Stacking Cores

[uzernaam]

I intend to wind my own transformer core for a custom application. I understand that with higher power requirements and higher currents through the transformer windings means that you need a physically larger core to handle all the flux without saturation.

Assuming you had 2 or more toroidal transformer cores, could you stack them to make something that looks less like a donut and more like a sort of "tube" and wind around them all at once to make for a larger core if you can't find one the size you need to begin with?

[ontoaba]

That was paralleling cores.
I use another way too, connecting flux in series to get 100KV secondary from 50Vprimary with only 1000turn secondary and 5turn primary, 10 cores connected in serial flux.

[DF96]

The problem with stacking too many cores is that the winding resistance goes up. This is because the allowed flux goes roughly as the cross-sectional area of the core, but the winding resistance goes as the length of the periphery. You get the best ratio by having a core which is roughly round/square in cross-section.

So stack two or maybe three. After that you will get diminishing returns.

[AndrewT]

are you talking about stacking toroid cores?

I think the power capability of the transformer and it's core varies as the square of the core area.
If that square rule applies and you stack two identical cores, then you increase the power roughly by four times.
That would need double the thickness (4 times the area) of wire to give four times the current and four times the power with the same voltage.

But you would have to re-wind the primary for this four times capability. Are you able to wind the primary/ies safely?

[luka]

what is your application? you can get several KW form single core, if your freq is ihgh enough. Stacking will increase that. also, depends on app. you could used more cores, wire secondary in series... really depends on what you need to do

[sawreyrw]

The answer to the basic question is yes you can stack cores. Just for clarification, the power handling capablility of a transformer is directly related to the core area, not core area squared.

[AndrewT]

Originally Posted by sawreyrw

the power handling capability of a transformer is directly related to the core area, not core area squared.

Are you sure?

xformer designer.exe gives the following
core 1square inch 31VA
core 2square inch 125VA
core 4square inch 502VA

all for mild steel 0.8T, 240Vac, 50Hz

[Andrew Eckhardt]

Twice the core volume, twice the throughput capacity. The most efficient windings have a square or round cross-section, as has already been mentioned. But for higher frequencies with enough core overdesign sometimes the problem of winding loss gets pretty small.

[AndrewT]

Andrew E,
how do you calculate core volume?
The bit of core inside the turns? which in a toroid is the whole iron.
Or in an EI is the length of the wound leg times the core area?
Or is it the whole iron of an EI?
Or R core the wound lengths (the straight bits) times the core area?

[Andrew Eckhardt]

You calculate the mean magnetic path length through the center of the lamination.

On a toroid this is pi(OD + ID)/2