Measuring current draw of home shop tools

Using Homebrew Coils To Measure Mains Current, And Taking The Circuit Breaker Challenge

Like many hackers, [Matthias Wandel] has a penchant for measuring the world around him, and quantifying the goings-on in his home is a bit of a hobby. And so when it came time to sense the current flowing in the wires of his house, he did what any of us would do: he built his own current sensing system.

What’s that you say? Any sane hacker would buy something like a Kill-a-Watt meter, or even perhaps use commercially available current transformers? Perhaps, but then one wouldn’t exactly be hacking, would one? [Matthias] opted to roll his own sensors for quite practical reasons: commercial meters don’t quite have the response time to catch the start-up spikes he was interested in seeing, and clamp-on current transformers require splitting the jacket on the nonmetallic cabling used in most residential wiring — doing so tends to run afoul of building codes. So his sensors were simply coils of wire shaped to fit the outside of the NM cable, with a bit of filtering to provide a cleaner signal in the high-noise environment of a lot of switch-mode power supplies.

Fed through an ADC board into a Raspberry Pi, [Matthias]’ sensor system did a surprisingly good job of catching the start-up surge of some tools around the shop. That led to the entertaining “Circuit Breaker Challenge” part of the video below, wherein we learn just what it really takes to pop the breaker on a 15-Amp branch circuit. Spoiler alert: it’s a lot.

Speaking of staying safe with mains current, we’ve covered a little bit about how circuit protection works before. If you need a deeper dive into circuit breakers, we’ve got that too.

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Automatic Coil Winder Gets It Done With Simple Hardware And Software

We’ve grown to expect seeing mechatronics project incorporate a standard complement of components, things like stepper motors, Arduinos, lead screws, timing belts and pulleys, and aluminum extrusions. So when a project comes along that breaks that mold, even just a little, we sit up and take notice.

Departing somewhat from this hardware hacking lingua franca is [tuenhidiy]’s automatic coil winder, which instead of aluminum extrusions and 3D-printed connectors uses simple PVC pipe and fittings as a frame. Cheap, readily available, and easily worked, the PVC does a fine job here, and likely would on any project where forces are low and precision isn’t critical. The PVC frame holds two drive motors, one to wind the wire onto a form and one to drive a lead screw that moves the form back and forth. An Arduino with a CNC shield takes care of driving the motors, and the G-code needed to do so is generated by a simple spreadsheet that takes into account the number turns desired, the number of layers, the dimensions of the spool, and the diameters of the wire. The video below shows the machine going through its paces, with pretty neat and tidy results.

Being such a tedious task, this is far from the first coil winder we’ve seen. Some adhere to the standard design language, some take off in another direction entirely, but they’re all instructive and fun to watch in action.

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Homebrew Coil Winder Makes Toroids A Snap To Wind

Anyone who has ever wound a toroidal coil by hand can tell you that it’s not exactly a fun job. Even with the kinds of coils used in chokes and transformers for ham radio, which generally have relatively few windings, passing all that wire through the toroid time after time is a pain. And woe unto anyone who guesses wrong on how much wire the job will take.

To solve those problems, [Sandeep] came up with this clever and effective toroid winder. The idea is to pass a small spool of magnet wire through the toroid’s core while simultaneously rotating the toroid to spread the windings out as evenly as possible. That obviously requires a winding ring that can be opened up to allow the toroid form to be inserted; [Sandeep] chose to make his winding ring out of plywood with a slit in it. Carrying the wire spool, the winding ring rotates on a C-shaped fixture that brackets the toroid, which itself rotates under stepper motor control on a trio of rollers. An Arduino controls the rotation of both motors, controlling the number of windings and their spread on the form. lacking a ferrite core for testing, [Sandeep] used a plywood ring as a stand-in, but the results are satisfying enough to make any manual coil-winder envious.

We love tools like this that make a boring job a snap. Whether it’s cutting wires for wiring harnesses or winding guitar pickups, tools like these are well worth the time spent to build them. But we suppose when it comes to toroid winding, one could always cheat.

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Roll Your Own – Toilet Paper

Toilet paper has become a hot button issue over the last month or so, and the pandemic prompted panic buying, and consequent shortages. Now there are adequate supplies, at least where this is being written, but sometimes one’s rolls aren’t the domestic items we’re all used to. This happened to [Ebenezer], who had some of the large size rolls suitable for toilet roll dispensers rather than a domestic bathroom. To solve this problem he made a makeshift toilet roll winder.

The adventures of small dogs aside, we all know that toilet rolls unroll themselves very easily indeed but are a significant pain to get back on the roll once they have done so. Rolling toilet paper must therefore be an exact science of velocity and tension, which he approached with a 3D printed shaft that mounts a toilet roll tube in a Ryobi drill. Getting the tension right was a bit tricky, but we’re extremely impressed with the result. Like him we’d have expected some side-to-side movement, but there was very little and a near perfect toilet roll was the result.

This is a simple hack, but one extremely well executed, and that it does something we might normally consider near-impossible is a bonus. Of course, should you wish to ration your toilet paper, you can always print it.

3D-Printed Transformer Disappoints, But Enlightens

Transformers are deceptively simple devices. Just coils of wire sharing a common core, they tempt you into thinking you can make your own, and in many cases you can. But DIY transformers have their limits, as [Great Scott!] learned when he tried to 3D-print his own power transformer.

To be fair, the bulk of the video below has nothing to do with 3D-printing of transformer coils. The first part concentrates on building transformer cores up from scratch with commercially available punched steel laminations, in much the same way that manufacturers do it. Going through that exercise and the calculations it requires is a great intro to transformer design, and worth the price of admission alone. With the proper number of turns wound onto a bobbin, the laminated E and I pieces were woven together into a core, and the resulting transformer worked pretty much as expected.

The 3D-printed core was another story, though. [Great Scott!] printed E and I pieces from the same iron-infused PLA filament that he used when he 3D-printed a brushless DC motor. The laminations had nowhere near the magnetic flux density of the commercial stampings, though, completely changing the characteristics of the transformer. His conclusion is that a printed transformer isn’t possible, at least not at 50-Hz mains frequency. Printed cores might have a place at RF frequencies, though.

In the end, it wasn’t too surprising a result, but the video is a great intro to transformer design. And we always appreciate the “DIY or Buy” style videos that [Great Scott!] does, like his home-brew DC inverter or build vs. buy lithium-ion battery packs.

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Rewound And Rewired BLDC Makes A Half-Decent Generator

What’s the best way to turn a high-powered brushless DC motor optimized for hobby use into a decent low-RPM generator? Do you take a purely mechanical approach and slap a gearbox on the shaft? Or do you tackle the problem electrically?

The latter approach is what [GreatScott!] settled on with his BLDC rewinding and rewiring project. Having previously explored which motors have the best potential as generators, he knew the essential problem: in rough terms, hobby BLDCs are optimized for turning volts into RPMs, and not the other way around. He started with a teardown of a small motor, to understand the mechanical challenges involved, then moved onto a larger motor. The bigger motor was stubborn, but with some elbow grease, a lot of scratches, and some destroyed bearings, the motor was relieved of both its rotor and stator. The windings were stripped off and replaced with heavier magnet wire with more turns per pole than the original. The effect of this was to drive the Kv down and allow better performance at low RPMs. Things looked even better when the windings were rewired from delta to wye configuration.

The take-home lesson is probably to use a generator where you need a generator and let motors be motors. But we appreciate [GreatScott!]’s lesson on the innards of BLDCs nonetheless, and his other work in the “DIY or buy?” vein. Whether you want to make your own inverter, turn a hard drive motor into an encoder, or roll your own lithium battery pack, he’s done a lot of the dirty work already.

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Stepper Motor Mods Improve CNC Flat Coil Winder

Finding just the right off-the-shelf part to complete a project is a satisfying experience – buy it, bolt it on, get on with business. Things don’t always work out so easily, though, which often requires the even more satisfying experience of modifying an existing part to do the job. Modifying a stepper motor by drilling a hole down its shaft probably qualifies for the satisfying mod of the year award.

That’s what [Russ] did to make needed improvements to his CNC flat-coil winder, which uses a modified delta-style 3D-printer to roll fine magnet wire out onto adhesive paper to form beautiful coils of various sizes and shapes. [Russ] has been tweaking his design since we featured it and coming up with better and better coils. While experimenting, the passive roller at the business end proved to be a liability. The problem was that the contact point lagged behind the center axis of the delta, leading to problems with the G-code. [Russ] figured that a new tool with the contact point at the dead center would help. The downside would be having to actively swivel the tool in concert with the X- and Y-axis movements. The video below shows his mods, which include disassembling the NEMA-17 stepper and drilling out the shaft to pass the coil wire. [Russ] also spent some time reversing the rotor in the frame and provided a small preload spring to keep the coil roller in contact with the paper.

A real-time coil winding session starts at the 21:18 mark, and we’ve got to admit it’s oddly soothing to watch. We’re not sure exactly what [Russ] intends to do with these coils, and by his own admission, neither is he. But it’s still pretty cool to see, and the stepper motor mods are a neat trick to keep in mind.

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