Making own core from permalloy

[Spencerleehorton]

Hi,

Had a few ideas about making my own core for transformers and wanted to share and get some info.
I am aware that these are just ideas and probably have been thought of before and therefore already not been used for reason I'm not aware of, but that is really what I would like to find out.

Bobbin - with a lathe I can make a bobbin fairly easily from various plastics

Permalloy seems to be a good material to use as this is available in sheets.

My idea has ranged from using wire through the core area or sheets as per the EI standard way of doing things.
I understand that normally each sheet of the lams is insulated on the flat surface but not on the sides so the E and I connects continuity wise when put together, and I'm assuming this helps the magnetic field to radiate?
Each lam working independently of each other so to speak rather than a big lump, this must be so the direction of the flux is limited or rather forced to work across the lams? (Physics isn't my strong point!)
One ideas I had was to thread a insulated permalloy wire through the core, making two horse shoe type shapes then connecting each wire at the bottom, quite a task but using quite thick material I'm sure it could be done in principle, the only draw back would be each wire would only essentially not be insulated at the end, as compared to a lam where it is only insulated on top and bottom flat surface?
In principle what negative or positive effect would this have?

My second idea would be to use permalloy sheet and you can get this insulated on one side and has sticky on the other, so essentially insulated on both sides, if this could be wound starting inside the bobbin, having both coils going round as per an E and I would be, this in my mind would be much better.
Only draw backs I can see then is each wind round the bobbin would be one long piece of permalloy, what effect would this have? Negative and positive?
And it would have to be wound tight enough.

Would be interested in your thoughts.

Regards

Spence.

 

[PRR]

Don't bend Permalloy. It turns into plain iron.

Bending soft iron wire (fence wire) can make a good transformer if you are not seeking super high impedance.

 

[Spencerleehorton]

Hi,

Are you able to answer some of my questions as per above on how it's insulated and connected please?
Fence wire would be easy to work with but its not insulated? And connects differently.

Regards

Spence.

 

[CJ]

involved process, those lams, better off just buying them or the transformer, probably cheaper in the long run,

here is a good read>

http://www.sowter.co.uk/pdf/GAVS.pdf

 

[Spencerleehorton]

Hi,

I just wanted to understand the physics of it really, i'm understanding the flux as sort of the same thing as electrons travelling in a circle round the PRI/SEC windings but in a 3D shape, so that at the core there would be maximum permeability as the magnetic force would be strongest here?
but like i said physics certainly isn't my strong point, and also like i said before i'm not too worried as i have a company which can do the bobbins and core in M6, i'm just interested in the inner workings of what is actually going on and what would happen if it was played around with.

regards

Spence.

 

[Spencerleehorton]

Also just wanted to add, they do make Permalloy which is in very thin sheet form which bends, this must be ok to use right?

regards

Spence.

 

[Dylan W]

As I understand it, the issue with permalloy is that its perm goes way down when it's even a little bit mechanically stressed (bent, chipped, etc). That's what PRR's getting at. You'd have to reanneal once it's formed into the shape you want, which may be too involved for DIY--you'd have to research the temperatures/heating curve used, some of which may be proprietary info.

Top of pg 769 in CJ's link, which is a goldmine of info, btw.

 

[Spencerleehorton]

yes thats great advise and info indeed, could anyone suggest any other material, i'm just curious if there is another way to skin this cat!!

regards

Spence.