POWER SUPPLY CIRCUIT

12V Battery Charger for Sealed Lead Acid

noreply@blogger.com (Go2Media) — Fri, 09 Oct 2009 07:07:00 +0000

This battery charger is for 12V Seales Lead Acid (SLA) battery. It is actually a half-wave rectifier. It only charges the battery on every half cycle. The plug pack doesn't like this as it leaves residual flux in the core of the transformer and causes it to overheat.

There are a number of points we need to cover about the care and use of Sealed Lead Acid batteries.
Firstly, these batteries must be charged, discharged and stored very carefully.
We normally think batteries can be stored for months (if not years) and they will be available for immediate use.

This is not the case with SLA batteries.
If you store a NEW, full charged SLA battery for 6 months or more, you will find it may be fully discharged.
You may also find you cannot charge it!! It may be worthless.
That's how delicate SLA batteries are.

They must be charged on a regular basis to prevent them discharging to a very low voltage level.
If the terminal voltage of a SLA battery is allowed to go below 8v, a process called SULPHATION starts to cover the surface of the plates and prevents the battery being re-charged. The internal resistance of the battery increases and it becomes useless. See products Sealed Lead Acid Battery Charger on Amazon

Parts List of SLA Battery Charger

2 - 1R8 0.5watt resistors
1 - 150R 0.25 watt resistor
1 - 180R
1 - 560R
1 - 1k5
3 - 2k2
1 - 3k3
1 - 4k7
1 - 8k2
1 - 1k mini trim pot

1 - 1n ceramic
2 - 47u 25v electrolytics

1 - 5mm red LED

4 - 1N4148 signal diodes
1 - 10v 0.25watt zener
1 - BC 547 transistor
2 - BC557 transistors
1 - MCR100-6 SCR
1 - 1m red lead
1 - 1m black lead
2 - alligator clips
1 - 2m very fine solder

1 - SLA Battery Charger PCB

Also required:
1 - 12v AC transformer (500mA AC)
1 - power lead
1 - case

Available on Amazon Sealed Lead-Acid Battery Charger
Source : Battery Charger for 12v SLA (Sealed Lead-Acid) Batteries

Lead-Acid Batteries Charger with Solar Panel

noreply@blogger.com (Go2Media) — Mon, 21 Sep 2009 15:49:00 +0000

This Batteries Charger is intended for charging sealed lead-acid batteries with a solar panel in small and portable applications. The customary diode that prevents the battery from discharging through the solar panel has been replaced by a FET-comparator combination.

The batteries charger will stop charging once a pre-set voltage (temperature compensated) has been reached, and recommence charging when the voltage has dropped off sufficiently. The load is disconnected when the battery voltage drops below 11V and reconnected when it gets back to 12.5V.

Solar Batteries Charger Schematic

The batteries charger circuit has the following features:

Charges until Vbat = 13.8V (adjustable), then float charges;
Shuts down load when Vbat < 11V (adjustable), resets at 12.5V;
Temperature compensation;
Will work with cheap and readily available components like LM393 comparators and BUZ11 FETs;
Uses less than 0.5mA when using TLC393 comparators;
Burns less than 20mW in FETs when charging at 0,5A. (More expensive FETs with a lower RDSON will yield even better results). Note that the charging current is limited only by the solar panel used.

Solar Batteries Charger PCB

Note that I added three DC/DC-converters (for 9, 6 and 3V) on the PCB, the actual charger is less than half of the PCB. I don't have a silk screen, so if you want to build this, you'll have to figure out the PCB for yourself.

With all the components into place, some additional electronics to get the DC/DC-converters in and out of standby, two small SLA-batteries (2.2Ah each), some odd parts and wiring, a fuse, a front plate and housing.

A final word: you build everything at your own risk, no functionality is implied, the resulting apparatus might not work, be unfit for drying pet dogs, and contain small parts that could suffocate children when swallowed or inhaled.

Source: Solar charger for lead-acid batteries

Camera Battery Charger for Train Mounted

noreply@blogger.com (Go2Media) — Mon, 21 Sep 2009 15:13:00 +0000

This camera battery charger circuit will keep the battery for a train mounted camera charged and will shut the camera off after a few seconds when power is no longer applied to the track.

This camera battery charger circuit is designed for DCC systems and the battery is essentially used as a capacitor as it is not allowed to become discharged.

The battery also controls the voltage to the camera as any current passed through R1 that is not needed by the camera is shunted through the battery. This is an inefficient but cheap way to control the voltage. (Circuits Without Pages Of Their Own)

Source: Train Mounted Camera Battery Charger

Solar-Battery Regulator-Load Controller

noreply@blogger.com (Go2Media) — Sat, 12 Sep 2009 07:54:00 +0000

This Solar-Battery regulator allows solar cell arrays to be connected to either conventional lead-acid, sealed lead-acid, or lithium storage batteries without fear of overcharging. It allows two different electrical loads to be driven from the batteries at two different charge states to maximise power usage efficiency.

The existing power control circuit in this fridge aims to avoid discharging a car battery by ensuring that it only runs down to a certain voltage. This means that it will only run for a short time after the engine is turned off. While a sensible precaution, this prevents efficient use of solar power to drive it.

The existing circuit also suffers from oscillation caused by voltage drops in the wiring from the unit to the power source, generally a cigarette lighter socket; Rather than switching off cleanly the load relay spends several tens of minutes clicking on and off uselessly as the car battery voltage slowly drops back from its on-charge voltage.

I wanted to be able to get some level of refrigeration for a few minutes even if the weather was not especially sunny. What I needed was a storage battery of a few amp-hours, a solar panel for charging, and a controller circuit to turn on the fridge when enough charge had built up for a few minutes operation. The original relay based power control circuit in the fridge was removed and the power input wired direct to the fan and Peltier effect cooling unit. The nominal current draw of the fridge is 4A.

Batteries
There is space inside the regulator enclosure for about 7Amp-Hours worth of surplus mobile phone lithium batteries. Three 3.6V nominal voltage cells are wired in series which produces a battery of 10.8V, then multiple banks of three are wired in parallel. The voltage varies over the charge cycle from 3 X 3.0 = 9.0V when fully discharged to 3 X 4.1 = 12.3 V which is the maximum allowable on-charge voltage. Higher voltages will destroy these cells. The 12.3V maximum charge voltage allows the battery to be charged from 12V solar panels and the 9.0V full discharge voltage allows most non-critical 12V equipment to run the batteries right down to empty without over-discharging them.

An external battery can be connected if needed but if it is a different technology the internal one must be disconnected first. The external battery may be lithium as described, conventional lead acid, or sealed lead acid and the appropriate voltages are selected on an internal DIP switch. The circuit is designed to draw very little current so that some charge can be accumulated even when the weather is quite dull.

Circuit Operation

In the actual device the transistors are bolted to the aluminium case. The schematic diagram shown here represents how the circuit would be built if all components were on-board. Separate paths for load current and voltage sensing allow the battery voltage to be measured accurately even under loads of several amps.

The LM4041 provides an accurate low-power voltage reference for the sensing circuit. This 1.225V reference is used directly for the conventional lead-acid setting and via two alternative dividers for the sealed lead acid and lithium voltages. Using a 1% version for the voltage reference and 1% resistors in these dividers keeps us from going too far above the magic 4.1V limit on standard lithium cells without having a pesky trimmer, or worse, a set of trimmers. As the voltage across the battery rises under charge, the main load output will be switched on when a voltage some way above the fully discharged level is reached.

If the load current exceeds the available solar charge current, the batteries will drain back down to the fully discharged state and the load will be disconnected again. Some hysteresis avoids the load switching on and off too frequently, but this all depends on the available charge current, battery capacity and load current. If the charge current exceeds the load, the battery voltage will continue rising until the full charge voltage is reached. At this point the secondary load is turned on to prevent overcharging. If no secondary load is naturally available, one must be provided in the form of a resistor.

If the standard load current exceeds the maximum output of the solar array this is not needed. IRF350LC MOSFETS are used for load switching which allows loads of more than 10 amps to be switched. A dual CMOS rail-to-rail output op-amp is used which simplifies the calculation of the switching voltages. LED indicators drawing about 2mA each show which loads are turned on.

If lead acid batteries are used then its worth noting that there is no temperature compensation on the charge voltages, so it's best to keep them between 10 and 30 degreesC or the -2mV/K coefficient of this technology might result in overcharging of sealed gel units.

Switching Voltages

Source: Photovoltaic Solar Battery Regulator and Load Controller

DC-DC Converter 12V for Car

noreply@blogger.com (Go2Media) — Sat, 12 Sep 2009 06:59:00 +0000

This DC-DC converter circuit designed to accept a range of input voltages that are present in a car's electrical system, and provide a stable regulated voltage output of 12v. Nominally, the battery voltage is about 13.8v, but when the car engine is being started, the voltage can often droop down to 6 or 7 volts for a short time, and peaks can be present somewhat above the nominal voltage as well.

This converter project is now in the general electronics section, because I no longer use it in my MP3 Box, so now it's basically just a fun experiment that I did to explore the world of switching converters.

Download: Schematic - PCB

Note: all schematics and PCB files are Cadsoft Eagle 4.13 format

That is the design I am going with for my system, since the parts are cheap and more easily available. While based on a more antiquated controller IC, without the fancy features the newer-generation ones have, like charge-pump gate drive, it gives me a good starting point to tweak a more advanced design if need be. Not to mention, he claims it handles up to 8 amps output, and considering my MP3 box only drew less than 2 amps when I tested it last, I think that will be more than sufficient.

For those of you who are into this sort of thing and don't want to read the other page, this particular design is a SEPIC topology using a UC3843 controller chip. In addition to the two main inductors you normally see in a SEPIC design, there are two 12uH inductors, one each on the input and output. The two "main" inductors in this case are hand-wound on a common core, as coupling them is supposed to improve efficiency.

To wind the big black inductor you see in the pictures, which is the transformer-looking thing in the schematic, you need a $5.29 snap-on EMI suppressor from radio shack, part number 273-105, and you need some 18-20 gauge "magnet wire" (enamel-insulated copper wire). The magnet wire at radio shack is too small, you'll have to look elsewhere. Winding it is simple, you just need to wind two pieces of wire together, for 13 turns, around one half of the core. Then cut two strips of paper to place between the two halves of the core where they would touch. (Keeping the two halves of the core slightly separated with paper makes it not saturate as easily... ie - keeps bad things from happening) Then, eventually you should glue it all together so the core can't vibrate. Personally I chose not to glue it until I was sure it was performing properly.

Source: 12v Regulated Automotive Switching DC-DC Converter

DC-DC Converter With Variable VDC Input

noreply@blogger.com (Go2Media) — Sat, 12 Sep 2009 06:34:00 +0000

A DC-DC converter or another name known as buck regulator or switching regulator (because the input voltage can be either above or below the desired voltage output), provides stable regulated output voltage to supply electronic circuits.

LM2576 converter circuits perform same function as the commonly known voltage regulator LM7805 from National Semiconductor. The 7805 voltage regulator dissipates a lot heat. The higher input voltage, the more heat is generated. The extra input energy is converted to heat, keeping the output voltage regulated at 5V.

LM2576 DC-DC Converter Circuits
There a variety of capacitors out there in the market. Capacitance, voltage rating, dielectric material, etc... . Choose a suitable voltage rating across the capacitor. The circuits deals with high current, therefore it will be better to choose a low ESR (equivalent series resistance) Aluminum electrolytic capacitor. As a general guide, a higher voltage rating has lower ESR rating.

The inductor coil use should be able to handle the current passing through the inductor coil. If the wire is too thin, the coil may be burn or just fail. My previous circuit uses small wattage inductor (package like a big resistor). The circuit couldn't work and was later found to be IC problem. I have not yet do a test to check on the possibility of the inductor contributing to the failure.

Using a inductor meter to measure the inductance will be easier. Inductance value can be observe immediately for any modification to the coil of wire. The inductance value can also be calculated, depend on the coil size, number of turns, wire size used, dielectric of the core etc... .

The 1N5822 is a high current, high speed, schottky diode and is suitable for this digital switching circuit. Schottky diode (Schottky Barrier Rectifier), means that the forward voltage drop is low. For this application, a low forward voltage diode is necessary.

More DC-DC Converter Circuits

DC-DC Converter 12V to 120V 20W

noreply@blogger.com (Go2Media) — Sat, 12 Sep 2009 05:46:00 +0000

Here is a DC to DC Converter schematic. The design is a simple saturation-limited push-pull converter. There is no special reason to use PNP transistors. I used them simply because I had a box full of them around. You may well turn over the design to use NPN transistors.

The 2SC945 is a bias switch for startup. When applying 12V power, this transistor applies enough bias to the power transistors to get the oscillation started. Soon later, the 100uF capacitor charges up, the transistor goes off, and the power transistors self-bias into cut-off, such that cross-conduction is eliminated. After removing power, the 6k8 resistor discharges the bias timing capacitor, as otherwise the circuit would be unable to restart!

The secondary rectifiers are ultrafast diodes. These are NOT 1N4007! And the 220nF capacitors for the secondary filter are no typos; the diodes deliver almost pure DC, since the oscillation waveform is square, so only some noise filtering is needed. No electrolytics are necessary here.

Note the filters at both input and output, using ferrite cores. These are necessary to avoid polluting your environment with RF noise! Using these filters, and joining the input and output negative leads, this converter is very quiet and does not cause any problem in my combined HF, VHF and UHF station.

All ferrite cores (for the transformer and for the noise filters) are manufactured by Amidon Associates, and can be ordered directly from them in small quantities. Look for Amidon on the web. The 77-material core used for the transformer is less than ideal. A square-loop ferrite would work more efficiently! This one gets really warm, operating in saturation mode at 25 kHz. But it has worked well enough for two years now. The filter cores, on the other hand, are well chosen, so try to use the exact ones.

For all windings, the schematic states the number of turns. "7t" means 7 turns. As the transformer is quite small for the involved power, use as thick a wire as you can fit, leaving about half of the space for the 2x7 turns primary winding, and the other half for the secondary, while the feedback winding can be made from very thin wire.

The transistors do not need any heat sinks. They are large enough without, and they need to dissipate little heat!

Source: DC to DC Converters

12 to 28V Boost Regulator LM2585

noreply@blogger.com (Go2Media) — Fri, 11 Sep 2009 05:25:00 +0000

This boost regulator is for those times when you have a 28v relay, but want to use it with a 12v source. The circuit is built around the National Semiconductor LM2585, and uses the energy stored in an inductor to boost the 12 to 28v. Output voltage can be varied by adjusting the ratio of resistor values on the feedback pin.

The voltage regulator circuit does it's switching around 100 Khz, but generates no noise if SMT components are used. Output is good for about half an amp continuous, enough to power two or three large microwave relays. The board measures 1.5"x2".

It is important to note at least these three cautions before powering up the board:

A short-circuit on the output will kill U1 and D1. Always use a 1 ohm 5w resistor, or a 2.5A fast fuse on the 12v input lead.
Do not omit the LED (D2); It provides a visual indicator of a properly operating boost condition, but more importantly, it also provides a minimum load for the output, preventing an output "spike" which will otherwise appear when the load is disconnected abruptly.
Keep the ratio of r2 and r3 to 22 or less to keep the output voltage within the ratings of C4 (C4 on my board is rated at 35wvdc). This ratio plus 1, multiplied times 1.25v, determines the output voltage.

Source: 12 to 28V

Mini Bench Power Supply Circuit

noreply@blogger.com (Go2Media) — Thu, 16 Jul 2009 10:35:00 +0000

Every electronics engineer is familiar with the anxiety of the moment when power is first applied to a newly-built circuit, wondering whether hours of work are about to be destroyed in a puff of smoke. A high quality power supply with an adjustable current limit function is an excellent aid to steadying the nerves.

Unfortunately power supplies with good regulation performance are expensive and homebrew construction is not always straightforward. Many of the "laboratory power supplies" currently on the market are low-cost units based on switching regulators which, although certainly capable of delivering high currents, have rather poor ripple performance. Large output capacitors (which, in the case of a fault, will discharge into your circuit) and voltage overshoot are other problems.

The power supply described here is a simple unit, easily constructed from standard components. It is only suitable for small loads but otherwise has all the characteristics of its bigger brethren. Between 18 V and 24 V is applied to the input, for example from a laptop power supply. This avoids the need for an expensive transformer and accompanying smoothing. No negative supply is needed, but the output voltage is nevertheless adjustable down to 0 V.

A difficulty in the design of power supplies with current limiting is the shunt resistor needed to measure the output current, normally connected to a differential amplifier. Frequently in simple designs the amplifier is not powered from a regulated supply, which can lead to an unstable current regulation loop. This circuit avoids the difficulty by using a low-cost fixed voltage regulator to supply the feedback circuit with a stable voltage. This arrangement greatly simplifies current measurement and regulation.

To generate this intermediate supply voltage we use an LM7815. Its output passes through R17, which measures the output current, to MOSFET T1 which is driven by the voltage regulation opamp IC1C. Here R11 and C4 determine the bandwidth of the control loop, preventing oscillation at high frequencies. R15 ensures that capacitive loads with low effective resistance do not make the control loop unstable. The negative feedback of AC components of the current via R12 and C5 makes the circuit reliable even with a large capacitor at its output, and negative feedback of the DC component is via the low-pass filter formed by R14 and C6. This ensures that the voltage drop across R15 is correctly compensated for. C7 at the output provides a low impedance source for high-frequency loads, and R16 provides for the discharge of C17 when the set voltage is reduced with no load attached.

Current regulation is carried out by IC1D. Again to ensure stability, the bandwidth of the feedback loop is restricted by R19 and C8. If the voltage dropped across R17 exceeds the value set by P2, the current limit function comes into action and T2 begins to conduct. This in turn reduces the input voltage to the voltage regulation circuit until the desired current is reached. R7, R9 and C3 ensure that current regulation does not lead to output voltage overshoots and that resonance does not occur with inductive loads.

The controls of the power supply are all voltage-based. This means, for example¸ that P1 and P2 can be replaced by digital to analogue converters or digital potentiometers so that the whole unit can be driven by a microcontroller. IC1B acts as a buffer to ensure that the dynamic characteristics of the circuit are not affected by the setting of P1.

IC1A is used as a comparator whose output is used to drive two LEDs that indicate whether the supply is in voltage regulation or current regulation mode. If D2 lights the supply is in constant voltage mode; if D1 lights it is in constant current mode, for example if the output has been short circuited. The power supply thus boasts all the features of a top-class bench supply. IC1A and its surrounding circuitry can be dispensed with if the mode indication is not wanted.

A type LM324 operational amplifier is suggested as, in contrast to many other similar devices, it operates reliably with input voltages down to 0 V. Other rail-to-rail opamps could equally well be used. The particular n-channel MOSFET devices used are not critical: a BUZ21, IRF540, IRF542 or 2SK1428 could be used for T1, for example, and a BS170 could be used in place of the 2N7002. The capacitors should all be rated for a voltage of 35 V or higher, and R15 and R17 must be at least 0.5 W types. The fixed voltage regulator and T1 must both be equipped with an adequate heatsink. If they are mounted on the same heatsink, they must be isolated from it as the tabs of the two devices are at different potentials.

Uninterruptible Power Supply (UPS) Circuit

noreply@blogger.com (Go2Media) — Fri, 29 May 2009 04:38:00 +0000

An Uninterruptible Power Supply (UPS) is a device that sits between a power supply and a device to prevent undesired features of the power source (outages, sags, surges, bad harmonics, etc.) from the supply from adversely affecting the performance of the device.

The UPS may be split into 4 main circuits: Input Power Factor Correction, Battery Boost, Free-Running Chopper, and Inverter. The UPS is an online device which normally will have the Power Factor Correction circuit feeding the Chopper, which then feeds the Inverter. If the input power should be lost, the Power Factor Correction circuit falls out of the power flow and the Battery Boost circuit automatically provides power to the Chopper.

The Inverter is driven by the Inverter Drive circuitry, which in turn is controlled by the Inverter Control circuitry containing the microcontroller.

Basic Uninterruptible Power Supply Circuit

Basic uninterruptible power supply circuit consist of regular power supply adapter and battery connection. This basic system is a "hot" battery connection, meaning that there is no switching mechanism in connecting and disconnecting the battery, the battery is always connected! This hot connection is very simple to implement and very robust because there would be no switching delay, the output voltage will be 100% continue if a power down happens, until the battery loose its capacity.

5V Uninterrutible Power Supply for Sensitive Device

This circuit will provide electric power from a backup battery when AC power is cut, always providing a clean 5V power supply for sensitive equipment like microcontrollers and logic circuits.

The value of C1 is to be higher than 220 uF. the bigger the capacitance of this capacitor, the more power you can deliver to your circuits. The 9.6 NiMh Battery can be replaced with any equivalent battery whose voltage is more than 7.5V.

A charger can be constantly connected to the battery from the same 220V source as the rest of the circuit, but depending on the battery and charger type, this procedure can shorten its life.

For a clean transition from AC to Battery operation, especially with microcontrollers, use 10nF decoupling capacitors (ceramic capacitors) as near as possible from the concerned IC.

PIC Unintteruptible Power Supply

At times, power from a wall socket is neither clean nor uninterruptible. Many abnormalities such as blackouts, brownouts, spikes, surges, and noise can occur. Under the best conditions, power interruptions can be an inconvenience. At their worst, they can cause loss of data in computer systems or damage to electronic equipment. It is the function of an Uninterruptible Power Supply (UPS) to act as a buffer and provide clean, reliable power to vulnerable electronic equipment.

The basic concept of a UPS is to store energy during normal operation (through battery charging) and release energy (through DC to AC conversion) during a power failure.UPS systems are traditionally designed using analog components. Today these systems can integrate a microcontroller with AC sine wave generation, offering the many benefits listed below. Source: Microchip

Download Application Notes and Source Code: PICREF-1 PICREF-1 Firmware PICREF-1 Source Code PICREF-1 Schematic PICREF-1 Board

Offer available on Amazon: CyberPower CP1000AVRLCD UPS - 1000VA/600W Intelligent LCD, AVR 9-Outlet RJ11/RJ45/Coax Tower USB/Serial (36 customer reviews)

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DC DC Converter Circuit

noreply@blogger.com (Go2Media) — Mon, 04 May 2009 18:30:00 +0000

Electronic system is designed to operate from a supply voltage, which is usually assumed to be constant. A voltage regulator provides this constant DC output voltage and contains circuitry that continuously holds the output voltage at the design value regardless of changes in load current or input voltage, assuming that the load current and input voltage are within the specified operating range for that regulator. In portable systems, the input voltage is often a battery, a DC voltage.

A DC-to-DC converter is a device that accepts a DC input voltage and produces a DC output voltage. Typically the output produced is at a different voltage level than the input. In addition, DC-to-DC converters are used to provide noise isolation, power bus regulation, etc. This is a summary of some of the popular DC-DC Converter Topologies

When the output voltage set point is less than the input voltage, such regulator is called a Buck converter. When the output voltage set point is higher, it is a Boost converter. A feedback input is necessary for the regulator to know the state of the output voltage so that it can be kept with in the tolerances required by the power supply design requirements. The converters control the output voltage to the specifications by comparing the output voltage (or current or both) to an internal reference.
In case of a Linear regulator the power is transferred continuously from Vin to Vout.
In case of a Switching regulator the power is transferred from Vin to Vout in bursts. There are two main types of the switching regulators - inductive and charge pump (capacitive).
Not every electronic system needs a regulator. The electronics in a typical system can operate within a narrow band (5% or 10%) around their rated voltage. The battery output voltage declines as the battery discharges. To prolong the usable life of the system, one could use electronics that operate at voltages toward the low end of the battery discharge. But, then the fresh battery voltage would far exceed the upper tolerance of the electronics. If the electronics were to be chosen for the upper end of battery voltage, then the battery would soon discharge to the lower tolerance of the electronics. One way to address this issue is wider range electronics, but this could be an expensive proposition. Another way is to use a regulator. If the battery voltage range is narrow (e.g. from NiCd cells), a low-dropout linear regulator may be suitable to produce a regulated lower output voltage. If the system voltage is higher than the battery voltage range, or within the range, then a switching regulator in a boost or buck-boost configuration can be used.

Simple DC to DC converter circuits:
6V to 12V DC-DC Converter with Transistors
This converter circuit can provide up to 800mA of 12V power from a 6V supply.

6V to 12V DC-DC Converter with IC
This step-up converter is intended for use in a car, has a 6V battery and won't support a modern radio that needs 12V. The circuit described here converts 6V to 12V at 1A sustained load current.

See Also offer available on Amazon for DC DC Converter in largest selection and save Big!

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LED Circuit Power and Series Resistor Calculator

noreply@blogger.com (Go2Media) — Wed, 29 Apr 2009 17:19:00 +0000

This calculator requires the use of Javascript enabled and capable browsers. A question that often comes up in projects using LEDs is "what resistor should I use with my LED?" This calculator helps determine that for you. Enter the data required for Supply Battery Voltage in the range of 3 to 24 volts, the Diode Forward Voltage in the range of 2 to 4 volts, and the Diode Rated Current in the range of 10 to 50 milliamps (mA).

Click on Calculate for the results which assume for power calculations, the use of the standard value current-limiting resistor indicated. This calculator rounds the resistance up to the next standard resistor value. You should actually be able to buy a common 5% resistor with the value returned by the calculator. For more detailed LED information visit these two sites, which have good information and lead to others also; misti.com and also ledmuseum. For identification purposes, the negative side of the LED is the flat side and the shorter lead.

For the purposes of this howto, you only need to know that there are two leads coming out of your LED. The one which is slightly longer than the other is known as the anode. The shorter is the cathode. Anode is (+) and cathode is (-).

The longer lead must be facing the anode(+) of the circuit. Failing to do this will not do any damage in the currently discussed circuit, but may do so on later projects of yours. Check your LED package for the maximum backward voltage. Our first instict as children is to attach a wire from the (plus) end of the battery to the anode of the LED, and then another from the cathode to the (minus) side of the battery. This is almost correct, but still missing some details.

Let's first give an explanation of how your circuit will work in Layman's terms. To start out on your first LED circuit, you will have one resisitor and three LEDs in series. 'In series' means that they're daisy chained.

This is how we calculate this circuit:

(Source Voltage - LED Voltage Drop) / Amps = Ohms

Source Voltage Power Supply = 12 Volt
Voltage Drop = 9.3 Volt (3.1 typical for a blue or white LED)
Desired Current = 20 milliAmps (again, a typical value)

So the resistor we need is:

(12 - 9.3) / (20 / 1000) = 135 ohms

Visit this site for LED Circuit Power Calculator

You may be interested in reading Variable Voltage Regulator LM317T

Universal Laptop AC/DC Power Supply Adapter

noreply@blogger.com (Go2Media) — Wed, 29 Apr 2009 03:13:00 +0000

One of the things you may not think about when buying a new laptop is what will happen if you lose your laptop AC adapters. Sure this does not seem like something you would lose, but it is very easy to misplace. So it is always a good idea to know where to buy another one, or even have another one handy just in case something like this should ever happen.

If you are going to buy laptop AC adapters online you need to make sure it is the right one. The one that comes with the computer is, of course, the best one to have for it, however, if you buy one online just make sure it is going to fit your computer.

Also, be sure that it is a good model of laptop AC adapters. Some of them can get too hot and overheat. The best thing to do is read some online reviews of the notebook battery chargers, and see which ones work the best. From there you can choose the one that you are going to need. I think it is always a good idea to have a back up anyway. Nothing is worse than having a laptop and not being able to use it. So do not let that happen to you. Go out and get an extra one today.

Replacing notebook power supplies is sometimes an expensive process as it the purchase of an air/auto power supply for your laptop. However for those users who need a new power supply for their notebooks or for users planning to travel, Targus have available a Universal adapter series called the Universal 70 Watt AC/DC Power Adapter that gives the user a variety of ways to power their notebooks.

Features

Power on the go, anywhere: Works at home, office, car, boat, or aeroplane.
Lightweight design: At just 213g, this adaptor is lightweight, compact and ideal for travel.
Compatible with other mobile devices: With the optional Targus Accessory Powering System and device tips, you can power your mobile phone or PDA as well as your notebook.

Basically the Universal 70 Watt AC/DC Power Adapter allows you to plug your laptop into a car cigarette lighter, an aero plane power seat system or into the mains to give your notebook the electricity needed to run the unit. Best of all, the device is 98% compatible with popular 70W notebooks and covers a whopping 6,300 models.Visit Tagus Website

Technical Specifications

Compatibility: Airline Compatibility Chart Always call your airline to confirm inflight power seat system and Targus auto/air compatibility.
Varied models of Acer, Apple, Compaq/HP, Dell, Fujitsu, IBM, Panasonic, Sony and Toshiba.
Other: Includes9 tips 91cm AC input cord 91cm DC input cord 1.82m DC output cord User guide.
Size: 13.7 x 5.5 x 2.2 cm.
Technical: 100-230 VAC 11.75-16.00 VDC.
Warranty: Limited Two Year Warranty.
Weight: 213g

Targus Universal 70 Watt AC/DC Power Adapter is a must have device for those notebook users who travel or even for users that need a second power supply for their PC. The unit is relatively quite small and does not weigh much which is perfect for users on the go.

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You may be interested in reading 12V Battery Charger for Lead/Acid

How to Install a Marine Battery Charger

noreply@blogger.com (Go2Media) — Sat, 25 Apr 2009 07:57:00 +0000

When it comes to boating, few things are more frustrating than having a dead battery. Unlike car batteries, boat batteries experience a lot of down time, and they're also relied on while the engine isn't running. These factors can cause the power cells in a battery to die, unless you're diligent about charging on a regular basis. With an onboard charging system, you can automate this process instead of worrying about being stranded by a dead battery.

Step 1

First, select a mounting location that allows for free-air ventilation with a minimum of 8 inches of clear, unobstructed space around and in front of the charger. Open all battery and engine compartments, and ventilate for at least 15 minutes before actually starting the installation. Don't install the charger on carpeted, vinyl or varnished areas. Be sure to place the charger in an accessible area where all indicators are viewable. If you have more than one battery, as in this case, confirm that all battery cables can reach each of the batteries. In this demonstration, the unit is mounted on a 3/4-inch plywood support board in the engine compartment. Make sure that the surface you're mounting on is adequate in strength and thickness in order to hold the unit in place with the mounting screws you've selected.

Step 2

Once you've selected a sturdy surface to mount the unit on, clean each battery post with a wire brush until it becomes shiny. Run your cables free from sharp objects and hold each of them in place with cable ties. Be sure to coil any excess cable - don't cut or shorten the length of the cables, as there are inline fuses located 4 inches from the end of each red (positive) cable. Connect the D/C output cables to the battery, securing the positive (red) connections first, then securing the negative (black or yellow). Make sure all connections are tight and correct. Locate the A/C power cord in an open-air area of your boat at least 21 inches from the charger, batteries and fuel fill lines. NOTE: If you have gel batteries, please refer to the installation guide for instructions on how to set the charger for this operation.

Step 3

Next, install a universal plug holder to use in conjunction with the charger. Again, select a location that's easily accessible and at least 21 inches away from all batteries and fuel fill lines. Drill a 1/8-inch pilot hole in the center of the area selected. Now use a 1 3/4-inch hole saw to cut the mounting hole into the pilot hole. Mount the plug holder, and secure it in place with the three stainless-steel screws provided. Insert the A/C power cord into the plug holder. At this point, if you don't wish to install a battery switch, the installation is complete. Connect a UL-approved extension cord to the first, and then plug the extension cord into a nearby charger120 VAC GFCI-protected outlet. While it's charging, view the LED indicators. You should observe that both the green "power" LED and the red "charging" LED are on, indicating that the charging mode is in process.

Step 4

The boat used for this installation has two batteries, so cable extenders and a battery switch are also installed. It also has a 24-volt trolling motor, which needs to be powered along with several other 12-volt accessories, so a single-position switch is selected for easy switching from 24-volt to 12-volt. To install the extender cables, remove the A/C power from your onboard battery charger. Connect the red wire to the positive terminal of battery #1 and the ground wire to the negative terminal of battery #2. Finally, select an easily accessible location for the switch, and mount it using four stainless-steel wood screws. Connect the positive (red) wire to the terminal labeled "battery" and the ground wire to the terminal labeled "common." Tighten all connections, and you're finished. (Authorized By Steve Noury - Installing A Marine Battery Charger)

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How to Convert a PC Power Supply

noreply@blogger.com (Go2Media) — Thu, 23 Apr 2009 10:29:00 +0000

If you find building your own desktop power supply from a recycled PSU and a few parts from the local electronics store appealing, then grab some tools, pour yourself a cup of coffee (or personal preference) and let's get started. The LED (light emitting diode) was also salvaged from an old PC.

If you want to add a power on indicator, LED's add a nice touch and can easily be wired into the +5v rail. I do strongly encourge you to read the contents of this site and associated links before beginning your conversion -- there are a number of hints included in the associated pages.

This ATX PS board has leads for +5 (RED), -5 (WHITE), +12 (YELLOW), -12 (BLUE) volts, Ground (BLACK) and switch (GREEN). Be warned that some DELL power supplies manufactured between 1996 and 2000 do not follow the industry standard pinout and color codes. The fan has also been unplugged for better viewing. Since this PS was converted for use in the logic and robotics labs, the selected voltages were tapped. Other users may want combinations of +3.3 V (ORANGE), +5 V and/or +12 V if they are converting one of the newer supplies. For R/C applications, the 5 volt output can also serve as a desktop source to drive receivers and servos. If used as a power source for the micro and sub-micro servos, you must be careful not to drive the servo to either endpoint to avoid stripping the smaller gears in these units. Most standard servos have sufficiently robust gear trains and will simply stall if pushed to the mechanical stops..

Measured voltages on this particular PS (1996 P5-100 MHz Gateway) were about 5.15 and 11.75 volts. The remaining leads have been clipped off at the circuit board.

View of the case top with fan, binding posts and switch. The switch (SPST) and binding posts are available at Radio Shack or other electronics suppliers.

Power supplies in today's computers are known as SWITCH MODE or Switching Mode Power Supplies (SMPS) and require a load to continue to operate after being switched on (the term switching mode actually applies to the technique of A/C to D/C conversion and not to the power up action). This load is provided by a 10 watt, 10 ohm wire wound load resistor (sandbar - about $0.80 at Radio Shack) across the +5 volt supply. While many of the newer power supplies will Latch_On without a preload, you will find that adding the resistor will:

increase the measured voltage on the 12 volt rail slightly and
help stabilize the voltage level in this rail by minimizing voltage drop when the power supply is loaded with a charger.

Some inexpensive power supplies may fail if forced on without a load although the Design Guide states that the supplies should not be damaged if run without a sufficient load. The sandbar resistor has been zip tied to the case with a small amount of heat sink compound applied to the flattest side of the resistor . I will also take a file and remove any stamping flash that may remain around the ventilation slots. Without cooling, the resistor will get very hot and may fail prematurely; with this arrangement, the resistor will remain barely warm to the touch.

Be warned that many of the heat sink greases can be quite toxic and any excess should be cleaned up and disposed of properly. Also be sure to thoroughly clean your hands and tools after use. While most heatsink compounds are rated to 160 to 170 C, some may dry out over time and their effectiveness will diminish -- a periodic check for good contact between the case and resistor is a recommended practice. Source from an Interesting PC Power Supply Article: Converting a PC Power Supply

PC Power Supply Guide: Before You PC Power Supplies

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Computer Power Supply

noreply@blogger.com (Go2Media) — Wed, 22 Apr 2009 16:52:00 +0000

The power supply converts the alternating current (AC) line from your home to the direct current (DC) needed by the personal computer. In a personal computer (PC), the power supply is the metal box usually found in a corner of the case. The power supply is visible from the back of many systems because it contains the power-cord receptacle and the cooling fan. Typical computer power supply generates the voltages needed by the computer motherboard accessories. A typical modern PC power supply generates the following voltages:

+5V (+-5%) at up to tens of amperes for motherboard electronics, disk drives and cards
+12V (+-10%) at several ampreres for disk drives and some cards
+3.3V (+-5%) up to tens of amperes for the majority of modern logic electronics in motherboard
-12V (+-10%) usully less than one ampere for some accessory cards

Most other computer power supplies usually give voltage on this line, because those are the most commonly used voltage used in computer systems. Depending on the PC model, power supplies are rated anywhere between 150 and 350 W. A PC power supply on average is rated for 250-400 watts. PSUs above 300W are unusual and only tend to come in servers, or machines that have been designed for 'hardcore' applications such as gaming, where a hundred watt graphics card is not that unusual.

Typically if you have 300W available, and the computer is going to be using perhaps 150-220 W of that, depending on what's in it. Pc power are designed to provide +12, +5, -5 and -12 (usualy nowadays also +3.3V), with the power spread unevenly across those ranges. Grab an average computer PSU and take a look at it, and there will probably be a table on it listing how many amps can be delivered per voltage category.

PC power supplies are mainly primary switching power supplies with power switches arranged in a half-bridge configuration. The outputs can drive the usual 20 A (+5 V), 8 A (+12 V) and 0,5 A (-12 V, -5 V) at approx. 205 W output power. (modern ATX power supplies add considerable amount of 3.3V to this). A typical efficiency of a PC power supply is around 75 %. A typical power PC supply measures around 140 x 100 x 50 mm (W, D, H) and weights around 300-400 grams. The switching frequency of approx. 33 kHz is usual for PC power supplies.

The PC power supplies can be generally found at AT and ATX varieties. The older PCs used to use AT power supplies. Those power supplies supplied +5V, +12V, -12V, and -5V power to motherboard. Practically all new PCs use ATX format power supplies which have added to the picture following extra functions: +3.3V output, program/pushbutton turn on, standaby power (low current +5V output to some parts inside PC when the main power supply is off) and option to turn power supply off with software control.

Laptop computers use slightly different approach for power supply. Modern laptop computer typically comes with a switched mode power supply that plugs to the wall and supplies the needed power to the computer at some suitable low voltage. A typical voltage that those mains adapters supply to laptop are in 16-24V range, the actual voltage used can vary between different computer brands and models (check the computer manual and/or power supply markings for more details).

The power supplied by this kind of power supply is typically in aroun d 40-60W range maximum (check your computer manual and/or power supply for information on your system). The internal power supply electronics inside the laptop then generate the multiple voltages needed inside the laptop (typically at least 5V, 3.3V and processor internal core voltage). If you need to power your laptop from car voltage (12V), you have two options to do this: use a DC to AC converter or a DC-DC converter. When you use DC to AC inverter, you first take the car power (typically 12V from lighter plug) and turn it to a normal mains voltage (110-120V AC or 220-240V AC depending where you live) power.

Then the normal PC wall power supply is used to convert this power to voltage used by the laptop. This approach could work, but has it's downsides. The downsides are poor efficiency (power lost, both converter and laptop PSU get hot), and potential incompatibility with the DC to AC converter and computer power supplies. The DC to AC converters generally do not like computer power supply type load (very non-linear load that takes high current splikes, can lead to unreliable operation and potential converter failure) and the computer power supply might not always like the non-sinusoidal mains power that is put out by most cheap DC to AC converters (can cause more heating on power supply, even power supply damages).

An expensive high power sinewave DC to AC converter should work well with any load, also with computer power supplies, but is expensive. Another usually better approach is to use a DC-DC converter that replaces the original computer mains power supply. It takes in car 12V power and output the same output voltage that the normal mains adapter gives out. This kind of adapters are available from several laptop manufacturers. An adapter from the same manufacturer as your laptop is usually the easiest and safest choise, nut not usually cheapest option.

Nowadays there are also quite cheap general purpose laptop DC-DC converters that can be adapted to be used with many different laptops. Those adapters have typically an adjustable output voltage (should be adjusted to match you specific computer). Just select an adapter that can be adjusted to your laptop operating and has high enough power rating (same or higher power rating as the original mains adapter), and things should work well. Please note that in some cases using a DC-DC converter not approved by the computer manufacturer can void your laptop warranty.

Check this out for more computer power supplies info and Computer Power Supplies on Amazon

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2-25V DC Power Supply Schematic

noreply@blogger.com (Go2Media) — Sun, 19 Apr 2009 16:08:00 +0000

This DC power supply circuit uses a LM338 adjustable 3 terminal regulator to supply a current of up to 5A over a variable output voltage of 2V to 25V DC. It will come in handy to power up many electronic circuits when you are assembling or building any electronic devices. The schematic and parts list are designed for a power supply input of 240VAC. Change the ratings of the components if 110VAC power supply input is required.

As shown in the figure above, the mains input is applied to the circuit through fuse F1. The fuse will blow if a current greater than 8A is applied to the system. Varistor V1 is used to clamp down any surge of voltage from the mains to protect the components from breakdown. Transformer T1 is used to step down the incoming voltage to 24V AC where it is rectified by the four diodes D1, D2, D3 and D4. Electrolytic capacitor E1 is used to smoothen the ripple of the rectified DC voltage.

Diodes D5 and D6 are used as a protection devices to prevent capacitors E2 and E3 from discharging through low current points into the regulator. Capacitor C1 is used to bypass high frequency component from the circuit. Ensure that a large heat sink is mounted to LM338 to transfer the heat generated to the atmosphere. Source: 2V to 25V Power Supply Schematic

Check this out Mastech Variable Linear Lab Power Supply 30V 5A

Continue reading : 1000W Power Inverter by MOSFET

12V Car Battery Charger

noreply@blogger.com (Go2Media) — Sun, 19 Apr 2009 15:04:00 +0000

Most car battery chargers are simple devices that continuously charge the battery with a few amperes for the duration it is ON. If the charger is not switched OFF in time, the battery will overcharge, its electrolyte lost due to evaporation, and its plate-element will likely be destroyed.

The charger circuit below will eliminate these problems by monitoring the battery's condition of charge through its retroactive control circuit by applying a high charge current until the battery is completely charged. When charging is complete, it turns on the red LED (LD2) and deactivates the charging circuit.

This car battery charger circuit is drawn to charge 12V batteries ONLY. Certain emphasis should be taken when wiring up this circuit. They are the connections of the transformer to the circuit board, and those supplying current to the battery being charged. These connections should be made with cables having a large cross-sectional area to prevent voltage-drop and heat build-up when current flows through them.

Adjustment

After assembling of the circuit, adjust TR1 to null value, power-up and make the following adjustments

Without connecting the battery check that the 2 LED's are turned on.
Connect a car battery to the circuit and check that LD2 is OFF and a current (normally 2A to 4A) is flowing to the battery.
Adjust TR1 until LD2 turns ON and the charge current is cut.
Adjust TR1 to null value and charge the battery using the hydrometer technique (if you do not have or do not know how to use a hydrometer, then use a good condition battery and charge).

Carefully adjust TR1 so that LD2 begins to turn ON and the charge current falls to a few hundred milliamps (mA). If TR1 is set correctly then in the next round of charging you will noticed LD2 begin to flicker as the battery is being charged. When battery is completely charged, LD2 turns ON completely.TR1 does not need further adjustment anymore. Q1 is connected in line with the battery and is fired by R3, R4 and LD2. The R2, C1, TR1 and D2 sense the voltage of the battery terminal and activate Q2 when the voltage of the battery terminal exceeds the value predetermined by TR1. When an uncharged battery is connected, the terminal voltage is low. Under this circumstance, Q2 is turned OFF and Q1 is fired in each half cycle by R3, R4 and LD2. The Q1 functions as a simple rectifier and charges the battery. If the battery terminal voltage is increased above the level that had been fixed by TR1, then Q2 shifts the control of Q1 gate. This deactivates Q1 and cuts off the current supply to the battery and turns LD2 ON indicating that the charge has been completed. Q1 and bridge rectifier GR1 should be mounted on heatsinks to prevent overheating. M1 is a 5A DC ammeter to measure the charge current. Optionally a voltmeter can be connected in parallel with the battery, however it must have a high input resistance so as not to influence the measurement.

Car Charger's Part List

R1= 1Kohms D1= 1N4001 T1= 220V/17V 4A Transformer
R2= 1.2Kohms D2= 6.8V 0.5W zener LD1= Green LED
R3= 470 ohms TR1= 4.7Kohms trimmer LD2= Red LED
R4= 470 ohms Q1= BTY79 or similar 6A SCR M1= 0-5A DC Ampere meter
R5= 10Kohms Q2= C106D SCR S1= 10A D/P On/Off Switch
C1= 10uF 25V GR1= 50V 6A Bridge Rectifier F= 5A Fuse. Source: 12V Car Battery Charger

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Continue reading: Power Inverter by Mosfet

Power Supply AC - DC 12V

noreply@blogger.com (Go2Media) — Fri, 17 Apr 2009 11:46:00 +0000

The term power supply is more commonly abbreviated to PSU, this will be used from hereon in. Telecommunications equipment is designed to operate on voltages lower than the domestic Mains voltage. In order to reduce this voltage a PSU is used.

In order to power up the electronics experimental , many of electronics hobbyist have built there own 5v and 12v PSU by them self; which require a little bit of power. However, if the load requires too much amps, you have to calculate all the parameters to build a stable power supply.

The main function of power supply is to convert AC to DC, the first stage is to make full wave rectifier to the AC signals by using bridge rectifier, filter the rectified wave by using filtering capacitor and finally select the appropriate voltage regulator to generate pure DC signal.

To provide a useable low voltage the PSU needs to do a number of things:-

* Reduce the Mains AC (Alternating current) voltage to a lower level.
* Convert this lower voltage from AC to DC (Direct current)
* Regulate the DC output to compensate for varying load (current demand)
* Provide protection against excessive input/output voltages.

Current rating for bridge rectifier should be suitable with load current, also; the designer should consider the voltage drop across each diode, which is normally equal to 0.7v.
Note that only two diodes are required when using center-tapped transformer.

Calculation for the filtering capacitor:

5i
C = --------
Vp. f

C: Capacitor value.
Vp: Peak voltage. ("Bridge output max voltage")
f: Frequency of the AC supply.
i: Load current.

Note that the above equation for 10% ripple voltage.

To calculate the voltage required and the transformer secondary winding we first determine the input voltage for the regulator, which is 15v, plus a 10% of this value for ripple. For a regular transformer we have to consider a bridge rectifier, as a result; we will add 1.4v. So the secondary winding should be 15+1.5+1.4=18.9 lets say 18v @ 5 Amps. Now we will calculate the capacity of the filtering capacitor. By using equation number 1 and assuming that f=60Hz, we will get C=5 x 5 / ((18-1.4) x f) =25,100µF

The following power supply circuit uses LD1084#12 voltage regulator, which can provide up to 5Amps with only 1.3v dropout. Input voltage must be around 15v. It is highly recommended that you follow this value exactly, if the input voltage is more, the regulator temperature will increase more.

Tip: It is possible to build your power supply without adding a regulator, when you want to power up an electrical motor, a small ripple in voltage will not affect the performance, unlike the electronic circuits and devices!

You may be interested in reading: Power Inverter 12VDC to 220VAC

Microwave Oven Transformer AC Power Supply 2000 Watt

noreply@blogger.com (Go2Media) — Sat, 04 Apr 2009 06:10:00 +0000

These transformers are AC Power Supply with 120VAC input and 2kVAC output. Just wire the cores together (the cores are normally one of the High Voltage Terminals) and wire the primaries so they oppose each other. If you don't get a nice arc from this switch the input leads on one transformer.

This will not arc over that far, but if you start a small arc you can pull it out to about 5". These transformers will make an excellent supply for a Jacob's ladder. You will need at least a 20A breaker to run two of these. Watch the ouput of these they are 1000VA a piece. At 500mA at 2kVrms the ouput could easily kill you in an instant. There are several variations of these transformers.

I also have a 4kVrms unit that was taken from an old "radar range" microwave oven. Normally these transformers will also have two leads that come out of them. These leads can be clipped off since they are just low voltage windings that power the filament in the magnetron. Also it is a good idea to use power-factor correction capacitors on these. Use an AC capacitor to do this with a rating of about 30uF.

Adding the capacitor will keep your 15A circuit breaker from tripping. The reason the breaker will trip is because the current is not in phase with the voltage. The current lags the voltage in inductive circuits and current leads the voltage capacitive circuits. Combining the inductor (transformer) and the capacitor will make the circuit seem more resistive to the source. Here is what the current/voltage relationship would look like in an AC-inductive circuit.

You see the current is 90 degrees behind the voltage, the capacitor just causes the current to lead by an added 90 degrees. The waveform with the capacitor added will show a single sine wave like a resistive source would.

These transformers make an excellent supply, when three or more are used, for a medium to high power Tesla coil. Source: 4kV-5kV 2000VA AC power supply

See more : 500 Watt Power Inverter 12VDC to 2230VAC

Variable Voltage Regulator LM317T

noreply@blogger.com (Go2Media) — Fri, 03 Apr 2009 17:13:00 +0000

The LM317T Voltage Regulator integrated circuit is very useful in many renewable energy applications. LM317T can be used to regulate current - to regulate the current in a string of LEDs - or it can be used to provide a stable fixed voltage output.

The LM317T is a adjustable 3 terminal positive voltage regulator capable of supplying in excess of 1.5 amps over an output range of 1.25 to 37 volts. The device also has built in current limiting and thermal shutdown which makes it essentially blow-out proof.

Output voltage is set by two resistors R1 and R2 connected as shown below. The voltage across R1 is a constant 1.25 volts and the adjustment terminal current is less than 100uA. The output voltage can be closely approximated from Vout=1.25 * (1+(R2/R1)) which ignores the adjustment terminal current but will be close if the current through R1 and R2 is many times greater. A minimum load of about 10mA is required, so the value for R1 can be selected to drop 1.25 volts at 10mA or 120 ohms. Something less than 120 ohms can be used to insure the minimum current is greater than 10mA. The example below shows a LM317T used as 13.6 volt regulator. The 988 ohm resistor for R2 can be obtained with a standard 910 and 75 ohm in series.

When power is shut off to the regulator the output voltage should fall faster than the input. In case it doesn't, a diode can be connected across the input/output terminals to protect the regulator from possible reverse voltages. A 1uF tantalum or 25uF electrolytic capacitor across the output improves transient response and a small 0.1uF tantalum capacitor is recommended across the input if the regulator is located an appreciable distance from the power supply filter. The power transformer should be large enough so that the regulator input voltage remains 3 volts above the output at full load, or 16.6 volts for a 13.6 volt output. Source: LM317T Variable Voltage Regulator.

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12V Battery Charger for Lead/Acid

noreply@blogger.com (Go2Media) — Tue, 31 Mar 2009 19:19:00 +0000

The battery charger circuit below is very simple to build requiring only a handful of cheap parts and an extra winding on your power tranny (or a separate tranny). Since the charger described is not active during sound reproduction, I have made no criteria on parts quality, so el-cheapo was the way to go.

There are many circuits available for charging batteries, but many are for NiCd or NiMH batteries. They will not work for lead/acide batteries, so don't use these!!! The best way to charge a battery is with a current limited voltage regulator. This sets a maximum current (say 1A) that will flow to charge the battery. If the current rises over this set current, the regulator will be forced to put out a lower voltage. Since voltage drops, so will the current; hence current limited. While the battery is charging, the current should decrease slowly while voltage starts to increase. In the end the current will be next to zero and the voltage will be equal to the set voltage.

Use the following to design a charger:

The charging current should be kept to around 0.1 times the capacity of the battery. So a 10Ah battery should be charged with 1A of current (10 x 0.1 = 1). The battery will not be forced (quick charged) this way and assures a longer lifetime.
The charging voltage should be set to 2.3 - 2.4V per 2V cell. So a 12V battery (6 cells of 2V) is charged at 6 x 2.3 = 13.8V.
The transformer winding for the charger supply is chosen at the charging voltage plus 3V regulator drop plus 1.4V rectifier drop (two diodes) plus 10% safety. So for a 2V battery, the winding (AC) is 2V + 3V + 0.7V + 0.7V = 6.4V + 10% = 7V.
The charging current is limited by the small resistor in the common leg of the charger. The value for this resistor can be calculated with: R = 0.6V / max current. So if I want a maximum current of 0.5A, I will need 0.6V / 0.5A = 1.2 ohms. The 0.6V is the voltage required for the transistor to go fully into conduction. Between 0V and 0.6V the transistor will adjust the regulator to increase or decrease voltage depending on the current it is passing.
The charging voltage can be set using the potentiometer. Just hook up a volt-meter to the charger (without the battery attached) and adjust the output voltage until it macthes the charging voltage. Use a 1K pot for 2V batteries, use 5K for 6V and 12V batteries.
Use an extra fuse on the charger, about two times the maximum current you are charging with. Fusing is critical for safety reasons. A battery can deliver 100+ amperes during a short, so it can cause serious damage or even fires when something goes wrong with the charger. Put the fuse behind the regulator in the lead going to the battery. This fuse is not to protect the supply from a short in the charger, but to protect everything else from the battery in case of a short anywhere. Don't forget to fuse the primary winding of the charger as well...
You're set up to charge...

The diode over the regulator in my schematic prevents damage to the regulator when the supply is turned off. In this situation the battery that is still attached offers a negative voltage over the regulator, as the voltage on the output is greater than the voltage on the input. The diode shorts the regulator in this situation and avoids any problems. It is just a safety. Source: Lead/acid battery charger

See more: Power Adapter for Car

1000 Watt Power Inverter by Mosfet

noreply@blogger.com (Go2Media) — Tue, 31 Mar 2009 18:07:00 +0000

This power inverter circuit will provide a very stable "Square Wave" Output Voltage. Frequency of operation is determined by a pot and is normally set to 60 Hz. Various "off the shelf" transformers can be used. Or Custom wind your own for best results.

Additional MosFets can be paralleled for higher power. It is recommended to Have a "Fuse" in the Power Line and to always have a "Load connected", while power is being applied. The Fuse should be rated at 32 volts and should be aproximately 10 Amps per 100 watts of output.

The Power leads must be heavy enough wire to handle this High Current Draw! appropriate Heat Sinks Should be used on the RFP50N06 Fets. These Fets are rated at 50 Amps and 60 Volts. Other types of Mosfets can be substituted if you wish.

Note
There ARE Limitations! I have had numerous requests for an Inverter for 1000 watts and Even MORE. Sorry I Don't feel this is Practical. At 1000 Watts and operating from a 12 Volt Source, the Input Current will be close to 100 AMPS. That would Require a HUGH Size of a Primary Wire. Source: A Mos-Fet Power Inverter

Check out this Voltage Power Adapter for Car Power Supply

500 Watt Power Inverter 12VDC to 220VAC

noreply@blogger.com (Go2Media) — Tue, 31 Mar 2009 17:22:00 +0000

This power inverter takes 12 VDC and steps it up to 220 VAC. It can be used to run a TV, stereo or other appliance while on the road or camping. In this circuit 4047 is use to generate the square wave of 50 Hz and amplify the current and then amplify the voltage by using the step transformer.

Attention: This Circuit is using high voltage that is lethal. Please take appropriate precautions

How to Calculate Transformer Rating
The basic formula is P=VI and between input output of the transformer we have

Power input = Power output

For example:
If we want a 220W output at 220V then we need 1A at the output.
Then at the input we must have at least 18.3A at 12V because:

12V x 18.33 = 220v x 1

So you have to wind the step up transformer 12v to 220v but input winding must be capable to bear 20A.

Author: Ashad Mustufa
e-mail: mustufa66@hotmail.com
web site: http://www.electronics-lab.com

See more: Voltage Power Adapter for Car Power Supply

Voltage Power Adapter for Car Power Supply

noreply@blogger.com (Go2Media) — Sun, 29 Mar 2009 15:42:00 +0000

This voltage power adapter designed for car use only. And you know that a car voltage generally is 12 Volts. How about when you want to connect non 12 volts devices into your car?

The following power adapter circuit is the solution. Even the circuit is design for a car apppliance, it does not seem it can't be used for another purpose. But you can try modifying it for any purposes.

Here's power adapter circuit:

Voltage Adapter for Car Power Supply - Electronic Fuse - Simple Battery Charger for Car