You should realize that i did NOT talk about the static capacitance at all. I wrote EFFECTIVE capacitance ! May be you estimate, i am not estimating, i either measure or at least calculate the static capacicance and from it and from the voltagerelations, wich are also easely known and do not have to be estimated, calculate the REAL effective capacitance.
Not exactly brainsurgery, is it?
Anyone designing transformers should know the difference and how to calculate it or at least get into the ballpark by using Patrick Turners approach, anyway, am tired from getting purposly misunderstood so i will spare you guys from my other findings regarding how to make more of Yves calculator, am outta here
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Note that it is not unreasonable to wind this transformer more than once in order to find the opimum winding layout, number of interleaved windings, interconnection, materials, etc.
I have only wound very simple power transformers and precision air core inductors and have left the winding of more complex transformers to those more expert than myself. I may follow you down this path at some point. I have friend who roughly two decades ago started winding transformers for 300B and 845s, it took him a few tries to get it right.
Yes, but to a lesser extend, and spacing is beneficial regarding proximity losses. With wires that thick heavy interleaving is a good thing if you have the space and can keep capacitances in check
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Can you tell me the difference between static and effective?
Anyone MAKING transformers knows how difficult is to estimate the real capacitance simply because it depends a lot on how it is made! Have you ever made one?
Well the one asking for help about the Crowhurst article was you. I wonder how you could not figure it out and now you are the great calculator of capacitances! I wonder why people use FEA or other more complex calculations to estimate capacitance when here we have the genius that can calculate it easy peasy.....
This is abut SE OPT.
It's easy to figure out looking on my screenshots - Bdc, air gap and also SE checked 😉
Is it me, or discussions on audio transformers tend to quickly get hot?
@45 50% increase of Rdc quoted by you is a bit of overkill statement. Let's jump to one of my excell calculator, I always have a few opened on my computer. A 6S33S SE OPT with a two coiled C core with overall 12 P/S interfaces and an MLT of 225mm for P/S dielectrick thickness of 0.3mm, then changes to MLT of 238mm when P/S dielectric thickness becomes 1mm. Rdc is proportional to MLT, so...
It is Ls that jumps higher, from 0.49mH to 0.92mH
@45 50% increase of Rdc quoted by you is a bit of overkill statement. Let's jump to one of my excell calculator, I always have a few opened on my computer. A 6S33S SE OPT with a two coiled C core with overall 12 P/S interfaces and an MLT of 225mm for P/S dielectrick thickness of 0.3mm, then changes to MLT of 238mm when P/S dielectric thickness becomes 1mm. Rdc is proportional to MLT, so...
It is Ls that jumps higher, from 0.49mH to 0.92mH
It could be overkill, I have not done any calculation just guessed according to previous experience, But 30-35% is certainly possible, something like 110R primary DC resistance instead of the current 162R. This with the same number of turns, just using less insulation and larger wire.
In my opinion, for this specific transformer, vertical sectioning will be beneficial. 2 caves should be already a good step forward to comprehensively redistribute capacitance allowing more P-S interleaving.
Also according to my model, leakage inductance of the proposed design is not 9.1 mH but about half of that, while capacitance will be higher than 1 nF. This is why I think he should go ahead. He will get a smooth response. Then if f-3dB is at 35 KHz or 40 KHz it's not really a game changer....only then decide to go for a more complicated design or stop because already satisfactory.
In my opinion, for this specific transformer, vertical sectioning will be beneficial. 2 caves should be already a good step forward to comprehensively redistribute capacitance allowing more P-S interleaving.
Also according to my model, leakage inductance of the proposed design is not 9.1 mH but about half of that, while capacitance will be higher than 1 nF. This is why I think he should go ahead. He will get a smooth response. Then if f-3dB is at 35 KHz or 40 KHz it's not really a game changer....only then decide to go for a more complicated design or stop because already satisfactory.
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He quoted 16 P/S interfaces in his design. Im my designs I'd use 8, half of that. Yes, he'll definitely get smooth capacitance dominant roll-off.
However I just noted his primary turn counts. In this mode he desires:
L= 40H
Idc = 100mA
Vpri - 580Vrms (30W)
Afe = 23cm2
My calculator dictates for 4000 primary turns, with a Bac + Bdc = 1.00
My bad, I mistook the Rplate value for primary inductance. 11250R for 7k
That goes to 3500 primary turns. The nanocrystalline material usually begins to saturate at 1.0T
L= 40H
Idc = 100mA
Vpri - 580Vrms (30W)
Afe = 23cm2
My calculator dictates for 4000 primary turns, with a Bac + Bdc = 1.00
My bad, I mistook the Rplate value for primary inductance. 11250R for 7k
That goes to 3500 primary turns. The nanocrystalline material usually begins to saturate at 1.0T
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Yes i can, but i would have thougth you would know that. The static capacitance is what you could measure directly between 2 electrically isolated winding layers. The effective depends on the actual voltages between layers, ziz zag or z connection, strays a.s.o and there transformed appaerance at the input. Maybe appearend capacitance would be a better name
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Yes i asked if anyone could explain Crowhursts CORE DIMENSION OPTIMISATION to achieve the best possible inductance to leakage ratio. Instead of explaing you choosed to swipe it aside as unimportant. This only tells me that you not only, are just as i am unable to explain, regrettable, yes, am working on it and should i ever find out will make it known. In the meantime i hope others will ccome to understand the importance and advantages it could offer in respect to core choice.
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@gorgon53 I did give a answer, I did not wipe anything out but you still do not get it! I regret my decision to answer your questions. You don't have the knowledge, you don't have the experience to understand.
The best possible ratio between inductance and leakage inductance does not exist in practical terms because it does not mean the transformer is optimal. There is a practical, sensible limit as anything else. There is no best ratio of inductance to leakage because it is at expense of something else. At best one can optimize the product of leakage inductance and shunt capacitance but it still depends on the application, power rating and the efficiency. Hence, my answer: the best size is the smallest one can use.
Before optimizing the ratio between inductance and leakage inductance the very first requirement to satisfy is the power rating.
The approximate weight of the core can be estimated based on power rating at low frequency. This one can find from any manufacturer. It is referred to line frequency but it's easy to reformulate for lower frequency.
You will never be able to convince me that 20Hz is the right frequency and 30Hz is a worse compromise because my experience tells me this. The difference in core size between 20Hz and 30Hz is substantial. Core material can change, acceptable losses can change and the shape can change. A C core with a certain cross-section will have a very different winding volume respect to an EI core with same core cross-section. Why all these shapes exist if a toroid could be the only one to do it all? The answer is simple....
The right term is effective capacitance because it is the capacitance one gets once the transformer is in use as intended and the sequence of how internal connections are chosen does make some (useful or nasty) difference. Sorry but you are wrong again.
The best possible ratio between inductance and leakage inductance does not exist in practical terms because it does not mean the transformer is optimal. There is a practical, sensible limit as anything else. There is no best ratio of inductance to leakage because it is at expense of something else. At best one can optimize the product of leakage inductance and shunt capacitance but it still depends on the application, power rating and the efficiency. Hence, my answer: the best size is the smallest one can use.
Before optimizing the ratio between inductance and leakage inductance the very first requirement to satisfy is the power rating.
The approximate weight of the core can be estimated based on power rating at low frequency. This one can find from any manufacturer. It is referred to line frequency but it's easy to reformulate for lower frequency.
You will never be able to convince me that 20Hz is the right frequency and 30Hz is a worse compromise because my experience tells me this. The difference in core size between 20Hz and 30Hz is substantial. Core material can change, acceptable losses can change and the shape can change. A C core with a certain cross-section will have a very different winding volume respect to an EI core with same core cross-section. Why all these shapes exist if a toroid could be the only one to do it all? The answer is simple....
The right term is effective capacitance because it is the capacitance one gets once the transformer is in use as intended and the sequence of how internal connections are chosen does make some (useful or nasty) difference. Sorry but you are wrong again.
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“A C core with a certain cross-section will have a very different winding volume respect to an EI core with same core cross-section. Why all these shapes exist if a toroid could be the only one to do it all? The answer is simple....”
You can buy c-cores with exact the same winding volume of a EI core. There are also toroids with different ratios between inner and outer diameter, different high, different magnetic path length.
So what you mean by simple?
You can buy c-cores with exact the same winding volume of a EI core. There are also toroids with different ratios between inner and outer diameter, different high, different magnetic path length.
So what you mean by simple?
Yes, I know. FEMAG in Italy would make C cores that fit EI coil formers, for example, but you need to order a minimum of 100 Kg and this is not going to make you save money.It will be more expensive than standard C cores because they are not normally requested, while standard C cores they might already have them in stock. The standard C cores are the HWR type which is quite different. Want better price? Need to buy more. This has very little to do with DIY just like @daanve has already proved with his pointless comment.
The reason why SE tpyes are not common is that loose laminations have a BIG advantage: I buy one size and can do different cross-sections just changing the coil former. If I buy C cores I will spend more money if I want all possible cross sections.
I only meant that there is no single solution even at this basic level. More the SE C type with same winding space as EI is not equivalent because the the C type is 100% oriented and EI is not. The max usable B is higher for the C core, the required turns are less for the same power rating and all the rest can be different!
Then if you and @daanve (who normally uses massive cores for small jobs and I still remember a customer who published the poor frequency response of his expensive boutique transformers) know the answer,, why don't you give the answer? An analytic answer! What is the optimal ratio between inductance and leakge inductance? Come on great experts!!! Are you afraid?
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Where I buy my cores is irrelvent because SE type C cores are still NOT equivalnet to EI cores and that's the discussion about. If you throw them in the mix, which I dod NOT, the discussion doesn't move from where it is.
And EI core quality is not worse, it can be exactly the same. It is the cut that makes them only for 2/3 oriented. In fact does not result in lower qulity transformers. That is only a theorical assumption in the mind of those who never built the actual amplifier and don't even try to think how the hysteresis loop would look like for the actual trnasformer....
A massive C core SE transformer with a small air gap can have higher power loss than a smaller EI core with larger gap, same power rating and inductance. That's because core loss is dominated by the airgap in SE transformers. Here we are again: smallest size for the job!
And EI core quality is not worse, it can be exactly the same. It is the cut that makes them only for 2/3 oriented. In fact does not result in lower qulity transformers. That is only a theorical assumption in the mind of those who never built the actual amplifier and don't even try to think how the hysteresis loop would look like for the actual trnasformer....
A massive C core SE transformer with a small air gap can have higher power loss than a smaller EI core with larger gap, same power rating and inductance. That's because core loss is dominated by the airgap in SE transformers. Here we are again: smallest size for the job!
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