Electronic Rule-Breakers That Crept into Everything We Use

Students in grade school are usually taught square roots before or during junior high, and with these lessons comes one immutable fact: It’s forbidden to take the square root of a negative number. Not too much longer after that, however, the students all learn that this is a big fat lie and that taking square roots of negative numbers is critically important in many fields of study.

There’s a similar “lie” in existence for anyone studying electricity, whether they’re physicists, engineers, or electronics enthusiasts: it’s only possible to raise and lower voltage levels on alternating current (AC) circuits using a transformer. If you generate direct current (DC) voltage through the use of a generator or a battery and need a different voltage level for your new power distribution system in New York or your battery-powered electronics, well, you’re out of luck.

Of course we all know that DC-DC conversion, like taking square roots of negative numbers, is not only possible but fundamental to most modern electronics. After all, there are certain integrated circuits that we can drop into our projects to magically transform one DC voltage to another DC voltage without thinking too much about the problem. And we’re not just talking about linear regulators, which can only drop the source voltage to a smaller level by dissipating energy. Using switch mode DC-DC converters, it’s possible to decrease or increase a DC voltage, and do it at around 95% efficiency or higher for some applications (compared to around 30% efficiency for any linear regulator).  But unraveling the mystery of how switch-mode power supplies (SMPS) and other DC-DC converters work, and how they’re different from AC transformers, involves diving a little deeper.

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How a Hacker Jump Starts a Car

Here’s the Scenario: you need to get somewhere in a hurry. The problem is that your car has a dead battery and won’t turn over. The Obvious solution would be to call a friend for a jump. But is the friendless hacker out of luck in such a situation? Not if you can whip up a quick parts bin jump starter.

Clearly, [Kedar Nimbalkar]’s solution would be practical only under somewhat bizarre circumstances, so we’ll concentrate on what we can learn from it. A spare PC power supply provides the electrons – [Kedar]’s 250W supply pushes 15A at 12 volts, which is a pretty respectable amount of current. The voltage is a little anemic, though, so he pops it up to 14.2 volts with a 150W boost converter cooled with a PC fan. A dual panel meter reads out the voltage and current, but a VOM could substitute in a pinch. About the only thing you might not have on hand is a pair of  honking 10A diodes to keep current from creeping back into the boost converter. [Kedar] claims he got enough of a charge back in the battery in five minutes to start his car.

As jump-starting goes, this hack is a bit of a stretch. It’s not the first time we’ve seen a MacGyver’d jump starter, though, and you never know when the principles and hardware behind these hacks will come in handy.

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Programmable DC Backup Power Supply

The uninterruptible power supply was once a standard fixture in the small office/home office as a hedge against losing work when the electrons stop flowing from your AC outlet. Somewhat in decline as computing hardware shifts away from dedicated PCs toward tablets, phones and laptops, the UPS still has a lot of SOHO utility, and off-the-shelf AC units are easy to find. But if your needs run more to keeping the electrons flowing in one direction, then you might want to look at [Kedar Nimbalkar]’s programmable DC backup power system.

Built inside a recycled ATX power supply case, [Kedar]’s project is heavy on off-the-shelf components, like a laptop power supply for juice, a buck converter to charge the 12 volt sealed lead acid battery, and a boost converter to raise the output to 19.6 volts. An Arduino and an optoisolator are in charge of controlling the charging cycle and switching the UPS from charging the battery to using it when mains voltage drops.

 If you need a DC UPS but would rather skip the battery, you could try running a Raspberry Pi with electrons stashed in a supercapacitor. Or if you’ve got an aging AC UPS, why not try beefing it up with marine batteries?

[Thanks for the tip, Morris]

Crowdfunding Follies: Debunking The Batteriser

It’s not on Kickstarter yet, but this product is already making its media debut, with features in all the tech blogs, an astonishing amount of print outlets, and spouted from the gaping maws of easily impressed rubes the world over. What is it? It’s the Batteriser, a tiny metal contraption that clips over AA, C, and D cells that reclaims the power trapped inside every dead battery. Yes, every dead battery you’ve ever thrown away still has up to 80% of its power remaining. Sounds like complete hogwash, right? That’s because it is.

[Dave Jones] put together a great video on the how comes and why nots of the Batteriser, and while doing so gives a great tutorial for debunking a product, heavily inspired by [Carl Sagan]’s Baloney Detection Kit. The real  debunking starts by verifying any assumptions, and the biggest fault of the Batteriser campaign is claiming 80% of a battery’s power is unused. Lucky for us, [Dave] has tons of tools and graphs to demonstrate this is not the case.

To verify the assumption that battery-powered devices will brown out after using only 20% of a battery’s available power, [Dave] does the most logical thing and looks at the data sheets for a battery. After using 20% of available power, these datasheets claim these batteries should be around 1.3V. Do devices brown out at 1.3V? Hook it up to a programmable power supply and find out.

It turns out every battery-powered device [Dave] could find worked perfectly until around 1.1V. Yes, that’s only 0.3V difference from 1.4V claimed by the patent for the Batteriser, but because of the battery discharge curve, that means 80% of the power in a normal device is already being used up. The premise of the Batteriser is invalid, and [Dave] demonstrates it’s a complete scam.

If a through debunking of the Batteriser’s claims wasn’t enough, [Dave] goes on to explain how it may actually be dangerous. The positive terminal of a battery is also the metal can, while the negative terminal is just a tiny nib of metal seperated from the rest of the battery by a gasket. Since the Batteriser is made of metal and serves as the ground for the boost converter circuit, it’s very, very close to shorting through the branding and logo emblazoned on a mylar wrapping each battery is shrouded with. One tiny nick in this insulator, and you have a direct short across the battery. That’s going to turn to heat, and there’s a lot of energy in a D cell; a failure mode for the Batteriser is a fire. That’s just terrible product design.

Video below.

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A Primer on Buck (and Boost) Converters

We all know that the reason the electrical system uses alternating current is because it’s easy to step the voltage up and down using a transformer, a feature which just isn’t possible with a DC system… or is it? Perhaps you’ve heard of mysterious DC-DC transformers before but never really wanted to look at the wizardry that makes them possible. Now, SparkFun Director of Engineering [Pete Dokter] has a tutorial which explains how these mysterious devices work.

Known as buck converters if they step the input voltage down and boost converters if they step the voltage up, [Pete] explains how these circuits exploit the properties of an inductor to resist changes in current flow. He goes into exquisite detail to explain how components like transistors or MOSFETs are used to switch the current flow to the inductor very rapidly, and just exactly what happens to the magnetic field which makes these devices possible.

The video gives a good amount of background knowledge if you’ve always wanted to understand these devices a little bit better. There are also a few projects floating around that exploit these devices, such as one that uses an AVR microcontroller to perform the switching for a small circuit, or another that uses the interesting properties of these circuits to follow the I-V curve of a solar panel to help charge a bank of batteries. The possibilities are endless!

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An ATtiny Boost Converter

This schematic is all you need to build your own voltage converter. [Lutz] needed a converter that could boost 5 V to 30 V to power a string of LEDs. The solution was to use low cost ATtiny85 and some passive components to implement a boost converter.

This circuit follows the classic boost converter topology, using the ATtiny85 to control the switch. The 10 ohm resistor is fed back into the microcontroller’s ADC input, allowing it to sense the output voltage. By measuring the output voltage and adjusting the duty cycle accordingly, the circuit can regulate to a specified voltage setpoint.

A potentiometer is used to change the brightness of the LEDs. The software reads the potentiometer’s output voltage and adjusts the voltage output of the circuit accordingly. Higher voltages result in brighter LEDs.

Of course, there’s many other ways to implement a boost converter. Most practical designs will use a chip designed for this specific purpose. However, if you’re interested in rolling your own, the source and LTSpice simulation files are available.

Afroman Demonstrates Boost Converters

If you need to regulate your power input down to a reasonable voltage for a project, you reach for a switching regulator, or failing that, an inefficient linear regulator. What if you need to boost the voltage inside a project? It’s boost converter time, and Afrotechmods is here to show you how they work.

In its simplest form, a boost converter can be built from only an inductor, a diode, a capacitor, and a transistor. By switching the transistor on and off with varying duty cycles, energy is stored in the inductor, and then sent straight to the capacitor. Calculating the values for the duty cycle, frequency, inductor, and the other various parts of a boost converter means a whole bunch of math, but following the recommended layout in the datasheets for boost and switching converters is generally good enough.

boostconverter

[Afroman]’s example circuit for this tutorial is a simple boost converter built around an LT1370 switching regulator. In addition to that there’s also a small regulator, diode, a few big caps and resistors, and a pot for the feedback pin. This is all you need to build a simple boost converter, and the pot tied to the feedback pin varies the duty cycle of the regulator, changing the output voltage.

It’s an extremely efficient way to boost voltage, measured by [Afroman] at over 80%. It’s also exceptionally easy to build, with just a handful of parts soldered directly onto a piece of perfboard.

Video below.

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