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]
Steve Taranovich writes:
Mophie, a California-based designer and manufacturer of mobile intelligent devices and accessories, developed the juice pack, the first ever “Works with iPhone” portable battery case certified by Apple. I contacted the company via e-mail for its help clarifying this design as well as the component types. It has not yet responded, so I give you my educated guesses. EDN readers are encouraged to weigh in with their own thoughts and expertise.
Teardown: Cell-phone charger: nice idea done right - [Link]
A special circuit is needed when charging a battery from a Solar Panel. When the solar panel is not providing any power the battery might start draining current into the panel. One common solution is to have a diode in series with the charging circuit to keep the current from going back to the solar panel. The problem with using a diode is the voltage drop across the diode reduces the available voltage for charging.
This circuit is great because the LTC4357 prevents the current back feeding into the panel without having the voltage drop limitation of the diode circuit
Solar Panel Charging Circuit - [Link]
mic @ wemakethings.net writes:
For a long time I wanted to enter the 21st century by stopping using NiCad or NiMH batteries and upgrading to Lithium accumulators as they provide more power per volume and are cool in general. Constant flow of obsolete cell phones provides a nice source of reasonably high-performance batteries for free – I felt compelled to tap into this resource for my battery operated projects.
Open source Lithium battery charger modules - [Link]
Kennith needed a 1A constant current lead-acid battery charger for his HAM radios so he writes:
Since the SLAs are relatively small, and I only need them charged between radio outings, I opted to build a 1A constant current charger, based on the 555 Battery Charger which won first place in the 555 Design Contest Utility category. Using a 555 is a rather clever way to get two comparators and a Set-Reset latch in a single 8DIP package, which is needed for the high and low trip points. The major difference between my design and Mike’s is that instead of using a relay like him, I use an LM317 as a constant current source to limit my batteries charge rate.
555 based constant current lead-acid battery charger - [Link]
The LT®3651-8.2/LT3651-8.4 are 2-cell, 4A Li-Ion/Polymer battery chargers that operate over a 9V to 32V input voltage range. An efficient monolithic average current mode synchronous switching regulator provides constant current, constant voltage charging with programmable maximum charge current. A charging cycle starts with battery insertion or when the battery voltage drops 2.5% below the float voltage. Charger termination is selectable as either charge current or internal safety timer timeout. Charge current termination occurs when the charge current falls to one-tenth the programmed maximum current (C/10). Timer based termination is typically set to three hours and is user programmable (charging continues below C/10 until timeout).
LT3651-8.2 and 8.4 – Monolithic 4A High Voltage 2-Cell Li-Ion Battery Charger – [Link]
This is a simple li-ion charger without a dedicated li-ion charger IC. This circuit can be used to efficiently and intelligently charge any single cell Li-ion battery pack like mobile battery, digicam battery, etc.
- Charging via mini-USB connector which is very common.
- Charging status display by LED
- Simple circuit by using opamp, resistor, and not by any complex dedicated IC or micro-controller.
- Charges completely drained (0V) battery packs.
- Max charging current 500mA (limited by USB supply), depending on battery.
Simple USB DIY Li-ion battery charger - [Link]
Brian Chu writes:
Batteries often serve as the main energy source for portable electronic devices. Although they depend on batteries, portable consumer electronic products, such as GPS devices and multi-media players, often consume energy directly from an ac-dc wall adapter or accessory power adapter (or “Auto Adapter”) when the battery is low or the device is in a stationary mode. Due to their cost effectiveness over their useful life, rechargeable batteries are often used for the power source of the portable electronic device. Attributes such as “relatively high energy density” and “maintenance free” make Lithium-Ion (Li-Ion) batteries popular in the portable consumer electronic products. Refer to the application note, AN1088, “Selecting the Right Battery System For cost Sensitive Portable Applications While maintaining Excellent Quality” (DS01088) for characteristics of Li-Ion batteries. Some examples of how to properly design with Li-Ion batteries will be discussed in this application note.
Designing A Li-Ion Battery Charger and Load Sharing - [Link]
The example cases discussed in this application report provide a basic understanding of what needs to be done at production, as well as on the application level, to achieve the aforementioned goals. The associated software provides library functions to interface and communicate with the bq27410 fuel gauge, applicable to any USB-equipped MSP430 device. The software also includes a demo application that integrates the USB stacks and the fuel gauge library functions to read the battery information from the fuel gauge and transmit it to the PC through USB Communications Device Class (CDC).
MSP430 based USB Li-Ion battery charger with fuel gauge - [Link]
Sam Davis writes:
Individual solar-panel systems produce dc power for remote applications while also storing energy in a rechargeable battery supported by a battery-charger IC.
In non-utility grid applications solar panels produce dc power for emergency roadside telephones, navigation buoys, and other remote loads. Virtually all 12-V-system solar panels comprise a series of photovoltaic cells that have a maximum output power of less than 25 W. In producing this power the solar-panel system uses a battery to provide power when the panel is “dark.” The rechargeable battery can supply power for long periods of time, requiring a charger that can properly operate a solar panel.
Meeting this need is Linear Technology’s LT3652 monolithic buck-charger IC, which operates with a single solar panel. The IC uses average-current-mode control-loop architecture to provide constant current/constant voltage (CC/CV) charge characteristics with a programmable charge current. The charger can be programmed to produce a 14.4-V float voltage. Housed in a 3- × 3-mm DFN-12 package, the IC can charge a variety of battery configurations, including up to three Li-Ion/Polymer cells in series, up to four Lithium Iron Phosphate (LiFePO4) cells in series, and sealed lead-acid batteries up to 14.4 V.
Power-Tracking Battery-Charger IC Supports Solar-Power Systems - [Link]