I was up late last night (early morning?) working on my ball mill to pulvrize my iron, so when I sat down to check this thread before bed I was both sore and tired. I was hoping for a little inspiration,so when I got more of the "why bother it won't work" meme I sorta popped.
I didn't join this forum to engage in squibbling, I joined to share ideas. Re-reading this thread I can see we got off on the wrong foot...let’s try again
One thing I noticed, it seems some folks are posting without out actually reading my earlier posts. I say that because I seem to be getting some posts with points that had already been covered/answered.
I know what I am trying to do is far enough out of the diy norm that some skepticism is a healthy thing. What I hope to do in this post, is to lay out a little more clearly what it is I’m trying to accomplish , and show that I have the tools I need to do it.
One of the biggest frustrations I’ve had in the past is needing to do/make something only to find out midway I didn’t have access to a tool I needed. About a decade ago I set out to change that. To that end I have assembled a small hobby level machine shop, and aluminum sand casting foundry. I will never have every tool I want, but I can now make just about every tool I need (the ball mill I’m building now, for example) This has increased my fabricating capability’s several orders of magnitude . Now it’s a question of economy of time as to whether or not a project is worth it or not. I guess you can say I’m a uber-diyer.
Some folks seem to think I want to make trannies out of iron powder as a means to itself..it’s not.
First, IMHO silicon iron (steel) is still the best all-around material for OPT’s , medium permeability, and high saturation point (a little Nickel aint bad either). I settled on brake turnings because of its availability. Commercially available iron (not ferrite) powder is VERY expensive. Now if my tranny core idea(s) work out, I might make the plunge for the “good stuff” .
Why powder instead of laminations ? A couple of reasons. First, as everybody here probably knows, lots of thin laminations has better performance at the upper end of the spectrum, over fewer, thicker laminations. There are two reasons for this, 1) the reduction of losses to eddy currents, and 2) a smaller mass takes less time to align its molecules magnetically. Carried to its logical conclusion, the smallest possible mass/size, will have the fastest/loss-less magnetic path…hence powder. Secondly, by being able to mould the core, I can make any shape I want. The possible downside? Air-gap losses. No matter how tightly packed, or how fine the powder, there will still be a space occupied by the binder (epoxy). This isn’t a deal breaker for me. First this air-gap is distributed throughout the core, minimizing its effect, secondly, since I am building a SE amp with parallel 813’s, I’m going to have about 200ma of dc flowing through the primary. I NEED an air gap, a fairly large one at that. I’ll know it’s as good as it can be if I have to add an additional air gap. If not ,I’ll be forever tormented as to how much better it could be ( since its never good enough anyway, I’ll live).
To recap my methodology (again, I didn’t come up with this industry did, I’m just adapting here) I am rendering my materiel (brake turnings) into as fine a powder as I can. I am then oxidizing the surface of the powder to form an insulating layer. Next, the powder will be mulled with an epoxy binder, and rammed into a mould under about 1000-2000 psi with the aid of a hydraulic press…garnish and serve.
I hope this clears up a few things. I look forward to our future dialog.
I didn't join this forum to engage in squibbling, I joined to share ideas. Re-reading this thread I can see we got off on the wrong foot...let’s try again
One thing I noticed, it seems some folks are posting without out actually reading my earlier posts. I say that because I seem to be getting some posts with points that had already been covered/answered.
I know what I am trying to do is far enough out of the diy norm that some skepticism is a healthy thing. What I hope to do in this post, is to lay out a little more clearly what it is I’m trying to accomplish , and show that I have the tools I need to do it.
One of the biggest frustrations I’ve had in the past is needing to do/make something only to find out midway I didn’t have access to a tool I needed. About a decade ago I set out to change that. To that end I have assembled a small hobby level machine shop, and aluminum sand casting foundry. I will never have every tool I want, but I can now make just about every tool I need (the ball mill I’m building now, for example) This has increased my fabricating capability’s several orders of magnitude . Now it’s a question of economy of time as to whether or not a project is worth it or not. I guess you can say I’m a uber-diyer.
Some folks seem to think I want to make trannies out of iron powder as a means to itself..it’s not.
First, IMHO silicon iron (steel) is still the best all-around material for OPT’s , medium permeability, and high saturation point (a little Nickel aint bad either). I settled on brake turnings because of its availability. Commercially available iron (not ferrite) powder is VERY expensive. Now if my tranny core idea(s) work out, I might make the plunge for the “good stuff” .
Why powder instead of laminations ? A couple of reasons. First, as everybody here probably knows, lots of thin laminations has better performance at the upper end of the spectrum, over fewer, thicker laminations. There are two reasons for this, 1) the reduction of losses to eddy currents, and 2) a smaller mass takes less time to align its molecules magnetically. Carried to its logical conclusion, the smallest possible mass/size, will have the fastest/loss-less magnetic path…hence powder. Secondly, by being able to mould the core, I can make any shape I want. The possible downside? Air-gap losses. No matter how tightly packed, or how fine the powder, there will still be a space occupied by the binder (epoxy). This isn’t a deal breaker for me. First this air-gap is distributed throughout the core, minimizing its effect, secondly, since I am building a SE amp with parallel 813’s, I’m going to have about 200ma of dc flowing through the primary. I NEED an air gap, a fairly large one at that. I’ll know it’s as good as it can be if I have to add an additional air gap. If not ,I’ll be forever tormented as to how much better it could be ( since its never good enough anyway, I’ll live).
To recap my methodology (again, I didn’t come up with this industry did, I’m just adapting here) I am rendering my materiel (brake turnings) into as fine a powder as I can. I am then oxidizing the surface of the powder to form an insulating layer. Next, the powder will be mulled with an epoxy binder, and rammed into a mould under about 1000-2000 psi with the aid of a hydraulic press…garnish and serve.
I hope this clears up a few things. I look forward to our future dialog.
Hi,
Magnetics makes E powdered cores. Here is the link.
I think you will find that use of powdered cores is not suitable for high linearity signal transformers. All comercially available powdered cores (and I think that also yours will be the same) have a highly nonlinear B-H curve, contrary to the discrete airgap cores, where B-H curve is higly linear. But you are free to try.
Best regards,
Jaka Racman
Magnetics makes E powdered cores. Here is the link.
I think you will find that use of powdered cores is not suitable for high linearity signal transformers. All comercially available powdered cores (and I think that also yours will be the same) have a highly nonlinear B-H curve, contrary to the discrete airgap cores, where B-H curve is higly linear. But you are free to try.
Best regards,
Jaka Racman
I have no idea if this will work or not. But, I applaud you in pushing the boundaries of diy, and I can't wait to see your results. Positive or negative, ( though I hope the former, of course), you have the spirit of a true experimentalist. Good luck!
Though I would take careful note of some of the safety issues that have been raised.
Though I would take careful note of some of the safety issues that have been raised.
smoking-amp said:
Electrophoresis. Now that's a word I didn't expect to see here. I spent 15 years of my professional career involved in PAGE, though on the wet side. Actually worked at Bio Rad (source of the supply in the e-bay ad) at one time in chromatography. Like the PS's in consumer stuff, most of the new gear is SMPs. Lighter more flexible.
Actually, a working electrophoresis ps might be a good bench supply for experimenting. All of them have a wide range of adjustable output and, like the one shown, many can be selected for constant current, constant voltage, or sometimes constant watts.
I'll have to check out e-bay more often.
Sheldon
Mr. Valveitude
I can't figure out why you are making a ball mill when as an amateur foundryman you could use a rolling mill more for your sand mix and your crushing operation.
And I'm guessing that you have a hydraulic press or will rig up a jack to do the same. Good idea but you still may end up with air bubbles. Mix just enough to get the dough wet. No more than needed and you will entrain the least amount of air.
MArk
I can't figure out why you are making a ball mill when as an amateur foundryman you could use a rolling mill more for your sand mix and your crushing operation.
And I'm guessing that you have a hydraulic press or will rig up a jack to do the same. Good idea but you still may end up with air bubbles. Mix just enough to get the dough wet. No more than needed and you will entrain the least amount of air.
MArk
This source wins the prize for the closest "off the shelf" solution so far..closest not exactly close. First off..it is a "high permeability alloy not optimized for OPT, second its an E- core..I don't want to be confined to one physical configuration. I want to experiment with a cup/c-core hybrid , think c-core that that wraps 360 deg. providing a magnetic shield.
Correct.. ALL commercially available cores I've seen have this problem. This is the function of the core material not being simple Fe-Si. These guys are in the biz of making money (no problem there). When the market for tube OPT's becomes a multi-million a year industry (read never) they will pour their R&D into an alloy optimized for this purpose. Until then, they will continue to develop better and better cores for switchers, IF, and RF,and the like. That leaves wingnuts like me to try and fill the need..my need that is. To my knowledge (limited as it is
) there are NO commercially available powder cores suitable for OPT's.I do appreciate the effort for the link though.
Simplicity..I considered roll mills, hammer mills et al. I decided on a ball mill, as it is something I can "scab" together quickly. In addition I think it has the advantage of working by concussion, (the "balls" flinging around smacking into the wall of the drum) as opposed to pressure that a roll mill uses. The limit of concusion rendering is limited only by the porosity of the material.
Thank you.
First, I want to applaud your diy spirit; let the others rehash what's already been done!
I've thought about making powder cores, though it never occurred to me to make my own powder. Maybe one sunny Sunday afternoon this summer I'll take a grinder to an old PS transformer.... One thought I've had is to cast the windings into the core. I imagine suspending the wound coils in an empty container and then adding the slurry. Obviously, that's a one-shot deal, and neither high pressures nor high curing temps could be tolerated.
Anyway, I just want to warn you that you might be underestimating the effect of the distributed gap. One way to think about it is in terms of reluctance. The net reluctance is the sum of the reluctances of the iron path and the gap. (Like adding resistors in series.) The reluctance is proportional to l/u where l is the path length and u is the perm. We're talking relative perm, so for air u=1.
So, if the perm of the iron is something like 1000, then adding a gap that is 5% as long as the iron path will increase the reluctance by roughly .05*1000= 50 times that of the iron alone. Restating that in terms of permeability means that you'll end up with an effective perm of something like 1000/50 = 20. Make the gap 10% of the total path and you'll end up with an effective perm of 10. That's still 10 times better than air but it might not be what you were expecting.
My hunch is that if you start with a fine enough powder then eddy currents will not be too big an issue even if you use a very thin binder and maybe even skip the oxidation step. It will take only a tiny fraction of an ohm electrical resistance between grains to reduce eddy currents. Obviously, I haven't done any real analysis, just offering my intuition.
I've thought about making powder cores, though it never occurred to me to make my own powder. Maybe one sunny Sunday afternoon this summer I'll take a grinder to an old PS transformer.... One thought I've had is to cast the windings into the core. I imagine suspending the wound coils in an empty container and then adding the slurry. Obviously, that's a one-shot deal, and neither high pressures nor high curing temps could be tolerated.
Anyway, I just want to warn you that you might be underestimating the effect of the distributed gap. One way to think about it is in terms of reluctance. The net reluctance is the sum of the reluctances of the iron path and the gap. (Like adding resistors in series.) The reluctance is proportional to l/u where l is the path length and u is the perm. We're talking relative perm, so for air u=1.
So, if the perm of the iron is something like 1000, then adding a gap that is 5% as long as the iron path will increase the reluctance by roughly .05*1000= 50 times that of the iron alone. Restating that in terms of permeability means that you'll end up with an effective perm of something like 1000/50 = 20. Make the gap 10% of the total path and you'll end up with an effective perm of 10. That's still 10 times better than air
but it might not be what you were expecting.My hunch is that if you start with a fine enough powder then eddy currents will not be too big an issue even if you use a very thin binder and maybe even skip the oxidation step. It will take only a tiny fraction of an ohm electrical resistance between grains to reduce eddy currents. Obviously, I haven't done any real analysis, just offering my intuition.
Unconventional transformer
Here's a technique that a home Diy-er could use to make an unconventional output xfmr with possibly very good results. Start with a spool of Litz wire with maybe 20 strands of wire in it. (I see Litz wire on Ebay regularly) Unserved Litz is fine. (the serving on Litz is the fiber wrapping around the wire strands to hold them together and provide extra insulation)
Now you need a spool of approx. 1/2 inch wide amorphous magnetic alloy tape. Most likely have to buy this new from the manufacturer. This stuff is very thin. Be careful when handling this stuff, its got razor sharp edges on it. Now you need a rig that can spin the tape spool around the wire as the wire gets pulled thru. Essentially, one would be putting an amorphous film serve on the Litz wire. Can experiment with how dense a spiral layer gets put on by altering wire pull rate versus tape spool spin rate.
The final output xfmr. would be configured by connecting half of the Litz wire strands (the little wires in the Litz) in series for the primary and half the strands in parallel for the secondary. Should probably use triple enameled wire strands to reduce capacitance between "turns", but at least leakage inductance will be near zilch. (its the product of leakage inductance and distributed capacitance that determins xfmr bandwidth) Another approach to lower distributed capacitance further would be to use two (or more) Litz wires with serving on at least one or more of them. Wrap the amorphous tape around both (or more) Litz wires. One Litz wire gets used for primary turns and the other for the secondary.
The whole final length of Litz could be coiled up for compactness, but this won't have any effect on magnetic coupling. The equivalent of this technique is often used to make broadband RF transformers using ferrite beads strung on multiple wires.
You have to get enough inductance in the primary to handle the lowest frequency. While this technique does not get to take full advantage of a large number of turns to get inductance, it does take advantage of minimal magnetic path length around the wire circumference, which will provide a large boost to inductance.
Inductance = u*N*N*Area/(magn. path length)
Don
Here's a technique that a home Diy-er could use to make an unconventional output xfmr with possibly very good results. Start with a spool of Litz wire with maybe 20 strands of wire in it. (I see Litz wire on Ebay regularly) Unserved Litz is fine. (the serving on Litz is the fiber wrapping around the wire strands to hold them together and provide extra insulation)
Now you need a spool of approx. 1/2 inch wide amorphous magnetic alloy tape. Most likely have to buy this new from the manufacturer. This stuff is very thin. Be careful when handling this stuff, its got razor sharp edges on it. Now you need a rig that can spin the tape spool around the wire as the wire gets pulled thru. Essentially, one would be putting an amorphous film serve on the Litz wire. Can experiment with how dense a spiral layer gets put on by altering wire pull rate versus tape spool spin rate.
The final output xfmr. would be configured by connecting half of the Litz wire strands (the little wires in the Litz) in series for the primary and half the strands in parallel for the secondary. Should probably use triple enameled wire strands to reduce capacitance between "turns", but at least leakage inductance will be near zilch. (its the product of leakage inductance and distributed capacitance that determins xfmr bandwidth) Another approach to lower distributed capacitance further would be to use two (or more) Litz wires with serving on at least one or more of them. Wrap the amorphous tape around both (or more) Litz wires. One Litz wire gets used for primary turns and the other for the secondary.
The whole final length of Litz could be coiled up for compactness, but this won't have any effect on magnetic coupling. The equivalent of this technique is often used to make broadband RF transformers using ferrite beads strung on multiple wires.
You have to get enough inductance in the primary to handle the lowest frequency. While this technique does not get to take full advantage of a large number of turns to get inductance, it does take advantage of minimal magnetic path length around the wire circumference, which will provide a large boost to inductance.
Inductance = u*N*N*Area/(magn. path length)
Don
Ignore my discouraging remarks. If you are right, all the nay-sayers in the world can't make you wrong.
The lack of positive ideas is, of course, because you are working SO far outside the norm that none of us have caught up with you. Most of these thoughts must have crossed your mind too. Give us time to argue out loud. A new idea-seed needs time to grow.
> as everybody here probably knows, lots of thin laminations has better performance at the upper end of the spectrum, over fewer, thicker laminations. There are two reasons for this, 1) the reduction of losses to eddy currents, and.... Carried to its logical conclusion, the smallest possible mass/size, will have the fastest/loss-less magnetic path…hence powder.
To nay-say some more (to make you sure of your analysis): there is a diminishing-returns kink in the optimization. We use one lam-thickness for 50-400Hz power, somewhat thinner lams for HiFi. Thinner is better, yes. But at any specified frequency (and material resistivity) there is a size that gives "small" losses, and a thinner size that is "insignificantly" less loss, but significantly higher price to produce.
Roll or grind small, yes; but rolling/grinding "too small" is not better and consumes money/time that could be better spent on other imperfections. (Yes, in uber-DIY, money/time takes a different perspective; us hasty-hackers don't often commit enough hours or dollars to our dreams.)
Note that eddy-current is a 2-dimensional problem. It is a function of the smallest circle that can be drawn perpendicular to the flux lines. Indeed, long broad thin sheets have the smallest eddy circles per fabrication dollar. Drawing to wire or grinding to powder is much more work. On the eddy-losses arguement, you should be looking for thin foil, not powder. Of course, at some point the many layers of insulation reduce your core effective area.
Have you considered using the brake-shavings directly? Their thickness is somewhat thinner than "good audio" transformer lamination. Your cost of fabricating to that thickness is, as you say, zero (prepaid by brake-shop victims). Stacking-factor could be horrible without much shaking and pounding.
Oxidation is now the standard insulation for power transformers. It can be much thinner than varnish, won't burn. They even shave that by oxidizing just-enough to meet a loss spec, not to reduce loss to "zero".
Is oxidation needed when you have a non-conductive binder? A simple resistivity test on a scrap blob will quickly tell you if it is low-R, high-R, or too in-between to judge without further test.
Sintering sounds wrong (and darn hard to DIY sintered iron). It clearly increases the eddy-circle size bigger than the particle size. But if the sintering is light, the contacts are microscopic. Current-crowding at the contacts might give sufficiently high resistivity to make eddy loss small.
Hammer-out a closed core. It does not have to be a final product. Wrap a few turns, take the measurements, extrapolate the winding resistance for a full winding. My best-guess is that inductance and saturation will be lower than iron, copper loss higher. The other issue would be "fine sound": different irons (and lamination thickness and insulation) have different sound. The ear is a very fine instrument. If the powder material has a "better sound", the size and cost are secondary issues (or even features) for many audiophiles.
I say "copper loss" from habit. But since this is clearly a very specialized process for a well-heeled market (even a market of one), I'd be impressed even if you have to use Silver winding to get performance comparable to iron/copper materials. At this level of investment, Silver wire is an obvious detail anyway.
> 2) a smaller mass takes less time to align its molecules magnetically.
Will the entire particle flop as a unit? I believe magnetic domains are smaller than grains of powder, though I certainly am over my head here. Maybe there is coupling between domains, less so across particle boundaries?
IS there a time element? Being a mere audio-hack, I believe domain-flop is only about flux, not time. That's clearly wrong: nothing happens in zero time. But is the time anywhere near audio rate?
> by being able to mould the core, I can make any shape I want
What is the ideal shape? It is a many-splendored problem. But for the big power transformer business, optimization is profit, and quantity is high enough to forge novel processes.
The square-stack E-I core we usually use makes the winding wire take a long path. Graduated widths can approximate a round core, round windings, least winding length (resistance) for a given core area. GE used to strip-wind iron sheet cut on a taper to get this core-shape.
But big-power is different from audio. In POWER, reducing loss from 10% to 5% means half the cooling surface needed. MVA transformers are a lot about cooling, so half the cooling is a very significant advantage. But in audio, reducing loss from 10% to 5% means 0.5dB more output, inaudible.
Topologically, all the closed-core forms reduce to two conjoined toroids. In a common cheap tranny, the iron is a square toroid, the coil is another toroid. The squareness is not electrically optimum, but convenient for production. In a "toroid tranny" the core is round doughnut shape, the coil is a toroid stretched-out around the circumference. Good, though the winding can get a little tight inside the doughnut. This could be improved with vari-diameter wire: thin where it passes through the hole, fat around the other 90% of its length; this would be tough to produce.
We come down to two key dimensions. The mean length of turn is constrained by the core area needed. And the mean length of flux-path is constrained by winding window area needed. Both interact with each other, and with cost of copper versus iron, and design frequency and losses. The general optimization (ignoring cost) seems to be the common toroid, or the inverse (copper doughnut wrapped with iron; pot-core).
Offhand, I assert that either shape can be approximated to 60% perfection with plain square stamped iron, or to 80%(+) perfection with tape-wound(tapered) toroid.
What shape are you going for? Maybe there is an outside-the-box shape I can't imagine.
Silicon: as I said, in foundry work, silicon makes iron more fluid, easier casting of complex shapes. This is of course irrelevant to transformer steel which is brutally rolled, not cast. In transformer steel, increasing silicon from 1% to 4% increases resistivity, cost, and brittleness. 4% Si iron has about half the (power frequency) loss of 1% steel. This has to be weighed against cost of steel, cost of punching, and the possibility of using a thinner lam of cheaper steel. AFAICT, the resistivity is the main point of Silicon in transformer iron; if you drastically reduce the eddy-circles with a powder technique, is this still an important factor?
The lack of positive ideas is, of course, because you are working SO far outside the norm that none of us have caught up with you. Most of these thoughts must have crossed your mind too. Give us time to argue out loud. A new idea-seed needs time to grow.
> as everybody here probably knows, lots of thin laminations has better performance at the upper end of the spectrum, over fewer, thicker laminations. There are two reasons for this, 1) the reduction of losses to eddy currents, and.... Carried to its logical conclusion, the smallest possible mass/size, will have the fastest/loss-less magnetic path…hence powder.
To nay-say some more (to make you sure of your analysis): there is a diminishing-returns kink in the optimization. We use one lam-thickness for 50-400Hz power, somewhat thinner lams for HiFi. Thinner is better, yes. But at any specified frequency (and material resistivity) there is a size that gives "small" losses, and a thinner size that is "insignificantly" less loss, but significantly higher price to produce.
Roll or grind small, yes; but rolling/grinding "too small" is not better and consumes money/time that could be better spent on other imperfections. (Yes, in uber-DIY, money/time takes a different perspective; us hasty-hackers don't often commit enough hours or dollars to our dreams.)
Note that eddy-current is a 2-dimensional problem. It is a function of the smallest circle that can be drawn perpendicular to the flux lines. Indeed, long broad thin sheets have the smallest eddy circles per fabrication dollar. Drawing to wire or grinding to powder is much more work. On the eddy-losses arguement, you should be looking for thin foil, not powder. Of course, at some point the many layers of insulation reduce your core effective area.
Have you considered using the brake-shavings directly? Their thickness is somewhat thinner than "good audio" transformer lamination. Your cost of fabricating to that thickness is, as you say, zero (prepaid by brake-shop victims). Stacking-factor could be horrible without much shaking and pounding.
Oxidation is now the standard insulation for power transformers. It can be much thinner than varnish, won't burn. They even shave that by oxidizing just-enough to meet a loss spec, not to reduce loss to "zero".
Is oxidation needed when you have a non-conductive binder? A simple resistivity test on a scrap blob will quickly tell you if it is low-R, high-R, or too in-between to judge without further test.
Sintering sounds wrong (and darn hard to DIY sintered iron). It clearly increases the eddy-circle size bigger than the particle size. But if the sintering is light, the contacts are microscopic. Current-crowding at the contacts might give sufficiently high resistivity to make eddy loss small.
Hammer-out a closed core. It does not have to be a final product. Wrap a few turns, take the measurements, extrapolate the winding resistance for a full winding. My best-guess is that inductance and saturation will be lower than iron, copper loss higher. The other issue would be "fine sound": different irons (and lamination thickness and insulation) have different sound. The ear is a very fine instrument. If the powder material has a "better sound", the size and cost are secondary issues (or even features) for many audiophiles.
I say "copper loss" from habit. But since this is clearly a very specialized process for a well-heeled market (even a market of one), I'd be impressed even if you have to use Silver winding to get performance comparable to iron/copper materials. At this level of investment, Silver wire is an obvious detail anyway.
> 2) a smaller mass takes less time to align its molecules magnetically.
Will the entire particle flop as a unit? I believe magnetic domains are smaller than grains of powder, though I certainly am over my head here. Maybe there is coupling between domains, less so across particle boundaries?
IS there a time element? Being a mere audio-hack, I believe domain-flop is only about flux, not time. That's clearly wrong: nothing happens in zero time. But is the time anywhere near audio rate?
> by being able to mould the core, I can make any shape I want
What is the ideal shape? It is a many-splendored problem. But for the big power transformer business, optimization is profit, and quantity is high enough to forge novel processes.
The square-stack E-I core we usually use makes the winding wire take a long path. Graduated widths can approximate a round core, round windings, least winding length (resistance) for a given core area. GE used to strip-wind iron sheet cut on a taper to get this core-shape.
But big-power is different from audio. In POWER, reducing loss from 10% to 5% means half the cooling surface needed. MVA transformers are a lot about cooling, so half the cooling is a very significant advantage. But in audio, reducing loss from 10% to 5% means 0.5dB more output, inaudible.
Topologically, all the closed-core forms reduce to two conjoined toroids. In a common cheap tranny, the iron is a square toroid, the coil is another toroid. The squareness is not electrically optimum, but convenient for production. In a "toroid tranny" the core is round doughnut shape, the coil is a toroid stretched-out around the circumference. Good, though the winding can get a little tight inside the doughnut. This could be improved with vari-diameter wire: thin where it passes through the hole, fat around the other 90% of its length; this would be tough to produce.
We come down to two key dimensions. The mean length of turn is constrained by the core area needed. And the mean length of flux-path is constrained by winding window area needed. Both interact with each other, and with cost of copper versus iron, and design frequency and losses. The general optimization (ignoring cost) seems to be the common toroid, or the inverse (copper doughnut wrapped with iron; pot-core).
Offhand, I assert that either shape can be approximated to 60% perfection with plain square stamped iron, or to 80%(+) perfection with tape-wound(tapered) toroid.
What shape are you going for? Maybe there is an outside-the-box shape I can't imagine.
Silicon: as I said, in foundry work, silicon makes iron more fluid, easier casting of complex shapes. This is of course irrelevant to transformer steel which is brutally rolled, not cast. In transformer steel, increasing silicon from 1% to 4% increases resistivity, cost, and brittleness. 4% Si iron has about half the (power frequency) loss of 1% steel. This has to be weighed against cost of steel, cost of punching, and the possibility of using a thinner lam of cheaper steel. AFAICT, the resistivity is the main point of Silicon in transformer iron; if you drastically reduce the eddy-circles with a powder technique, is this still an important factor?
> The reluctance is proportional to l/u where l is the path length and u is the perm. We're talking relative perm, so for air u=1. ... a gap that is 5% as long as the iron path will increase the reluctance by roughly .05*1000= 50 times that of the iron alone. Restating that in terms of permeability means that you'll end up with an effective perm of something like 1000/50 = 20.
Thank you for saying it clearly. That was my first thought, but I could not quantify it.
I grant that 'tude's technique might get toward 1% gap. The overlap effect could be powerful. "Non-gapped" E-I cores are non-continuous so clearly have a gap, but the overlap is large enough to deliver nearly (not quite) the bulk permeability. Needles or flakes might get not far off, but (IMHO) not close enough to have any "advantage" over transformer steel, not in gross properties.
Thank you for saying it clearly. That was my first thought, but I could not quantify it.
I grant that 'tude's technique might get toward 1% gap. The overlap effect could be powerful. "Non-gapped" E-I cores are non-continuous so clearly have a gap, but the overlap is large enough to deliver nearly (not quite) the bulk permeability. Needles or flakes might get not far off, but (IMHO) not close enough to have any "advantage" over transformer steel, not in gross properties.
I can't comment on the physics part, but three simple thoughts on the mechanicals:
If you want to minimize the void volume (I don't know if you do or not), use a mixture of particle sizes. An infinitely varied mixture can integrate to zero void volume at the limit.
I would put the mold low on the list to optimize, in preference to methods to get good uniform compression. Machining later should be relatively easy.
And the most obvious one, use the thinnest binder possible. You might even find something like a thermoset resin to coat a portion of the particles, then mix the rest, compress, and heat in your form.
Sheldon
If you want to minimize the void volume (I don't know if you do or not), use a mixture of particle sizes. An infinitely varied mixture can integrate to zero void volume at the limit.
I would put the mold low on the list to optimize, in preference to methods to get good uniform compression. Machining later should be relatively easy.
And the most obvious one, use the thinnest binder possible. You might even find something like a thermoset resin to coat a portion of the particles, then mix the rest, compress, and heat in your form.
Sheldon
just some random thoughts in support of the original poster.
everything he has said makes perfect sense to me!
I have often thought of simply suspending a coil in a large vat of appropriate powder.
all of the elements can be bought in powderd form of varying sizes so you can essentially make your own alloy (it would not be anywhare near as econimical as the brake shavings though.)
as for binder, since its a SE transformer, why do you need one? the DC current will pull the core together and any binder would just get in the way increasing the gap.
Maybe we all need to get off the "high perm" crack pipe, and look at it from the other direction. Insead of starting with a lab perm of 10,000 or more and complaining of the losses in air, lets start with the ideal of air and a perm of 1 and enjoy anything beyond that we get.
dave
everything he has said makes perfect sense to me!
I have often thought of simply suspending a coil in a large vat of appropriate powder.
all of the elements can be bought in powderd form of varying sizes so you can essentially make your own alloy
(it would not be anywhare near as econimical as the brake shavings though.)as for binder, since its a SE transformer, why do you need one? the DC current will pull the core together and any binder would just get in the way increasing the gap.
Maybe we all need to get off the "high perm" crack pipe, and look at it from the other direction. Insead of starting with a lab perm of 10,000 or more and complaining of the losses in air, lets start with the ideal of air and a perm of 1 and enjoy anything beyond that we get.
dave
Other than the permeability issues, which have been well hashed over, there still remains the high non-linearity issue of powdered core material mentioned earlier. This is not really solvable using some special alloy.
The non-linearity arises due to the powder particles contacting each other at small contact points. This causes the magnetic field to be concentrated there and leads to premature magnetic saturation across these contact points. This effectively makes the effective core air gap modulate with field level, leading to the non-linearity. This can be partially remedied by compressing the core with enormous pressure so more particle surface area comes into contact, but then the particles need to have an oxide coating to prevent one solid block of metal from forming. I don't think you will have an inexpensive core anymore if you do all that, material cost will be insignificant compared to fabrication cost. Of course, this is Diy, and cost may be no concern. (Maybe a diamond anvil to compress the material is already on order?)
How about superconducting wire and air core? (OK, just kidding)
Maybe if someone found some magnetic monopoles, we could let them circulate around the magnetic core like electrons in wire.
Don
The non-linearity arises due to the powder particles contacting each other at small contact points. This causes the magnetic field to be concentrated there and leads to premature magnetic saturation across these contact points. This effectively makes the effective core air gap modulate with field level, leading to the non-linearity. This can be partially remedied by compressing the core with enormous pressure so more particle surface area comes into contact, but then the particles need to have an oxide coating to prevent one solid block of metal from forming. I don't think you will have an inexpensive core anymore if you do all that, material cost will be insignificant compared to fabrication cost. Of course, this is Diy, and cost may be no concern. (Maybe a diamond anvil to compress the material is already on order?)
How about superconducting wire and air core? (OK, just kidding)
Maybe if someone found some magnetic monopoles, we could let them circulate around the magnetic core like electrons in wire.
Don
NOW WE'RE COOKING!!
The quality of the last group of replies have been excellent!!
First off, I do realize that this project seems..um..out there at first blush. I tend to forget I have been thinking about this concept off and on for the better part of 5 years, not working on it mind you, just thinking about it from time to time. So a lot that seems self evident to me now, didn't at first. Its understandable why I got an initial inrush of "what choo talkin' 'bout Willis" replies.
Anyway, no hard feelings.
A lot of very good questions and points have been made. Rather than answer each individually I'll try to cover them generally.
How Far to Go: I learned a long time ago that test equipment is good as general guide to design only. Ultimately, the final arbitrator is our ears. Where is the point of diminishing return on this project, or any other for that matter? Who knows. I good friend of mine told me several years ago “Trying to get the absolute sound is like tying to reach absolute zero, you have to expend twice the energy to get half as far, knowing you will never quite make it” I’ve never heard a better description of our dilemma.
Air-gap: The biggest unknown in this project. Figured linearly (95% fill=5% gap), it would be a big problem. Fortunately I don’t think it works this way. Picture a tube full of metal balls, for every vertical pair, there is a third ball laying in the crotch formed by the curve of the balls. Now visualize flux lines running threw them. As the flux line approaches the gap of a vertical pair, it will flex horizontally to the ball resting in the crotch. In other words it is following the path of least resistance. There is still a loss, but less so. How much, I don’t know.
Eddy Currents: Commercial powder cores rate them by ohms/cm. The higher the resistance, the less loss. I read that real iron cores range from 10-100 ohms/cm. I did make a crude test core by filling up a toilet paper tube with untreated, partially crushed chips with 5% by weight epoxy, putting metal plugs in the ends, and cranking it in a vise. This is no where near the pressure needed for the final product,in fact it is so porous that you can blow threw it, but it has given me a relative point to measure from. On the ends, where it was best compacted, I get about 25 ohms per inch, and towards the middle I get around twice that. This shows that the more pressure, the less resistance. So, if we convert my 25 ohms per inch to 10 oms/cm, and assuming the relationship to pressure is linear (big assumption), if we applied 10 times the pressure we get 1 ohm/cm. This is a tenth of the low end of the range stated above…I think I need more. Even if I wasn’t trying to insulate the particles, oxide would be a by-product of the processing. First I fully harden the chips so they break easily. According to the Radiotron Handbook, chapter 5, page 208- “To retain high permeability at low level flux densities, the strips or laminations should be annealed after shearing and punching”. Clearly it’s important that the metal be in it’s relaxed state, so after pulverizing the powder it will be annealed. Both of these tempering processes creates oxide.
I’m sure I’m missing some points that were brought up. I’ll re-read the thread and post a follow up if needed…right now though, I’m heading back to the shop.
The quality of the last group of replies have been excellent!!
First off, I do realize that this project seems..um..out there at first blush. I tend to forget I have been thinking about this concept off and on for the better part of 5 years, not working on it mind you, just thinking about it from time to time. So a lot that seems self evident to me now, didn't at first. Its understandable why I got an initial inrush of "what choo talkin' 'bout Willis" replies.
Anyway, no hard feelings.
A lot of very good questions and points have been made. Rather than answer each individually I'll try to cover them generally.
How Far to Go: I learned a long time ago that test equipment is good as general guide to design only. Ultimately, the final arbitrator is our ears. Where is the point of diminishing return on this project, or any other for that matter? Who knows. I good friend of mine told me several years ago “Trying to get the absolute sound is like tying to reach absolute zero, you have to expend twice the energy to get half as far, knowing you will never quite make it” I’ve never heard a better description of our dilemma.
Air-gap: The biggest unknown in this project. Figured linearly (95% fill=5% gap), it would be a big problem. Fortunately I don’t think it works this way. Picture a tube full of metal balls, for every vertical pair, there is a third ball laying in the crotch formed by the curve of the balls. Now visualize flux lines running threw them. As the flux line approaches the gap of a vertical pair, it will flex horizontally to the ball resting in the crotch. In other words it is following the path of least resistance. There is still a loss, but less so. How much, I don’t know.
Eddy Currents: Commercial powder cores rate them by ohms/cm. The higher the resistance, the less loss. I read that real iron cores range from 10-100 ohms/cm. I did make a crude test core by filling up a toilet paper tube with untreated, partially crushed chips with 5% by weight epoxy, putting metal plugs in the ends, and cranking it in a vise. This is no where near the pressure needed for the final product,in fact it is so porous that you can blow threw it, but it has given me a relative point to measure from. On the ends, where it was best compacted, I get about 25 ohms per inch, and towards the middle I get around twice that. This shows that the more pressure, the less resistance. So, if we convert my 25 ohms per inch to 10 oms/cm, and assuming the relationship to pressure is linear (big assumption), if we applied 10 times the pressure we get 1 ohm/cm. This is a tenth of the low end of the range stated above…I think I need more. Even if I wasn’t trying to insulate the particles, oxide would be a by-product of the processing. First I fully harden the chips so they break easily. According to the Radiotron Handbook, chapter 5, page 208- “To retain high permeability at low level flux densities, the strips or laminations should be annealed after shearing and punching”. Clearly it’s important that the metal be in it’s relaxed state, so after pulverizing the powder it will be annealed. Both of these tempering processes creates oxide.
I’m sure I’m missing some points that were brought up. I’ll re-read the thread and post a follow up if needed…right now though, I’m heading back to the shop.
I see your point, however, I think your still in a ferrite frame of mind. Ferrite, being a ceramic, is exceedingly hard. Fully annealed iron, on the other hand, by comparison is a marshmallow. As the powder is compressed, the adjoining particles deform to each others surface irregularities, making the contact area bigger. The resistance decreasing as the pressure increases described in my last post seems to bare this out. I believe (hope) a ordinary automotive bottle jack can provide enough pressure to accomplish this. Though I have to say, a diamond anvil, especially with its matching rail-gun ram would be cool
.On the other hand, if this effect can't be minimized, I believe by manipulating the weight of the core vs. idle current, I can find a portion of the curve that is linear enough.
I have seen several people pointing out the need for a "thin" binder. It is the relative volume of the binder that will determine the thickness of boundaries, not its viscosity. A low viscosity binder would make mulling easier though.
Not exactly. Brake rotors are made of gray cast iron and the silicon (2% - 4%) is added to promote the formation of free graphite in a matrix of ferrite (alpha iron-carbon solution, not iron oxide). I don't know the exact composition of the ferrite matrix and it may not contain very much silicon iron alloy. The powder being made by Valvitude will be about 90% - 95% of the ferrite matrix with most of the remaining powder being pure graphite (read high conductivity) with some iron carbides present. Is this mixture a good one for an audio transformer? I doubt it.
John
furthermore:
"The magnetization process is influenced by impurities, grain orientation, grain size, strain, strip thickness, and surface smoothness. One of the most important ways to improve soft magnetic materials is to remove impurities, which interfere with domain-wall movement; they are least harmful if present in solid solution. Compared with other commercial steels, silicon steel is exceptionally pure. Because carbon, an interstitial impurity, can harm low induction permeability, it must be removed before the steel is annealed to develop the final texture."
Quoted from an article from this website:
http://www.key-to-steel.com
John
"The magnetization process is influenced by impurities, grain orientation, grain size, strain, strip thickness, and surface smoothness. One of the most important ways to improve soft magnetic materials is to remove impurities, which interfere with domain-wall movement; they are least harmful if present in solid solution. Compared with other commercial steels, silicon steel is exceptionally pure. Because carbon, an interstitial impurity, can harm low induction permeability, it must be removed before the steel is annealed to develop the final texture."
Quoted from an article from this website:
http://www.key-to-steel.com
John
valveitude said:
Perhaps you stated, and I didn't catch, how you would apply the binder. I assumed that you'd work with some kind of slurry. If that's the case, a viscous binder will be very difficult to express from the cake during compression. If you've got a different method that doesn't have that issue, then carry on.
Sheldon
First, I want to thank you for the research..knowledge is power.
I thought from the start that the break iron probably contained some "uglies" in its composition, as alluded two in my first post I decided to work with it because its cheap (free), and plentiful. The "Rosetta Stone" of tranny materials it aint.
Good
Bad
But the "bad" isn't as bad as the "good" is good.
Anything taking up space, increasing the air-gap conundrum , needs to be minimized. As for the fact that carbon is conductive, it’s a non-starter.
I’ve been thinking about magnetic “cleaning” of the powder to improve its purity, and if carbon powder is its main impurity, that would seem to be a good idea. I haven’t figured out exactly how to do that though.
All that said, this tranny core is a process rather than an event. If all the potential advantages of a powder core pan out it could, it seems to me, offset a good many problems with the material. As I stated earlier, making my own iron powder isn’t a means to an end. I want to experiment with different core geometry’s, specifically a cup/c-core hybrid. If I get close to the performance I believe is possible, I’ll source some “real” iron. If not, I’ll have to be satisfied with everything I’ll have learned in the process.
Of course there is always the possibility that ,properly processed, my lowly break iron kicks butt.
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