Tuesday, February 4, 2014

Storage Battery Solutions for Energy Harvesting Applications

Ambient light, thermal gradients, vibration/motion, or electromagnetic radiation can be harvested to power electronic devices. At the same time, all energy-harvesting-based systems need energy storage for times when the energy cannot be harvested (e.g., at night for solar-powered systems). Rechargeable batteries ‒ known as “secondary” cells to differentiate them from “primary” or single-use cells ‒ are usually specified for this task. This article will examine the various secondary cell technologies available to energy harvesting system designers looking for a cost-effective and powerful battery solution.
Storage Battery Solutions for Energy Harvesting Applications
Primary and secondary batteries contain the same basic structure of a cathode, an anode, an electrolyte for moving charge between the terminals, and a means to separate them. Secondary cells are distinguished by the type of rechargeable chemistry employed, such as nickel-cadmium or lithium-polymer, or solid-state thin film. [Link]
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Friday, January 10, 2014

Solar Powered SLA Battery Maintenance

This circuit was designed to ‘baby-sit’ SLA (sealed lead-acid or ‘gel’) batteries using freely available solar power. SLA batteries suffer from relatively high internal energy loss which is not normally a problem until you go on holidays and disconnect them from their trickle current charger. In some cases, the absence of trickle charging current may cause SLA batteries to go completely flat within a few weeks. The circuit shown here is intended to prevent this from happening.

Two 3-volt solar panels, each shunted by a diode to bypass them when no electricity is generated, power a MAX762 step-up voltage converter IC. The ‘762 is the 15-volt-out version of the perhaps more familiar MAX761 (12 V out) and is used here to boost 6 V to 15 V. C1 and C2 are decoupling capacitors that suppress high and low frequency spurious components produced by the switch-mode regulator IC. Using Schottky diode D3, energy is stored in inductor L1 in the form of a magnetic field.

Solar Powered SLA Battery Maintenance Circuit Diagram
Solar Powered SLA Battery Maintenance Circuit Diagram

When pin 7 of IC1 is open-circuited by the internal switching signal, the stored energy is diverted to the 15-volt output of the circuit. The V+ (sense) input of the MAX762, pin 8, is used to maintain the output voltage at 15 V. C4 and C5 serve to keep the ripple on the output voltage as small as possible. R1, LED D4 and pushbutton S1 allow you to check the presence of the 15-V output voltage.

D5 and D6 reduce the 15-volts to about 13.6 V which is a frequently quoted nominal standby trickle charging voltage for SLA batteries. This corresponds well with the IC’s maximum, internally limited, output current of about 120 mA. The value of inductor L1 is not critical — 22 µH or 47 µH will also work fine. The coil has to be rated at 1 A though in view of the peak current through it.

The switching frequency is about 300 kHz. A suggestion for a practical coil is type M from the WEPD series supplied by Würth (www.we-online.com). Remarkably, Würth supply one-off inductors to individual customers. At the time of writing, it was possible, under certain conditions, to obtain samples, or order small quantities, of the MAX762 IC through the Maxim website at www.maxim-ic.com.

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Inverter Overload Protector With Delayed Auto Rest

An overload condition in an inverter may  permanently  damage  the  power transistor array or burn off the transformer. Some of the domestic inverters sold in the market do not feature an overload shutdown facility, while those incorporating this feature come with a price tag.the circuit presented here is an overload detector which shuts down the inverter  in  an  overload  condition. 

Inverter Overload Protector With Delayed Auto Rest Circuit diagram:

Inverter Overload Protector With Delayed Auto Rest -Circuit -Diagram


It  hasthe following desirable features:
  • It shuts down the inverter and also provides  audio-visual  indication  of  the overload condition.
  • after  shutdown,  it  automatically restarts  the  inverter  with  a  delay  of  6 seconds. thus, it saves the user from the inconvenience  caused  due  to  manually resetting the system or running around in darkness to reset the system at night.
  • It  permanently  shuts  down  the inverter  and  continues  to  give  audio warning,  in  case  there  are  more  than three  successive  overloads.  Under  this condition, the system has to be manually reset.(Successive overload condition indicates that the inverter  output  is  short-circuited or a heavy current is being drawn by the connected load.)
Inverter Overload Protector
Inverter Overload Protector With Delayed Auto Rest

The circuit uses an ammeter  (0-30a)  as  a  transducer  to  detect  overload condition.  Such  an  am-meter  is  generally  present in  almost  all  inverters.  this  ammeter  is connected between the negative supply of the battery and the inverter, as shown in Fig. 2. the voltage developed across this ammeter, due to the flow of current, is very small. It is amplified by IC2, which is wired as a differential amplifier having a gain  of 100. IC3 (NE555) is connected as a Schmitt ‘trigger’, whose output goes low when the voltage at its pin 2 exceeds 3.3V. IC4 (again an NE555 timer) is configured as  a  monostable  multivibrator  with  a pulsewidth of 6 seconds. IC5 (CD4017) is a CMOS counter which counts the three overload  conditions,  after  which  the  sys-tem has to be reset manually, by pressing push-to-on switch S1. the  circuit  can  be  powered  from  the inverter battery. In standby condition, it consumes 8-10 ma of current and around 70 mA with relay (RL1), buzzer (PZ1), and LED1 energised.

Please note the following points carefully:
  • Points A and B at the input of IC2 should be connected to the corresponding points (A and B respectively) across the ammeter.
  • Points C and D on the relay terminals  have  to  be  connected  in  series  with the  already  existing  ‘on’/‘off’  switch  leads of inverter as shown in Fig. 1. this means that one of the two leads terminated on the existing  switch  has  to  be  cut  and  the  cut ends have to be connected to the pole and N/O contacts respectively of relay RL1.
  • The  ammeter  should  be  connected in series with the negative terminal of the battery and inverter, as shown in Fig. 2.Move the wiper of preset VR1 to the extreme position which is grounded. Switch ‘on’ the inverter. For a 300W inverter, connect about 250-260W of load. Now adjust VR1 slowly, until the inverter just trips or shuts down.  repeat the step if necessary. Use good-quality preset with dust cover (e.g. multiturn trimpot) for reliable operation.the circuit can be easily and success-fully installed with minimum modifications to the existing inverter. all the components used are cheap and readily avail-able. the whole circuit can be assembled on a general-purpose PCB. The cost of the whole circuit including relay, buzzer, and PCB does not exceed Rs 100.
Source:  http://www.ecircuitslab.com/2011/11/inverter-overload-protector-with.html






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Build a 200Ma 12v ni cad Battery Charger Circuit Diagram

This 200Ma-12v ni-cad Battery Charger Circuit Diagram charges the battery at 75 mA battery can be left in the charger indefinitely, until the battery is charged, then it reduces the To set the shut-off point, connect a 270-ohm, current to a trickle rate

It will completely 2-watt resistor across the charge terminals and recharge a dead battery in four hours and the adjust the pot for 15 volts across the resistor. 

 200Ma-12v ni-cad Battery Charger Circuit Diagram


200Ma-12v ni-cad Battery Charger Circuit Diagram
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Thursday, January 9, 2014

Simple Frequency Voltage Converter Circuit Diagram

This is the simple frequency voltage converter circuit diagram. Teledyne Semiconductor`s Type TSC9402 is a versatile IC. Not only can it convert voltage into frequency, but also frequency into voltage. It is thus eminently suitable for use in an add-on unit for measuring frequencies with a multimeter. 

Only a few additional components are required for this.. Just one calibration point sets the center of the measuring range (or of that part of the range that is used most frequently). The frequency-proportional direct voltage at the output (pin 12—amp out) contains interference pulses at levels up to 0.7 V. If these have an adverse effect on the multimeter, they can be suppressed with the aid of a simple RC network. 

The output voltage, U0, is calculated by: tfo=C/rei(Ci + 12 pF) R2fm Because the internal capacitance often has a greater value than the 12 pF taken here, the formula does not yield an absolute value. The circuit has a frequency range of dc to 10 kHz. At 10 kHz, the formula gives a value of 3.4 V. The circuit draws a current of not more than 1 mA.

Frequency Voltage Converter Circuit Diagram

Simple Frequency Voltage Converter Circuit Diagram

Simple Frequency Voltage Converter Circuit Diagram
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