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  1. #21
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    Tell me 9100. Why do my tube fired machines run smooth in open belt to 200 rpms???

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    Quote Originally Posted by 9100 View Post
    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.
    Turns the Diode into shards, trips an overcurrent fault and shut down on the 4Q DC drive as soon as you command reverse, though!

    Once the diode has been blown to "OPEN" and is out of the circuit?

    No further problem!



    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
    It might be handy for testing. Not for running. There's no sensing nor load regulation, no RPM-holding as the DC Drives have.

    You could get good results if you built the saturable-reactor rig we've discussed, That could be golden because .. it is so inherently uber-rugged ..as well as requiring near-zero long-term maintenance.

    Annnnnd.. It is all a manual-lathe NEEDS, regardless of how sweet the spindle-bearing TIR.

    Even so, the off-the-shelf, mass-produced SSD drive delivers seriously good regulation off the back of no extra components internal, inherent IR sensing, and borderline silly overkill figures if given a decent tachogenerator input, to wit:

    Built-in IR Sensing: 2% over a 20:1 RPM range @ full rated load

    Tachogenerator feedback: 0.1 % over a 100:1 RPM range @ full rated load
    (page 1-8 of the manual)

    So, too, is the single-phase-only SSD 514C-16 "smooth enough" with either of the Lenze "swinging" choke, the Hammond 20 mH @ 20A one, or for at least the lower current-draw 3 HP motors, the Rex one.

    That gets the 3 HP "large frame" down to a "smooth enough" one revolution in 15 seconds - or less - 20 seconds? I didn't have the patience left to see - in reduction gear, AKA "1/4" RPM.

    Around one or two RPM in direct belt?

    Dunno if Evereteengr has ever bothered to record his best LOW RPM. He has the 20 mH @ 20 A Hammond choke, but his GE Kinematic 5 HP has a far higher "base" RPM than my 3 HP large-frame has.

    I'd guess that would give him a smooth 10 or 15 RPM in open-belt?

    No real need of that slow even for creep/jog.

    But wot the hey.. at least no need of a tach to measure it. Just use the wall-clock!



    End-result is that it is REALLY smooth up where the actual work is to be done - 50 or 100 RPM.... and up, of course. UNlike a VFD's "variable Hz, it is always clocking off a fixed-by-utility-mains 120 CPS rate, so filter implementation is dirt-simple.

    Then, too, the more power demanded, the smoother a Thyratron gets, as it has a lower and lower percentage of "OFF" time for a shorter "coast-through" time gap and is moving closer to utilizing the whole smooth sine-curve of each pulse from zero-cross to zero-cross.
    Last edited by thermite; 03-23-2021 at 12:02 PM.

  4. #23
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    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

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    Quote Originally Posted by 9100 View Post
    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
    ^^^ THIS ^^^ "Region of reverse control" thing, landing environment ..to a pilot.

    Been covered. Not new. Problematic on lifts before ever a 10EE arrived.

    The answer was "Field REGULATION". Not just regulated field supply.

    The Field control loop is given primacy over the Armature control loop.

    Works a treat. John Shackelton's bright lads published an elegantly simple white-paper that explains it.

    They even shipped it. Several firms did. In single-phase-only as well as 3-Phase-only.

    Finding a CURRENT PRODUCTION single-phase-only implementation has been the elusive part. Not all 3-Phase-only DC Drives even do the full Magilla. Make the Field the outer control loop. Nest the Armature control loop inside of it. "Current" realm. the both of them. As it must be.

    That RTWL again. Round Tuit Wish List.

    So many women. So little time. Err.. sorry.... wrong sub-set...

    "So many interesting challenges, so little time!"


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    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









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







    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.





    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.





    I still need to clean up between the commutator bars.


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    You also should de-burr/chanfer the edges...all hand work...Phil

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    Quote Originally Posted by Phil in Montana View Post
    You also should de-burr/chanfer the edges...all hand work...Phil
    Yep, left it in the lathe so I could easily hold it while I "clean up between the commutator bars", and then polish out any scratches.

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    When you are done with the undercutting use some of the purple scotch brite to polish... works real well...Phil

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    Quote Originally Posted by Phil in Montana View Post
    When you are done with the undercutting use some of the purple scotch brite to polish... works real well...Phil
    Thanks, I’ll give that a try.

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    The armature has more commutator bars than slots, so it has some form of multiplex winding, which is used to give more smaller increments to torque. If convenient, see if the brushes are exactly 180 degrees apart or shifted half of one commutator bar from each other. That is the difference between taking steps with one foot at a time instead of jumping with both together. One more way to make a smooth running motor.

    Bill

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    Bill have you ever worked on a dc motor or rewound one?? What you just wrote is from the outer-limits...Phil

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    I see the stator is varnished on the outside, and the end bells still have grey paint.
    Someone has been inside this motor before, maybe just dunked the stator
    in varnish, maybe more.

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    Quote Originally Posted by 9100 View Post
    The armature has more commutator bars than slots, so it has some form of multiplex winding, which is used to give more smaller increments to torque. If convenient, see if the brushes are exactly 180 degrees apart or shifted half of one commutator bar from each other. That is the difference between taking steps with one foot at a time instead of jumping with both together. One more way to make a smooth running motor.

    Bill
    I was wondering about the winding. (I know nothing about motors from an engineering perspective). I did pull out my Fluke meter to test the resistance between adjacent commutator bars, thinking that would be a good way to verify I'd cleaned up between the commutators reasonably. Adjacent bars seem to be about .2 ohms, increasing by about that much for each bar. Thinking about it, it makes sense to have some sort of staggered winding that gradually steps the current between windings rather than cutting one off and the next one on.

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    Quote Originally Posted by digger doug View Post
    I see the stator is varnished on the outside, and the end bells still have grey paint.
    Someone has been inside this motor before, maybe just dunked the stator
    in varnish, maybe more.
    That someone gets my award for being a total asshat. This is the cooling fan rotor. Note the ding on the upper right, and one the bottom there is a fairly good bend. Someone obviously pried the back end off by prying against this fan rotor. It is about 3/8" out of true. Not sure how I'm going to fix that but I'm sure that isn't helping the motor's balance.



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    The whole winding is in series, probably 3 coils per slot, it could be progressive or regressive but make no difference unless you are going to rewind it... I would leave the fan alone, not much could be gained unless you replace the fan, with the belt drive on the ee I don't think you will tell the wobble is there Phil ...Phil

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    Quote Originally Posted by Phil in Montana View Post
    Bill have you ever worked on a dc motor or rewound one?? What you just wrote is from the outer-limits...Phil
    Well.. the DC motors Monarch purchased actually WERE "from the outer limits", Phil.



    The 3 HP "large frame" Reliance elevator/hoist motor - with uber-complex interleave windings plus interpole coils most of all. "Smooth" is what it was built to do, and the energy conversion efficiency suffered a tad to deliver that.

    BFD. "Tough act to follow".

    The least-common "small frame" Reliance 3HP was Type T WITH S coil. My (former) one had been run with a GE tachogenerator in its former life - early-day DoD contract Solid State upgrade from Hollow State WiaD, almost certainly.

    The 5 HP GE and Louis-Allis "special machine tool duty" were not "straight shunt" (only) or "Type T". They had a compounding or compensating series winding brought out on S1, S2 leads as well as the A1, A2, and F1, F2.

    Data plate tells the tale. I've posted it on PM before. Others have posted the physics of how it works to manage compensation for variable load, and the challenges when reversing. PM has threads on that very issue.

    Those last two - as is the case here - were not "cheap" goods but aren't really all that "special" as that was a common commodity DC item in its day. Less costly than a type T. As was the need and goal.

    And Old(er) Bill does know his DC motors, BTW.

    Not to imply that you do not.

    Monarch simply used whatever "niche" goods they needed to optimize for the work intended for any given machine tool.

    Some were "more special" than others, and it was 10EE amd 13EE/1000EE that housed them.


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    Quote Originally Posted by rabler View Post
    That someone gets my award for being a total asshat. This is the cooling fan rotor. Note the ding on the upper right, and one the bottom there is a fairly good bend. Someone obviously pried the back end off by prying against this fan rotor. It is about 3/8" out of true. Not sure how I'm going to fix that but I'm sure that isn't helping the motor's balance.


    That's not very nice.....The fan mangling might have come later.
    The fact that the stator has been re-varnished (either plain dunk or VPI) shows it went
    to a real motor shop at one time.

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    Quote Originally Posted by digger doug View Post
    That's not very nice.....The fan mangling might have come later.
    Replacement fans exist in the market. Better to adapt a known-good one than have cracks that cause this one to come apart under power, later.

    Or shed it entirely, and put a squad of PAMOTER "muffin" fans onto the azures, "blower-duty" writ small style?

    That's been done before. And "right here, on PM", too.

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    Quote Originally Posted by Phil in Montana View Post
    Bill have you ever worked on a dc motor or rewound one?? What you just wrote is from the outer-limits...Phil
    I have worked on lots of them, beginning in 1951 when I got a summer job in the P. E. Chapman Electrical Works at 1820 Choteau in St. Louis. I got a basic education, really basic. Penrose Embry "Pappy" Chapman was a crazy old coot, but a smart and extremely penurious one. Their product was armature winding, taping and soldering machines. They didn't sell motors and transformers as products but made them for their machines. Chapman salvaged old transformers and cut the laminations down by hand. My first job was cutting them on a square shear. Besides being oily, the pieces had bad burrs and my hands were masses of little cuts. I then graduated to painting machines, stacking laminations, and prepping armatures, fitting paper in slots, etc. Because I was 15 and Missouri law required a powered machine operator to be at least 18, I never got to actually wind an armature but saw it done and worked on the machines.

    I had a Kabar lock back knife that I learned to open with one hand, useful when I had wires in my left hand needing stripping. Unfortunately some folks thought the skill belonged in West Side Story rather in a factory. As Chapman said when he regretfully told me that I was not invited back the next summer, they objected to "my penchant for dangerous weapons and dexterity in their use." We stayed friends, though.

    The experience has been very useful since. I have rewound lots of electrical items, mostly transformers and DC motor field coils, and have a vapor pressure inpregnation chamber. I treated a lot of locomotive fuel transfer pump motor armatures. They would absorb moisture and flunk a megger test. I would bake them and leave them in a vacuum overnight to remove virtually every trace of moisture, then let transformer varnish in to cover the armature and let in air pressure to force the varnish into every space, then bake them to cure the varnish. That usually would bring the megger reading to infinity.

    So yes, I have worked on a few motors

    Bill

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    Is it worth trying to revarnish anything? My inclination is not to mess with it more than necessary, but it is apart now, so this would be the time to do any other work on it. Still haven't ordered in new bearings, need to pull the reduction gear apart to see what is in there that might need to be replaced before doing that.


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