, hold a button til it gets to the desired speed. Speed does vary with load but it never has been enough of an issue to do anything about it. It has the original little tach generator and analog meter and I have added a digital one. I would add braking before I would worry about speed compensation, but have a tuit shortage in that area.

I have made both single and three phase saturable reactors for my 10EE and run it on them. One thing I found was that it takes a well regulated field supply or the RPM in field weakening territory is all over the place.

Bill
 
I put the DC motor out from under the test bench and got it up on the workbench, and took it apart. Note my special anti-gravity workbench :)

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The brushes obviously need to be replaced, as they're barely sticking out of the holder here, bottom right of the picture:

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Got the rotor chucked up in the 4-jaw with a copper strip between the shaft and jaws, trued in, and the right side running on the bearing in the steady rest. I backed the tailstock off just to the point that the live center wasn't turning.

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It took about .075 cutting off the diameter to get it completely cleaned up. The commutator is probably twice the width of the brushes, and the groove the brushes had made didn't start cleaning up until around .030 in. Those grooves were significantly out of round. One concern I need to work on is that the fan rotor is about 3/8" out of true, looks like someone had previously pried the back end of the motor off by prying against the fan rotor. Haven't figured out how to straighten this, or maybe I should try to just balance it as is.

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I still need to clean up between the commutator bars.

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