Voltage Inverter II

This simple and inexpensive circuit can produce a dual (positive and negative) voltage from a single supply input. It is therefore extremely useful for powering opamp and other circuits that require a dual voltage from a single battery. The circuit will operate at an input voltage from around 5V to 20V and produce a output from +-2.5V to +-10V.

Schematic

Parts

Part Total Qty. Description Substitutions R1 1 1M Linear Pot C1,C2 2 15uf 25V Electrolytic Capacitor U1 1 LM380 Audio Amp Chip MISC 1 Heatsink For U1, Binding Posts (For Input/Output), Wire, Board

Notes

1. U1 dissipates around 1W and will therefore require a heatsink.
2. R1 is used to equalize the outputs. The first time you use the circuit, it should be set to mid range and then adjusted with the aid of a voltmeter. Measure each output while adjusting. The circuit is calibrated when both outputs read the same voltage (either positive or negative).

Voltage Inverter

This simple circuit is a good solution to the powering a dual supply op amp from a single battery problem. The circuit simply takes a positive voltage and inverts it. It uses only one 555 timer and a few other passive components, so it doesn't add much in the way of size and cost to a project.

Schematic

Parts

Part Total Qty. Description Substitutions R1 1 24K 1/4 Watt Resistor R2 1 56K 1/4 Watt Resistor C1 1 3300pF 25V Ceramic Capacitor C2 1 47uF 25V Electrolytic Capacitor C3 1 10uF 25V Electrolytic Capacitor C4 1 100uF 25V Electrolytic Capacitor D1, D2 2 1N4148 Silicon Diode U1 1 555 Timer MISC 1 Wire, Board

Notes

1. V+ can be anywhere from 4 to 16V. -V is one volt less than V+. So for -12V output, use +13V input. The maximum current output of the circuit is about 280mA, more than enough for a few op amps.
2. For better regulation, a 79LOxx series regulator can be used.
3. A zener diode may also be used to regualte the output voltage.
4. Thanks to audioguru for correcting some errors in the original schematic. Read about it in this forum topic

Transformerless Power Supply

I have received a few emails asking for a transformerless power supply. Here is such a supply. This supply uses no heavy step down transformer and has an extremely low parts count. The circuit can be built very small and can supply small currents for small projects. The major downfall of this supply is that it is not isolated from the AC line and can only supply small currents.

Schematic

Parts

Part Total Qty. Description Substitutions C1 1 0.39uF 250V Capacitor C2 1 220uF 25V Electrolytic Capacitor D1 1 1N4741 11V Zener Diode (See Notes) BR1 1 1 Amp 200V Bridge Rectifier MISC 1 Line Cord, Board, Wire, Case

Notes

1. The value of C1 can be increased to increase the amount of current the circuit can supply. With the values shown, the circuit can supply up to about 15mA. Remember to increase the size of C2 also.
A different value can be used for D1 to increase or decrease the voltage as needed.
2. Please note that this circuit is not isolated from 120VAC. Because of this, the circuit must be treated with caution and encosed at all times. Do not work on the circuit (or any other circuits attached to it) when it is plugged in.
3. You may want to add a resisor in series with C1 to limit current if the circuit is plugged in and the mains is at its full voltage.
4. If you are running the circuit from 220VAC, then use a capacitor rated at greater than 400V for C1.
5. If you want isolation from the AC line, you can connect up a small isolation transformer at the inputs of the circuit. Small 600ohm:600ohm audio transformers work nicely.

Solid State Tesla Coil/High Voltage Generator

This is a fun and useful circuit for demonstrating high frequency high voltge. It can produce up to about 30KV, depending on the transformer used. It is cheap and easy to make, thanks to the standard TV flyback transformer used. It can power LASERS (although I have never tried), demonstrate St.Elmo's fire, and even cause a fluorescent bulb to light from as much as 2 feet away.

    

Schematic

Parts

Part Total Qty. Description Substitutions R1 1 27 Ohm 5W Resistor 27 Ohm 10W Resistor R2 1 240 Ohm 5W Resistor 240 Ohm 10W Resistor BR1 1 50 Volt, 6 Amp Bridge Rectifier C1 1 8000uf, 35 Volt Capacitor Q1, Q2 2 2N3055 NPN Power Transistor T1 1 24V 5A Transformer (See "Notes") T2 1 TV Flyback Transformer (See "Notes") S1 1 115V 3A SPST Switch MISC 1 Case, Wire, Heatsinks, Line Cord

Notes

1. T2 is a high voltage flyback transformer salvaged from an old TV, or ordered from Fair Radio Sales (see Where To Get Parts). Look for the biggest, most intimidating transformer you can find. Old tube TV's are a good place to look. The transformer should not have a rectifier built in.
2. You will need to rewind the transformer's primary. First, remove the old primary, being careful not to damage the high voltage secondary. If the transformer is wound with all windings incased in plastic, use another transformer. Second, wind on 5 turns of 18 AWG wire, twist a loop (center tap), and then wind on 5 more turns. This becomes winding C-D. Now, wind on 2 turns of 22 AWG wire, twist a loop, and wind on 2 more turns. This becomes winding A-B.
3. Q1 and Q2 will run HOT if not used with a large heatsink. After the circuit has been running for a minute or two, you should still be able to put your finger on the transistors without being burnt. Also, R1 and R2 will run hot.
4. If you experience arcing on the exposed transformer leads, select a lower voltage for T1. If you are powering the circuit with a power supply (see Power Supply), just crank down the voltage.
5. For a real high voltage output, connect a voltage multiplier (from an old TV or computer monitor) to the output of T2.
6. If the circuit does not work, reverse connections A and B.
7. I finally got around to taking some pictures of the circuit in operation. Here they are:
   
   The first picture is the high voltage generator without the voltage multiplier. Notice how hot the arc looks. The second picture is the high voltage generator with a voltage multiplier installed. Notice how much brighter the arc is.
   
   The above pictures of myself were taken with me standing on an pie plate that was resting on the top of a plastic bucket. The pie plate was connected to the high voltage generator and charged to about 40,000V. If you do this, be sure to have someone else turn on and off the high voltage generator. Also, don't touch anything when you are charged. Have everything you are going to hold/play with already sitting on the bucket and away from grounded objects. Remember to take off your watch...

Solid State Tesla Coil Circuit

Similar to the two transistor solid state Tesla Coil already on this site, this solid state Tesla Coil design uses a normal flyback transformer to generate it's high voltage output. Unlike the other circuit, this one does not use two huge power transistors and high wattage resistors. Instead it uses a 555 timer to more efficiently drive a single MOSFET. It's waveform has adjustable off and on time, making for an efficient circuit with little waste heat. It can be adjusted to drive most commonly found flyback transformers and can operate from a 12V to 18V supply. HV output can reach 60KV or more depending on the transformer and supply voltage.

    

Schematic

Parts

Part Total Qty. Description Substitutions R1, R5, R9 3 180 Ohm 1/4W Resistor R2 1 10K Pot R3, R7 2 10 Ohm 1/4W Resistor R4 1 5K Pot R6 1 7.5K 1/4W Resistor R8 1 150 Ohm 1/4W Resistor R10 1 1 Ohm 5W Resistor C1 1 0.0047uF 50V Polyester Capacitor C2 1 0.05uF 50V Polyester Capacitor C3 1 220uF 25V Electrolytic Capacitor C4 1 0.01uF 1200V Polyester Capacitor Q1, Q2 2 2N2222 NPN Transistor 2N3904 Q3 1 SSM5N55 MOSFET U1 1 555 Timer Integrated Circuit U2 1 LM7809 9V Linear Regulator L1 1 100uH Choke Coil T1 1 Penn-Tran 1-017-5372 Flyback Transformer See Notes MISC 1 Board, Wire, Case, Socket for U1, Heatsink For Q3, Output Terminal (See Notes)

Notes

1. T1 as specified in the parts list is going to be almost impossible to find, but don't worry. Penn-Tran was bought by Wiltron and no longer exists. However, most any medium to large flyback transformer will work as long as it does not have an internal rectifier. Suitable units are most often found in TVs made during the 1970s and 1980s. Look for the most impressive, dangerous, menacing transformer you can find. If you need an idea, a picture of a great transformer for use in this circuit:
   
   These can be found in a small metal box generally in the corner of the TV case, complete with a very handy voltage multiplier unit and usually a nice heatsink.
   You will need to either look up the datasheet for the transformer you have, or probe it with an ohmmeter to identify the coil connections. Most flybacks have a load of taps on the HV side to provide focusing, horizontal and vertical signals. These taps are generally of no use to you. To find the primary (coil B-A on the schematic) you need to find the two lowest resistance connections that are not also connected to the HV secondary wiring. Alternately, if your flyback has an open frame like the one in the picture, you can wind on 5 or so turns of 16 gauge magnet wire as a primary. You will need to experiment with the number of turns to get maximum output. The HV ground lead (connection C on the schematic) is generally easy to locate. It will come from the HV secondary and be tied to the frame of the transformer or chassis ground.
   If by some miracle you were able to locate the Penn-Tran transformer, then connection B is the red dot on the transformer, A corresponds to the black dot, and C matches the orange dot.
2. If the TV you salvaged the transformer from has a voltage multiplier unit (visible slightly at the far right of the above picture), then take it as well. It can multiply the output of this circuit into very high (over 100KV) DC voltages.
3. When building the circuit, leave the flyback disconnected. Connect a 10 Ohm 10W resistor in place of the primary of T1 and connect a scope to the collector of Q3. Adjust R4 to produce an off time of about 10 microseconds. Adjust R2 for an on time of about 70 microseconds. Now remove the scope, 10 ohm resistor, and connect up T1. Power the circuit back on and you should have a high voltage available at the output. If you do not have a scope, just set both pots in their middle position and then adjust them by trail and error until you get the biggest spark at the output of T1.
4. Q3 will require a heatsink.
5. Needless to say, this circuit can produce dangerous voltage. At the very least you are looking at a painful shock. More then likely a decent burn will result from contact with the HV output, as well as instant and uncontrollable muscle contraction. If you have heart problems, don't build this circuit. Be careful!.

Power Supply

When working with electronics, you always need one basic thing; power. This power supply is great for powering all kinds of electronic projects. It produces a well filtered, variable 1.2-30 volts at 5 amps. It is easy to build and the parts are realitively easy to find.

Schematic

Parts

Part Total Qty. Description Substitutions C1 1 14000uF or 10000uf 40 VDC Electrolytic Capacitor C2 1 100uF 50Vdc Electrolytic Capacitor C3 1 0.1uF Disc Capacitor C4 1 0.01uF Disc Capacitor R1 1 5K Pot R2 1 240 Ohm 1/4 W Resistor See Notes U1 1 LM338K 1.2 to 30 Volt 5 Amp Regulator BR1 1 10 Amp 50 PIV Bridge Rectifier T1 1 24 V 5 Amp Transformer S1 1 SPST Toggle Switch MISC 1 Wire, Line Cord, Case, Binding Posts (for output)

Notes

1. The regulator comes in a TO-3 case and MUST be used with a LARGE heatsink. You may want to mount a small fan to blow air across the regulator (I did).
2. The filter capacitor is large. It won't fit on any board so bolt it to the case.
3. You can, of course, add a volt and amp meter.
4. Since this project operates from 120 VAC, you must include a fuse and build the project in a case.
5. R2 may need to be decreased to 120 Ohm if you experience voltage drift at light loads. 240 Ohm may not load the output appropriately on some regulators. The datasheet for the LM338K does specify 120 Ohm (I suggest you use a 1/2W unit) so you may just want to use 120 Ohm and not bother with the 240 Ohm resistor showin the parts list. This has been discussed on the forum.

Portable CD Player Adapter For Car

Whenever I'm in the car listening to my favourite CD, it always happens; my batteries go dead. To solve that problem, I built this extremely simple regulator circuit. It steps down the 12V from the lighter socket to 9V which is used by the CD player. Different CD players (I have a Sony Discman) may require different voltages, so just use the correct regulator. All the 78xx series regulators have the same pin out, so the circuit is universal.

Schematic

Parts

Part Total Qty. Description Substitutions C1 1 1000uF 25V Electrolytic Capacitor C2 1 10uF 25V Electrolytic Capacitor C3 1 1uF 15V Elextrolytic Capacitor C4 1 0.1uF 15V Electrolytic Capacitor U1 1 7809 Or Other Regulator (See "Notes") See Notes MISC 1 Cigarette Lighter Plug, Plug For CD Player (See "Notes"), Heat Sink For U1, Wire, Case.

Notes

1. The voltage your CD player needs will determine which regulator you use. For 9V, use the 7809. For 6V, use the 7806. For the unlikely 5V use the 7805. Remember that whatever regulator you use, you will need to heat sink it. The metal case or metal cover on the case makes a great heat sink.
2. I built the circuit in a small case with the long wire to the cigaratte lighter plug coming out one end, then another, slightly shorter wire going out the other end to the CD player.
3. Triple check your wiring. You would hate to ruin an expensive CD player because you reversed one of the connections or hooked the regulator up backwards.

LASER Power Supply

Please note that some people may have trouble with this supply. This is due to the slight difference in transformers. For more information on LASER power supplies, take a look at Sam Goldwasser's Laser Supply Info Page.

   

Schematic

Parts

Part Total Qty. Description Substitutions R1 1 10 Ohm 10W Or Greater Resistor R2 1 Ballast Resistor, See "Notes" D1, D2, D3 3 1N4007 Silicon Diode C1, C2, C3 3 0.1 uF 2000V Capacitor T1 1 9V 1A Transformer S1 1 115V 2A SPST Switch MISC 1 Case, Wire, Binding Posts (for output), Line Cord

Notes

1. T1 is an ordinary 9V 1A transformer connected backwards for step up.
2. R1 MUST be installed on a LARGE heatsink. A good heatsink is the metal case the supply is built in.
3. R2 Protects the laser tube from excess current. It should be soldered directly to the anode terminal on the tube. To find R2, start with a 500K 10W resistor and work down until the tube lights and remains stable.
4. If you have trouble with the tube not starting easily, use a longer anode lead that is wrapped around the tube.
5. Depending on the transformer you use, the circuit may or may not work. I cannot guarantee the operation of this circuit. Build at your own risk. Some transformers contain very few secondary windings which will quickly saturate the core and basically act like a direct short. The more secondary windings (that is, primary in this circuit) the better.

High Voltage High Current Power Supply

A while ago I came up with the idea of using a microwave transformer as a high voltage, high current power supply. Even though I had no use for such a supply, I decided to design one anyway. This is a very simple design mainly to show that there are uncommon uses for common parts. Note: I have not built this supply because I have no use for it. Really it is nothing more then a transformer, rectifier and filter. If you build this supply without knowledge in electronics or high voltage, you have basically signed your own death certificate. This supply can be very dangerous if not treated properly. DO NOT BUILD THIS SUPPLY UNLESS YOU KNOW EXACTLY WHAT YOU ARE DOING! I assume no responsibility for any damages or injuries caused by this supply.

Schematic

Parts

Part Total Qty. Description Substitutions C1 1 0.68uF 2200V Capacitor T1 1 2KV Microwave Transformer S1 1 10 Amp 120VAC Switch C4 1 2000uf Electrolytic Capacitor MISC 1 Wire, Line Cord, Output Terminals

Notes

1. This circuit is dangerous! Do not build it if you do not have any experience with electronics or high voltage.
2. The circuit can produce about 250-500mA at 2KV, depending on the transformer.
3. For C1, you can use the capacitor out of an old microwave.
4. This circuit is mainly provided as a demonstration of using commonly available parts for something uncommon.

High Voltage High Current Power Supply

A while ago I came up with the idea of using a microwave transformer as a high voltage, high current power supply. Even though I had no use for such a supply, I decided to design one anyway. This is a very simple design mainly to show that there are uncommon uses for common parts. Note: I have not built this supply because I have no use for it. Really it is nothing more then a transformer, rectifier and filter. If you build this supply without knowledge in electronics or high voltage, you have basically signed your own death certificate. This supply can be very dangerous if not treated properly. DO NOT BUILD THIS SUPPLY UNLESS YOU KNOW EXACTLY WHAT YOU ARE DOING! I assume no responsibility for any damages or injuries caused by this supply.

Schematic

Parts

Part Total Qty. Description Substitutions C1 1 0.68uF 2200V Capacitor T1 1 2KV Microwave Transformer S1 1 10 Amp 120VAC Switch C4 1 2000uf Electrolytic Capacitor MISC 1 Wire, Line Cord, Output Terminals

Notes

1. This circuit is dangerous! Do not build it if you do not have any experience with electronics or high voltage.
2. The circuit can produce about 250-500mA at 2KV, depending on the transformer.
3. For C1, you can use the capacitor out of an old microwave.
4. This circuit is mainly provided as a demonstration of using commonly available parts for something uncommon.

High Current Power Supply

Since my page was first posted, I have received a number of emails asking about a high current power supply. I looked around, but couldn't find one that was suitable. So, I designed this. It is a linear supply, which might have a few of you rolling your eyes, but it takes very few parts, is simple to build and can supply huge currents.

Schematic

Parts

Part Total Qty. Description Substitutions R1 1 680 Ohm 1/4 Watt Resistor C1 1 20,000 - 50,000uF 20-40 Volt Capacitor C2, C3 2 100uF 50 Volt Capacitor C4 1 0.1uF 50 Volt Capacitor C5 1 0.01uF 50 Volt Capacitor D1 1 Zener Diode (See Notes) Q1 1 2N3055 Or Other (See Notes) T1 1 Transformer (See Notes) BR1 1 Bridge Rectifier (See Notes) S1 1 SPST 250 VAC 10 A Switch MISC 1 Case, Line Cord, Heatsink For Q1, Binding Posts For Output

Notes

1. D1 should be rated at about one volt higher than then desired output of the supply. A half watt diode will do.
2. Q1 can be a transistor similar to the 2N3055. I chose the 2N3055 for it's availability and power handling (150 watts).
3. T1 should be about 5 volts higher than the desired output of the supply, and rated for about one amp more of current. The voltage overhead is required by the regulator section. The extra current is to keep the transformer from over heating.
The choice of BR1 will depend on the voltage and current of your transformer. The rectifier should be rated for 50 volts more than the transformer, and 5 amps more than the transformer.
4. The value of R1 will be smaller when supplying high currents. Expiriment until you get what you need.
5. You are going to need to heatsink Q1 and BR1. Use a small PC case style fan unless you are going to run large heatsinks.

Fixed Voltage Power Supply

The fixed voltage power supply is useful in applications where an adjustable output is not required. This supply is simple, but very flexable as the voltage it outputs is dependant only on the regulator and transformer you choose. The maximum output current is 1.5A.

Schematic

Parts

Part Total Qty. Description Substitutions C1 1 2200uF 35V Electrolytic Capacitor C2, C4 2 0.1uF Ceramic Disc Capacitor C3 1 10uF 35V Electrolytic Capacitor D1, D2 2 1N4007 Silicon Diode BR1 1 2A 30V Bridge Rectifier U1 1 Regulator (See Notes) T1 1 Transformer (See Notes) S1 1 SPST 2 Amp Switch F1 1 2A 250V Fuse and Holder MISC 1 Heatsink For U1, Line Cord, Case, Wire

Notes

1. Since this project operates from 120 (or 220, or 240, etc.) volts AC, it MUST be built inside a case.
2. U1 will reauire a heatsink.
3. You will need to choose T1 and U1 to match the voltage you want. Use the table below as a reference.
   

   Output Voltage	T1	U1
   5V	6V, 1.5A	7805
   6V	6V, 1.5A	7806
   9V	12V, 1.5A	7809
   12V	12V, 1.5A	7812
   15V	24V, 1.5A	7815
   18V	24V, 1.5A	7818

Dual Polarity Power Supply

This dual polarity power supply is easy to build, requires few parts, and is adjustable from 0-15 volts. It is great for powering op amp circuits, as well as other circuits that require a dual supply voltage.

Schematic

Parts

Part Total Qty. Description Substitutions C1, C2 2 2200uF 35V Electrolytic Capacitor C3, C4, C5, C7 4 1uF 35V Electrolytic Capacitor C6, C8 2 100uF 35V Electrolytic Capacitor R1, R4 2 5K Pot R2, R3 2 240 Ohm 1/4 W Resistor BR1 1 2A 30V Bridge Rectifier U1 1 LM317 Adjustable Positive Regulator U2 1 LM337 Adjustable Negative Regulator T1 1 30V Center Tapped 2 Amp Transformer S1 1 SPST 2 Amp Switch MISC 1 Heatsinks For U1 And U2, Line Cord, Case, Knobs For Pots, Wire

Notes

1. Since this project operates from 120 (or 220, or 240, etc.) volts AC, it MUST be built inside a case.
2. U1 and U2 get quite hot and will require heatsinks. A fan is usually not needed.
3. You can, of course, add a volt and amp meter.
4. U1 and U2 can only go down to a minimum of +-1.2V. If you need to go lower, you can add two 1N4003 diodes in series with the output of the regulator. The diodes drop about 0.6V each, which will allow the supply to go to 0. Note that this will also decrease your maximum output voltage by 1.2V. (Thanks to Steve Horvath for the suggestion).

Car Battery Charger

This charger will quickly and easily charge most any lead acid battery. The charger delivers full current until the current drawn by the battery falls to 150 mA. At this time, a lower voltage is applied to finish off and keep from over charging. When the battery is fully charged, the circuit switches off and lights a LED, telling you that the cycle has finished.

Schematic

Parts

Part Total Qty. Description Substitutions R1 1 500 Ohm 1/4 W Resistor R2 1 3K 1/4 W Resistor R3 1 1K 1/4 W Resistor R4 1 15 Ohm 1/4 W Resistor R5 1 230 Ohm 1/4 W Resistor R6 1 15K 1/4 W Resistor R7 1 0.2 Ohm 10 W Resistor C1 1 0.1uF 25V Ceramic Capacitor C2 1 1uF 25V Electrolytic Capacitor C3 1 1000pF 25V Ceramic Capacitor D1 1 1N457 Diode Q1 1 2N2905 PNP Transistor U1 1 LM350 Regulator U2 1 LM301A Op Amp S1 1 Normally Open Push Button Switch MISC 1 Wire, Board, Heatsink For U1, Case, Binding Posts or Alligator Clips For Output

Notes

1. The circuit was meant to be powered by a power supply, which is why there is no transformer, rectifier, or filter capacitors on the schematic. There is no reason why you cannot add these.
2. A heatsink will be needed for U1.
3. To use the circuit, hook it up to a power supply/plug it in. Then, connect the battery to be charged to the output terminals. All you have to do now is push S1 (the "Start" switch), and wait for the circuit to finish.
4. If you want to use the charger without having to provide an external power supply, use the following circuit.
   
   

   Part	Total Qty.	Description	Substitutions
   C1	1	6800uF 25V Electrolytic Capcitor
   T1	1	3A 15V Transformer
   BR1	1	5A 50V Bridge Rectifier	10A 50V Bridge Rectifier
   S1	1	5A SPST Switch
   F1	1	4A 250V Fuse

5. The first time you use the circuit, you should check up on it every once and a while to make sure that it is working properly and the battery is not being over charged.

Automatic Load Sensing Power Switch

This circuit will automatically switch on several mains-powered "slave" loads when a "master" load is turned on. For example, it will switch on the amplifier and CD player in a stereo system when the receiver is turned on. It works by sensing the current draw of the "master" device through a low value high wattage resistor using a comparator. The output of that comparator then switches on the "slave" relay. The circuit can be built into a power bar, extension cord or power center to provide a convenient set of "smart" outlets that switch on when the master appliance is powered (turn on the computer monitor and the computer, printer and other peripherals come on as well).

Schematic

Parts

Part Total Qty. Description Substitutions C1, C3 2 10uF 35V Electrolytic Capacitor C2 1 1uF 35V Electrolytic Capacitor R1 1 0.1 Ohm 10W Resistor R2 1 27K 1/2W Resistor R3, R4 1 1K 1/4W Resistor R5 1 470K 1/4W Resistor R6 1 4.7K 1/2W Resistor R7 1 10K 1/4W Resistor D1, D2, D4 3 1N4004 Rectifier Diode D3 1 1N4744 15V 1 Watt Zener Diode U1 1 LM358N Dual Op Amp IC Q1 1 2N3904 NPN Transistor K1 1 Relay, 12VDC Coil, 120VAC 10A Contacts S1 1 SPST Switch 120AVC, 10A MISC 1 Board, Wire, Socket For U1, Case, Mains Plug, Socket

Notes

1. This circuit is designed for 120V operation. For 240V operation, resistors R2 and R6 will need to be changed.
2. A maximum of 5A can be used as the master unless the wattage of R1 is increased
3. S1 provides a manual bypass switch.
4. THis circuit is not isolated from the mains supply. Because of this, you must exercise extreme caution when working around the circuit if it is plugged in.

Automatic 12V Lead Acid Battery Charger

This charger will charge any 12V lead acid battery including flooded, gel and AGM. It is fully automatic and will charge at a rate up to about 4A until the battery voltage reaches a preset point at which it will switch to a very low current float charge. If the battery voltage drops again the charger will begin charging until the voltage once again reaches the cut off point. In this way it can be left connected to a battery indefinitely to maintain full charge without causing damage. An LED indicates when the battery is fully charged.

Schematic

Parts

Part Total Qty. Description Substitutions R1, R3 2 330 Ohm 1/4W Resistor R2 1 100 Ohm 1/4W Pot R4, R5, R7, R8 4 82 Ohm 2W Resistor R6 1 100 Ohm 1/4W Resistor R9 1 1K 1/4W Resistor C1 1 220uF 25V Electrolytic Capacitor D1 1 P600 Diode Any 50V 5A or greater rectifier diode D2 1 1N4004 Diode 1N4002, 1N4007 D3 1 5.6V Zener Diode D4 1 LED (Red, Green or Yellow) Q1 1 BT136 TRIAC Q2 1 BRX49 SCR T1 1 12V 4A Transformer See Notes F1 1 3A Fuse S1 1 SPST Switch, 120VAC 5A MISC 1 Wire, Board, Heatsink For U1, Case, Binding Posts or Alligator Clips For Output, Fuse Holder

Notes

1. R2 will have to be adjusted to set the proper finish charge voltage. Flooded and gel batteries are generally charged to 13.8V. If you are cycling the battery (AGM or gel) then 14.5V to 14.9V is generally recommended by battery manufacturers. To set up the charger, set the pot to midway, turn on the charger and then connect a battery to it's output. Monitor the charge with a voltmeter until the battery reaches the proper end voltage and then adjust the pot until the LED glows steadily. The charger has now been set. To charge multiple battery types you can mount the pot on the front of the case and have each position marked for the appropriate voltage.
2. Q1 will need a heatsink. If the circuit is mounted in a case then a small fan might be necessary and can generally be powered right off the output of D1.
3. T1 is a transformer with a primary voltage appropriate to your location (120V, 220V, etc.) and a secondary around 12V. Using a higher voltage secondary (16V-18V) will allow you to charge 16V batteries sometimes used in racing applications.
4. If the circuit is powered off, the battery should be disconnected from it's output otherwise the circuit will drain the battery slowly.

6V to 12V Converter

This inverter circuit can provide up to 800mA of 12V power from a 6V supply. For example, you could run 12V car accessories in a 6V (British?) car. The circuit is simple, about 75% efficient and quite useful. By changing just a few components, you can also modify it for different voltages.

Schematic

Parts

Part Total Qty. Description Substitutions R1, R4 2 2.2K 1/4W Resistor R2, R3 2 4.7K 1/4W Resistor R5 1 1K 1/4W Resistor R6 1 1.5K 1/4W Resistor R7 1 33K 1/4W Resistor R8 1 10K 1/4W Resistor C1,C2 2 0.1uF Ceramic Disc Capacitor C3 1 470uF 25V Electrolytic Capcitor D1 1 1N914 Diode D2 1 1N4004 Diode D3 1 12V 400mW Zener Diode Q1, Q2, Q4 3 BC547 NPN Transistor Q3 1 BD679 NPN Transistor L1 1 See Notes MISC 1 Heatsink For Q3, Binding Posts (For Input/Output), Wire, Board

Notes

1. L1 is a custom inductor wound with about 80 turns of 0.5mm magnet wire around a toroidal core with a 40mm outside diameter.
2. Different values of D3 can be used to get different output voltages from about 0.6V to around 30V. Note that at higher voltages the circuit might not perform as well and may not produce as much current. You may also need to use a larger C3 for higher voltages and/or higher currents.
3. You can use a larger value for C3 to provide better filtering.
4. The circuit will require about 2A from the 6V supply to provide the full 800mA at 12V.

12V to 120V Inverter

Schematic

Parts

Part Total Qty. Description Substitutions C1, C2 2 68 uf, 25 V Tantalum Capacitor R1, R2 2 10 Ohm, 5 Watt Resistor R3, R4 2 180 Ohm, 1 Watt Resistor D1, D2 2 HEP 154 Silicon Diode Q1, Q2 2 2N3055 NPN Transistor (see "Notes") T1 1 24V, Center Tapped Transformer (see "Notes") MISC 1 Wire, Case, Receptical (For Output)

Notes

1. Q1 and Q2, as well as T1, determine how much wattage the inverter can supply. With Q1,Q2=2N3055 and T1= 15 A, the inverter can supply about 300 watts. Larger transformers and more powerful transistors can be substituted for T1, Q1 and Q2 for more power.
2. The easiest and least expensive way to get a large T1 is to re-wind an old microwave transformer. These transformers are rated at about 1KW and are perfect. Go to a local TV repair shop and dig through the dumpster until you get the largest microwave you can find. The bigger the microwave the bigger transformer. Remove the transformer, being careful not to touch the large high voltage capacitor that might still be charged. If you want, you can test the transformer, but they are usually still good. Now, remove the old 2000 V secondary, being careful not to damage the primary. Leave the primary in tact. Now, wind on 12 turns of wire, twist a loop (center tap), and wind on 12 more turns. The guage of the wire will depend on how much current you plan to have the transformer supply. Enamel covered magnet wire works great for this. Now secure the windings with tape. Thats all there is to it. Remember to use high current transistors for Q1 and Q2. The 2N3055's in the parts list can only handle 15 amps each.
3. Remember, when operating at high wattages, this circuit draws huge amounts of current. Don't let your battery go dead :-).
4. Since this project produces 120 VAC, you must include a fuse and build the project in a case.
5. You must use tantalum capacitors for C1 and C2. Regular electrolytics will overheat and explode. And yes, 68uF is the correct value. There are no substitutions.
6. This circuit can be tricky to get going. Differences in transformers, transistors, parts substitutions or anything else not on this page may cause it to not function.
7. If you want to make 220/240 VAC instead of 120 VAC, you need a transformer with a 220/240 primary (used as the secondary in this circuit as the transformer is backwards) instead of the 120V unit specified here. The rest of the circuit stays the same. But it takes twice the current at 12V to produce 240V as it does 120V.
8. Check out this forum topic to answer many of the most commonly asked questions about this circuit: 12 - 120V Inverter Again. It covers the most common problems encountered and has some helpful suggestions