Electric Motor Secrets

[theremart]

Here I have a video that might be of some interest. I must say that not all might be clear since this a part of a bigger video but is shows that although they are all silicon steel there are very big differences in core behavior especially when it comes to residual magnetism and how fast a core releases its static magnetic fields. Also you will see some coil 'tricks'. It boils down to that steel grain orientation plays a big role.

http://home.planet.nl/~sintt000//02_.../CoreTests.wmv

Regards,
Steven

Awesome video, I also have been testing cores to see draw for the ssg, I think from your video I have a means of testing good core material from poor.

[Aaron]

free download: Armature Winding and Motor Repair

Thanks!

Here is a link so anyone can get the book for free in dejavu, pdf or txt format:
Internet Archive: Details: Armature winding and motor repair; practical information and data covering winding and reconnectig procedure for direct and alternating current machines, compiled for electrical men responsible for the operation and repair

Hello Jetijs & All,

One of my favorite books on this subject is - Armature Winding and Motor Repair 1st edition (1920)
Practical Information and Data Covering Winding and Reconnecting Procedure for Direct and Alternating Current Machines, ... Armature Winders in Electrical Repair Shops

- Schpankme

[nali2001]

Cores

Here I have a video that might be of some interest. I must say that not all might be clear since this a part of a bigger video but is shows that although they are all silicon steel there are very big differences in core behavior especially when it comes to residual magnetism and how fast a core releases its static magnetic fields. Also you will see some coil 'tricks'. It boils down to that steel grain orientation plays a big role.

http://home.planet.nl/~sintt000//02_.../CoreTests.wmv

Regards,
Steven

[Schpankme]

Winding and Motor Repair

Jetijs,

You only have 24 coils to wind, so by the time you wind the last ones, you'll be really good at it.

Peter

Hello Jetijs & All,

One of my favorite books on this subject is - Armature Winding and Motor Repair 1st edition (1920)
Practical Information and Data Covering Winding and Reconnecting Procedure for Direct and Alternating Current Machines, ... Armature Winders in Electrical Repair Shops

- Schpankme

[Peter Lindemann]

Insulators in the Slots

Steven,
thanks for the explanation and the picture. But why is such a winding method not possible in our case? Why can't we just prewind each coil and then just put it in those slots? After all windings are done, we simply need to solder the needed coil ends together in series.

Jetijs,

Everything Lighty and Steven are saying is correct.

All motors that I know of are wound by hand. To prevent the damage at the edges, where the wire comes around the stator section, they insert a thin layer of material in a U shape to fill the slot. You can see these insulators in Steven's photograph. This is what Lighty was referring to as sheets of mylar. Even a thick paper is sufficient for this. Here in the USA, we use a thick paper material for file folders. It's about .010" thick (ten thousandths of an inch). If you have a similar material, just make your own slot insulators. Make them slightly longer than the slots, so the wire bends the paper around the edge as you wind the coil.

Another trick is to glue little pieces of wooden doweling cut in half to the ends of the stator pieces, to produce a semi-round end to the stator cores. This, along with the paper insulators makes winding the coils easy (ha ha ha) and prevents all possibility of breaking the insulation on the wires.

The "trick" to being able to wind a good coil is the ability to provide tension on the wire. If you mount your stator in a vise that is firmly mounted to your work bench, and then tie the beginning of the wire strand you are winding to some immovable object, then you will have BOTH HANDS free to manipulate the wire and keep tension on the turns as you make them, as well as on the turns you have already wound. It is a tiring and tedious operation. Your hands get very tired, but HEY, that's how it is done!

Wind one coil, leaving about a foot of extra wire at each end. Fill each slot to about half way. Then, unwind this coil and measure the length of the wire. This is the standard length all the coils will be. Cut 23 more lengths of wire at this length and wind each coil separately. Tie off the ends of each coil when it is done.

You only have 24 coils to wind, so by the time you wind the last ones, you'll be really good at it.

Remember, magnetic field strength is AMPERE-TURNS. You need to be able to get enough turns on the pole faces to create sufficient magnetism to attract the rotor. Since this is very similar to Steven's design, you may wish to take directions from him on what wire size to use and how to switch the currents.

This motor is a much more ambitious project than your first design, but if you stay focussed, you can do it.

I say, "GO FOR IT!

Peter

[Jetijs]

Steven,
thanks for the explanation and the picture. But why is such a winding method not possible in our case? Why can't we just prewind each coil and then just put it in those slots? After all windings are done, we simply need to solder the needed coil ends together in series.

[nali2001]

Winding

Yes winding these cores is a real pain. At least the way we/you want to wind it. I have been in some motor winding shops and they indeed do these 3 phase windings by hand and it is easy since they just pre wind much of it on a wooden form or something and than chuck the whole lot into the slots:
http://normandy-repairs.com/images/p...INDING%202.jpg
But that is not possible in our case. But anyway I had to rewind the thing at least like 5 times because somewhere along the way there was a short (use the ohm meter) I finally used cloth soaked with resin/epoxy on the edges. When this hardens it is a very tough and isolated surface. I still can not think of another realistic way of doing it otherwise.

Your core is from what I can see 90% identical to mine. Although I had no weldings seams. But that is no issue.

Regards,
Steven

[lighty]

but there is the same problem Steven had, the sharp edges of the cores scrap the isolation of the windings off and that makes a short to the core. The isolation will be a hard task.

Contact the winding shop and convince them to sell you some mylar sheets. They're usually used for isolation and to prevent chaffing in the windings of the motor. There are some similar materials also used by winding guys that you could use and they're all extremely cheap.

[Jetijs]

Peter,
I like your idea of three phases I tried to do some test winding today to see how hard it will be. I had a gauge 21 and gauge 16 wire. First I tried the AWG 16 wire, I must say, that this is very hard, because the wire is thick and hard to straighten out in the long gaps. Then I tried the AWG 21 wire. This was a bit easier, I could get about 15 turns on a single core so that there is enough space for 15 windings on the next core, but there is the same problem Steven had, the sharp edges of the cores scrap the isolation of the windings off and that makes a short to the core. The isolation will be a hard task. Also it is very difficult to make a bifilat coil arount each core. I think that If I used a thinner wire, it would be a lot easier, but in that case I would need to run the motor on higher voltage. How do they wind the motor cores industrially? I doubt that they do that by hand
We have a small motor rewinding company some 40 miles away, I will wisit them and see how they do this. Maybe they can help me with this

Edit: I figured, that if the coil rewinding company wont be able to help me, then maybe I could make my own startor core with a design similar that in the pictures above. That design allows the startor core to be machined in the lathe and to get the maximum precision and minimal air gap. My previous startor could not be machined in a lathe because of its geometry and that was a big problem. Also, If I will make my own startor, then I can make as much cores as I want and also the space between them will be adjustable. The winding of such a custom made core would be alot easier, because there would be more space between cores. I will make a 3D CAD drawing of such startor and post some pictures, then you could tell me what you think

Thanks,
Jetijs

[Peter Lindemann]

An Idea...

Hi all
Just realized that I forgot to include the switching current in my calculations. If I subtract that form the input current, I get a better IN/OUT ratio. I recalculated my data and found out that instead of 24% I am getting back 30% form my core. It is still too little, but this is just for information.
Anyway, I got my hands on a bigger induction motor core. I took it out form an old Russian 180W AC motor, that I found laying around. The plates are not isolated form each other, you can see four welding stitches on each side of the core. I think, that the hardest part will be the wiring of this core, I will this and see how it goes. If I manage to do this, the rest should be easy





Thanks,
Jetijs

Jetijs,

The cores look fine and I doubt if the welding ribs will cause much of a problem. What I suggest is this, wind each leg with at a bi-filar winding (so you have the option of an isolated output) and bring each set of windings out by themselves. This way you can series or parallel various windings to create different configurations without having to rewind the core.

My recommendations would be to make your first rotor have eight (8) pole faces to match with 1/3rd of the stator core pole faces at one time. The motor would be wired so there are three sets of 8 coils to come on sequentially. The cycle begins when the #1 coil set comes on to attract the rotor, turn off, and then SKIP the #2 pole face. Next, the #3 coil set would turn on and attract the rotor, turn off, and then skip the #1 pole face again. Next, the #2 coil set would come on and attract the rotor and turn off. Then skip the #3 coil set to start over at the #1 coils.

This gives the motor the time to breathe I am talking about. These pole faces are quite narrow, so you will need some pretty big gauge wire to get a rapid rise time.

You'll need three optical sensors for the commutator control.

The fact that your stator section has 24 sections makes this design possible. This may have good possibilities.

What do you think?

Peter

[Jetijs]

Hi all
Just realized that I forgot to include the switching current in my calculations. If I subtract that form the input current, I get a better IN/OUT ratio. I recalculated my data and found out that instead of 24% I am getting back 30% form my core. It is still too little, but this is just for information.
Anyway, I got my hands on a bigger induction motor core. I took it out form an old Russian 180W AC motor, that I found laying around. The plates are not isolated form each other, you can see four welding stitches on each side of the core. I think, that the hardest part will be the wiring of this core, I will this and see how it goes. If I manage to do this, the rest should be easy





Thanks,
Jetijs

[Peter Lindemann]

Thanks For The Up-date

Well there is not much going on with my motor since it is broken. You know the ends parts of each side of the motor are made of an aluminum plate with a Plexiglas plate on top of that, which actually holds the bearing. Well these two plates are glued and also bolted together and after that machined at the same time to get the accuracy needed. But not too long ago I lubricated the bearing and so there was also oil on the Plexiglas plate. Well now stupid as I am I took a cloth with some thinner to clean it off. Well thinner and Plexiglas gives you a real interesting effect. The thinners actually creeps in all these sub-little machined grooves and kind of works its way from there into the Plexiglas cracking it like mad. In just 2 seconds the whole plate was cracked up. There are countless of cracks running the whole length of the Plexiglas. Looks the same as these 'fractures' you see sometimes in crystals. So in other words it is useless now. And on top of that I have no material right now to remake that end piece. So don't expect results any time soon.

Steven

Steven,

Thanks for the up-date. I'm sorry to hear of the breakdown of your plastic end plates. So, at this point, your excellent motor design remains untested.

I really appreciate your participation in this forum. Your advanced insights are very useful to other experienced model builders. I know it seems that I tend to suggest things that contradict your posts, but I am trying to illuminate a path for less experienced experimenters. Your suggestions and solutions are viable and I was looking forward to hearing of the test results of your motor. So, again, I'm sorry that will be delayed.

OK, Everybody: This is a good reminder for experimentalists that all kinds of unexpected problems can arise during a project like this. And even seasoned model builders, like Steven, run into these things. So, if things seem to being going slow for you, don't be discouraged!! This is what R&D looks like.

Peter

[Jetijs]

That's a shame, Steven.
I also had some breaking experience with plexi glass. It does not love any acids or solvents and breaks at the weakest stressed spots. I found that polycarbonate works a lot better, it is as easy to machine, but it is more dense and wont break if bent or hammered. Maybe you can get your hands on that?
Keep us informed about your success
Thanks,
Jetijs

[nali2001]

Some input

One thing I feel that also must be addressed is that, on the one hand it is nice to have coils with a low impedance since it gives good squarewave rise times. But on the other hand one needs to keep in mind that if your core material can not 'keep up' with that sharp rise time there is actually a loss. When you overlay the rise time of the coil and the maximum magnetic rise time of the core material you can see what you are wasting. The coil should not be faster then the core material will allow.

Plus also it might be advantages to reverse the input polarity of each attraction cycle since if you are constantly blasting the core with the same polarity it might be causing some 'permanent' residual same polarity magnetism while running. Especially in non grain oriented steel. (this can't really be tested at stand still) which hinders real magnetic gradient changes. Reversing the polarity actually pulls the magnetism to a zero state before it reverses. So more drastic magnetic changes should occur.

Regards,
Steven

[nali2001]

Motor

Well there is not much going on with my motor since it is broken. You know the ends parts of each side of the motor are made of an aluminum plate with a Plexiglas plate on top of that, which actually holds the bearing. Well these two plates are glued and also bolted together and after that machined at the same time to get the accuracy needed. But not too long ago I lubricated the bearing and so there was also oil on the Plexiglas plate. Well now stupid as I am I took a cloth with some thinner to clean it off. Well thinner and Plexiglas gives you a real interesting effect. The thinners actually creeps in all these sub-little machined grooves and kind of works its way from there into the Plexiglas cracking it like mad. In just 2 seconds the whole plate was cracked up. There are countless of cracks running the whole length of the Plexiglas. Looks the same as these 'fractures' you see sometimes in crystals. So in other words it is useless now. And on top of that I have no material right now to remake that end piece. So don't expect results any time soon.

Steven