Although [pinomelean's] Lithium-ion battery guide sounds like the topic is a bit specific, you’ll find a number of rechargeable battery basics discussed at length. Don’t know what a C-rate is? Pfffft. Roll up those sleeves and let’s dive into some theory.
As if you needed a reminder, many lithium battery types are prone to outbursts if mishandled: a proper charging technique is essential. [pinomelean] provides a detailed breakdown of the typical stages involved in a charge cycle and offers some tips on the advantages to lower voltage thresholds before turning his attention to the practical side: designing your own charger circuit from scratch.
The circuit itself is based around a handful of LM324 op-amps, creating a current and voltage-limited power supply. Voltage limits to 4.2V, and current is adjustable: from 160mA to 1600mA. This charger may take a few hours to juice up your batteries, but it does so safely, and [pinomelean's] step-by-step description of the device helps illustrate exactly how the process works.
Tesla Motors club user [wk057], a Tesla model S owner himself, wants to build an awesome solar storage system. He’s purchased a battery pack from a salvaged Tesla Model S, and is tearing it down. Thankfully he’s posting pictures for everyone to follow along at home. The closest thing we’ve seen to this was [Charles] tearing into a Ford Fusion battery. While the Ford battery is NiMH, the Tesla is a completely different animal. Comprised of over 7000 individual lithium-ion cells in 16 modules, the Tesla battery pack packs a punch. It’s rated capacity is 85kWh at 400VDC.
[wk057] found each cell connected by a thin wire to the module buses. These wires act as cell level fuses, contributing to the overall safety of the pack. He also found the water cooling loops were still charged with coolant, under a bit of pressure. [wk057] scanned and uploaded high res images of the Tesla battery management system PCBs (large image link). It is a bit difficult to read the individual part numbers due the conformal coating on the boards.
A second forum link shows images of [wk057] pulling the modules out of the pack. To do this he had to chip away the pack’s spine, which consisted of a 2/0 gauge wire potted in some sort of RTV rubber compound.
We’re sure Tesla doesn’t support hackers using their packs to power houses. Ironically this is exactly the sort of thing Elon Musk is working on over at Solar City.
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.
Lithium ion batteries are becoming more and more common these days, but some of the larger capacity batteries can still carry a pretty hefty price tag. After finding Acer’s motherboard schematics online and doing a little reverse-engineering, [Tiziano] has found a way to reuse batteries from his dead laptop, not only saving the batteries from the landfill but also cutting costs on future projects.
These types of batteries have been used for many things in the past, but what makes this project different is that [Tiziano] is able to monitor the status of the batteries and charge them using I2C with an Arduino and a separate power supply, freeing the batteries from the bonds of the now-useless laptop.
With this level of communication between the microcontroller and the battery pack, there is little chance of the batteries catching on fire when they’re used in another project. Since the Arduino can also monitor the current amount of charge in the batteries, there is also a reduced risk that they will be damaged from under- or over-charging.
This wasn’t just as simple as hooking up the positive and negative leads of a power supply to the battery. [Tiziano] also had to model the internal resistance of the motherboard that the battery expects to see, and get the supply voltage just right so the battery’s safety protocols wouldn’t kick in to prevent them from charging. After a few other hurdles were jumped, [Tiziano] now has a large capacity lithium ion battery at his disposal for any future projects.
Lithium ion supercapacitors. No, not lithium ion batteries, and yes, they’re a real thing. While they’re astonishingly expensive per Farad, they are extremely small and used as the first line of defense in some seriously expensive heavy-duty UPS installations. Here’s a Kickstarter using these supercaps to replace the common AA, C, and D cell batteries. Even better, they can be recharged in seconds.
For each size battery, the caps used actually have a slightly higher energy density than a similarly sized dollar store battery. By adding a little bit of circuitry to drop the 3.8 Volts out of the cap down to the 1.5 V you expect from a battery, this supercap becomes a very expensive rechargeable battery, but one that can be recharged in seconds.
This is one of those crowdfunding campaigns we really like: an interesting tool, but something we just can’t figure out what the use case would be. These lithium ion supercaps are too expensive to be practical in anything we would build (save for a Gauss pistol), but the tech is just too cool to ignore. If you have a use case for these caps in mind, please leave a note in the comments.
Somewhat relevant Mouser link.
Now we don’t sit around reading application notes for fun. But if hard pressed we would have to admit that we do read quite a few of them even if the concepts aren’t currently on our project list. That’s because they’re a great way to learn stuff and for the most part the information within is trustworthy.
The latest one that we looked at is this Maxim app note 5681 on recycling Lithium-ion batteries. It’s more a reuse than a recycle but you get the point. If you have some Lithium-Ion cells left over from older equipment this resource delivers a lot of good information on how to use them to power something else.
Obviously they’re showing off their own hardware here, but that’s okay. The MAX8677A chips has a ton of features and can be had for $3-5 depending on your vendor. It automatically switches between powering your device from the battery, or from the charging source if connected. This allows you to source up to 500mA when connected to USB or 2A when charging from an external DC supply. There is also all of the protection you would normally want with a Li-ion setup, including temperature monitoring.
The catch is the not-so-hand-solderable QFN package. They’ve got a solution to this as well. The diagram on the right shows how to hand solder the chip — albeit with a hot air pencil — by drilling through the board to get at the ground pad from the underside of the PCB.
[Thanks Jaded and Amos]
[Dr. Iguana's] experience moving from projects powered by disposable Alkaline cells and linear regulators to recycled Lithium Ion cells using the buck regulators seen above might serve as an inspiration to make the transition in your own projects.
The recycled cells he’s talking about are pulled out of larger battery packs. As we’ve seen in the past, dead battery packs for rechargeable tools, laptops, etc., are often plagued by a few bad apples. A small number of dead cells can bork the entire battery even though many perfectly usable cells remain. Once he decided to make the switch it was time to consider power regulation. He first looked at whether to use the cells in parallel or series. Parallel are easier to charge, but boosting the voltage to the desired level ends up costing more. He decided to go with cells in series, which can be regulated with the a less expensive buck converter. In this case he made a board for the RT8289 chip. The drawback of this method requires that you monitor each cell individually during charging to ensure you don’t have the same problem that killed the battery from which you pulled these good cells.