Stephen Evanczuk writes:
Lithium-ion batteries have emerged as a common energy-storage device in many energy-harvesting applications. For engineers, maximizing battery performance and lifecycle requires use of battery charging circuitry able to account for the specialized characteristics of Li-ion cells. Engineers can cost-effectively build in Li-ion-charging functionality using available ICs from manufacturers including Analog Devices, Diodes Inc., Fairchild Semiconductor, Fujitsu Semiconductor, Intersil, Linear Technology, Maxim Integrated, Micrel, Microchip Technology, and Texas Instruments.
Unlike many other battery technologies, Li-ion cells require a charging profile maintained within a tight envelope. An undercharged Li-ion battery simply cannot provide its full rated energy output. On the other hand, charging circuits cannot afford to push Li-ion battery voltage above recommended limits or apply charging currents that exceed manufacturer-recommended levels. In either case, application of overvoltage or excessive charging current begins to break down Li-ion cells, reducing overall battery life or even resulting in catastrophic failures. For engineers, the challenge is maximizing charging rate and cell voltage without overcharging the cells.
Constant-Voltage/Constant-Current Devices Optimize Li-Ion Battery Charging for Energy-Harvesting - [Link]
Here is a montage of photos that I took while modifying my iPhone 4s to build in wireless charging. There are wireless charging options out there such as the powermat system but they all involve slipping on a jacket around the iPhone. I wanted to internalize the technology so that the beauty of the iPhone is not hidden away! It’s taken a while to complete but it’s finally done.
iPhone 4s Wireless Charging Hack - [Link]
Don Scansen writes:
For any complete energy-harvesting system designed to provide power to anything but small, short-duration loads, storage batteries represent a necessary but significant portion of the initial expense. The cost of batteries over the lifetime of the system can have an even larger impact if care is not taken to maximize the useful life of the battery component. What’s more, if unit growth continues for photovoltaic and other energy-harvesting systems relying on large-capacity storage batteries, designs that fail to maximize battery life could have a negative environmental impact due to the extra material and energy consumption needed to manufacture replacement systems as well as dispose of exhausted units.
Charge Controller Design for Maximum Battery Lifetime in PV Systems - [Link]
Electrical engineers of the University of Princeton are working on a cheap solar-powered charging system that can be printed on plastic and that transfers the produced electricity wirelessly. The solar cells are made from amorphous silicon (a-Si), a non-crystalline form of silicon. Crystalline silicon (c-Si) is much more efficient when it comes to converting sunlight into electricity but a-Si has the advantage that it can be processed at much lower temperatures (75 °C against 300 °C for c-Si), allowing it to be printed on plastic sheets.
The electric circuit is made out of the same material as the solar cells. And although a-Si has a lower electrical performance than c-Si, when it comes to producing cheap electricity-generating plastic sheet which can be put up anywhere, a-Si is best. By making the charging system available at a large scale, the Princeton engineers aim to have wireless electricity everywhere. [via]
Omnipresent Sun-Powered Wireless Charging Stations - [Link]
A photoflash unit is a Resistor-Capacitor circuit. It utilizes a fundamental property of capacitors. A capacitor opposes an abrupt change in the voltage and this ability of a capacitor is put to use.
Circuit design of a photoflash unit:
A photoflash unit has a simple circuit design: a high-voltage direct current (DC) supply is connected in series with a high-resistance resistor (which we’ll call ‘R1′). This resistor limits the current flow. A capacitor ‘C’ is connected in parallel with a flash lamp. The resistance ‘R2’ of a flash lamp is of small value. The circuit contains a switch between the large resistance ‘R1’ and a small resistance flash lamp ‘R2’, such that it can connect either resistance at any time during the process.
How does it work?
When the switch connects R1, the capacitor begins to become charged. The charging of a capacitor is time consuming due to a large ‘time constant’. The time constant is the product of the resistance ‘R1’ and the capacitance ‘C’, given by the following expression:
Time Constant = Resistance of large Resistance * Capacitance
T = R1*C
During the charging process, the potential of the capacitor starts rising gradually. Initially it has the value of zero but by the charging it rises to a steady value of ‘Vs’. As the voltage increases, the value of the electric current passing through it decreases from peak value to zero. This limiting of current happens due to the large resistance R1. The charging time of a capacitor is approximately equal to five times the time constant. That is;
Charging time of capacitor = 5*Time constant
The discharging process of a capacitor takes place when switch connects with the flash lamp (with small resistance ‘R2’). The low resistance of the flash lamp allows a high discharge electric current to flow in a brief period of time. The discharging time is almost five times the product of small resistance ‘R2’ and the capacitance ‘C’, given by the following relation:
Discharging time of a capacitor = 5* (R2*C)
The photoflash unit circuit emits a high current pulse of short duration during the complete charging and discharging process of this simple Resistor- Capacitor Circuit. Such an RC circuit has many other practical applications, including Radar Transmitter Tubes and Electric Spot Welding.
A few folks (including us) have iPhone 3Gs units that sometimes say ‘Charging is not supported with this accessory’ – it appears to be a wonky dock connector… jsappo writes -
Hey everybody! I just encountered this same problem and fixed it! It’s a wonky dock connector straight up. I have outlined the entire process for fixing it.. Hit me up with any questions.
iPhone 3gs FIX! – ‘Charging is not supported with this accessory’ - [Link]
Car battery and charging system monitor
This project is about making a simple electronic voltage monitor system for car’s battery and its charging system. It plugs into the car’s cigarette lighter receptacle and displays the instantaneous output voltage across the battery terminals on a 4-digit seven segment LED display. This helps you to get early warnings for possible battery and its charging system problems.
Voltage monitor for car’s battery and its charging system - [Link]
An introduction to USB battery charging: a survival guide. [via]
Arguably the most useful part of USB’s power capabilities is the ability to charge batteries in portable devices, but there is more to battery charging than picking a power source, USB or otherwise. This is particularly true for Li+ batteries, where improper charging can not only shorten battery life, but also can be a safety hazard. A well-designed charger optimizes safety and the user experience. It also lowers cost by reducing customer returns and warranty repairs. Charging batteries from USB requires balancing battery “care and feeding” with the power limitations of USB as well as the size and cost barriers ever present in portable consumer device designs. This article discusses how to achieve this balance.
The basics of USB battery charging: a survival guide – [Link]
Graham explores a popular method for charging NiMH cells – float charging.
Float charging has the advantage of keeping the cells fully charged and ready to use without the potential damage of long-term trickle charging or the cost of low-discharge cells. This approach works because NiMH cells do not have the memory problems associated with Nicads.
Float Charging NiMH Cells - [Link]