Afroman And The Case Of The Suspect Inverter

If you search the internet for 12 volt to mains AC inverter designs, the chances are you’ll encounter a simple circuit which has become rather ubiquitous. It features a 4047 CMOS astable multivibrator chip driving a pair of MOSFETs in a push-pull configuration which in turn drive a centre-tapped mains transformer in reverse. Not a new design, its variants and antecedents could be found even in those pre-Internet days when circuits came from books on the shelves of your local lending library.

afroman-inverter-featured[Afroman], no stranger to these pages, has published a video in which he investigates the 4047 inverter, and draws attention to some of its shortcomings. It is not the circuit’s lack of frequency stability with voltage that worries him, but the high-frequency ringing at the point of the square-wave switching when the device has an inadequate load. This can reach nearly 600 volts peak-to-peak with a 120 volt American transformer, or over a kilovolt if you live somewhere with 230 volt mains. The Internet’s suggested refinement, a capacitor on the output, only made the situation worse. As he remarks, it’s fine for powering a lightbulb, but you wouldn’t want it near your iPhone charger.

If this video achieves anything, it is a lesson to the uninitiated that while simple and popular designs can sometimes be absolute gems it must not be assumed that this is always the case.

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Build an Efficient Inverter, Win a Million Dollars

Little Box Challenge

Google and the IEEE are giving away a million dollar prize to an individual or team, that can build the most efficient and compact DC to AC inverter. The goal is to design and build a 2kW inverter with a power density greater than 50W per cubic inch. To put that in perspective, conventional solar string inverters have power densities around 0.5-3W per cubic Inch, and microinverters around 5W per cubic Inch. So in other words, an order of magnitude more efficient than what we have now.

For the challenge, the inverter needs to convert 450VDC, with a 10 ohm series resistor simulating a solar array, to 240VAC @ 60Hz. Testing will consist of powering various resistive, inductive and capacitive loads ranging from 0-2kVA. The inverter is expected to regulate voltage within 5%, and frequency within 0.05%, while keeping the enclosure below 60 degrees C, and conforming to FCC Part 15 B (Unintentional radiators).

If you and/or your team can figure out the most efficient topology, switching frequency, novel use of high power wide bandgap (WBG) semiconductors, physically reduce the size of the input and output filters, and keep the whole thing running cool. Then get registered before the September 30, 2014 deadline. Inverters need to be functional and the results of this test procedure (PDF warning) sent in before July 22, 2015, then 18 finalists will be chosen to bring their inverters in person to a testing facility in the United States by October 21, 2015. The grand prize winner will be announced sometime in January, 2016

[Thanks for the tip Dmytro]

This Arduino power inverter would need a serious upgrade to enter. And speaking of entering challenges, it’s still not too late to enter our very own Hackaday Prize!

An Arduino power inverter

If you’ve got a few solar panels lying around, or even if you want some 120/230 V AC power from a few 12 Volt batteries, you’ll need a power inverter. Sure, you can drop on down to any big box store and pick one of these up, or you can be like [Michael] and build your own (Danish, translation).

[Michael] found himself in the possession of a few halogen light transformers and decided to make use of them by building a DC to AC power inverter. The inverter is fairly simple – just the transformer, a few MOSFETS, and an ATMega0168 for software control that includes a ‘soft start’ feature that prevents power surges on startup.

The circuit is simple enough to etch at home, although a soldermask and a nice insulated enclosure would probably be ideal for this application.

Hackaday Links: December 3, 2011

Honey, would you like some cheese? WHIRRRRRRRRR

[The Timmy] broke his manual cheese grater. It would be a waste to throw away a perfectly functional tool that’s only missing a handle, so he kicked it up a notch with a cordless drill. Now [Tim], “can grate with incredible speed and power for even the toughest of cheeses.” Anyone have a broken pepper mill?

The most adorable oscilloscope

We’re not much for plugging products, but this scope is really cool. It’s designed to fit on a breadboard and is smaller than some ICs we’ve seen (68000, so yes, it is). We’re wondering why there hasn’t been a homebrew version of this yet.

Now do an R/C castle

Here’s a minifig-sized R/C LEGO car made by [brickmodder]. It has a custom drive train and steering mechanism that uses the smallest servos [brickmodder] could find. How about an R/C pirate ship next?

It’s probably an ad for something

Here’s some sort of code thing that asks the question, “Can you crack it?” Apparently, it’s for UK cryptanalyst recruiting. You won’t get a 00-designation, but woo Bletchley Park.

Inverting an inverter

[Manfred] is putting an alternative energy setup on his land. Of course he needed an inverter to charge his batteries, so he went with a highly regarded (high price) box. What he got was anything but. You’re going to need at least ten minutes to go through this hilariously sad teardown of a high quality Taiwanese inverter. Oh, [Manfred] is awesome. Just look at his microhydro plant.