Tag Archives: Batteries

Monitoring Batteries Wirelessly

Lithium-ion batteries, when used to drive automobiles, can operate reliably over long periods, but require considerable care. That means not operating them to the extreme ends of their state of charge or SOC. With passage of time and usage, the capacity of a lithium ion cell changes, and therefore, each cell in the system has to be managed so that it remains within its constrained SOC.

As vehicle operation requires generating as much as 1000 V or higher, tens or hundreds of cells are necessary, configured in series and parallel strings, to provide sufficient power for the vehicle. The battery electronics has to operate at these high voltages, while rejecting common mode voltage effects, and differentially measuring and controlling each cell in the strings. At the same time, the electronics has to transmit the information from each cell in the battery stack to a central point for processing.

High-power applications such as vehicles employing a high voltage battery stack impose tough conditions, including operation with wide operating temperatures and significant electrical noise. Therefore, the battery management electronics has to maximize its operating range, safety, lifetime, and reliability. At the same time, it has to minimize the weight, size, and cost.

Linear Technology has made steady advances in battery cell monitoring, increasing the life and reliability of battery packs in automobiles, and enabling high performance. For further improving the safety and reliability of full battery systems, Linear Technology is moving towards wireless Battery Management Systems or BMS.

Monitoring Batteries

Each LTC68xx IC from Linear Technology can monitor up to 12 Li-ion cells and they can be connected in series to enable simultaneous monitoring of every cell within a long, high voltage battery string. This enables precision battery management in hybrid/electric vehicles, electric vehicles, and other high power, high voltage battery stacks.

For instance, each LTC6811 has two built-in serial interfaces operating at 1 MHz each, one SPI interface for connecting to a local microprocessor, and the proprietary 2-wire isoSPI interface. Two communication options are possible with the isoSPI interface—you can connect and address multiple devices in parallel to the BMS master, or connect multiple devices in a daisy chain to the BMS master.

Wireless BMS

When employing a wireless BMS, a wireless connection interconnects each module rather than the twisted pair of the isoSPI. For instance, Linear Technology combines its SmartMesh wireless mesh networking with the LTC811 battery stack monitors to replace the traditional wired connections between the battery packs and the battery management system. This is a significant breakthrough offering a huge potential for lowering costs, reducing wiring complexity, thereby improving the reliability for large multicell battery stacks for electric and hybrid vehicles.

Automakers are ensuring the safety and reliability of their electric and hybrid vehicles by addressing the potential mechanical failure of connectors, cables, and wiring harness, as these have to operate in high-vibration automotive environments. Until now, automakers were under the impression that wireless systems would be unreliable in the metal and high-EMI surroundings within a vehicle. With SmartMesh networking, the interconnect system has proved to be truly redundant.

How Safe Are the Batteries You Use?

There is occasional news about exploding smartphone batteries. As this is a safety related issue, the topic has generated a lot of interest. Several researchers, from the National Physical Laboratory, UK, the Imperial College, London, ESRF the European Synchrotron, and UCL, the University College, London have tried to find out the reasons and the mechanism behind batteries exploding. Their research reveals how damage to the internal structure of the batteries can spread to neighboring batteries.

Now, researchers at the Stanford University, San Francisco, have developed a safe lithium-ion battery. Based on the temperature inside, the battery can shut itself down to prevent starting a fire.

When lithium batteries are packed tightly, they can overheat and catch fire if they experience short circuits or damage in some way. In fact, fires from lithium batteries have brought down two cargo jets in the past decade. Tests conducted by the US Federal Aviation Administration have found that overheating batteries can cause major fires.

When punctured or shorted, traditional lithium-ion batteries can catch fire. Temperatures inside the battery under these conditions can rise to 300 degrees Fahrenheit, causing the battery to explode. Preventive techniques of adding flame-retardants to the electrolyte of the battery usually do not work because they make the battery nonfunctional, thus defeating the purpose.

Zhenan Bao, professor of chemical engineering, and Zheng Chen, a postdoctoral scholar, have turned to nanotechnology for solving the issue of explosion of lithium-ion batteries. For this, they used a wearable body temperature monitor that Bao has recently invented. The sensor, made of plastic material, has tiny particles of nickel embedded inside. Nano scale spikes protrude from the surface of these nickel particles. To use the sensor in batteries, researchers used a one-atom thick graphene layer to coat the spiky nickel particles. They embedded the coated particles in a thin film of elastic polyethylene.

The researchers attached the polyethylene film to one electrode of the battery such that the load current of the battery would flow through the film. Under normal temperatures, the spiky particles touch one another and allow conduction of electricity. If the temperature rises, the polyethylene stretches due to thermal expansion. This makes the particles to spread out leading to the film becoming non-conductive. That stops the flow of electricity through the battery, until it cools down.

The polyethylene film starts expanding above 160 degrees Fahrenheit. That causes the spikes on the particles to move apart, causing the battery to shut down. As temperatures drop below 160 degrees, the particles come into contact again with each other, allowing the battery to start functioning again and generate electricity. According to the researchers, they can tune the temperature based on the type of polymer used and the number of nickel particles.

With the film in place, the battery shut down as soon as it got too hot and stopped working. Moreover, it resumed operation quickly as soon as the battery cooled down. As there is no electricity flowing when the battery is hot, chances of it catching fire and exploding are practically nil.

SOUNDBOKS: Batteries to Power the Next Speakers

Your next portable speakers may be able to violate county noise ordinances without the necessity of them being plugged into a vehicle power inverter, a portable generator or even a wall socket. This is what Soundboks is claiming, and their speakers will be battery-powered.

Most portable speakers are limited in their size and their power output. Usually, if you want sizes and power capacity beyond those, it becomes necessary to power the speakers through AC adapters or wall plugs so they can output continuous power. That does not help when catering to outdoor gatherings, where truly wireless music at extreme volumes is the norm. With the battery-operated speakers from Soundboks, you can now expect 30-hours of nightclub-level decibels on a single charge.

In the market, one can find plenty of audiophile-grade boom-box sized speakers such as the Nano HiFi NH1 or the rugged JBL Xtreme suitable for supplying ample amounts of power for pool events, camping, or backyard cookouts. However, the portable speakers from Soundboks beats them hollow, as they house a pair of low-frequency drivers each of 96 dB, and a pair of high-frequency drivers, also of 96 dB SPL or sound pressure level speaker units, along with 42 W digital amplifiers.

With high-efficiency custom-designed amplifiers, Soundboks speakers enhance the life of the driving batteries while optimizing the sound for outdoor usage. They have designed the speakers for dual-phase boost function and these can belt out a maximum of 119 dB of sound. You can easily get an experience of a live concert, simply by turning up the volume dial on the speaker to position 11.

Weighing in at 14.5 Kg (32 lb.), the 66x43x32 cm (26x17x13 in) Soundboks speaker is not much different from other carry-on luggage used. The low weight is because of the wood and aluminum construction of the case and that makes it shockproof, weather proof and temperature resistant. The case has an integrated side handle that makes it easy to carry about on the beach as easily as a cooler filled with beverages and ice. Wireless and wired connectivity are offered. Bluetooth 3.0 with extended range allows you to connect wirelessly while a 3.5 mm audio input provides the wired connectivity.

The truly remarkable thing about the Soundboks speaker is its ability to play music for 30 hours at 113 dB. That easily violates the county noise ordinance and that too without any help from a vehicle power inverter, portable generator, or wall socket. Each speaker comes with two external batteries, which you can swap and that gives the capability to play for a total 60 hours continuously.
The batteries are special, as they are not the usual lithium-ion type. Rather, Soundboks uses LiFePO4 or lithium-Ferro phosphate batteries that need only three hours to charge, can meet power demands and are safe. Therefore, you only need six hours of charging time, and then enjoy a full weekend-long festival program or a complete week with the volume toned down. Shipments are scheduled to start this April, as Soundboks has already raised 174% of its Kickstarter goal in one day.

Can capacitors act as a replacement for batteries?

It is common knowledge that capacitors store electrical energy. One could infer that this energy could be extracted and used in much the same way as a battery. Why can capacitors then not replace batteries?

Conventional capacitors discharge rapidly, whereas batteries discharge slowly as required for most electrical loads. A new type of capacitors with capacitances of the order of 1 Farad or higher, called Supercapacitors:

• Are capable of storing electrical energy, much like batteries
• Can be discharged gradually, similar to batteries
• Recharged rapidly – in seconds rather than hours (batteries need hours to recharge)
• Can be recharged again and again, without degradation (batteries have a limited life and hold increasingly lower charge with age, until they can be recharged no longer)

The Supercapacitor would thus appear to be one up on the batteries in terms of performance and longevity, and some more research could actually lead to a viable alternative to conventional fuel for automobiles. It is this concept that created the hybrid, fuel-efficient cars.

However, let us not jump to conclusions without considering all the aspects. For one, the research required to refine this technology would be both time and cost intensive. The outcome must justify the efforts in terms of both time and cost. The negatives must be carefully weighed against the advantages enumerated above, some of which are:

• Supercapacitors’ energy density (Watt-hours per kg) is much lower compared to batteries, leading to gigantically sized capacitors
• For quick charging, one would need to apply very high voltages and/or currents. As an illustration, charging a 100KWH battery in 10 seconds would need a 500V supply with a current of 72,000 Amps. This would be a challenge for safety, besides needing huge cables with solid insulation, along with a stout structure for support
• The sheer size of the charging infrastructure would call for robotic systems, a cumbersome and expensive set up. The cost and complexity of its operation and maintenance at multiple locations could defeat its purpose
• Primary power to enable the stations to function may not be available at remote locations.
Many prefer to opt for the traditional “battery bank” instead. The major problem of lead acid battery banks is the phenomenal hike in the cost of lead and the use of corrosive acid. Warm climates accelerate the chemical degradation leading to a shorter battery life.

A better solution, as often advocated, is to use a century-old technology in which nickel-iron (NiFe) batteries were used. These batteries need minimal maintenance, where the electrolyte, a non-corrosive and safe lithium compound, has to be changed once every 12-15 years. To charge fully, it is preferable to charge NiFe batteries using a capacitor bank in parallel with the bank rather than charging with a lead-acid-battery charger.

Though NiFe batteries are typically up to one and a half times more expensive, lower maintenance cost more than offsets the same over its lifetime.

To summarize, the Supercapacitor technology would still have to evolve in a big way before actually replacing batteries although the former offers a promising alternative to batteries.

image courtesy of eet.com

What is a battery and how do they work?

CR2032 battery

CR2032 battery

Batteries power most of our mobile gadgets. These are small chemical powerhouses, which generate electricity by the chemical reaction within the battery housing. Although there are different types of batteries available, all batteries contain cells that have two electrodes and a chemical or an electrolyte between them. Various combinations of series and parallel connections of the electrodes make up a certain voltage rating for the battery. For ease of understanding, we will treat the battery as made up of a single cell.

One of the electrodes is the cathode or the positive (+) terminal and the other is an anode or the negative (-) terminal. Because of the reaction between the two electrodes and the electrolyte inside, there is a buildup of electrons at the anode and a corresponding lack of electrons at the cathode. Although this is an unstable condition, and the electrons want to distribute themselves evenly between the electrodes, they cannot do so because of the presence of the electrolyte and its reaction with the electrodes. An isolated battery soon reaches a chemical equilibrium, and no further reaction occurs.

If the electrons find an alternate path to travel from the anode to the cathode, they will redistribute themselves and the number of electrons will gradually reduce, forcing the chemical reaction to start over again and create more electrons. This process continues until an inert layer covers one or both the electrodes. Usually, the alternate path is through a metal wire, which is a good conductor of electricity and links the two electrodes of the battery through a load or the mobile gadget requiring power.

Electrons flowing from the anode of the battery through the external wire to the load and back to the battery cathode constitute an electric current. Since it is usual to consider the direction of current flow as opposite to that of electron flow, we commonly say current flows from the cathode of the battery through the load and back to the battery’s anode.

Since the physical size of the battery restricts the quantity of chemical inside it, the current produced by the battery is also limited. The battery specification, as mAH or AH, is the product of the current and the number of hours the battery can produce this current continuously. In general, once the chemical within the battery has depleted itself or inert material has covered up the electrodes, the battery becomes useless. However, it is possible to revive or recharge certain types of batteries. These are the rechargeable batteries.

Once a rechargeable battery depletes itself, you can charge it up again by sending a current through it in a direction reverse to what it normally produces when connected to a load. This reverses the chemical reaction inside, and the electrolyte and the electrodes return to their initial condition. You can repeat this discharging and recharging process many times, until the electrolyte exhausts itself totally, and no further revival is possible.