Abel Raynus writes:
Rechargeable NiCd (nickel-cadmium) cells are widely used in consumer devices because of their high energy density, long life, and small self-discharge rate. As a part of one project, I needed to design a reliable and inexpensive charger for a battery pack containing two NiCd AA-size 1200-mAh cells. In the process of the charger design, I needed to solve two main problems: first, setting a proper charge-current value, and second, stopping the charging process when the cell is full to avoid overcharging. This Design Idea describes a way to overcome both problems.
Charge a nickel-cadmium cell reliably and inexpensively - [Link]
by Fran Hoffart:
A circuit that properly charges sealed lead-acid batteries ensures long, trouble-free service. Fig 1 is one such circuit; it provides the correct temperature-compensated charge voltage for batteries having from one to as many as 12 cells, regardless of the number of cells being charged.
The Fig 1 circuit furnishes an initial charging voltage of 2.5V per cell at 25°C to rapidly charge a battery. The charging current decreases as the battery charges, and when the current drops to 180 mA, the charging circuit reduces the output voltage to 2.35V per cell, floating the battery in a fully charged state. This lower voltage prevents the battery from overcharging, which would shorten its life.
Charger extends lead-acid-battery life – [Link]
By Steven Keeping
Switching DC/DC voltage converters are popular because they provide efficient power conversion that can exceed 90 percent. That is an advantage both when input power is at a premium and when it is difficult to get the heat out (common challenges for engineers designing compact portable products).
With key power component manufacturers offering products that appear virtually identical on the specification sheet, it is tempting for an engineer to just pick a switching converter with the highest peak efficiency from a shortlist that meets their product’s general requirements. However, that would be a mistake because apparently identical converters can offer markedly different performance.
This article considers the major implications for power dissipation and associated heat rise that just a few percentage points difference in efficiency can make. The article then leads on to discuss how, depending on the load pattern, a converter with lower peak efficiency, but a flatter efficiency curve, could well be the better choice for a particular application.
Selecting the Right Voltage Converter Is Not Just About Peak Efficiency - [Link]
Joohansson @ instructables.com writes:
The reason for this project was to solve a problem I have. I sometimes do several days of hiking/backpacking in the wild and I always bring a smartphone with GPS and maybe other electronics. They need electricity and I have used spare batteries and solar chargers to keep them running. The sun in Sweden is not very reliable. When you need it as most it´s either raining or other circumstances that makes it impossible to charge with solar panels. Even when it´s clear weather it simply take too long to charge. Batteries are good but heavy. I have looked for alternatives but they are either very expensive or too large.
Smartphone Charger Powered by Fire - [Link]
Dimitar Kolev writes:
I test both, just with one LED for now (like 15mA) – they was working quite OK for distances up to 1-2cm, just some paper and thin air between TX and RX coils. With appropriate ferite it seems distance and coupling can be even better.
Just to fire further my interest, chip labels on board were erased, but fortunately I found a good picture where most of the labels were visible. Unfortunately no results after some googling, but finally I think I found the manufacturer of chips and some other wireless power/charging modules – it should be Elecoteq Electronics Website is only in Chinese, so I read what I can via Google translate. I found no datasheets, but for one there was some basic description
Wireless power and charging test and some reverse engineering - [Link]
Bill Schweber writes:
The power-management IC (PMIC) supports and manages the transducer and energy-collection channel, the energy-storage element (battery, conventional capacitor or supercapacitor), and the processor/wireless link. This critical block of any energy-harvesting design implements several major functions: Captures and extracts the random, miniscule energy from the source transducer, Transforms that extracted power into energy for the storage element, usually via a DC/DC converter, Manages the outflow of power from the storage element, while ensuring that power is not drawn when the stored energy is below a threshold value and would be wasted, Perhaps most challenging, it has to manage its own start-up sequence in the transition from when there is insufficient available stored energy for the PMIC itself.
Choosing a Power Management IC for Energy-Harvesting Applications - [Link]
by Publitek European Editors:
In today’s wireless, connected world, ambient Radio Frequency (RF) energy is everywhere. Technically, this free-flowing energy can be captured, converted and stored for use in other applications. In fact, it is already in use in a number of ultra-low-power, battery-free applications, such as RFID tags, contactless smart cards, and wireless sensor networks. As a result of technological advances, harvested RF energy is just beginning to realize its wider potential, including charging batteries in smartphones and other portable devices. These enabling technologies include RF transceivers, power conversion circuits, and ultra-low-power microcontrollers, all of which are becoming ever more efficient.
Tune In, Charge Up: RF Energy Harvesting Shows its Potential - [Link]
JN Lygouras, University of Thrace writes:
The control circuit in Figure 1a allows you to manually adjust the power delivered to a load. By changing the setting of potentiometer R3, you change the phase angle at which the thyristor (Q3) fires (Figure 1b), thereby altering the load current’s duty cycle. The adjustment range is about 0 to 180°. Q3’s off time is linear with R3, but of course the resulting load power is not linear with R3.
555 timer triggers phase-control circuit - [Link]
Battery-Charging Controllers for Energy Harvesters by Jon Gabay:
Whether your energy harvesting application uses large solar panels with high voltages and currents or, more often the case, must make do with minute amounts of power derived from various other ambient energy sources, one thing is almost certain: some type of energy storage is on board, whether in the form of a small rechargeable lithium ion battery, a supercapacitor, or solid-state energy storage technology. For the engineer this means that not only do we need to design circuits to harvest and convert ambient energy, but we also have to include an energy-harvesting interface (and protection circuitry) as well as a charge controller. This article looks at single chip energy harvesting devices that also provide some form of charge control. It discusses the different conditions under which energy can be extracted as well as what to expect when trying to squeeze power out of the ambient environment. Finally, the article will present some typical integrated solutions for small-sized low-power energy-harvesting designs.
Battery-Charging Controllers for Energy Harvesters - [Link]
Publitek European Editors writes:
Many security and motion detector systems rely on small, semi-autonomous nodes that are easy and simple to install. This implies the use of a battery-based power source and low-power operation in order to minimize the number of battery changes during the lifetime of the product.
Over its lifetime, the output voltage of a battery falls, with the biggest decline when the charge is nearing full depletion. A converter type that can accommodate this change in voltage but can still provide relatively high voltages for sensors and RF transmitters is the buck-boost converter – it operates the buck part of the circuit when the battery is fresh, moving to boost operation when the voltage falls below the threshold of the electronic circuitry it powers. A number of vendors have developed integrated buck-boost converters optimized for battery systems
Buck-Boost Converters Help Extend Battery Life for Motion Detection - [Link]