Electronic – Transformer: Number of turns om primary winding

transformer

I'm researching electromagnetism for a guitaramp project. I would like to experiment with different homemade transformers.

Find myself stuck trying to get a grip on the effect of the number of turns on the primary winding in relation to the risk of a saturated core. One the one hand more turns imply more inductance according to Inductance (L) = number of turns (N) times magnetic flux(Wb)/current (I). On the other hand it is well known that decreasing the number of turns on primary will increase flux density and the risk of saturation. I guess it must be the relation between number of turns and current that gives the answer, but find it hard to find good explanations. Anyone with a good advice?

Best Answer

I guess it must be the relation between number of turns and current that gives the answer

Correct - amps x turns is called magneto motive force and it's what drives magnetism and potential saturation. It's related to the magnetic field strength (H) by dividing MMF by the distance the flux path takes around the core so: -

$$\dfrac{MMF}{\ell_e} = H$$

And H is related to flux density (B) by the permeability of the core material: -

$$B = \mu\cdot H$$

So, too much flux density goes right back to having too many ampere turns.

For AC, the inductance of a transformer winding is proportional to turns squared so, if you double the turns you get 4 times more inductance and one-quarter the current for a given voltage/frequency. This generally means that more turns means less core saturation because although the turns might (say) double, the amps reduce to a quarter.

The picture below (hopefully and intuitively) explains how inductance is proportional to turns squared: -

enter image description here

Anyone with a good advice?

That's dependent on the reader!

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