Author Topic: Micrometals torroid core loss calculator for PFC inductor?  (Read 396 times)

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Offline Faringdon

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Micrometals torroid core loss calculator for PFC inductor?
« on: December 03, 2022, 09:40:08 pm »
Does anyone understand the Micrometals "inductor designer" and "inductor analyzer" tools?

We have a spec for PFC inductor
HF130125-2 Torroid
50 turns of 0.4mm ECW
115VAC input

Myself and a consultant SMPS designer have come up with 8W of core loss for this.
But The micrometals inductor analyzer gives 6W of loss.
Another method, called the dB/dH method gives 9.8W of loss.

We are wondering which result is correct?

The Micrometals tools are a little unusual......

They ask for "peak inductor current", but it looks like they mean "mains peak current input level"
They also ask for the inductance at the peak inductor current...but again, they must mean at the mains peak input current level.
Does anyone know?

The "inductor designer tool" also gives turns of far too thick wire, in two  strands, and with less than 0.2W of winding loss, meaning you could have used much thinner and easier wire, in a single strand.
The Inductor designer recomends  57 turns of 2 strands of AWG17 round a MP130125-2 torroid, which isnt physically possible.
The micrometals inductor designer....IMHO, always assumes that you are doing very highly continuosu mode PFC inductor , with little ripple current....because they take the "peak inductor current" as being the "peak mains input current". They also work out the delta I (pkpk) be assuming that the inductance is constant across the switching period, which of course, it very nearly is if your inductance value is very high.

..However, people like us are going PFC with a small-as-possible  torroid......and so we end up with much ripple current in the inductor.....and it is thence that the micrometals inductor designer is not  so useful for us.....because their inductor current ripple calculation, as discussed, assumes one value of inductance across the switching period. And that is deffo not the case with these non linear inductors.
If we look at the attached excel, the green columns show the build up of B as current increases in the torroid (non linear) inductor.

In the “accumulated B” column, the accumulated B builds up as the current rises…this is the correct behaviour, since B is akin to energy and one cannot just suddenly get rid of energy.

The “Simple B” column shows a simple calculation of B from B=uo.ur.H and takes the new ur as that at that current level…..

…This “simple B” column is quite clearly incorrect….as the current rises above 10A, the “simple B” starts going down!! This cannot be correct…..the B must go up, since you cannot just suddenly get rid of B, because B is a form of energy…….if the B really went down, then what happened to that energy?…the energy stored in the magnetic field…it cannot simply be gotten rid of…..conservation of energy is the law of physics at play here.
Would you agree with the above?
It must be so, if it were simple, then the Micrometals web site would show it so....but Micrometals do not show it at all...they do not offer a bona fide calculator for core losses**
**...well, you mjust take the micrometals core loss calculator with a big pinch of salt with PFC inductors........the more inductor ripple current you have, the more salt you take.
Micrometals assume that the peak inductor current in a PFC, is the peak mains input current.....they also calculate the inductor ipkpk, using only one value of inductance over the whole switching period. (and that L value is that value of L that you get at the peak mains input current level)
...Now this is incorrect....but if you know its going on.....then you can kind of work with it, and assess just how much "pinch of salt" you must take.
« Last Edit: December 04, 2022, 01:38:05 pm by Faringdon »

Offline jonpaul

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Re: Micrometals torroid core loss calculator for PFC inductor?
« Reply #1 on: December 07, 2022, 08:34:26 am »
Farrington Treez Time Sink....FTTS

the  loss calculator is a ballpark estimation, way too many unknown variables

The result will be +/-50%, not a precision figure.

Founder of Micrometals, Jim C. old friend, a super engineer, a ham, decade's of experience.

Don't ask us, send your babble to Micrometals technical support.

Sadly  for Micrometals, you will never generate a product design nor be a customer.

Another's 5 minutes down the black hole of time, FTTS


Jean-Paul (EE 1968, the Internet Dinosaur)
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Offline Faringdon

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Re: Micrometals torroid core loss calculator for PFC inductor?
« Reply #2 on: December 11, 2022, 02:15:34 pm »
Thanks, though the attached is the bona fide way to calculate core losses in  micrometals  alloy powder torroids...
This will literally bring Micrometals Alloy powder cores (and others) for PFC to the world.....

So, The method of calculating core losses as in the attached excel concurs very well with the "Inductor anlyzer" method on the micrometals website.

So....the method is......
1...use their relation for ur vs H to get the ur value at each current step from say 0.1A to 10A say....stepping up by say 0.1A at a time
2....Then calc the H and dH for each step
3....then calc dB from dB = uo.ur.dH
4...then accumulate the dB into the running B total.

...thats it.

Also, there is further important news on  alloy powder cores for PFC.....basically , use "Sendust" type alloy powder torroids with a low  nickel content......other torroids contain much nickel and are way too expensive now, due to nickel price going up, as attached, due to EV batteries.

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