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]

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.


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


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

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

Friday, December 27, 2013

Preamplifier for Microphones and Tape Heads

This circuit consists of a single transistor as amplifier and it gives a nice amplification to weakest and unipolar signals for feeding to a real amplifier. The center of this circuit is a BC547 OR BC548 transistor and the rest of the circuit is few resistors, and capacitors. The diagram and also the PCB layout is below. [Link]


Tuesday, December 24, 2013

Telephone Ring Repeater

Even though cordless phones have invaded our homes and offices, you don’t always have them at hand, and as their ringtones are usually very much quieter than the old rotary-dial- type analogue phones, it can happen that you miss a call you’ve been waiting for while you’ve been going about your daily business.

Until quite recently, you could still find remote ringers that could be plugged into any standard phone socket in order to have an additional ringer, but it seems as if these accessories are currently being phased out as everyone is ‘going cordless’. So we decided to suggest something better, with this phone ring repeater that makes it possible to control any device connected to the AC power outlet using the ringtone available on any subscriber line, and naturally, with all the guarantees of safety and isolation that are of course rightly expected. So it’s capable of driving a ringer, or indeed even a high-powered sounder to alert you when you are in the  garden, for example; but it is equally able to light a lamp for a ‘silent ring’ so as to avoid waking a sleeping baby or elderly person.

 Telephone Ring Repeater Circuit Diagram
Phone Ring Repeater Circuit
This circuit has been designed to be compatible with all phone systems the author is  aware of and also to be totally stand-alone. What’s more, the circuit can be connected to the phone system without any danger though in some countries, it is forbidden to connect non-approved devices to the public  switched telephone network (PSTN). Check local regulations in this respect.

In order to understand the principle of it, we just need to remember that the ringtone present on a phone installation is an alternating voltage, whose amplitude and frequency vary somewhat between countries, but always with comparable orders of magnitude except in the case of exchange systems  used in large companies. However, when the  line is quiescent or a call is in progress, it carries only a direct voltage. Capacitor C1 makes  it possible to pick off just the AC ringing volt-age, which is then rectified by D2 and amplitude-limited by D1. The resulting DC voltage charges capacitor C2, which makes it possible to light LED D3 as well as the LED in the  optocoupler IC1. This is no ordinary optocoupler, but is in fact an AC power zero-crossing  detecting optotriac, which allows us to con-trol the chosen load while generating no, or  less, interference, which would not be the  case using a standard optotriac.

The output triac it contains is not powerful  enough to drive a load directly connected  to the mains, so it is used to drive the trigger of triac TRI1, which is a totally standard  400 V device, rated at x amps, where x is chosen to suit the maximum power of the load  you want to control using this circuit. Resistors and capacitors R5 and C3 on the one  hand, and R6 and C4 on the other help, serve  to suppress the switching transients, which  are already inherently low because of the AC  zero-crossing switching provided by IC1.
Construction is not at all difficult, but does  require a few precautions in choosing some of the components. First of all, capacitor C1  must be an MKT type, mylar or equivalent,  with a 250 V operating voltage because of  the relatively high amplitude of the ringing  voltage. For safety reasons, it is essential that  capacitors C3 and C4 are self-healing types  intended for AC power use at 250 VAC. These  capacitors are generally known as Class X or  X2 capacitors.

As for the triac, it should have a 400 V operating voltage (but see below for users on 120  VAC power) and maximum current slightly  greater than the maximum current drawn by the load being driven. As this will usually be a sounder or a common lamp, a 2 A type will  usually be more than adequate in most situations. As the circuit can be expected to operate for short periods only, there is no need to  mount the triac on a heatsink. One final important point: as the right hand  part of the circuit is connected directly to AC  power, it is vital to fit this inside a fully-insulated housing, for obvious safety reasons.  Make sure you cannot touch any part when  the circuit is in use.

The circuit should work at once and without  any problems, but if you notice that D3 doesn’t  light up fully, and hence incorrect or erratic  triggering of the triac, because of too low a  ringing voltage, all you need to put things to rights is reduce the value of resistor R1.  The circuit as shown was dimensioned for  operation from 230 VAC power. Readers on  120 VAC power should modify the following  component values: R4 = 180 Ω; R5 = 220 Ω;  TRI = 200 V model; IC1 = MOC3031. Option-ally, C3 and C4 may be rated at 120 VAC.

Source:  http://www.ecircuitslab.com/2012/05/telephone-ring-repeater.html