Saturation flux density of this ferrite core?

[Al (astral highway)]

EPCOS B64290L82X830

I only have path length, inductance factor (Al=8.7uH)and effective cross section area (Ae).

It's N30 material.

The datasheet lists about 100 abbreviations that are generic but I just can't find saturation flux density for this particular core.

Any help much appreciated,

Cheers!

[Al (astral highway)]

Even an approximation would be helpful if any power engineers out there can help. I’m guessing 0.3T from other cores of similar dimensions and material, but an informed view would be a far better thing here. Trial and error is too fiddly for the critical number of turns I need.

Thank you

[Radio Wrangler]

They expect you to calculate it yourself.

Saturation is progressive. It is a curve not a single number. So you're supposed to look at the datasheet for the material, decide how much reduction in inductance is acceptable, and then look at the flux density associated with that level of saturation.

Then looking at the path length and cross section area and the permeability and calculate the gap length and then calculate the MMF needed to reach that flux density and then you have your chosen point in ampere turns.

Helpful, aren't they?

You'll need to read any of the texts or applications notes on magnetics design to find the formulae.... BEWARE OF STUFF WRITTEN IN OLD IMPERIAL UNITS

David

[Al (astral highway)]

....you're supposed to look at the datasheet for the material, decide how much reduction in inductance is acceptable, and then look at the flux density associated with that level of saturation.

Then looking at the path length and cross section area and the permeability and calculate the gap length and then calculate the MMF needed to reach that flux density and then you have your chosen point in ampere turns.

Helpful, aren't they?

Haha! I wasn’t expecting that level of interdependencies! They could give a range in typical usage, if they wanted to be helpful?

The array of abbreviations associated with magnetics is bewildering. I only need a handful of variables, so at least that’s on my side!

Thank you David

Cheers

[trobbins]

It can also be the core loss that dictates what flux density you reach.

Practically you can set up a test coil and check for change in current ramp rate with a step voltage applied - easy if you have a storage scope, and it can confirm what gap / AL factor you may have.

[Ed_Dinning]

Hi Al, typically SMPS operate at 250mT so that everything stays reasonably cool; a good figure to start with.
As David mentioned, stick with MKS units. The mixture of Imperial, and the pointless cgs as taught in schools, has been sufficient to total put people off magnetics for life!!!

I may be in London on 12 Nov, will you be about?

Cheers, Ed

[kalee20]

A good rule of thumb for ferrite is stick below 0.3T.

Some grades of ferrite saturate at 0.4 T or more - but you're well round the knee of the B/H loop by then!

As with generic transformer iron, sometimes you have to operate well below saturation anyway - you just might need more inductance so have to use extra turns; or you might need to reduce core losses (which kick in at a few hundred kHz or a few MHz, depending on ferrite grade) so you decide to operate at a lower flux density.

Even if the material is absolutely brick-wall square in its saturation characteristics, when fashioned into a toroidal shape, the core exhibits a 'soft' shape. That's because , given any current through a winding, the flux isn't uniform in the core - more exists on the inner circumference (where the path length is short) than the outer. So the inner saturates first, effectively dropping out of consideration, the active cross-sectional area reduces, and the inductance drops a bit.

You won't go far wrong if you keep below 0.3T average, though.

Ferrite cores are rather uncertain if you want a specific inductance. They vary massively with temperature. A design which depends on a particular inductance is a bad design - like expecting a particular hfe for a transistor. Usually inductance is not important as long as it's high enough; if you do need a specific inductance, you use a ferrite core with an air gap (where the characteristics of the precision-ground gap dominate the situation).

[John_BS]

N30 material (Siemens MnZn) saturates at about 350mT @ 20 C, and 250mT @ 100 C. It's specified for low power wideband applicaitons, e.g pulse transformers, rather than power applications.

Source: Snelling: Soft Ferrites.



John

[Al (astral highway)]

Originally Posted by Ed_Dinning

As David mentioned, stick with MKS units. The mixture of Imperial, and the pointless cgs as taught in schools, has been sufficient to total put people off magnetics for life!!!

Thanks, Ed! I'll remember that!

Originally Posted by Ed_Dinning

may be in London on 12 Nov, will you be about?

Yes, at the moment it's pretty clear! I'd love to meet if the timings can work out. Maybe drop me a PM with details and let's make it happen!

[Al (astral highway)]

Originally Posted by kalee20

A good rule of thumb for ferrite is stick below 0.3T.

...

Even if the material is absolutely brick-wall square in its saturation characteristics, when fashioned into a toroidal shape, the core exhibits a 'soft' shape. That's because , given any current through a winding, the flux isn't uniform in the core - more exists on the inner circumference (where the path length is short) than the outer. So the inner saturates first, effectively dropping out of consideration, the active cross-sectional area reduces, and the inductance drops a bit.

Great insight into what's going on here, Peter. Thanks!

Of all the aspects of power electronics, these magnetics seem among the most complex I've encountered to model accurately in order to get the results needed.

[Al (astral highway)]

Originally Posted by John_BS

N30 material (Siemens MnZn) saturates at about 350mT @ 20 C, and 250mT

Thanks, John. The concensus does seem to be as you say around the 0.25T to 0.3T level for these sorts of cores.