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Please confirm if i see soldering on the welding wire to keep them fixed to each other?
If yes then I think it is a problem causing eddy current loss, unfortunately by short-circuiting the welding wires, giving way to current flow.
Another problem is the joining surfaces at the corners: I know the wire ends are hard to make smooth to touch without having air gaps, air gap increases reluctance in the magnetic path, leading to less output. Maybe you could form a closed core by cutting and bunching long pieces of wire to have only a single air gap, by bending the long wire bunch at the corners where needed.
What is the frequency involved in this test? With such wire cores you may wish to choose lower frequencies, for you never know how it behaves higher.
Finally, as I mentioned earlier, the input power is defined by the voltage actually feeding the coil via the MOSFET switch and the input current and the duty cycle. The voltage drop method across the 20 Ohm is good for checking the input current or indicating whether the input current changes when you connect the load. So the input voltage to be considered for input power is to be measured in your setup across the filter capacitor you connected between the common point of the primary coil and the 20 Ohm and the ground. In my opinion, this is what is important and not what you show as a 3mV change only while the output has 120mV.
Sorry that I mentioned some objections to your setup, I did this with helping intentions.
The mig wire is indeed soldered together. Each core joint was filed down to
remove nearly all the airgaps and vised together for joining.
Perhaps with a hydrogen furnace the er70s metal could be melted down into
solid peices without changing its magnetic properties? Bending joints from
larger peices would require much pressure... Its difficult to even get a
single strand to hold bent shapes.
The mig wire is indeed soldered together. Each core joint was filed down to
remove nearly all the airgaps and vised together for joining.
Ok, and if you feel like using individually insulated soft iron wires guided together as a thick bunch, I referred to in my previous post, then either 2 or even one air gap remains to be joined and matched (two horse shoe shapes turned towards each other gives 2 gaps or forming a total oval shape results in 1 gap. The garden wires will be much softer than the welding rods
(In Nikola Tesla's era transformer cores were built from soft iron wires, the insulation between the parallel wires were some oxid or paint layer.)
By using such iron wires as cores the frequency should be low, even lower than 200-300Hz because of losses: tests run at higher power levels and with varying test frequencies can give answer on the usefulness of such cores.
Perhaps with a hydrogen furnace the er70s metal could be melted down into
solid pieces without changing its magnetic properties?
All I can tell you on this is that the smallest harm happens when the heating and cooling of a magnetic core is very gradual and not excessive or sudden. So just heat it up to the melting point of the solder used (maybe max 200-250°C) and then let it cool by its own. By the way you can check how the permeability of such rods might change to heat by first inserting a known number of such rods into an air core coil, measure the inductance and then heat up the rods to about 200-250°C and watch how the inductance changes.
Geotron-- I appreciate your hands-on build; I have a couple of questions:
1. Did you wind the primary on a core that is elevated above the central core-rectangle? that's what I see in your picture (attached).
If so, why wouldn't you put this primary-core like the bar on an "H", rather than elevated above?
2. Can you calculate for us n = Poutput / Pinput (even if this is approximate), so we can get an idea of the efficiency of your xformer?
Pls keep up the good work.
Your build is reminiscent of this one --
3. pls let me know what you think of it, if you get a chance to watch it:
...
2. Can you calculate for us n = Poutput / Pinput (even if this is approximate), so we can get an idea of the efficiency of your xformer?
...
Here is some help: because he measured the filtered DC voltage drop across the series primary 20 Ohm resistor as about 1V, the DC current via this resistor is 1/20 Amper i.e. 50mA. This is what also goes into his primary coil as an average current. So if he used 12V DC voltage from his two series 6V batteries and 1V was wasted by the 20 Ohm, then the transformer input power was about (12-1)*0.05=0.55W.
Regarding the output power he measured 38-40mV DC across the secondary 20 Ohm resistor, after the diode bridge plus the filter cap. So taking 40mV as output DC voltage, the output power in the 20 Ohm is (0.04*0.04)/20=0.08mW.
Although the output diode bridge has its usual forward voltage drop losses, the main loss surely manifests in the transformer, mainly in the cores.
Couldn't the change in power into the primary resistor on load also be calculated
as V^2/R ? 1mV * 1mV / 20 is .05mW, in which case the relative output power would be 160%
Couldn't the change in power into the primary resistor on load also be calculated
as V^2/R ? 1mV * 1mV / 20 is .05mW, in which case the relative output power would be 160%
Decimal-point check: 1mV * 1mV = 1 microV-squared, and divided by 20 gives 0.05 uW (MICRO watts), not .05 mW. right? (sorry) please check my math.
..... also @ Muon, the picture you've made reference to in which the primary
core is sitting atop the others is previous to the final construction. It was
only to show the individual peices before connecting them together.
( .001 * .001 ) / 20 = .000,000,05 watts in input power producing .000,08 watts.
If this is truly the case, relative output is 1600% in excess.
Hi geotron,
It is ok that you consider the relative output but I cannot see why it is good for calculating that way? What can you do with a mathematical excess number in practice?
Because I think you have to maintain continuosly the 0.55W input power I referred to above to experience your alleged gain. And this 0.55W comes from the two 6V batteries you use as a primary source for your transformer via a switch. Without the 0.55W power as an "investment" you could not see the relative output either.
It is ok that the input power changes only some fraction of microwatts when you apply a load but the 50mA input current is still consumed in the meantime by the primary coil of the transformer.
Sorry if I may sound negative again but my common sense tries to work too... Maybe there is something I am missing.
..... also @ Muon, the picture you've made reference to in which the primary
core is sitting atop the others is previous to the final construction. It was
only to show the individual peices before connecting them together.
OK -- thanks, and for checking my math. I thank Gyula also.
For construction -- please help me on this as I climb the learning curve here; would like to understand. Calling the core holding the PRIMARY coil the "inner core" and the other the "outer core" -- what would be the BEST material(s) to use for the inner core and the outer core?
Soft iron? or - Ferrite -- or -- Nano-crystalline amorphous material?
And should these be the same materials, or have different permeabilities??
Also, being a bit lazy when it comes to winding (although I've done a lot of wire-winding!) -- could one use pre-wound coils, and place these on the "legs" of the cores BEFORE joining the legs together? The cheapest -- if these would work -- would be spools of wire "as purchased", for the pre-wound coils (if one could get at the inner-most wire for connections).
Thanks for the pointers... I'd like to do a build soon, see if I can contribute something to humanity.
The answer would be how to recover the energy going into the primary coil.
Pressing iron oxide blocks instead of casting them with resin? Glue seems like
it holds the particles in a state less available to magnetic change.
How to recover the energy going into the primary: perhaps collecting the collapsing field's energy when you switch the primary off and store it in a capacitor?
There are flat ferrite rods like the ones used in AM pocket radios, sandwiching them in an overlapped fashion to form a closed core could avoid most of the gaps and eddy losses would not be a problem even in the lower MHz range.
See some link what I think of:
Ferrite Rods, Bars, Plates and Tubes go down to the bottom to see the chart on Antenna Plates and even lower to Antenna Strips.
The permeability can be chosen in the range from 20 to 10,000 but these products are non-stock and made to order only, a price quote may be worth asking for.
OK -- thanks, and for checking my math. I thank Gyula also.
For construction -- please help me on this as I climb the learning curve here; would like to understand. Calling the core holding the PRIMARY coil the "inner core" and the other the "outer core" -- what would be the BEST material(s) to use for the inner core and the outer core?
Soft iron? or - Ferrite -- or -- Nano-crystalline amorphous material?
And should these be the same materials, or have different permeabilities??
Also, being a bit lazy when it comes to winding (although I've done a lot of wire-winding!) -- could one use pre-wound coils, and place these on the "legs" of the cores BEFORE joining the legs together? The cheapest -- if these would work -- would be spools of wire "as purchased", for the pre-wound coils (if one could get at the inner-most wire for connections).
Thanks for the pointers... I'd like to do a build soon, see if I can contribute something to humanity.
Hi Muon,
The best magnetic cores nowadays are nano-crystalline or metglas but these are the most expensive of course. What is important: a negligible eddy current loss at the operating frequency
You could use prewound coils but it is hard to match the inner diameter of such bobbins with the available cores. Also a spool of wire as purchased might have too big DC resistance unless you unwind from it...
You surely noticed flat ferrite rod choices I googled for geotron.
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