A Thought Experiment

[Pete10001]

Is this a wind up?

 

[Andy™]

Is this a wind up?

unlike most 5DW questions of 'whats a fuse', no. this is not a wind up

 

[Sidewinder]

Is this a wind up?

Why would it be a wind up?

It seems then you have an answer so please post away.

I read the question, elsewhere, and it is not something that I had ever thought about, hence the title "Thought Experiment".

Several members have analysed the possible circuits, via resistance and come up with the conclusion that you cannot ID the difference by resistance.

I have posted a circuit analysis that works in theory, but have not tried this out in practice.

So please post the answer, which you obviously know going by your post.

The place where I read this the question has had about 100 replies and all have been further away from the result than those on here, and almost all posted by professional Engineers from all over the world.

 

[Apache]

I've got an endoscope. Can we make a little hole?

 

[Doc Hudson]

I've got an endoscope. Can we make a little hole?

I think you will find that a drill is better for making small holes. But I could be wrong?

Doc H.

 

[Sidewinder]

OK I've done some bench tests and in doing so and going through the theory, my voltage divider will not work with just 3 wires, because even though in a delta motor, the current divides first the 3rd wire is always half way through a voltage divider.

However, the 1/2 voltage thing does hold true.

Back to the drawing board!

 

[SPECIAL LOCATION]

What about physical dimensions....?

We know our 'X' reading and we have two possible solutions for the coil sizes

0.5X   and  1.5X

According to the snake these coils are wound from 2.5mm copper wire....

How about if you calculate the length of copper needed to achieve either of the two possible coil resistances..

Wind them up..

see how big they are and if they would physically fit inside your motor??

By my reckoning you will have two possible coils one of which is three times the size of the other.... 

Then if you have to fit three of the said coils inside you motor housing that you have in front of you..

It just may be physically impossible to fit the one option inside???

Or one may look like its going to rattle around cuz there is just tooo much motor space ...

opcorn

Well I now go back and re propose my previous 'Physical dimensions analysis' of post #100!

:innocent

 

[Sidewinder]

No Specs, the coils are NOT wound from 2.5mm sq copper it is merely the tails presented that are 2.5mm sq copper, or are they, hey don't have to be, it would be unusual for a motor, but, you can't tell, because the detail of the windings is inside the motor and you can't get in there!

Back to the thought cloud mate.

 

[Technician]

Looks like this thread may have slowed down so, here

is another one.

Imagine a motor comes back to you after a rewire but

the starts & finishes have not been identified or tagged

up, or someone has removed the tags/ferrules.

How would, or how could you identify them and what is

the procedure you would adopt?

This happened to me and I quickly thought of a method

and it worked.

 

[Lurch]

Anyone got any further with this, I've just spent 10 mins scribbling and have an idea of testing winding impedance to see if it is star or delta. Seems to work on paper.

 

[Sidewinder]

No Lurch, I've not had time.

I thought that impedance would work, but, you have no terms of reference.

 

[Lurch]

Turns out I ****ed it up, so I'm not anywhere as it turns out, back to the drawing board!

 

[Sidewinder]

I bet you had the same thought process as I did, until you realised that you had mucked up!

 

[Lurch]

I put a 2 instead of a 4. Too many numbers and letters in my head at the same time!

 

[Lurch]

So I was playing with constant voltage sources. Pretty sure this doesn't work either.

Essentially the fact that all the resistances are the same and also relatively identical then any current or voltage you stick across the terminals will always drop by the same amount. I think you will need something more complicated than simply a power source and meter to get the answer to this.

 

[Sidewinder]

You've done pretty much the same what if's as I did perhaps.

IMHO the thing is you have no terms of reference.

I even played with it on the bench with a motor with a full TB links etc. a d.c, constant, limited current source, and a few high accuracy DMM's, Fluke 85, 87, 189 & 289, along with a scope meter 125 & an 867B graphical multimeter, all have various quirks that allow them to measure subtle differences.

I also tried with an LCR meter.

I could not find, nor think of a definitive solution at the time, and I've not given it much thought since tbh.

 

[Lurch]

Are we allowed to connect the motor up to a supply and use a scope ?

Which may not help in reality.......

I thought about that as well, not the full supply voltage though and some RC networks. No matter what I did it all ended up coming back to the same thing, the relative results between star and delta connected windings were the same so the input and output ratios were still the same.

 

[Blue Duck]

It's a shame technician hasn't been online since June 14.

Nice fellow too.

 

[Lurch]

It's a shame technician hasn't been online since June 14.

Looks like he wore his enter key out.

 

[Marvo]

You've done pretty much the same what if's as I did perhaps.

IMHO the thing is you have no terms of reference.

I even played with it on the bench with a motor with a full TB links etc. a d.c, constant, limited current source, and a few high accuracy DMM's, Fluke 85, 87, 189 & 289, along with a scope meter 125 & an 867B graphical multimeter, all have various quirks that allow them to measure subtle differences.

I also tried with an LCR meter.

I could not find, nor think of a definitive solution at the time, and I've not given it much thought since tbh.

 If you have a motor and a thermal camera feel free to try my battery and Flir camera suggestion.