Ask Hackaday: Dude, Where’s My MOSFET?

(Bipolar Junction) Transistors versus MOSFETs: both have their obvious niches. FETs are great for relatively high power applications because they have such a low on-resistance, but transistors are often easier to drive from low voltage microcontrollers because all they require is a current. It’s uncanny, though, how often we find ourselves in the middle between these extremes. What we’d really love is a part that has the virtues of both.

The ask in today’s Ask Hackaday is for your favorite part that fills a particular gap: a MOSFET device that’s able to move a handful of amps of low-voltage current without losing too much to heat, that is still drivable from a 3.3 V microcontroller, with bonus points for PWM ability at a frequency above human hearing. Imagine driving a moderately robust small DC robot motor forwards with a microcontroller, all running on a LiPo — a simple application that doesn’t need a full motor driver IC, but requires a high-efficiency, moderate current, and low-voltage-logic compatible transistor. If you’ve been here and done that, what did you use?

Continue reading “Ask Hackaday: Dude, Where’s My MOSFET?”

DIYing A Raspberry Pi Power Bank

Over the last decade or so, battery technology has improved massively. While those lithium cells have enabled thin, powerful smartphones and quadcopters, [patrick] thought it would be a good idea to do something a little simpler. He built a USB power bank with an 18650 cell. While it would be easier to simply buy a USB power bank, that’s not really the point, is it?

This project is the follow-up to one of [patrick]’s earlier projects, a battery backup for the Raspberry Pi. This earlier project used an 14500 cell and an MSP430 microcontroller to shut the Pi down gracefully when the battery was nearing depletion.

While the original project worked well with the low power consumption Pi Model A and Pi Zero, it struggled with UPS duties on the higher power Pi 3. [patrick] upgraded the cell and changed the electronics to provide enough current to keep a high-power Pi on even at 100% CPU load.

The end result is a USB power bank that’s able to keep a Raspberry Pi alive for a few hours and stays relatively cool.

Graphene Batteries Appear, Results Questionable

If you listen to the zeitgeist, graphene is the next big thing. It’s the end of the oil industry, the solution to global warming, will feed and clothe millions, cure disease, is the foundation of a space elevator that will allow humanity to venture forth into the galaxy. Graphene makes you more attractive, feel younger, and allows you to win friends and influence people. Needless to say, there’s a little bit of hype surrounding graphene.

With hype comes marketing, and with marketing comes products making dubious claims. The latest of which is graphene batteries from HobbyKing. According to the literature, these lithium polymer battery packs for RC planes and quadcopters, ‘utilize carbon in the battery structure to form a single layer of graphene… The graphene particles for a highly dense compound allowing electrons to flow with less resistance compared to traditional Lipoly battery technologies” These batteries also come packaged in black shrink tubing and have a black battery connector, making them look much cooler than their non-graphene equivalent. That alone will add at least 5mph to the top speed of any RC airplane.

For the last several years, one of the most interesting potential applications for graphene is energy storage. Graphene ultracapacitors are on the horizon, promising incredible charge densities and fast recharge times. Hopefully, in a decade or two, we might see electric cars powered not by traditional lithium batteries, but graphene supercapacitors. They’ll be able to recharge in minutes and drive further, allowing the world to transition away from a fossil fuel-based economy. World peace commences about two weeks after that happens.

No one expected graphene batteries to show up now, though, and especially not from a company whose biggest market is selling parts to people who build their own quadcopters. How do these batteries hold up? According to the first independent review, it’s a good battery, but the graphene is mostly on the label.

[rampman] on the RCgroups forums did a few tests on the first production runs of the battery, and they’re actually quite good. You can pull a lot of amps out of them, they last through a lot of charging cycles, and the packaging – important for something that will be in a crash – is very good. Are these batteries actually using graphene in their chemistry? That’s the unanswered question, isn’t it?

To be fair, the graphene batteries shipped out to reviewers before HobbyKing’s official launch do perform remarkably well. In the interest of fairness, though, these are most certainly not stock ‘graphene’ battery packs. The reviewers probably aren’t shills, but these battery packs are the best HobbyKing can produce, and not necessarily representative of what we can buy.

It’s also doubtful these batteries use a significant amount of graphene in their construction. According to the available research, graphene increases the power and energy density of batteries. The new graphene batteries store about as much energy as the nano-tech batteries that have been around for years, but weigh significantly more. This might be due to the different construction of the battery pack itself, but the graphene battery should be lighter and smaller, not 20 grams heavier and 5 mm thicker.

In the RC world, HobbyKing is known as being ‘good enough’. It’s not the best stuff you can get, but it is cheap. It’s the Wal-Mart of the RC world, and Wal-Mart isn’t introducing bleeding edge technologies that will purportedly save the planet. Is there real graphene in these batteries? We await an in-depth teardown, preferably with an electron microscope, with baited breath.

Better Batteries For Electronic Gadgets

We’re not using 9 Volt batteries to power our projects anymore; the world of hobby electronics has moved on to cheap LiPo batteries for most of our mobile power storage. LiPos aren’t the best solution, evidenced by hundreds of YouTube videos of exploding batteries, and more than a few puffy cells in our junk drawer. The solution? LiFePO4, or lithium iron phosphate cells. They’re a safer chemistry, they have low self discharge, and have more recharge than other chemistry of lithium cells.

LiFePO4 cells aren’t easy to deal with if you’re working with breadboard electronics, though. Most of that is because there aren’t many breakout boards for these cells. [Patrick] is working on changing that with his LiFePO4werd USB charger.

The concept is simple: use an off-the-shelf part for LiFePO4 batteries – in this case an MCP73123 – and make a board that charges the batteries with a USB port. It’s exactly the same idea as the many USB LiPo chargers out there, only this one uses a better battery chemistry.

[Patrick] is using a 550mAh battery for this project, but there’s no reason why it couldn’t be upgraded to a 18650-sized cell with more than 2000mAh stuffed inside. Add a boost converter to the circuit, and he’ll have the perfect power source for every portable electronics project imaginable.

Hacklet 43 – Flashlight projects

Mankind has always looked for ways to light up the night as they walk around. Fires are great for this, but they aren’t very safe or portable. Even kept safe in a lantern, an open flame is still dangerous – especially around cows.  Enter the flashlight, or torch if you’re from the other side of the pond. Since its invention in 1899, the flashlight has become a vital tool in modern society. From patrolling the dark corners of the city, to reading a book under the covers, flashlights enable us to beat back the night. The last decade or so has seen the everyday flashlight change from incandescent bulbs to LEDs as a light source. Hackers and makers were some of the first people to try out LED flashlights, and they’re still tinkering and improving them today. This weeks Hacklet focuses on some of the best flashlight projects on!

light1We start with [Norman], and the LED Flashlight V2. Norman built a flashlight around a 100 Watt LED. These LEDs used to be quite expensive, but thanks to mass production, they’ve gotten down to around $6 USD or so. Norman mounted his LED a custom aluminum case. At this power level, even LEDs get hot. An extruded aluminum heatsink and fan keeps things cool. Power is from a 6 cell LiPo battery, which powers the LED through a boost converter. It goes without saying that this flashing is incredibly bright. Even if the low-cost LEDs aren’t quite 100 Watts, they still put many automotive headlights to shame! Nice work, [Norman].

light2A tip of the fedora to [Terrence Kayne] and his Grain-Of-Light LED LIGHT. [Terrence] loves LED flashlights, be he wanted one that had a bit of old school elegance. Anyone familiar with LEDs knows CREE is one of the biggest names in the industry. [Terrence] used a CREE XM-L2 emitter for his flashlight. He coupled the LED to a reflector package from Carlco Optics. The power source is an 18650 Lithium cell, which powers a multi-mode LED driver. [Terrence] spent much of his time turning down the wooden shell and aluminum tube frame of the flashlight. His workmanship shows! Our only suggestion would be to go with a lower profile switch. The toggle [Terrence] used would have us constantly checking our pockets to make sure the flashlight hadn’t accidentally been activated.

light3Harbor Freight’s flashlights are a lot like their multimeters: They generally work, but you wouldn’t want to trust your life to them. That wasn’t a problem for [Steel_9] since he needed a strobe/party light. [Steel_9] hacked a $5 “27 LED” light into a stylish strobe light. He started by cutting the power traces running to the LED array. He then added in an adjustable oscillator circuit: two BJTs and a handful of discrete components make up an astable multivibrator. A third transistor switches the LEDs. Switching a load like this with a 2N3906 probably isn’t the most efficient way to do things, but it works, and the magic smoke is still safely inside the semiconductors.  [Steel_9] built the circuit dead bug style, and was able to fit everything inside the original plastic case.  Rave on, [Steel_9]!

If you want to see more flashlight projects, check out our new list on! That’s about all the time we have for this week’s Hacklet. As always, see you next week. Same hack time, same hack channel, bringing you the best of!

Hacklet 39: Battery Power

3296371398740598106[robin] has a Red Camera (lucky!), an absurdly expensive digital video camera. As you would expect the batteries are also absurdly expensive. What’s the solution? Battery packs from cordless drills.

Cordless drills are interesting pieces of tech that can be easily repurposed; there are huge battery packs in them, big, beefy motors, and enough hardware to build an Automatic Cat Feeder or a motorized bicycle.

What if those old Makita batteries don’t charge? That usually means only one or two cells are dead, not the whole pack. Free LiIon cells, but you need to charge them. Here’s a single cell charger/boost converter that will do the trick.


A problem faced by amateur radio operators around the world is the lack of commercial power. Plugging a portable shack into a wall will work, but for uninterrupted power car batteries are everywhere. How do you combine wall power and car batteries for the best of both worlds? With an In-line battery backup module.

9k=All of the projects above rely on charging a battery through wall power, and sometimes even that is impossible. Solar is where we’re headed, with solar LiPo chargers, and solar LiFe chargers. That’s more than enough to keep a smartphone charged, but if you want to go completely off the grid, you’re going to need something bigger.

[Michel] has been off the power grid 80% of the time since he installed his home PV system a few years ago. How’s he doing it? A literal ton of batteries, huge chargers, and a 5kW inverter.


An Obsessively Thorough Battery (and more) Showdown

There are a number of resources scattered across the Internet that provide detailed breakdowns of common products, such as batteries, but we haven’t seen anything quite as impressive as this site. It’s an overwhelming presentation of data that addresses batteries of all types, including 18650’s (and others close in size)26650’s, and more chargers than you can shake a LiPo at. It’s an amazing site with pictures of the product both assembled and disassembled, graphs for charge and discharge rates, comparisons for different chemistries, and even some thermal images to illustrate how the chargers deal with heat dissipation.

Check out the review for the SysMax Intellicharger i4 to see a typical example. If you make it to the bottom of that novel-length repository of information, you’ll see that each entry includes a link to the methodology used for testing these chargers.

But wait, there’s more! You can also find equally thorough reviews of flashlights, USB chargers, LED drivers, and a few miscellaneous overviews of the equipment used for these tests.

[Thanks TM]