What is the proper tool/method

Hey Guys, and Fitch (I hope),

OK....my turn for Questions and Answers (hopefully) on the rotary convertor I'm about to attempt to hook up.

First.... the question.... I have a 3 phase wound rotor motor to use as a convertor for 220VAC single phase to 220VAC three phase. How do I "hook up" with this? Do I short-out the slip-rings and just consider it a squirrel cage, or do I wire to both the rotor and stator, or wire to the stator and take the three phase off the slip-rings (actually I don't think THAT works), or.....or....or???? ..................................................

Now for the description, for those that are still reading. Long-winded, as usual, but it helps me out to do so. Sorry.

I was fairly recently blessed with two freebie 20HP motors. Except, different to any earlier postings here that I recall, these are wound rotor motors.

These were in use on AC geared traction elevators, and were wired for "Dynac" use, which is a 1960's method of getting speed control almost like a DC operation from AC motors, using some special mechanical features and controls and incorporating either 2 or 4 medium size thyratron tubes. Gladly get into details for anybody that wants, but this is merely explanatory/descriptive here as I won't be using any of that mode.

The motors were made by Bull Motors, England, as 208 VAC, 3Phase,

60Hz, 1150 RPM, 67 Amp, all copper windings. One pair of 1/2" X 5/8" brushes on each slip-ring. One of the two motors has had the stator redone locally fairly recently (and that's the one I want to use), and in the external junction box it just has three stator lead connections ,and three direct to the slip-rings connections for the rotor. The second motor has some BAD gooey rubbery disintegration of the 3 of the wires as they feed through the motor frame to the stator, and so I don't want to use this motor; BUT.. it has a small Bull original print diagram in the junction box showing that the motors had 9 leads... 3 to the slip-rings for the Delta connected rotor, and 3 to the STAR stator field pieces and 3 connected together to form the STAR. I assume that the STAR shorted leads are done internally on the rewound motor I hope to use..

These motors are fairly beasty things, with about a 20 pound flange coupling still in place on a 2-3/8" rotor shaft turned down to 2" for the coupling. I may well cut the couplings off later, but I can't pull them in situ here without a largish puller. And I've wondered, and maybe somebody can tell me, if the heavy coupling would actually assist in strengthening the output after reaching full RPM. If so, would heavier be even better? I can pour lead in to do that!. In original operation, this flange was coupled to a special 20" diameter X 12" long brake drum with1" thick flange with the external diameter having pressed in copper bars through it parallel to the motor shaft, so they were pretty heavy and added a lot of inertia "smoothing" to the speed variations in operation.

Any suggestions? Or do I still need to call Marty for the rotary he has for sale????

Take care.

Brian Lawson, Bothwell, Ontario.

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ps..... Also posted to modeleng-list

The 3 leads from the wound rotor would normally go to a starter/speed control box. The box would have a sequence of resistors that would be inserted between the leads coming off the rotor, with maximum resistance for starting/ slowest speed and zero resistance for max speed.

The difference between starter service and speed control service is that for speed control, the resistors have to be able to dissipate heat on a continuous basis. For starting service, they are rated for intermittent duty and don't have to be as big, wattage wise.

I don't have a clue as to what a good starting resistance would be. If I were doing this, I'd probably try 100-200 watts of light bulb for each resistance to see if it would start.

I can check my books at home tonight. I have an old Audel's book on elevator controls and it might have more information.

The cold resistance of the bulbs might be too low to allow soft start. Something on the order of 20 to 40 ohms sounds about right for starting a 20 hp wound rotor motor.

Gary

How about some of those old screw-in heater elements, that have light bulb bases, but are conical ceramic with resistance wire wound around them, for old time space heaters?

Jim

================================================== please reply to: JRR(zero) at yktvmv (dot) vnet (dot) ibm (dot) com ==================================================

Or one of those water heater elements that you some times see in the surplus catalogs. The important part is to take that resistance out of the circuit and short the rotor leads together once its running. The low speed (relatively) wound rotor motor with the rotor leads shorted together to minimize rotor losses ought to make a great converter once its running.

Fitch

Hey Guys,

Me again. Need more help. Doing some interior changes inside the new house.

To create some additional closet space, I want to extend a wall in my back hallway about 3 feet along an easily viewed path. I want to make it longer from an "outside" corner, and that existing corner has a nice metal bead.

My question is: Should I remove that existing corner-bead so I can get at the actual "edge" of the existing drywall for the mud and new tape, or should I hope to just tape over the existing corner-bead to the new portion of the wall extension? I want the extended wall to be "flat" from end-to-end. I suspect that I should remove the beading, but I don't want to damage the ceiling where it joins if I don't need to.

If I should rip out the old corner-bead, I should do that before I frame the extension, because then the beading will be "trapped" and impossible to get out..

All comments and suggestions welcome, but ASAP please, because SWMBO says I'm just dinking around here trying to get out of doing it. and we all, know THAT'S not true, eh!

Thanks! Take care.

Brian Lawson, Bothwell, Ontario.

cross-posted to modeleng-list

If you look carefully at the corner or hold a straightedge against it, you will notice it is flared out, that is the corner is a bit proud WRT the rest of the wall. If you don't take the cornerbead out it will be obvious when you look down that wall. I would go even further and take the sheetrock out a stud bay or two beyond the corner. Also, nailing a new stud up against existing sheetrock/corner bead is not the best practice, better to nail wood against wood with no sheetrock between them.

I definitely would.

I think that this would just create (buried) problems down the road.

should remove the beading,

Indeed, that's the best way to get it flat.

The ceiling went up first, so the bead should stop a "touch" before it.

Right. Note that the bead may be fastened up with tabs punched out of itself with a special tool, or with drywall screws. Nails are possible, I suppose.

You have my sympathy.

Bob

Hey ATP,

OK. I will remove the beading. This was the most descriptive reply, and all makes sense when I think about it too. But it will mean a lot of extra work to cut back to the next stud due to the shortness of the wall. I will also have to be really lucky to be able to do the one "around the corner" too, but I will have at it!!

I've done plain drywalling before, but never had to "join" to any existing, so this is all good advice.

Thanks again to all. See you all on the other side of the wall!!

Brian.

Brian Lawson wrote in news: snipped-for-privacy@4ax.com:

remove the bead. You are going to have to patch near the ceiling anyway. Mud will hide a lot of stuff :)

You need to remove the corner bead entirely. It might not be a bad idea to remove about 12" of drywall in the hallway to get rid of the build-up that tapers back from the corner bead. If you don't do both, there will be a hump in your wall. And definitely do it before you frame. Gary Brady Austin, TX

In order for the result to be flat,

1. Remove metal corner bead which is vertical;
2. Ensure that the added 3' of framing lines up with existing framing

- otherwise there will be a high or low ridge at the boundary;

1. Shave down the drywall after the corner bead is removed - there may be mud build-up prior to the corner.
2. Tack up a strip of drywall on the last new stud (the new corner). Using a drywall square or a string line (no chalk) span the old joint to see how far into the old work sanding/shaving must occur in order to make it look like one original wall.
3. After mudding/taping/sanding the joint, shine a flashlight down the wall at night. I have found ocean waves under such examination.

Dust everywhere, Tom

Hey Tom,

'Nother good >In order for the result to be flat,

My access to newsgroups is through Google and they don't do asap

Lay a straightedge against the existing wall and see if there is room for the mud at the corner, if so leave the corner bead. Because it is an oudside corner you can just hacksaw a kerf through the corner bead 1/2 in from the cieling and remove it from that point down and not disturb the cieling if you do end up removing it.

Hey guys,

Looks like some items of interest for some of us. No lathes or mills though, but have a quick peek.

Take care.

Brian Lawson, Bothwell, Ontario.

cross-posted to modeleng-list XXXXXXXXXXXXXXXXXXXXX

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