I have a lot of different recycled cores leached from various power supplies. I want to use them for my own projects and mainly it is my passion for the electromagnetic field.what is the purpose of the testing ?
Is that why my Br is shifted relative to the documentation?Usually this sort of characterization is done with thin toroidal cores, in order to ensure no air gap and uniform field.
Yes, you are right, Br is different, but this is probably because the EE core has a gap resulting from inaccurate grinding and inaccurate assembly of the core??BH curve to the one in the material datasheet (at 25C) shows it's very different. Mainly the Br (the y-intercept) in the datasheet is much larger than your data.
measures the voltage at the output and calculate the integral. Magnetic induction B is the integral of voltage over timeHow are you measuring B(t)?
That's my first guess at why your Br and ua are much lower than the values in the datasheet, but your Bsat looks similar.Is that why my Br is shifted relative to the documentation?
Because the core is not perfectly assembled?
Depends on what your objective is. If your objective is to characterize the core material itself, then your results are off. If your objective is to characterize this particular core assembly (as opposed to the properties of the material itself), then your measurements are probably valid, but only for this particular core assembly.But such a measurement means that I have more reliable data than from the datasheet?
AFAIK the shape of the waveforms doesn't significantly impact core loss. Just the peak to peak B ripple and frequency.Especially since the manufacturer tests the core for one harmonic and here I have a lot of harmonics like in a real system. I understand this correctly?
Assuming this is on a secondary winding which carries no current. that should be fine.measures the voltage at the output and calculate the integral. Magnetic induction B is the integral of voltage over time
Again, I don't expect the results to change significantly based on whether your applied B waveform is sinusoidal or triangular. So long as the min/max of the waveform is the same, the resulting BH curve should still take the same shape. Changing the waveform shape just changes the rate at which you traverse the BH curve, not its shape. I'm sure that under extreme circumstances (like if your waveform is non-monotonic, or if your frequency is very high) then this assumption breaks down, but I don't think that's relevant in your case.I made an FFT(screenshot below) of the current and it shows that the 3rd harmonic is 2dB lower than the 1st, which shows that individual harmonics have large values. Does a larger number of harmonics result in higher core losses than stated by the manufacturer?
I can't see any flaw in your math. But it's hard to verify it too...Did I calculate it correctly?
I think you might be misunderstanding the meaning of the fig 7 data. The different curves aren't for different harmonics of a waveform. Those frequencies refer to the fundamental frequency at which core loss was measured. That 180kW/m3 value you're pointing to is measured with a fundamental frequency of 10kHz and a peak flux density of B=200mT. Your experiment has a different frequency and B, so your value should be different (I'm guessing somewhat higher).I compared it with the data sheet (data for the 1st harmonic) and the result is about 180kW/m3. What do you think about it?
The goal is to estimate the capabilities and losses of unknown cores and have knowledge of what I currently have in hand. Determining remanence, coercivity and maximum induction B if possible, then more or less estimate what type of core it is, e.g. 3F3 or 3C95 etc. I will also be happy and I think it can be estimated to some extent, but it is not the main goal. From what I have read, the accuracy of ferrites is not ideal and I consider the results of +-10% to be reasonable (440mT vs 490mT is approximately 10%), the aging process of the material also matters plus, what the manufacturer tests on a uniform core in them lab. It's important to me what I have in real case in which I will use the core for the DC/DC converter. I also want to check the core, for which I even have documentation in order to check how it actually behaves with a voltage rectangle and not for 1 harmonic.Depends on what your objective is. If your objective is to characterize the core material itself, then your results are off. If your objective is to characterize this particular core assembly (as opposed to the properties of the material itself), then your measurements are probably valid, but only for this particular core assembly.
yes on the secondary sideAssuming this is on a secondary winding which carries no current. that should be fine.
Again, I don't expect the results to change significantly based on whether your applied B waveform is sinusoidal or triangular. So long as the min/max of the waveform is the same, the resulting BH curve should still take the same shape. Changing the waveform shape just changes the rate at which you traverse the BH curve, not its shape. I'm sure that under extreme circumstances (like if your waveform is non-monotonic, or if your frequency is very high) then this assumption breaks down, but I don't think that's relevant in your case.
[/QUOTE]The goal is to estimate the capabilities and losses of unknown cores and have knowledge of what I currently have in hand. Determining remanence, coercivity and maximum induction B if possible, then more or less estimate what type of core it is, e.g. 3F3 or 3C95 etc.
It's still unclear why you keep bringing up harmonics... It sounds like you're assuming that you can break a waveform into harmonics, calculate the power dissipated of each harmonic, then sum those powers to get the power dissipated by the original waveform. That's not valid, even for linear systems.If we have a resistor and connect a distorted waveform to it, the power loss emitted on it depends on each harmonic of this waveform. The same is true for magnetic material, which also has its own bandwidth on which the losses in the core depend. This is also given by the complex graph of u' and u'' (I placed it below). Each harmonic will cause losses in the core, so the losses I calculate are reliable in my opinion. Below I present a test that could confirm this
It's still unclear why you keep bringing up harmonics... It sounds like you're assuming that you can break a waveform into harmonics, calculate the power dissipated of each harmonic, then sum those powers to get the power dissipated by the original waveform. That's not valid, even for linear systems.
Thanks for the correction. In my head I somehow conflated RMS and power, and had written out a proof that the sum of RMS values of harmonics is not equal to the RMS of the original waveform, which is true but obviously useless in hindsight.If you decompose the Fourier transform signal and calculate the power of each harmonic, the sum of the power of these harmonics will be equal to the power of the original signal, even if this signal is distorted. This follows from Parseval's theorem.
Parseval's theorem states that the sum of the squares of the Fourier coefficients (i.e. the power of individual harmonics) equals the total signal power in the time domain. In other words, the total energy of the signal in the time domain is equal to the total energy in the frequency domain.
If a signal is distorted, it means that it will contain more harmonics, but the sum of the powers of these harmonics (both fundamental and higher) will correspond to the total power of that signal.
I don't think estimating core losses from core temperature is valid, unless you have already "calibrated" the effective thermal impedance in your setup via temperature measurements with a known core loss. And that calibration will likely be very delicate, depending on core shape, orientation, exposure to airflow, etc. And you would have to ensure that heat from the windings do not contribute to the core heating, which is very difficult in practice.And what do you think about the method in which I presented how I determined the power losses in the core? And what do you think about these numerical values of losses?
I described earlier that I verified it with the power drawn from the power supply and based on thermal resistance where I estimated the thermal energy.
Good question. I think one of my reference books had an explanation of how core manufacturers derive curves of max power transmission (which is a function of shape, material, frequency, temperature, and whether the flux swing is bipolar or unipolar). IIRC it's not dependent on air gap, except for flyback (which is its own topic). Let me see if I can dig it up.How to calculate the maximum power that a core can transfer? How to estimate it? For a core with a gap, it can be calculated from energy, but what about a core without a gap? For example, I have an ETD34/17/11 - 3F3 core, and how can I know if it is suitable for a 500W power supply?
The temperature test was not supposed to show me the result exactly up to 10%, I even wanted to estimate that the results were not significantly wrong. I did not saturate the core then, it worked nicely in a loop, so the losses included hysteresis and eddy current losses. I only calculate hysteresis. I was remember about the eddy current losses and the winding resistance losses, it is true, but they are not that large in percentage terms compared to the hysteresis losses at such a moment of core operation.I don't think estimating core losses from core temperature is valid, unless you have already "calibrated" the effective thermal impedance in your setup via temperature measurements with a known core loss. And that calibration will likely be very delicate, depending on core shape, orientation, exposure to airflow, etc. And you would have to ensure that heat from the windings do not contribute to the core heating, which is very difficult in practice.
What exactly do you mean by over full wave? Don't saturate the core? If it saturates, I will have losses in the cable. In my opinion, I can't saturate it, it must work normally in a loop close to saturation and then measure the voltage and current and count the power?loss of a core:
in time domain: you multiply I(t) with V(t) to get P(t). Integrate it over a full wave. This is the loss over a full wave.
Good question. I think one of my reference books had an explanation of how core manufacturers derive curves of max power transmission (which is a function of shape, material, frequency, temperature, and whether the flux swing is bipolar or unipolar). IIRC it's not dependent on air gap, except for flyback (which is its own topic). Let me see if I can dig it up.
INTEGRATE over TIME.What exactly do you mean by over full wave?
The degree of saturation surely has influence on loss.Don't saturate the core?
Copper loss?. For sure there is copper loss at any time. (With and without saturation)If it saturates, I will have losses in the cable
This sort of makes it unreliable even as a sanity check for other measurements. Thermal behavior is at least as complicated to accurately model as magnetic behavior, so a guesstimated model of one shouldn't be used to check the other. Stick to more direct methods like Pc=I*V.I didn't even know the thermal resistance of the core, so I estimated it.
Saturation will cause the current to increase, which will increase the copper losses in the winding. But this can still be corrected for, at least to a first order. So instead of Pc=V*I it would be Pc=(V-I*Rcu)*I, where Rcu is the effective series resistance of windings at your excitation frequency.What exactly do you mean by over full wave? Don't saturate the core? If it saturates, I will have losses in the cable. In my opinion, I can't saturate it, it must work normally in a loop close to saturation and then measure the voltage and current and count the power?
I couldn't find my Keith Billings book, but I did find my old Epcos/TDK reference book on ferrites. Actually I found a pdf version, here you go: https://www.tdk-electronics.tdk.com...2ba503/ferrites-and-accessories-db-130501.pdfoh great, I will be very grateful for such information and help on how to approach it. Even more so now that we have information about the core itself and its capabilities.
Some manufacturers offer tools meant to aid engineers in designing or simulating transformers. In the past I tried to use one offered by Epcos/TDK, but I don't think I ever got it to produce useful results. Not sure if that was because it was buggy or I was not using it correctly.The tabulated power capacities provide a means for making a selection among cores, although
the absolute values will not be met in practice for the reasons explained before.
Sure, I'll test it under power. Apart from this test, what I did was to measure the power at the power input. Transformer not saturated and power consumption from the power supply 2.4W, calculated loop 1.9W. This also proves something, but I will confirm it by measuring the power on the primary winding of the transformer.This sort of makes it unreliable even as a sanity check for other measurements. Thermal behavior is at least as complicated to accurately model as magnetic behavior, so a guesstimated model of one shouldn't be used to check the other. Stick to more direct methods like Pc=I*V.
Using the DC power measurement is valid so long as the efficiency of your bridge is high. Should be feasible at lower excitation frequencies. Though you will still want to correct for copper losses (you could also include the bridge resistance into the copper losses).Sure, I'll test it under power. Apart from this test, what I did was to measure the power at the power input. Transformer not saturated and power consumption from the power supply 2.4W, calculated loop 1.9W. This also proves something, but I will confirm it by measuring the power on the primary winding of the transformer.
Yes, area product is another figure of merit commonly referred to. It's been a long time since I used it in a design, but I recall going through the steps to derive it myself, and it took quite a bit of effort. IIRC it's complicated because it considers the windings in much more detail (as opposed to Ptrans which simply assumes via the PIDOOMA method that copper loss and core loss are equal).I found something to estimate the transformer power. From this formula we can derive the formula for P. What do you think about it?
Understand that these figures of merit are not useful for calculating the actual power dissipated by a transformer, only for estimating how much power throughput a transformer (or its bobbin) can handle and for comparing cores/bobbins against each other (under the various assumptions involved in their calculation).
"core power" can only be found in your last post. Where exactly did you ask about it?Sure, I just wanted to be able to estimate the maximum core power. I asked about this previously. The topic of losses is another issue too.
Where exactly did you ask about it?
How to calculate the maximum power that a core can transfer? How to estimate it? For a core with a gap, it can be calculated from energy, but what about a core without a gap? For example, I have an ETD34/17/11 - 3F3 core, and how can I know if it is suitable for a 500W power supply?
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