Mysterious Files PH

Electrostatic discharge machining (EDM) may be slower than alternatives like laser cutting, water jets, or a milling machine, but for some applications there’s no alternative: it can cut through any conductive material, no matter how hard, and it leaves no mechanical or thermal stress in the workpiece. Best of all, they’re relatively accessible for a resourceful hacker, such as [Inofid], who recently built the second iteration of his desktop wire EDM.

The EDM’s motion system comes from a cheap desktop CNC router, which had a water tank mounted in its workspace and had the spindle replaced with a wire-management mechanism. The wire-management mechanism needs to continuously wind a tensioned brass wire from one spool through the cutting zone onto another spool. The tensioning system uses two motors: one to pull the wire through, and one to maintain tension by slightly counteracting it, with a tension sensor and Ardunio to maintain the proper tension. If it detects that the wire has broken, it can stop the CNC controller. To keep the wire from breaking or short-circuiting with the workpiece, a current monitor counts sparks between the wire and workpiece and uses this to predict whether the wire is getting too close to the metal, in which case it slows down the movement.

As a first test, [Inofid] cut through a five by three centimeters-thick block of aluminium, taking two hours but producing a clean cut. To speed up the next cut, [Inofid] added a pump and filter to remove sludge from the cutting area. The next cut was an aluminium gear, and then a meshing steel gear, which took about ten hours but turned out well.

EDMs of various kinds appear here from time to time, particularly since the popularization of 3D printers. We’ve even seen one built into a lathe.

Thanks to [Keith Olson] for the tip!

It shouldn’t be any surprise that NFC and similar RFID implementations are capable of providing power to a receiver, since this is after all how RFID tags can work without a battery. The question is more whether you can do more with NFC than just briefly power some low-power circuitry to spit out some data. This is the topic of a recent [Denki Otaku] video.

Although both Qi and NFC use electromagnetic induction, they differ in the frequency and correspondingly the maximum power that they can deliver to a receiver. For NFC this is around a Watt, with the used NFC module supporting up to 250 mW, which already sets the rough scope of what one can expect from an NFC-powered device. That said, an NFC transmitter and receiver can be significantly smaller than those for Qi due to the much higher frequency.

An additional benefit of NFC is that it offers more freedom to the user in its protocol in terms of user data, which is useful for applications where you don’t just want to power a device. In the video an MCU and IMU are powered along with an OLED display, which demonstrates wireless charging as well as data transfer of the IMU data to a second MCU.

The benefits of NFC over Qi would thus be the smaller antenna size, and depending on the used NFC implementation also charging and data transfer at the same time.

If you’ve been paying any attention to the renewable energy space, you’ll know that generation isn’t really the problem anymore. Solar panels are cheap, and wind turbines are everywhere. The problem is matching generation with demand—sometimes there’s too much wind and sun, and sometimes there’s not enough. Ideally, you could store that energy somewhere, and deploy it when you need it.

The answer everyone keeps reaching for is lithium-ion batteries, and they work just fine. However, there’s a competing technology that’s been quietly scaling up in the background—the vanadium flow battery. It has some unique advantages that could see it rise to prominence in the world of large-scale grid storage.

The Juice That Stores Juice

Flow batteries are beautiful in their simplicity, storing charge in huge tanks full of liquid electrolyte rather than in gel-like materials sandwiched between solid electrodes as per a regular battery. Specifically, two big tanks of vanadium ions, typically dissolved in sulfuric acid. By pumping the electrolyte through a cell stack where the electrochemical reaction happens, you generate electricity. Getting more power is as simple as adding more cell stacks, while increasing the battery’s capacity is as simple as getting bigger tanks full of more electrolyte. The two variables are almost entirely decoupled, which is an extremely elegant property for a grid-scale storage system. It makes right-sizing the system a cinch, it’s simply a matter of scale. These batteries also have the property of surviving tens of thousands of charge cycles without damage, and lifespans measured in decades.

The chemistry itself works out quite tidily. Both the positive and negative electrolyte use vanadium, just in different oxidation states. The positive side hosts VO₂⁺ and VO²⁺ ions, while the negative side works with V²⁺ and V³⁺ ions. These solutions are pumped through a cell, either side of a permeable membrane that allows proton exchange. When the battery is being discharged, electrons leave the anode electrolyte and are transferred through the external load to the cathode electrolyte; this is balanced by the transfer of protons across the membrane. During charging, the opposite occurs.

A neat side-benefit of this is that because the battery uses the same element on both sides of the membrane, cross-contamination between the two tanks — an inevitable consequence of some ions sneaking through the membrane over thousands of cycles — doesn’t actually kill the battery. The electrolyte merely needs to be rebalanced and normal operation can resume. This single-element trick also means the electrolyte has a very long service life. It doesn’t degrade in the way an electrolyte in a regular battery might. A well-maintained vanadium flow battery can run for ten to twenty years with minimal capacity loss, and at end of life, that vanadium electrolyte still has value. It can be sold, recycled, or reprocessed as needed. Meanwhile, the electrodes in the cell stack and the pumps and machinery that moves the electrolyte around can be serviced or replaced as needed. It’s a very different scenario compared to lithium-ion cells, where recycling the raw materials involves great mechanical and chemical complexity. 

There is a complexity gain versus traditional batteries, in that moving all the electrolyte around requires mechanical pumps that in turn draw power to operate. These batteries are also not particularly compact, nor efficient in terms of energy-to-volume ratio. However, these problems are offset with the ease of scaling and maintaining them.

Deployment

In the real world, vanadium flow batteries are starting to hit the big time. The largest example in the world is a Chinese project, consisting of a 200 MW battery in Jimusaer, with a total capacity of 1000 MWh, built by Rongke Power.  The second largest installation, installed in the city of Ushi in 2024, has a capacity of 700 MWh and can discharge 175 MW to the grid, and was constructed by the same firm. These batteries are comparable in power output to the Victorian Big Battery, a lithium ion installation that outputs 300 MW at peak, but far larger in capacity, as the Australian installation tops out at just 450 MWh by comparison. These installs build upon a previous effort to install a 100 MW battery in Dalian with 400 MWh capacity, along with smaller projects in Shenyang and Zongkyang that operate at sub-10MW levels. The batteries are intended to be used to support grid stability in their local grids. They also have grid-forming capabilities, which means that the flow battery can be used to do a black start, helping to bring traditional thermal generation units online in the event of a total grid collapse.

Australia has also been leaping to adopt vanadium flow battery technology, too. The country is well known for having a huge install base of rooftop solar, which has created a difficult-to-control grid at times. The abundance of sunlight and solar generation during the day has lead to huge peaks where power prices at times turn negative, and the goal is to add storage so that this power can be stored for more effective use over longer time periods.

In South Australia, a small project has proven the viability of vanadium flow batteries in local conditions. The Co-Located Vanadium Flow Battery Storage and Solar project in Neuroodla was installed by Yadlamalka Energy, and combined photovoltaic generation and storage into a single site. The project’s goal was to demonstrate the value of vanadium flow batteries for providing both simple energy storage and frequency control services to the grid. It’s a relatively small installation, of just 2MW output and 8MWh capacity, paired with 6MWp of solar panels on site. The build was located adjacent to the Neuroodla substation for easy connection to the grid. The project faced some challenges in terms of power derating during the hottest local conditions, and with some limitations on power deployment and energy trading based on the inverter capabilities at the site. Ultimately, though, the project was able to generate serious revenue even with its limited capacity, thanks in part to energy price volatility in the local market as solar peaks and troughs occurred on a regular basis.

Over in Western Australia, sights are being set much higher. The state government has put out an expression of interest for a 50 MW, 500MWh vanadium flow battery to be installed in Kalgoorlie. The project is backed by $150 million in government funding, and hopes to offer a mighty 10-hour discharge capability to the grid. The project hopes to be up and running by 2029, relying on locally-produced vanadium to fill the tanks.

Every now and then in our travels we come upon a project with such an obvious need that it’s almost a surprise nobody has thought of doing it before. So it is with [Elehobica]’s project, an audio recorder for S/PDIF audio streams. It’s the device you could have used, years ago!

S/PDIF, or its optical fiber cousin TOSLINK, is the digital output you’ll find on the back of Hi-Fi equipment, it’s a serial encoding of an uncompressed digital audio data stream dating from the era when CDs were new. Its relative simplicity may be what’s given it longevity — it’s easy to implement so it plugs into pretty much everything.

Perhaps back in the day it might have been a pain for an 8-bit microprocessor to handle, but in 2026 it’s no bother for a Raspberry Pi Pico. The project is a small PCB with the Pico, a few interface components, and an SD card socket, and it sends what it hears on the input to the card as WAV files. We particularly like its smart sample rate and bit depth detection, and the way it cuts up tracks based on periods of silence. If you work with SPD/IF, this is going to be a useful tool.

Perhaps it could even be fed with a laser!

When life gives you lemons, you make lemonade. What if life gives you a pile of old e-book readers? Well, when [spiritplumber] got box of old Nook Simple Touch devices, he decided to design solar-powered cases to help boost the old batteries. It makes perfect sense to us: sunlight readable screen, sunlight chargeable battery.

It looks like he’s got a pair of panels built into the 3D printed case. He recommends using any TP4056-based charger, and tying into the battery test points, not the 5 V supply. It won’t hurt anything if you do, apparently, but the device will think it’s plugged in an refuse to turn off the WiFi. That’s no big deal when you’ve got a continental power grid on the other end of the cable, but charging from a small panel on the back of the case doesn’t always give you enough juice to waste on unneeded radio activity. Especially indoors — these panels are apparently big enough to trickle-charge the device under artificial light, which is a nice, if doubtless slow feature.

The design is open source, and includes SketchUp design files as well as the exported .STL, so if you’ve got a hankering to edit this to fit a different e-book reader, you can. He also provides a handy-dandy guide to root this model of Nook, and if you’re on Hackaday we probably don’t need to explain why you might want to.

We’ve seen the Nook Simple Touch go some interesting places — like into the clouds as a glider computer — but solar power is a new hack for this device, at least on this site. We don’t know if [spiritplumber] has a green thumb, but he’s evidently got some environmental bones in his body: his last featured project was about improving quadcopter efficiency with a wing and a prayer.

The ionosphere is of great importance to shortwave radio transmissions, since it allows radio waves to be refracted and reflected over the horizon, and it’s therefore unfortunate that the height and thickness of the ionosphere depends on the time of day or night, weather, season, and the solar cycle. To get a better idea of current transmission conditions, [mircemk] built this shortwave propagation monitor.

The monitor provides a basic measure of ionosphere conditions by measuring the strength of received shortwave signals: if the conditions for transmission are good, it should receive a relatively high level of existing signals, and a weak signal if conditions are bad. It has an external antenna connected to a signal strength indicator circuit based on the CA3089, which amplifies signals in the 1-40 MHz range and outputs a smoothed voltage indicating the RF energy in this range. The output signal can be read by any voltmeter, in this case an Arduino Nano with an OLED display. Assuming the same antenna is always used, the signal should noticeably fluctuate between night and day as the solar wind affects the ionosphere.

Of course, the distance at which you’ll be receiving a signal means nothing unless you have a receiver, which can range from the antique to the modern.

Making stuff cool and keeping it that way has been a pretty essential part of human civilization for thousands of years, with only in the past few hundred years man-made methods having become available that remove the reliance on the whims of nature and lugging around massive blocks of ice. The most important cooling method is undoubtedly that of vapor-compression refrigeration, but this is hardly the only method to transfer thermal energy from one location to another.

For example, we recently covered an elastocaloric cooling project by a group of scientists that uses strips of NiTi metal. By flexing these they induce a cooling effect which when put in a number of stages serves to transfer a significant amount of thermal energy between both sides, much like a vapor-compression system but without the gases and compressor. Meanwhile the Seebeck effect is relatively well-known from Peltier thermocouple devices, and features heavily in portable refrigerators and kin where these solid-state devices can also transfer thermal energy.

Of course, along with how they function the major question with all of these cooling technologies is how efficient they are, as this determines when you’d want to even consider them for a specific application.

The Science Of Cold

Although as animals we have an intuitive understanding of what concepts like ‘cold’ and ‘hot’ are in the sense of comfort levels, on a fundamental level the related concept of temperature is about the kinetic energy of the particles in a system. Essentially, the more kinetic energy exists in the system, the higher the temperature of said system is, regardless of whether it’s a liquid, gas, solid or plasma. Hence a temperature of zero Kelvin is the complete absence of any such kinetic energy in the system, also known as the Third Law of thermodynamics:

As the temperature of a system approaches absolute zero, all processes cease and the entropy of the system approaches a minimum value.

When we talk about moving thermal energy from one location to another – as in refrigeration – this thus means transferring said energy from one system to another in some fashion, something which is covered by the First Law of thermodynamics:

In a process without transfer of matter, the change in internal energy, , of a thermodynamic system is equal to the energy gained as heat, , less the thermodynamic work, , done by the system on its surroundings.

In the case of a hot water bottle or ice bag we are actively changing the energy balance of a system by transferring matter. This makes such transfers rather lossy, which is not a quality that is generally desirable in a refrigeration system. Thus we prefer a closed system in which the matter is ideally never lost, and thus all the energy transfer occurs via reversible processes.

Vapor-Compression

In vapor-compression refrigeration a liquid – the refrigerant – is circulated through the system, alternately changing state into a gas by absorbing thermal energy from the environment, before shedding this energy again while condensing back into a liquid.

A key component in this system is the compressor, which takes in the saturated vapor. This means that said vapor contains enough energy to effect the liquid-gaseous transition, but is still pretty close to the condensing point.

By compressing this vapor into a smaller volume its temperature increases since roughly the same amount of kinetic energy exists within the system. This superheated vapor then passes through the condenser, like the radiator found at the back of the average kitchen refrigerator. Here the superheated vapor condenses back into a liquid, with the higher temperature and pressure helping to make the condensing process more efficient. This is also why said refrigerator radiator can feel so warm to the touch.

The role of the expansion valve is effectively the opposite of the compressor: as the name suggests this is where the liquid refrigerant at high pressure suddenly transitions back to a low pressure, causing adiabatic flash evaporation of part of the liquid into a vapor. This reduces the temperature of the refrigerant, making it colder than e.g. the inside of the refrigerator and drawing in kinetic energy from the air inside said refrigerator before the vapor makes its way to the compressor again.

Elastocaloric Cooling

With elastocaloric cooling (ECC) there is no liquid refrigerant or a pressure differential. Instead they rely on the elastocaloric effect, which is thermomechanical in nature.

Similar to how the refrigerant with vapor-compression refrigeration can absorb energy as it transitions from liquid to vapor and vice versa, with the elastocaloric effect it is the material itself that absorbs thermal energy from its environment when it’s mechanically loaded.

The aforementioned NiTi alloy is also known as a shape-memory alloy (SMA), which are generally known to be heat sensitive, finding use in applications like thermal fuses and sensors.

While the application of heat or cold can cause the deformation, this also works the other way around when mechanical force is applied. This is readily demonstrated with a strip of NiTi SMA and a thermal camera, as in this video by Helge Wurst:

As the strip is bent, the area experiencing the deformation becomes rather warm to the touch, with subsequent relaxation causing the same area to become cold to the touch.

Using such strips and mechanical actuators capable of applying 900 MPa of pressure, Guoan Zhou et al. were able to achieve freezing temperatures. They did this by combining multiple of such elastocaloric stages with CaCl₂ as heat-exchange fluid. This is not a mainstream cooling method so far, but it should be quite reliable and low-maintenance.

Magnetocaloric Cooling

The magnetocaloric effect (MCE) was first observed in 1881 by German physicist Emil Warburg, with the early 20th century seeing significant progress towards using it for cooling applications. This particular effect as the name suggests consists of exposing a material to a magnetic field, with this material then drawing in thermal energy. Upon removal of the magnetic field the material sheds this gained energy as well as some additional energy, thus cooling down relative to its environment.

Similar to the elastocaloric effect, this relies on an adiabatic process: without the transfer of any matter or entropy. This makes it a fully reversible process that can be repeated by successive applications of said magnetic field.

The biggest disadvantage with this effect for cooling purposes is that it’s only a very strong effect (giant MCE, or GMCE) in a limited number of alloys discovered so far. The first significant here was a rare-earth gadolinium-based alloy, Gd₅(Si₂Ge₂), that showed GMCE at 270 K. This relatively low temperature and the use of rare-earths made this a tough sell.

More recently discovered alloys like Ni₂Mn-X, where X is a variety of additives, display the GMCE near room temperature and even saw GE demonstrate an Ni-Mn-based magnetic refrigerator in 2014. So far commercialization of GMCE-based refrigeration is still rather limited but there is a push to make it work for generally less efficient vapor-compression-based home refrigerators.

Electrocaloric Cooling

Although easy to confuse with the magnetocaloric effect, the electrocaloric effect (ECE) pertains to the application of an electric field in dielectric materials. The effect is roughly the same, with the dipoles in the material either assuming an ordered or disordered state, depending on whether the field is respectively applied or turned off.

So far ECE-based cooling hasn’t seen commercialization yet either, though the past years there have been a range of breakthroughs, with for example Xin Chen et al. demonstrating ECE polymer films in 2023 that was subsequently used to create a thin-film refrigerator prototype with. This was claimed to achieve a Coefficient of Performance (COP) of a rather astounding 24, which compared to traditional heat pumps would make it a rather interesting solution if it can be commercialized.

Thermoelectric Cooling

The thermoelectric effect and the associated Peltier cooling devices are probably the most well-known and most heavily commercialized on this list along with vapor-compression. Within the thermoelectric effect, the Peltier effect concerns thermocouples and their associated temperature differences, thus lending its name to what are alternatively called ‘Peltier coolers’ as well as ‘thermoelectric coolers’, or TECs.

Rather than a refrigerant or rearranging of dipoles here the transfer of kinetic energy is performed using charge carriers within the TEC. On average charge carriers move to the ‘cool’ side, allowing them to transfer heat away from the other side.

As is well-known, this Peltier effect is rather limited when used as a heat pump, with very low efficiency and strict limitations on temperature differences. This is why their use in dehumidifiers and portable refrigerators is at best questionable.

The main reason why TECs are so popular can be said to be due to vapor-compression refrigeration being so bulky and neither elastocaloric, nor MCE, nor ECE solid-state coolers being quite ready for prime-time yet at the low-low price level that TECs can achieve due to being dead-simple semiconductor devices.

Pulse Tube Cooling

Another interesting, partially solid-state cooling method is the pulse tube refrigerator (PTR), which has seen limited use in commercial and other applications. Its main advantage is that it can be used as a cryocooler, making it ideal for space telescopes where sensors have to remain super-cold.

At its core it’s reminiscent of vapor-compression refrigerating, in that it uses a gas and a compressor, yet there’s no circulating loop of refrigerant. Inside the tube a piston alternately compresses the gas – often helium – which forces it through the regenerator. As the compression raises the temperature of the gas, this heat is then passed onto the material of the regenerator. On its way back through the regenerator this heat is then returned to the gas, explaining the name of this component.

The hot and cold sides of the regenerator are hereby used for cooling, though other PTR configurations are possible, such as the coaxial design. The relatively straightforward mechanical design and low temperatures achievable are why hobbyists are tinkering with PTRs in order to do things like making their own liquid nitrogen.

Chill Choices

Ultimately the question of what the right cooling method is for your particular task depends on a range of factors, including the required efficiency, available space and whether or not that big research grant budget just became available.

In terms of commercially available options that aren’t outrageously expensive, your options are somewhat limited, especially if you do not have a lot of space available. It’s possible that in a number of years these alternate technologies will be commercialized and wipe the floor with TECs in particular, but unless you’re currently heavily into tinkering with strips of NiTi SMA to build your own cooler, the primary options would seem to be either vapor-compression or TECs.

That said, considering that only a hundred years ago we were only just beginning to transition from iceboxes to vapor-compression refrigeration, it’s already pretty neat that we have some rather chill options to use today, and absolutely cool ones to look forward to.

Featured image: “Frosted Flakes“, National Park Service photo by [Neal Herbert]. Thumbnail image: “Frost” by [XoMEoX].