Monthly Archives: April 2016

Solar Deployment Component Selection

The market for renewable energy is in turmoil right now, mainly because of lower utility costs, a desire for energy independence, incentivized solar installations, and low-cost batteries. Homeowners are now trending towards storing energy from solar cells rather than selling it back to the grid. However, that requires selecting storage components wisely.

Although 2016 was the cutoff year for the current solar energy tax incentives, there has been a successful bid to the Congress to extend the incentives up to 2020. As a result, the solar industry finds itself rejuvenated and this is having a reflective effect on the battery-based energy storage systems as well.

This has created a massive surge for ESS or energy storage systems in general, with particular emphasis on RES or renewable energy storage systems. Designers of inverters and power conversion architectures now have enormous opportunities, especially those designing for home applications. For instance, Tesla has announced the Powerwall, a 10-kWh storage system suitable for homes, businesses, and utilities.

Designers and manufacturers are looking at advanced storage options such as ultra-capacitors and battery chemistry such as solid electrolytes, magnesium-ion, lithium sulfur, and next-generation flow and metal-air. The next-generation technologies for energy storage are expected to increase from near zero in 2015, to above $9 billion by 2030. Overall, the demand for batteries will increase from 66 GWh in 2014 to over 225 GWh in 2023
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Traditionally, people assumed that any excess power generated from solar panels and not used by the homeowner would be sold back to the utility. However, they are beginning to realize that saving the extra energy in batteries can help in the evenings, when the energy consumption is the highest and so are the utility rates. In the evenings, when there is no sun, the home can be less reliant on the grid, and be more self-sufficient if it relies on the backup batteries to supply electricity.

So far, people had to buy all parts separately and put them together for a solar system. This included the battery, inverter and metering. However, all this involved multiple voltage conversions leading to unnecessary losses and overall lower efficiency.

Now, all that is changing. You can opt for a fully integrated system. This includes the PV monitoring, the inverter, and the DC/DC conversion to charge the battery. Metering now is highly advanced, with wireless technologies such as ZigBee, providing either computerized or application-based monitoring of the entire system.

However, that does not mean it simplifies optimizing the PV conversion. One still needs MPPT or maximum power point tracking to make sure of capturing the varying PV energy and transferring it to the battery with the minimum of power losses, regardless of the strength of the sun. For instance, this involves using a capacitor for stabilizing the PV voltage and dropping it sufficiently, ensuring the charging voltage matches the battery chemistry.

Although efficiency, cost, and ease of use are all factors critical to the system level, safety is still the highest priority. The emphasis is on isolation including both digital isolators and opt couplers to meet the IEC 62109-1 standards.

What are Optically Isolated Relays?

Popularly, relays are known to be electromechanical devices. However, engineers today have access to solid-state relays that operate without any electromagnetic or moving parts. Where reliability and performance is paramount, engineers prefer to use solid-state relays to their electromagnetic versions. However, solid-state relays are more expensive.

While traditional relays have several mechanical failure modes associated with moving parts, solid-state relays offer several advantages in performance and design. These include low power consumption, low leakage current, stable on-resistance, high reliability, extremely long life, small size, fast switching speeds, high vibration and shock resistance, and no switching noise from contact bounce.

Another important feature of solid-state relays is they are optically isolated. That means the relays use an LED or light emitting diode on their input side, MOSFETs or metal oxide semiconductor field effect transistors on their output side, and an array of photo sensors isolating the two.

The design and packaging affect the relay’s performance crucially. Translucent resin molds the electronic and optical components – the LED, photo array, and the MOSFETs – allowing light to pass through, while applying a dielectric barrier between the input and the output.

That means you only need to drive a switchable voltage directly to the input pin of the solid-state relay through a resistor to limit the current through the LED and control the relay. The value of the resistor has to be selected carefully, so the LED can reach its full intensity without being overdriven.

Optically isolated relays are increasingly used in sophisticated test and measurement systems. However, these systems require solid state relays to have characteristics such as low capacitance, low on-resistance, physical isolation, and high linearity. As data acquisition devices become faster and more precise, the above characteristics play an increasingly important role.

Low capacitance results in improved switching times and better isolation characteristics when switching high-frequency load signals. You need low on-resistance for reducing power dissipation when switching high currents. This also improves switching speeds improving the precision of measurement. Temperature range of the relay is an important factor when considering on-resistance values, as rising temperatures drive up the on-resistance.

To enhance precision by minimizing noise, physical isolation between the input and the output of a relay plays an important part. Expect isolation voltages as high as 5 KV AC for optically isolated relays as these offer a truly physical separation between their input and the output. Solid-state relays also offer high linearity leading to accurate measurements.

Industrial applications also benefit from using optically isolated relays, although the requirements here are different. For instance, an industrial plant using several relays, the low power consumption of optically isolated relays offers substantial savings. Where an electromagnetic relay requires 50-100 mA to actuate, a typical optically isolated relay requires only 5 mA.

Latching-type models of solid state relays have built-in protective circuits that safeguard power supplies, motors, and other industrial devices susceptible to disturbances from the output side. Such disturbances come from voltage peaks or overcurrent conditions arising from short circuits or improper use. Their reliability and small form factor saves space, while speeding up development.

Do You Need A 2K Display on your Smartphone?

One of the biggest selling points of flagship smartphones is their display resolution. A high resolution allows for better rendering of images and text on the screen and enhances the overall viewing pleasure. While grainy displays have become a thing of the past, with even sub $100 smartphones touting qHD and HD displays, the question now is, how much is too much.

Phone manufacturers are constantly striving to equip their devices with the sharpest displays, outperforming rivals in terms of clarity and accuracy of color reproduction. While shopping for a new smartphone, you might have come across terms like retina, HD, 2K and 4K displays. However, post a certain figure, it is doubtful if there is any discernible improvement in the clarity.

When launching the iPhone 4, Apple had claimed that a resolution of 960×640 pixels on a 3.5″ screen (translating to 326 pixels per inch) was as much as a normal human eye could discern when viewing from a distance of 9″. Going by that statement, a screen resolution north of 326 ppi would not cause any tangible improvement in clarity, while increasing production costs. Though iPhones have bigger screens now, their ppi remains constant at 326, whereas some other manufacturers have been pushing increasingly higher resolution screens on their latest releases. Most smartphones launched in the past year by tech giants like Samsung, LG and newcomer Oppo have panels with pixel densities of and above 415. The first smartphone to feature a 2K display was the Xplay 3S, launched by Vivo with a 6″ screen that sported 491 ppi. Soon after, Oppo launched the Find 7 smartphone, also with a 2K display of 2560×1440 or an astronomical 538 ppi. These figures are way ahead of retina displays, but in case of smartphone displays, after a certain point, more might not always be merrier.

Of course, the screen size has a huge role in determining how many pixels need to be packed in per square inch for delivering the perfect viewing experience. Moreover, a lot depends on the distance at which the screen is kept from the eyes, as closer viewing distances mean that more pixels can be resolved by the human eye. However, in no way is the average smartphone user going to be able to appreciate the difference between say, a 350- and a 500-ppi display. Stuffing more pixels per inch into an LCD panel is only more taxing on the battery. Therefore, an ultra-high resolution 2K display needs to be powered by a bigger battery as well, along with a superfast CPU to provide juice for all those extra pixels.

A 2K display, or the absence of it, should not be the only factor to consider when looking for a new smartphone. While it does make for a great viewing experience, it is more than likely a slightly less ppi count will not cause any noticeable decrease in clarity. It is a good feature to have on a smartphone to boast about, but it comes at the cost of battery life and processing speed.

The ExaGear Desktop for the Raspberry Pi

Normally, the Raspberry Pi or RBPi does not allow running Intel x86 applications. This is because the RBPi is ARM-based. That means it has a different architecture from the Intel-based PCs we are used to using. This is as if a letter addressed to a Russian town landing up in Denmark – the address is all wrong, so it is tough to deliver.
Virtual machines are available that create a local environment for running applications where the basic architecture differs. For the x86 platform, the most popular virtual machine software are VMware and VirtualBox. With virtual machines, you may be running Linux as your main operating system, but you can also run a full-fledged Windows operating system simultaneously and vice versa. The main operating system is termed the Host, while the OS running under the virtual machine is termed the Guest.
Eltech has produced such a virtual machine for RBPi that have ARM platforms as their base. This is the ExaGear Desktop and it allows you to run Intel x86 applications directly on your RBPi through a virtual x86 Linux container on ARM. For example, on the ExaGear Desktop, if you install Wine, the open source compatibility layer software application will allow you to run even Windows applications on your RBPi.
You can run the ExaGear Desktop on most ARM-based Mini PCs operating with Linux such as the RBPi, Banana Pi, Wandboard, Jetson TK1, Utilite, CuBox, CubieBoard, ODROID including the ARM-based Chromebook. Unlike Linux, ExaGear Desktop is not free and you can download it only after paying for its license key. However, before buying, it is prudent to check up if your Mini PC has the proper hardware and software base to allow ExaGear Desktop to run on it.
If you are using the RBPi ver1, you will need the ARMv6 instruction set with VFP32. For other RBPi versions and ARM devices, you will require the ARMv7 instruction set with VFP32. If you are planning to use x86 applications that require MMX/SSE, you will also need NEON as support. On the software side, you must be using the Linux operating system variants such as Raspbian, Debian 7, Ubuntu 14.04 or Ubuntu 12.04. Check with the Eltechs Tech Forum if you still harbor doubts about system requirements.
Eltech has published some test results to demonstrate the speed with which the ExaGear Desktop works. For benchmarking, they have used SysBench, which was built for ARM and Intel x86 platforms. Using the same ARM machine for both tests, they have compared the results of ARM-based tests against x86 tests running under the ExaGear Desktop. The tests cover parameters such as File IO read/write, CPU cycles, Memory usage, Threads speed and Mutex. Results show ExaGear to be superior to QEMU in almost all parameters.
Using their setup, Eltech has also compared the performance of ExaGear against the performance of QEMU, the user mode emulator. For benchmarking, they used GeoBenchmark and found that ExaGear Desktop was nearly five times as fast as QEMU was.
Eltech has also compared the ExaGear Desktop performance against QEMU using the nbench benchmark. Here too, ExaGear Desktop was able to show far superior performance compared to the performance of QEMU when both were run on the same platform.

Stackable Pi-Plates for the Raspberry Pi

If you are faced with a paucity of projects for your Raspberry Pi or RBPi, the tiny, credit card sized single board computer, you should get the circuit boards from Pi-Plates and connect your RBPi to the outside world. Pi-Plates offer a family of stackable, add-on boards that provide your SBC with a robust set of features at a minimal cost.

Pi-Plates design their circuit boards to be economical with the GPIO pins they use from the RBPi header. For example, when using the DAQCplate board, it uses only two dedicated GPIO pins. However, you can stack eight of these Pi-Plates to get 64 digital inputs, 56 open-collector outputs, 64 analog inputs and 16 analog outputs. Whether you are an experimenter, a hobbyist or a professional, Pi-Plates have designed these boards to be useful for all. Additionally, these are mechanically and electrically compatible with all revisions of the RBPi. That includes versions A, B, A+, B+ and the new version 2.

At present, Pi-Plates offer four products. The flagship product is the DAQCplate board that has ADCs or Analog to Digital Converters, DACs or Digital to Analog Converters and expanded digital IO. MOTORplate is a new product for controlling motors and you can use it to drive two stepper motors or four DC motors, while its onboard software can handle all drive logic including acceleration profiles. If you want to add custom hardware on your Pi-Plate stack, you can use the PROTOplate board.

When stacking Pi-Plates, you will need a secure structure and this is provided by the BASEplate mounting system. All hardware necessary for mounting to the BASEplate is already available with each Pi-Plate board. Pi-Plate also offers two great kits.

The DAQC kit comprises two BASEplates and one DAQCplate boards for the price of a single unit. This makes a great beginning for those starting with the DAQCplate for the first time.

For those starting with a MOTORCplate, the MOTOR Kit may be very useful. This kit comprises one MOTORplate and two BASEplate boards for the price of a single unit.

For example, the DAQCplate is a data acquisition and control board. Its digital output section has a connector that provides seven open-collector outputs and a pair of 5VDC outputs that you can use for driving loads. You can protect these with a flyback diode connected to the terminals.

You can use these outputs to drive incandescent automotive light bulbs, ultrasonic rangefinders, resistive heating elements, unipolar stepper motors, buzzers, solenoids, relays, DC motors or LED strings. Green LEDs connected to each digital output light up to indicate a high on the output. To light up these LEDs, you do not require connecting anything to these outputs. At the same time, these LEDs will not affect anything that you connect to these outputs.

Darlington pair transistors drive the seven open-collector digital outputs. They can sink a maximum of 350mA and handle a maximum load voltage of 12VDC. With a load voltage of 200mA, the on voltage is typically 1.1V. When using inductive loads such as solenoids or relays, you must connect the high side power supply to the flyback protection terminal.