Splitting and rejoining ferrite cores

[JulesP]

I'm planning on constructing a step-up transformer using a circular ferrite core (see pic) and wondered if it's feasible to cut it into two semi-circles (which will lose some material) to make it easier to wind the 100 and 300 turns and then to glue it back together?

I appreciate that it wouldn't perform as well in RF terms but as a transformer would it still work ok?

Thanks

 

[ronsimpson]

Ferrite is very hard, brittle and probably will shatter if you stress it. I have had bad luck cutting it. Not good luck even sanding it.
There are machines that wind wire on toroidal cores. It is fun to watch. I have done it by hand some.

It seem wrong to have a toroidal core that does not spill flux into the air and then cut it which will kill that effect.
Here is a picture of a large "CRT" yoke core that is split. It is wound as two pieces.

To make a transformer use transformer parts.

Here is a off the shelf part you can get ready to do.

There are some youtube videos that show how to wind. winder
Found a better video. winder-2
This shows how the machine is loaded. winder-3 and #4

 

[JulesP]

Thanks, so you're saying use the right kit for the job. I've heard that one can get self-assembly transformer kits as an alternative to off the shelf units so one can customise the item. However, it can't be too hard to find a 3-4 step-up unit of the right power.

 

[ronsimpson]

What voltage, current, power level, any information will help.
coilcraft
Link to a series of transformers that are "configurable". It is pretty clear what (voltage*time) and (current*inductance) each transformer can handle. There is a wide range of inductances. You need 100:300 so connect three windings in series to make 300 and you could connect the last three windings in parallel for the 100.

 

[gophert]

Semicircular and air-gapped circular cores exist on the market. Any ferrite core (E core, semicircular cores, etc) all have specified tolerances of flatness to insure maximum magnetic coupling to complete the magnetic circuit. Any attempt to cut/break a ferrite part will cause roughness and poor magnetic coupling.

 

[unclejed613]

actually, a toroid can be wound easily by hand. you need to figure out how much wire length you need and pre-cut it (if in doubt add extra length. then you need a piece of plastic in the shape of an elongated butterfly that fits not only through the core, but through the smallest remaining diameter after all the wire is wound on the core... something like this

______________________________
\_                          _/
   \_                     _/
   _|                    |_
_/                         \_
/_____________________________\

then wind the wire onto the shuttle (piece of plastic... you want something stiff, not HDPE which bends after you start filling it with wire). you wind the first turn by hand, then pass the shuttle through the core for each turn.