Identical windings in parallel

[ruffrecords]

Just been checking some output transformers mainly to make sure I have the pinout right before committing to a PCB layout. I measured the inductance of two identical primary windings. I measured them individually and say they are both 25H. If I connect them is series I expect the inductance to be 100H because inductance is proportional to turns squared and we have double the number of turns so the inductance should increase four fold.

Then I wire them in parallel. I am not sure what to expect but to my surprise the inductance remains the same as each winding alone. I have never really thought about this before but I guess the total mumber of turns is the same as for one windings so the inductance must be the same, Is that right?

Cheers

ian

 

[Tubetec]

Maybe theres a lesson to be taken from the dual primary 110/220 mains transformer discussion from earlier,
having the abillity to change ratios in an audio transformer easily without confusion is a good thing , either solder tabs with links or switched ,
It might afford 600 ohm loads to be driven when the need arrises or a better match into 25kohms on the other hand .
Is it a DPDT switch required or do you need four sets of contacts ?

https://www.instructables.com/SIMPLE-ParallelSeries-Select-Switch/thats probably it .
If anything its a usefull way of varying the basic gain of the pre amp .

 

[CJ]

the reason the inductance is the same is because the turns count is the same when the coils are wired in parallel,

you are just providing two different paths for the electrons, resistance of course is about half, but that does not matter since the XL resistance is the dominant factor,

you can think of it as a bi-filar wind with both ends connected,

sometimes they wind a section like that because two smaller wires will lay flatter than one larger wire,

 

[rafafredd]

I have never really thought about this before but I guess the total mumber of turns is the same as for one windings so the inductance must be the same, Is that right?

Having both word in parallel through the same path is just like using a thicker wire, same number of turns. Lower resistance, same inductance.

 

[CJ]

rafa where you been!