Unless you’ve been living under a high voltage transformer, you’ve heard about the potential for Samsung’s latest phone, the Note7, to turn into a little pocket grenade without warning. With over 2.5 million devices in existence, it’s creating quite a headache for the company and its consumers.
They quickly tied the problem to faulty Li-ion batteries and started replacing them, while issuing a firmware update to stop charging at 60 percent capacity. But after 5 of the replacement phones caught fire, Samsung killed the Note7 completely. There is now a Total Recall on all Note7 phones and they are no longer for sale. If you have one, you are to turn it off immediately. And don’t even think about strapping it into a VR headset — Oculus no longer supports it. If needed, Samsung will even send you a fireproof box and safety gloves to return it.
It should be noted that the problem only affects 0.01% of the phones out there, so they’re not exactly going to set the world on fire. However, it has generated yet another discussion about the safety of Li-ion battery technology.
It was just a few months ago we all heard about those hoverboards that would catch fire. Those questionably-engineered (and poorly-named) toys used Li-ion batteries as well, and they were the source of the fire problem. In the wake of this you would think all companies manufacturing products with Li-ion batteries in them would be extra careful. And Samsung is no upstart in the electronics industry — this should be a solved problem for them.
Why has this happened? What is the deal with Li-ion batteries? Join me after the break to answer these questions.
Batteries wear out. If you are an electric vehicle enthusiast, it’s a certainty that at some time in your not-too-distant future there will be a point at which your vehicle’s batteries have reached the end of their lives and will need to be replaced. If you have bought a new electric vehicle the chances are that you will be signed up to a leasing deal with the manufacturer which will take care of this replacement, but if you have an older vehicle this is likely to be an expensive moment.
Fortunately there is a tempting solution. As an increasing number of electric vehicles from large manufacturers appear on our roads, a corresponding number of them have become available on the scrap market from accident damage. It is thus not impossible to secure a fairly new lithium-ion battery pack from a modern electric car, and for a significantly lower price than you would pay for new cells. As always though, there is a snag. Such packs are designed only for the cars they came with, and have proprietary connectors and protocols with which they communicate with their host vehicle. Fitting them to another car is thus not a task for the faint hearted.
Hackaday reader [Wolf] has an electric truck, a Solectria E10. It has a set of elderly lead-acid batteries and would benefit hugely from an upgrade to lithium-ion. He secured a battery pack from a 2013 Nissan Leaf electric car, and he set about reverse engineering its battery management system (BMS). The Solectria will use a different battery configuration from the Leaf, so while he would like to use the Leaf’s BMS, he has had to reverse engineer its protocols so that he can replace its Nissan microcontroller with one of his own.
His description of the reverse engineering process is lengthy and detailed, and with its many photos and videos is well worth a read. He employs some clever techniques, such as making his own hardware simulation of a Li-ion cell so that he can supply the BMS known values that he can then sniff from the serial data stream.
[Glen], at Maker Space Newcastle Upon Tyne, is refreshingly honest. As he puts it, he’s too cheap to buy a proper battery.
He needed a 1AH battery pack to power his quadcopter controller and FPV headset, and since inadequate discharge warnings had led him to damage lithium polymer cells with these devices, he wanted his pack to use lithium-ion cells. His requirements were that the cells be as cheap, lightweight, and small as possible, so to satisfy them he turned to a stack of mobile phone cells. Nokia BL-4U cells could be had for under a pound ($1.46) including delivery, so they certainly satisfied his requirement for cheapness.
It might seem a simple procedure, to put together a battery pack, and in terms of physical wiring it certainly is. But lithium-ion cells are not simply connected together in the way dry cells are, to avoid a significant fire risk they need to have the voltage of each individual cell monitored with a special balanced charger. Thus each cell junction needs to be brought out to another connector to the charger.
[Glen]’s write-up takes the reader through all the requirements of safe lithium-ion pack construction and charging, and is a useful read for any lithium-ion newbies. If nothing else it serves as a useful reminder that mobile phone cells can be surprisingly cheap.
Battery technology is a constant chemical war between the laws of physics and the desire of engineers to make devices smaller. On one side, the laws of physics declare that there are limits to how much energy you can store inside a battery, and on the other side are the engineers looking for ways to sneak around these laws. For many devices, the best compromise between these two sides is the lithium ion battery, usually abbreviated to Li-ion.
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.
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.