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I advise reading previous update ("Bye, DC!"), it's a crucial part - it contains important ideas about power & energy in electric circuits, revealing phenomenon of inductance and resistance on a new level - now it's my instrument of choice for working with electromagnetic processes.
I submerged my electromagnet into a vessel with water and powered it up, recording changes in temperature. It takes about an hour to temperature to drop down for a 2 degrees in this setup, as it features some thermal insulation after all, water volume stayed untouched
Here are results:
Control circuit changed situation a lot - reducing energy dissipation for about 30%
On the right side you can see oscilloscope date, isn't it looks familiar? :)
That then, 30% is our upper limit? Not at all! Retention of energy goes on a constant rate independently of a charging rate, as it is a typical LC oscillatory circuit. We can use it in our favour, increasing charging speed. Here are few samples with another electromagnet:
This log would be very strange, I wanna introduce new physic theory
Well, I tried to stop myself from doing that kind of work, kept saying "Just use that, don't trash your head with such an outrageous things, you have a lot of another stuff to do" - and here I am!
Now, I want to list, what I don't like in conventional conception of electrical engineering:
- If dissipated power is really U*I (according to Joule's Law), why then it's possible to perform any kind of work? To generate a field, which has energy, you should take that energy from somewhere, as we say that U*I equation is right 100% of time - it should be impossible, however, transformers, oscillatory circuits and electric motors have no problem with it.
- If we say, that coil has an energy of field proportional to flowing current (L*I^2/2), then how on Earth it starts to charge? Traditional chicken & egg question. If we say, that there is no power without a current and no current without an energy...
Needless to say, that traditional laws of physics had no chance to uncover the mystery how my circuit really works even partly. And I was OK with that, until I found efficiency problems in my design and tried to find a reason.
I'm not pretending on universal truth and I have no intention to convince someone, but this theory explains electromagnetic processes much better, in my view, makes a lot of things clearer than ever.
And it's fair to say, that as we have potential difference, we have potential energy between charged particles at least. Then I thought about reasons why my circuit is not as effective as needed, it was the first thing which came onto my mind: as I have diodes, it must be a tough work for magnetic field, to power up electric field and break through potential barrier!
Idea of two energies on the surface of a conductor was very catchy and since that time I started thinking about it, as it seemed, that that charge is responsible not only for current, but for magnetic field, inductance and... resistance! Typically, we say, that we have two types of resistance: resistance and electrical reactance, probably it's an artificial division, caused by urge of numerical description and lack of understanding. That was OK for a typical AC applications, but not enough now, then we are talking about behaviour of an electromagnetic field. Let's have a look:
I wouldn't comment that a lot, as imagination is more important here. With same applied voltage, conductor with bigger section area have greater electric flux, and current raises proportional to R^2. On the other hand, electrical resistivity defines surface density of charge for a specific applied voltage, not a conventional "friction"
So every conductor has that properties. Difference is only how much "inductance" and "resistance" it has. Important to say, that potential energy between charged particle and energy of magnetic field are tied together. There is no magnetic-field energy without proper electric-field energy and vice versa! For example: then you wrap wire around a steel rode, you add an object, which your wire needs to magnetize - it's harder now to cover a conductor with electrons and generate current, each potential difference there "costs" a part of magnetization process.
Funny enough - there is even an interesting relation between temperature and energy, which you need to pump in. For some reason, potential energy between charges decreases with lower temperatures and conductor can gain more electrons proportional to that. I found that, then efficiency of my circuit increased as I put electromagnet in fridge. I think, same process takes place in superconductors (more pronounced) and in batteries at cold - amount of charge stays the same, energy decreases, there is no...
Hello everyone! I try not to miss my train, so this log gonna be short. : )
Just want to write a little about experience I had with magnetic locks, which I bought yesterday:
I wasn't there for a while, however I have some amazing news now!
After 1 month of struggling, after a month of trying different complicated electromagnetic structures, I finally found electromagnet (which was lying on my table for 4 years for now and was a part of various experiments with control board) nice enough to try out something with them.
As I told in previous post, I wanna utilize magnetic field better, then... here we go!
Looks evident? Well, it wasn't evident for me, even if I knew, what magnet (which I have) produces same attraction force, as a reference permanent magnet. I thought, that field shape isn't proper for this use. Today, experiment shown, that there is nothing bad with it at all, silly me!
And there is even a magnet with desired shape on a market!
This time I faced with another sort of problem. I've decided to install smaller capacitor to check if it has anything to do with efficiency, I was interested to get significant voltage increase on capacitor during charging cycle, and I've got it ;D
Well, lazy me soldered high side MOSFET driver yesterday, in replace of strange IR2117 (probably, burned)
Now it use three transistors instead of IC, it gives bug-fix freedom. Happily, it worked "right from the box", transistor opens as needed, as bootstrap capacitor sends needed amount of voltage to drain.
Yes, I cannot feel any heat, so I would return to surface-mount housings instead of heavy-lifters like TO-247 (however I like them, ahaha) - but it's not the interesting part!
Now I have fully-working electromagnet driver, and I've made some test. Results were kind of intriguing. First of all, I found, that you can maintain semi-constant current on coil, it wouldn't affect efficiency.
As you can see, current is quite stable. I'm not sure if I can achieve greater efficiency by increasing amount of withdrawn energy. So we can forget about kind of PWMed magnetic field! Hooray!
But question of efficiency remains unsolved for now:
I wasn't there for long, but that's for reason! I made a small vacation for myself, also - 3d printer arrived. So I've been working onto fixing some printing issues, caused by troublesome Z-axis mechanics. Now everything seems to be fixed, I regained access to 3d printing stuff, hooray! :)
Of course, I tested modular electromagnets
It seems, that I failed to produce reasonable design of winding, ahaha
And I want to say, that it performs very well! Self-proclaimed "modular" electromagnets are pretty small and light, use a little amount of cooper wire and also pretty strong compared to beefy convenient electromagnets, even with nails used as a core material. So I can say, that with nice core material or control circuit, which can sustain powerful magnetic field, it's a win : )
Now about core material, I thought a lot about using induction heater and I already have one, of course, but this method requires deep vacuum pump, I think I can do it without low pressures.
On last week I played with coils, and played a lot
Now I have 18 coils, all what's needed to complete one modular electromagnet:
As I'm too lazy to wind them by hands, I had some extreme prototyping experience ->
Yeah, it's winding machine made from a building kit! Works surprisingly well!
I would design something more reliable later, of course, )
Since I have some troubles with accessing 3d printer and drilling machine for now, I haven't completed modular electromagnet yet, however I fixed problem with transistor's opening!
It seems what I've figured out what's gone wrong with new PCB
For the reason, I use transistor to cut off connection between coil and power supply, ground is connected permanently and control circuit tracks current on electromagnet to choose duty cycle properly.
That's why transistor works like common-drain-amplifier.
Drain current derives from difference between gate-voltage and drain-voltage multiplied by forward transconductance of a transistor, so drain voltage cannot be greater than gate voltage minus voltage drop on gate-drain junction, that's why you can see something like this:
Hello everyone. After a couple weeks I've got my PCB's and assembled first one.
Big thanks to PCBway, never seen so much enthusiasm from a PCB manufacturer
Quote: "power of chaos" - such a pearl! It was a fun time talking with you, guys : )
^ wire here - bridges VCC and V_TRG, leaving possibility to use high voltages in coil circuit
without bad outcomes for the little 5V linear stabilizer, used to power up logic circuitry!
I was able to control it via MCU (Arduino) directly, hooray!
First of all - never trust PWM->Voltage article on Instructables. It's totally wrong - instead of using 0.1uF capacitor in Low-Pass filter, I highly recommend 10uF, it is fixed in project files which I gonna upload in future, however, I think I should mention it
Well, not that simple! All circuitry, responsible for a giveaway-reserve energy cycle works fine - it generates control signal in right time and then sends it to the gate of MOSFET
And then strange thing happened - IRLZ44NS (that mosfet) fails to output more than 5V:
- source voltage - is OK, much greater than 5V
- it obviously not from logic elements, how they can output half-amp currents? no way!
- stabilizer heats? not at all, but MOSFET does
FETs were connected similarly back in the days, then I tested previous version. If anyone has a theory why that can happen - would be happy to hear, because I have no idea at the moment
Here is schematics again, if needed: