When it comes to lithium batteries, you basically have two types. LiPoly batteries usually come in pouches wrapped in heat shrink, whereas lithium ion cells are best represented by the ubiquitous cylindrical 18650 cells. Are there exceptions? Yes. Is that nomenclature technically correct? No, LiPoly cells are technically, ‘lithium ion polymer cells’, but we’ll just ignore the ‘ion’ in that name for now.
Lithium ion cells are found in millions of ground-based modes of transportation, and LiPoly cells are the standard for drones and RC aircraft. [Tom Stanton] wondered why that was, so he decided to test the energy density per mass of these battery chemistries, and what he found was very interesting.
The goal of [Tom]’s experiment was to test LiPoly against lithium ion batteries in the context of a remote-controlled aircraft. Since weight is what determines flight time, cutting even a few grams from an airframe can vastly extend the capabilities of an aircraft. The test articles for this experiment come in the form of a standard 1800 mAh LiPoly battery and four 18650 cells wired together as a 3000 mAh battery. Here’s where things get interesting: the LiPoly battery weighs 216 grams for an energy density of 0.14 Watt-hours per gram. The lithium ion battery weighs 202 grams for an energy density of 0.25 Watt-hours per gram. If you just look at the math, all drones are doing it wrong. 18650 cells appear to have a much higher energy density per mass than the usual LiPoly cells. How does that hold up in a real-world test, though?
Using his neat plane with 3D printed wing ribs as the testbed, [Tom] plugged in the batteries and flew around a field for the better part of an afternoon. The LiPo flew for 41.5 minutes, whereas the much more energy dense lithium ion battery flew for 36.5 minutes. What’s going on here?
While the lithium ion battery has a much higher capacity, the problem here is the internal resistance of each battery chemistry. The end voltage for the LiPo was a bit lower than the lithium ion battery, suggesting the 18650 cells can be run down a bit further than [Tom]’s test protocol allowed. After recharging each of these batteries and doing a bit of math, [Tom] found the lithium ion batteries can fly for about twice as long as their LiPo counterparts. That means an incredibly long test of flying a plane in a circle over a field; not fun, but we are looking forward to other people replicating this experiment.
To describe the constraints on developing consumer battery technology as ‘challenging’ is an enormous understatement. The ideal rechargeable battery has conflicting properties – it has to store large amounts of energy, safely release or absorb large amounts of it on demand, and must be unable to release that energy upon failure. It also has to be cheap, nontoxic, lightweight, and scalable.
As a result, consumer battery technologies represent a compromise between competing goals. Modern rechargeable lithium batteries are no exception, although overall they are a marvel of engineering. Mobile technology would not be anywhere near as good as it is today without them. We’re not saying you cannot have cellphones based on lead-acid batteries (in fact the Motorola 2600 ‘Bag Phone’ was one), but you had better have large pockets. Also a stout belt or… some type of harness? It turns out lead is heavy.
Rechargeable lithium cells have evolved tremendously over the years since their commercial release in 1991. Early on in their development, small grains plated with lithium metal were used, which had several disadvantages including loss of cell capacity over time, internal short circuits, and fairly high levels of heat generation. To solve these problems, there were two main approaches: the use of polymer electrolytes, and the use of graphite electrodes to contain the lithium ions rather than use lithium metal. From these two approaches, lithium-ion (Li-ion) and lithium-polymer (Li-Po) cells were developed (Vincent, 2009, p. 163). Since then, many different chemistries have been developed.
Whenever we see a coil gun project on the Internet, it seems to involve a bank of huge capacitors. [miroslavus] took a different approach with his gun–he wanted his project to be built without those monster caps.
It’s powered by quadcopter LiPo batteries, 2x 1400 MaH drone batteries wired up in series and triggering 21SWG copper coils that [miroslavus] created with the help of a custom 3D-printed winding rig he designed. The rigs have ridges to help you lay the coils down neatly, and they also have mounts for photodiodes, ensuring the gun knows when it’s loaded.
When triggered, the Arduino Nano activates a pair of IRF3205 MOSFETS with logic signals stepped up to 20V, shooting lengths of 7mm or 8mm steel rod. The gun isn’t exactly creating plasma discharges with its launches, but it’s a fascinating project nonetheless.
That said, this shield by Electro-Labs might be the perfect transition for the die-hard-‘duino fanatic looking to migrate to tougher projects. The build features an LCD and four-button interface to fiddle with settings, and is based around an LT1510 constant current/constant voltage charger IC. You can find the schematic, bill of materials, code, and PCB design on the Electro-Labs webpage, as well as a brief rundown explaining how the circuit works. Still want to add on the design? Throw in one of these Li-ion holders for quick battery swapping action.
[NeXT] got himself an IBM ThinkPad TransNote and yeah, we’re pretty jealous. For the uninitiated, the TransNote was IBM’s foray into intelligent note transcription from roughly fifteen years ago. The ThinkPad doesn’t even have to be on to capture your notes because the proprietary pen has 2MB of flash memory. It won an award and everything. Not the pen, the TransNote.
Unfortunately, the battery life is poor in [NeXT]’s machine. The TransNote was (perhaps) ahead of its time. Since it didn’t last on the market very long, there isn’t a Chinese market for replacement batteries. [NeXT] decided to rebuild the replacement battery pack himself after sending it off with no luck.
The TransNote’s battery pack uses some weird, flat Samsung 103450 cells that are both expensive and rare. [NeXT] eventually found some camera batteries that have a single cell and a charge controller. He had to rearrange the wiring because the tabs were on the same side, but ultimately, they did work. He got the cells together in the right configuration, took steps to prevent shorts, and added the TransNote’s charge controller back into the circuit.
Nothing blew up, and the ThinkPad went through POST just fine. He plugged it in to charge and waited a total of 90 minutes. The charging rate was pretty lousy, though. At 94% charge, the estimated life showed 28 minutes, which is worse than before. What are your thoughts on the outcome and if it were you, what would be the next move?
Fail of the Week is a Hackaday column which runs every Wednesday. Help keep the fun rolling by writing about your past failures and sending us a link to the story — or sending in links to fail write ups you find in your Internet travels.
Just about anyone can build this UV index sensing wearable that detects heat rays from the sun and reminds the user to put on sunscreen. There is no soldering required, which makes this a nice beginners projects for those unfamiliar with hooking up electronic sensors.
All that is needed is a FLORA main board, one UV index sensor, a piezo Buzzer, a 500mAh lipoly battery, 2-ply conductive thread, a couple of household tools, and your favorite summer’s hat.
Once the materials have been rounded up, the rest of the process is relatively simple. Threading the FLORA in and place and connecting the Piezo only takes a few minutes. Then the UV sensor is added allowing the hat to start collecting data. A little bit of coding later, and the whole system is ready to be worn out in the sun.
What’s great about this project is that the hat can be programmed to play a song when it is time to apply more sunscreen. Everyone from beach bums, to sun-bathing beauties, to music festival attendees will be able to find this hat useful. And, it is cheap and easy to make.
The video on the Adafruit tutorial page shows how simple it is to rig up the system.
We first wrote about the MintyBoost back in 2006. Today, Adafruit has created a tutorial for making a solar powered MintyBoost. Using a MintyBoost, a solar panel, LiPo battery and a charger, they built on their Solar LiPoly tutorial. They fed the power tap output of the LiPoly charger into the battery input of the MintyBoost to perform the voltage step-up for USB devices. Based on an instructable that used SparkFun parts, this tutorial shows how to use parts that are available from one source. We hear that there will be some evolution of the MintyBoost coming down the line that will including charging capabilities.
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