inverter

66 Articles

The Vibrating Reed Inverter: Possibly The Simplest Inverter You Can Make

March 29, 2021 by 27 Comments

Those of us who work on the road have a constant dread of being stuck somewhere without power, facing a race between a publication deadline and a fast-failing laptop battery. We’re extremely fortunate then to live in an age in which a cheap, lightweight, and efficient solid-state switch-mode inverter can give us mains power from a car cigarette lighter socket and save the day. Before these inverters came much heavier devices whose transistors switched at the 50Hz line speed, and before them came electromechanical devices such as the rotary converter or the vibrating reed inverter. It’s this last type that [Robert Murray-Smith] has taken a look at, making what he positions as the simplest inverter that it’s possible.

If you’ve ever played with relays, you’ll probably be aware that a relay can be wired as a buzzer, and it’s this property that a vibrating reed inverter harnesses. He takes an octal relay and wires it up with a small mains transformer for an immediate and very cheap inverter. It’s not perfect, as he points out the frequency isn’t right. The relay will eventually wear out unless the arcing problem is improved with the addition of a capacitor. But it does make a rough and ready inverter if you find yourself in a MacGyver-style tight spot with only your junk box for salvation.

If inverters pique your interest, it might benefit you to know how they work.

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3D Printed Electric Motor Wants To Take Flight

November 18, 2020 by 49 Comments

Airplanes and spacecraft have a big problem. The more engine or fuel you have, the more engine and fuel you need. That’s why aircraft use techniques to have lightweight structural members and do everything they can to minimize weight. A lighter craft can go further and carry more payload or supercargo. Electric motors are very attractive for aircraft, but they suffer from having less efficiency per kilogram than competing technologies. H3X thinks they can change that with their HPDM-250 integrated motor and inverter.

Although the 15 kg motor is still in testing, the claimed specifications are impressive: a peak power of 250 kW for 30 seconds and continuous torque of 95 Nm and 200 kW sustained. The company claims 96.7% efficiency. The claims are for the motor running at 20,000 RPM, so you’d need to add the weight of a gearbox for practical applications, but the company says this adds a mere 3 kg to the overall weight.

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Heavy Metal Power Bank Uses Tool Batteries

October 10, 2020 by 17 Comments

At one time or another, most of us have seen a gadget for sale and thought we could build something similar for cheaper. Of course, we’re almost always wrong. Not about being able to build it, mind you. But when you add up the cost of the materials, the tool or two you almost inevitably end up buying, and the time spent chasing perfection, you’re lucky if you haven’t doubled the original price.

We’re not sure how much money [Taylor Hay] ended up saving by building his own portable power bank. But we do know it’s a gorgeous piece of hardware that’s certainly built far better than the average consumer gadget. The CNC-cut aluminum side panels look like something pulled out of a tank, and while we know some might balk at the 3D printed internal frame, we’re confident you could use this thing as an impromptu step stool without a problem.

Inside there’s 150 watt 240 VAC inverter, complete with a temperature-controlled fan to keep it cool under load. There are also four USB ports providing 2.1 A each, a standard 12 VDC accessory port, and a LED display that shows battery voltage and current being drawn. Rather than come up with his own battery pack, [Taylor] used a 3D printed interface that accepts an 18 V Milwaukee cordless tool battery. Naturally, the design could be adapted to take another brand’s cells if you were so inclined.

Around these parts, we know that a good project doesn’t have to be cheaper or even more practical than what’s already on the market. There’s an inherent value in building something exactly the way you want it that you simply can’t put a monetary price on.

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Build Your Own Grid Tie Inverter

May 29, 2020 by 39 Comments

Inverters that convert DC into AC are pretty commonplace, some cars even have standard AC receptacles in them for you to plug in your favorite appliance. However, there’s a particular type of inverter called a grid tie inverter that allows you not only to make AC, but also inject it back through an AC outlet to power other devices in conjunction with the normal AC service. Why? Maybe you want to use your own generator or solar power. In some cases, the power company will pay you if you produce more power than you consume. Maybe you just want to know you can do it. That seems to be the motivation behind [fotherby’s] build, which is quite substantial.

The setup only handles about 60 watts, but it does all the functions you need: DC to AC conversion as well as phase and voltage matching. Actually, just converting DC to AC is almost trivial if you don’t care about the waveform. But in this case, you do care that you can create an AC signal to match the one already on the line.

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Improbably Cheap Pocket Welder Gets An ESP32 Makeover

November 4, 2019 by 25 Comments

If you move in certain shady circles, you may have noticed the crop of improbably cheap “pocket welders” popping up on the market these days. They’re all variations on a theme, most with wildly optimistic specs minimal accessories of the lowest possible quality. But their tiny size and matching price make them irresistible to the would-be welder, as well as attractive to hardware hackers.

With a 220-V outlet in the garage waiting to be filled and well-knowing the risks, [Mr. RC-Cam] purchased one of these diminutive welding machines. Its shortcomings were immediately apparent, and a complete rework of the welder was undertaken. After addressing safety issues like the lack of a ground connection, [Mr. RC-Cam] added a color-matched 3D-printed hood to house a fancy new LCD touchscreen display. Backing that up is an ESP32 with Bluetooth, which supports remote control via a key fob. He also added a current sense board that uses the welder’s current shunt to measure welding current. Expediently calibrated using a waffle iron and a milli-ohmmeter, the sensor showed that the 200A max advertised for the welder was more like 100A. He tried adding some big electrolytics to fix the current issues, but no dice. With a decent stinger and ground clamp, the modified welder is good enough for his needs, and much was learned in the process. We call that a hacking win.

As an aside, [This Old Tony] recently did a review on a similar welder if you want more details on the internals. We also covered the conversion of a buzz-box to a TIG welder recently, should that be more your style.

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A Lot Of Volts For Not A Lot

July 13, 2019 by 23 Comments

There was a time when high voltage in electronic devices was commonplace, and projects driving some form of vacuum or ionisation tube simply had to make use of a mains transformer from a handy tube radio or similar. In 2019 we don’t often have the need for more than a few volts, so when a Geiger–Müller tube needs a bit of juice, we’re stumped. [David Christensen] approached this problem by creating his own inverter, which can produce up to 1 kV from a 12 V supply.

Instead of opting for a flyback supply he’s taken a traditional step-up approach, winding his own transformer on a ferrite core. It has a centre-tapped primary which he drives in push-pull with a couple of MOSFETS, and on its secondary is a voltage multiplier chain. The MOSFETs take their drive at between 25 kHz and 50 kHz from a 555 timer circuit, and there is no feedback circuit.

It’s fair to say that this is a somewhat hair-raising circuit, particularly as he claims that it is capable of delivering that 1 kV at 20 W. It’s usual for high-voltage supplies driving very high impedance loads to incorporate a set of high-value resistors on their outputs to increase their internal impedance such that their danger is reduced. We’d thus exercise extreme care around this device, though we can see a lot of value in his description of the transformer winding.

We can’t criticise this circuit too much though, because some of us have been known to produce far hackier high voltage PSUs.

Split Flap Clock Keeps Time Thanks To Custom Frequency Converter

June 23, 2019 by 6 Comments

Why would anyone put as much effort into resurrecting a 1970s split-flap clock as [mitxela] did when he built this custom PLL frequency converter? We’re not sure, but we do like the results.

The clock is a recreation of the prop from the classic 1993 film, Groundhog Day, rigged to play nothing but “I Got You Babe” using the usual sound boards and such. But the interesting part was getting the clock mechanism keeping decent time. Sourced from the US, the clock wanted 120 VAC at 60 Hz rather than the 240 VAC, 50 Hz UK standard. The voltage difference could be easily handled, but the frequency mismatch left the clock running unacceptably slow.

That’s when [mitxela] went all in and designed a custom circuit to convert the 50 Hz mains to 60 Hz. What’s more, he decided to lock his synthesized waveform to the supply current, to take advantage of the long-term frequency control power producers are known for. The write-up goes into great detail about the design of the phase-locked loop (PLL), which uses an ATtiny85 to monitor the rising edge of the mains supply and generate the PWM signal that results in six cycles out for every five cycles in. The result is that the clock keeps decent time now, and he learned a little something too.

If the name [mitxela] seems familiar, it’s probably because we’ve featured many of his awesome builds before. From ludicrous-scale soldering to a thermal printer Polaroid to a Morse-to-USB keyboard, he’s always got something cool going on.