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aw... I don't want to disagree with you too much... and I'm a big fan of the lower numbered M core materials.... but that said, I think you've oversimplified important technical and performance issues when you make a near universal claim as above. As with most things--- there are advantages and disadvantages--- to using say M4, M3, M2 etc. First off we should recognize that M6 is itself no slouch. It's losses are a third of the next lam grade below it. It's perm several whole numbers greater than the lam grade below it. It's highly processed to acheive it's performance parameters. And for many applications has a desirable "BALANCE" of properties. And look at the level of performance that we can obtain with the use of M6 laminations. With this grade of lamination it is possible to achieve 100 plus henries of inductance per thousand ohms of relected primary impedance. And still get frequency response within the limits of plus or minus one db from 20 hz to 100khz or greater. Not too shabby. Nothing to be ashamed of. now, you might ask or assert that one of the super M lams (M4, M3, M2, etc) would make this "better"... the super M's are neat... I like them very much... in many applications but not all applications. The super M's have less hysteresis losses and decreased eddy current losses compared to M6 and some measure of greater perm than M6. So all is good, heh? Back to advantages and disadvantages--- is there a fly in the ointment--- I'll pick out two considerations to explore--- one of the drawbacks to the super M's is that they are thinner than M6.
M6 is nominally .014" thick. M4 is nominally .011", M3 .009", and M2 is nominally .007" thick. While many folks will assume this to be auniversal plus--- argument that the thinner lams decrease the eddy current losses (which is true)--- but in the greatest majority of applications with M6 edddy current losses aren't much of a gremlin to begin. On the flip side--- the super M's because they are so thin--- does present one drawback on their own. It's that they have a poorer "stacking factor" (often referred to as the K factor). the stacking factor is a measure of how much of your nominal stack is actually comprised of "magnetic material". No matter the grade of lam all of the individual pieces (say in an EI type lam) are individually insulated from one another. this insulation is very thin... but it does have some real world thickness to it... so that the K factor (stacking factor) will always be less than 1 (one). How much less you ask? Partly depending on the craft skills of the person doing the stacking--- the default value for M6 is in the range of say .9 to .92 (or 90% to 92%)... awe... now those thin lams (which have the same insulation thickness on them) are going to have a decrease in the stacking factor... and the thinner the lam gets the worse the stacking factor becomes... (I'm doing the stacking factors for the super M's from memory)... so M4 drops the stacking factor to say the range of .8 to .85, M3 drops even more (so you have even less actual magnetic material in your stack), and M2 lowers the boom-boom even more... what this does is that instead of having a two inch stack of lams we have something less than two inches effective... use the multipliers above... so tha with M6 we might have 1.8" of stack... and with M4 say 1.6" of effective stack.... the less stack we have--- is going to increase our AC flux density (all other things being equal)--- we will end up working the core material harder with one of the super M's than if we used M6. and this is a linear relationship--- if we decrease the core stack by 10% we'll make the AC flux density 10% greater. AS AC flux density varies (inversely) with frequency--- the less effective core stack we have reduces the power handling of the structure as you go lower in frequency. To compensate we could make the core stack greater--- an easy fix, heh? Aw... it is a potential "fix" but now if we increase the stack we will make the winding coil larger and increase the capacitances of and within the coil itself--- which is not a good thing. Our mean length of turn (of the copper circuit) will be greater which means we will increase our winding resistances (DCR) and hence our copper losses will become greater. So... though they are in many respects super materials--- the M4, M3, and M2 lams must be evaluated from the vantage point of both the strengths as well as the weaknesses of the material.
MSL
Builder of MagneQuest & Peerless transformers since 1989
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