Single-phase Power for Motor-Generator 10EEs
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  1. #1
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    It is well-known that WiaD and Modular 10EEs may be powered by single-phase.

    Herein I present a modification to Motor-Generator 10EEs which will allow these machines to be powered by single-phase. Both a 230 volt and a 460 volt modification are presented.

    The underlying technology is adapted from Henry Steelman's U.S. Patent 2,922,942 (which see), and is extended by me to incorporate power factor correction (not claimed by Steelman in his patent) and easy adaptation to the 10EE's AC Section.

    (An essential feature, and requirement of Steelman's idea is a twelve-wire three-phase motor, or a nine-wire motor which has been modified to add the three "missing" wires implicit in that motor's "star point", may be very easily powered by single phase, provided a starting circuit is provided and the motor winding components are wired in an innovative way. This innovation simulates a capacitor start/capacitor run single-phase motor. I have added power factor correction, which Steelman did not claim, and which further improves upon Steelman's idea).

    The first Figure describes in the abstract how a three-phase motor may be powered by single-phase without sacrificing motor power. This is more-or-less directly from Steelman's patent, extended by information included in Steelman Industries, Inc's modification to that patent for 460 volt applications.

    The second Figure describes the 10EE AC Section, with all loads except for the "three-wire control station" removed, and with each terminal to which the converted motor and its support circuitry is to be connected.

    The third Figure shows details the 230 volt modification, showing how each part of the motor-generator, and the additional starting and power factor correcting circuits are to be integrated into the AC Section. The 90-66 potential relay coil is across the entire start winding. The run windings are split across two poles of the magnetic motor starter thereby reducing the stress on the Size 1 starter. There are two power factor correcting capacitors, corresponding to each pole of the starter. As is required by the NEC, the capacitors are placed after the disconnecting means, and before the motor protection means. Bleeder resistors are not shown for clarity.

    The fourth Figure shows details the 460 volt modification, showing how each part of the motor-generator, and the additional starting and power factor correcting circuits are to be integrated into the AC Section. The 90-66 potential relay coil is across one-half of the start winding. Each capacitor shown is actually two identical capacitors in series.


    I have not detailed the values of the capacitors. Clearly, the run capacitors must be 370 VAC, minimum (740 volts when placed in series for 460 volts), and the start capacitors must be 250 VAC, minimum (500 volts when placed in series for 460 volts).

    Initial values for C may be obtained from

    I = 2 * π * F * C * V

    where I is the FLA in Amperes, π is the constant 3.14, F is the frequency in Hertz (the factor 2π converts this frequency from Hz to radians/second), C is the capacitance in Farads, and V is the voltage in Volts.

    Final values for each C may be obtained by tuning.


    References:

    1) Henry A. Steelman's patent

    http://www.pat2pdf.org/patents/pat2922942.pdf


    2) Steelman Industries Inc installation information for Steelman's H.A.S. converter

    http://www.capacitorconvertors.com/p...structions.pdf


    Recommended initial values for Cr are 11.53 µF per FLA amp for 230 volts and 5.77 µF per FLA amp for 460 volts. Use a clamp meter to ensure the current in the start winding doesn't exceed FLA amperes.

    Recommended initial value for Cs is ten times the value of Cr, tuning for starting in two seconds or less.

    Recommended initial value for Cpf is 0.1 times the value of Cr, tuning for just under minimum current, on the under-compensated side of 1.0 P.F.
    Attached Thumbnails Attached Thumbnails small_figure_1.jpg   small_figure_2.jpg   small_figure_3.jpg   small_figure_4.jpg  
    Last edited by peterh5322; 03-03-2008 at 02:20 PM.

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    Thumbs up Way Cool!

    Peter- this is way cool!!!

    I was originally planning on 10hp VFD with backgear... at the moment, I'm working on the J-head 56C VFD project right now, but when I get it done (on both the radial drill AND the BRJ), I'll try this out on my '42 MG system.

    Thanks!!!

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    "Peter- this is way cool!"

    Thanks.

    I have also designed a similar modification for Monarch engine and toolroom lathes with geared reversing heads, such as the Series 61, and which will allow those machines to be powered by single-phase as well.

    One limitation on those machines, which doesn't exist on the 10EE, is the presence of a reversing magnetic starter, and which may limit such single-phase conversions to the lower range of motor horsepower when powered by 230 volts, but which limitation may not exist when powered by 460 volts. This limitation comes down to the motor horsepower and the single-phase horsepower rating of the starter, hence its NEMA size designation.
    Last edited by peterh5322; 03-08-2008 at 04:16 PM.

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    Hi Peter,

    Thanks for posting this! This is a very exciting and interesting concept.

    Do you have this working on an MG machine? Where do you suggest mounting the start circuit relays and the capacitors?

    Cal

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    "Do you have this working on an MG machine?"

    Not at the present time.

    It is next on my "to do" list.


    "Where do you suggest mounting the start circuit relays and the capacitors?"

    In an enclosed box (Hoffman, or equal), mounted above the spindle motor and backgear.

    There are spare threaded bores (1/2" electrical trade size) within the C-H starter compartment from which a length of flex can be routed to the box.

    Also, a length of flex would be routed from the M-G unit to the box.

    The contents of the box would be: the P.R. and the auxiliary starting contactor (I don't trust the 90-66 with a 6+ HP starting load, besides the way I have designed the modification it is good for 230 and 460 volts, and not just 230 volts), and all caps with their bleeders.

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    Thanks Peter,

    I don't have a coolant pump, so that space is another option to mount the Hoffman box.

    I assume that the currents through OL1 and OL2 will be different, and heaters will need to be adjusted accordingly?

    Cal

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    "I assume that the currents through OL1 and OL2 will be different, and heaters will need to be adjusted accordingly?"

    Indeed so.

    About 1/2 of the run winding for the start/run winding.

    That's one good thing about the old two-overload starters, each side is independently changeable.

    The Steelman manual gives suggested values for FLA vs. HP, and also a way of computing the overload current setting vs. FLA.

    If you have coolant, the same converter concept would work there, too, only on a much smaller scale, 0.33 HP vs. 6+ HP.

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    FWIW, on many machines with a B&S 200 coolant pump, the motor is an ordinary NEMA 56C motor, and these are available in single-phase, just as the B&S 200 pump was available in single-phase.

    The coolant pump compartment isn't tall enough to house a B&S 200 single-phase pump, though, although you could detach the starting capacitor and mount it elsewhere.

    Buying a 1/3 HP single-phase NEMA 56C motor locally (or from Surplus Center) will probably cost less than duplicating the conversion for the original B&S pump motor, although if you're doing the 9-wire to 12-wire conversion yourself it would remain an economical option.


    (If you operate the M-G from a Cedarberg 7.5 HP heavy duty static ... no longer available, I'm told ... as Donie did for quite a while, the three-phase which is generated by the M-G could be back-fed into the coolant pump circuit, and then used to operate the coolant pump motor on internally manufactured three-phase).

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    Here's a clearer version of the second diagram of

    http://www.practicalmachinist.com/vb...46&postcount=1
    Attached Thumbnails Attached Thumbnails sheet_2.jpg  

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    "An essential feature, and requirement of Steelman's idea is a ....a nine-wire motor which has been modified to add the three "missing" wires implicit in that motor's "star point", may be very easily powered by single phase...."

    Peter or anyone who has tried this: I recently consulted a local reputedly knowledgeable motor rebuilder about converting my newly acquired 1943 EE MG unit from 3-phase to single-phase 220 power. Mine is a nine-wire motor (I think). He advised me that adding the three wires was no small undertaking. It would require disassembly of the MG unit and heating the windings to soften the varnish and separate the wiring and then a fair bit of work to find the correct windings and then add in the additional three wires. Sounded like this process might easily cost 1K and likely more. Does this sound like correct information?

    How can I be sure my motor is a nine-wire motor and not a twelve-wire?

    I was hoping to avoid the expense of a phase converter.

    This is my first post to this group. I hope I am following proper procedure. Any advice is sincerely appreciated.

    Denis

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    "How can I be sure my motor is a nine-wire motor and not a twelve-wire?"

    They're all nine-wires.

    There is a star-point in there, somewhere, with the three wires twisted together and brazed, then insulated.

    The Steelman concept is dependent upon access to that star-point.

    But, a 7.5 HP "heavy duty static" also works with an M-G model, and that doesn't require access to the star-point.

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    Peter,

    Thanks for your very quick reply.

    Sorry I am so dense, but is that star point likely located in the box pictured at the following URL?
    http://s349.photobucket.com/albums/q...DSCF5344-1.jpg

    Or is it buried in the motor imbedded in varnish and not a little bit of grease? I can see some wires wrapped together and laying beneath wires heading to GS1, GS2, GA1, and GA2. Maybe this is the star point you are referring to? I think you are referring to a connection within the motor case--I just want to be sure I understand correctly.

    Incidentally, I did try to Google "star point" in electrical terminology but did not find much that was helpful.

    Denis

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    The star point will be inside the motor. Like the motor guy said, you got to go inside to find the junction where the leads come together.

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    Well, that finishes the idea of rewiring the motor. It would cost way too much and I would still be wondering if the motor would fail for some age-related reason a few weeks or months later.

    So, I think my next option would be to consider a rotary phase converter. If anyone has any pointers on how to choose a quality converter I would appreciate it. I think I can get one for about 425 with shipping. That would be for a cast iron TEFC motor and panel box with necessary caps.

    Thanks,
    Denis

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    Denis,

    PNW is not a very descriptive location, but assuming that it means Pacific North West, you might try Eylander Electric in Everett, WA. They've been building them for a long time. I bougth several from them (migrated to larger sizes) during the late 1980's and early '90s.

    They are still there and making them. They are a full motor shop as well, so you might ask them about going into your MG set.

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    Thanks, Peter.

    I am just one hour north of you.

    Denis

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    On a nine-wire machine, including a 10EE M-G, I would expect to see the three wires, which would be labeled T10, T11 and T12, if these were brought out, twisted and brazed, then insulated and laced down to the set of coils before varnishing.

    When wiring a nine-wire motor for low voltage, 230 in this case, you actually have two star-points, one which is internal to the motor, and another which you create by connecting T4, T5 and T6 together and insulating these.

    Then, you connect T1-T7, T2-T8 and T3-T9, and, as always, connect T1, T2 and T3 to the line.

    So, for the Steelman method, you have to open up the motor, identify and isolate what would be T10, T11 and T12, and then bring these out as independent leads.

    Steelman's patent shows only two being brought out, and that is indeed the minimum required for his method, but bringing all three out is a more general solution, and allows for greater flexibility, including the 230 and 460 single-phase adaptations which I described earlier.

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    Thanks Peterh,

    I would love to try the opening the motor and isolating the leads if this were something I could do myself. But it sounds like it would require special equipment to do this job.

    From a cost and time perspective, I think I will go with a rotary converter. That is an off-the-shelf solution that will not cost as much as the expense of the work being done in a motor shop and will be much quicker too. If, for some reason, the MG set is not functional when I power it up, I can sell the converter and then I would just put in a VFD setup. I was told the MG unit was working just fine when the machine was "unplugged" a couple of weeks ago.

    I am very appreciative of you providing the information about the Steelman method and your refinements of it. I had no idea this was possible and most of the people I have consulted about my problem have not been aware if it either.

    Denis

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    I dont think you would need special tools short of a socket wrench and sockets. The junctions are made inside of either fish paper or fiberglass tubing. Its just a matter of finding the tube with the three wires you need and bringing them out. Ideally you should use a silphos brazing rod to do the connections but you can get away with normal rosin core solder.

    If varnish is in the way you could heat the area with a heat gun to soften it.

    I am going to be looking at a surface grinder sometime next week and if I get it I may look into doing this mod to the motor.

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    Default MG 12 wire conversion

    My manual for my MG EE doesn't say anything about about changing voltage, but it came from a US Navy base and is set up for 208 VAC, which for some reason the military seems to love, so it may be atypical. Assuming the unit is a nine wire one, getting to the star point wires should not be too challenging, considering how open everything is. Judging by the work I see posted on this forum, the conversion should be well within the skill range of most of the contributors. Probably the most work would be pulling the unit out of the lathe and getting to the windings. I know of an MG that a shop replaced with an AC drive. If I get time and the owner agrees, I may open it.

    Re phase converters, they are mostly just capacitors, sometimes with a motor that idles on the line to improve phase balance. One of my friends (who doesn't want to be identified because of concerns that someone may start a fire) has been using them for years and says that 40 mfd, between one side of the single phase and the third leg, per horsepower is a good starting point. More may be needed for starting the idle motor and then switched out after it reaches near running speed. The idle motor should be larger than the working motor and started first. Since the MG runs continuously, an idle motor may not be necessary. The capacitors should be oil filled motor running capacitors, not electrolytic starting ones, of course rated well above the peak voltage, which is 1.414 times the nominal voltage. I have had two phase converters, one a simple switched capacitor unit on a Bridgeport sized mill and the other a RotoPhase one with a motor. Both worked, but neither delivered full power. If I had to have one again, I would not spend the money for a commercial one.

    Bill


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