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Inductor saturation

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Mosaic

Well-Known Member
Hi:
I expect to drive an ac rectified pulsed current (6A peak DC) thru this linked inductor @ 120hz to charge a couple large 15KuF caps.

https://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_387268_-1

Spice shows an oscillating AC current of around 6 to 13A P-P in the inductor. Pi filter arrangement with 2kUf, 220u inductor, then 30KuF.

Since the DC saturation is 5.8A is this inductor adequate or will it go into saturation?
 
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Anytime you go over the peak rated current of magnetic core inductor, it will start to seriously saturate. If you look at the data sheet you will see that, even at its rated current, the inductance is down nearly 50% from the low level AC value.
 
The core will go into saturation.
It would be nice to know what the two wave forms are? Your spice does not show saturation because it is not using real world inductors.
 
Hmm, Perhaps if I crack the toroid (in a vise) I can bump up its saturation at the cost of some inductance. I have quite a few of these.
 
Hi,

Cracking the core and then gluing it back together again means the permeability of the core goes down which means the inductance goes down which means the peak current goes up. The inductance could go down quite a bit so it may still saturate depending on how high the peak goes up to.

If you have "quite a few" of them then you can try putting two in parallel. That will give you one half the inductance at twice the rated current approximately. Once half the inductance means the peak still goes up, but it may not go up as far as with a cracked core. You'll have to check for saturation by looking at the current wave shape.
 
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Ok I got a proper saturation model for the inductor and using the spec sheet I spice'd this 'Flux = 246u*11*tanh(x/11)' as an array of 2 series rows of 4 inductors placed in parallel, thus using 8 inductors (total 0.108 ohm). This uses the 123uH inductance @ max current to derive the 246uH.

Spice shows the current spike when the average current thru the inductor array exceeds 11A. My spec calls for about max 10A avg so that should be ok.

I find post # 9 here useful!
https://www.electro-tech-online.com/threads/transformer-design.127986/
 
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Hi again,

Oh you have that many that's good. Yes, connecting two sets in series and then putting those in parallel brings us back to the same inductance at twice the rated current. You've taken that basic concept farther and so it seems you have what you need now.
 
if you need inductance is 120uH at DC current, you can use the choke, core is powder iron, it can pass some DC current, however loss is bigger, the inductance at 5.8A drop off 40%, it is not very good, you can use Fe-Si-Al core to make the choke, better DC bias and loss, however price is expensiver than powder iron.
 
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