How to Make a Simple DC to DC Cell Phone Charger CircuitPosted byhitmanIt is estimated that there are probably more cell phones in India than the number of toilets present here. Astonishing, but true.A cell phonecharger is one mate of cell phone that cannot be ignored becausea cell phonewould become dead without a charger.

Normallya cell phonecharger come as anintegralpart ofa cell phonepackage and we use it in conjunction with our AC mains supply.But what happens if your cell phone gasps for power in the middle of a journey, probably when you are driving or biking away on a middle of a highway?A very simple yet reasonably effective DC to DCcell phone chargercircuit is discussed in this article, which can be easily built at home even by a layman.Though the proposed charger circuit won't charge your cell phone at the rate equal to a normal AC to DC charger, nevertheless it will complete the function without fail and won'tbetrayyou for sure.Thecircuit diagramcan be understood with the followingpoints:We all know the general specs ofacellphonebattery, it's around 3.7 volts and 800 mAH.It means the cell phone would require at around 4.5 volts for initiating thechargingprocess.However a Li-Ion battery which is employed inside cell phones are pretty sensitive to bad voltages and may just blow off causing serious life and property issues.Keeping this in mind the cell phone internal circuitry is specifically dimensioned very strictly.The parameters just won't permit any voltage which may be even slightly out of the range of the battery specifications.The use of the versatile IC 7805 in the circuit answers the above issue just perfectly, such that the charging voltage at its output becomes ideally suitable for charging thecell phone battery.A high wattage resistor connected at the output of the IC makes sure that the current to the cell phone stays wellwithinthe specified range, though this might have not been a problem anyway, the cell phone would just refuse to charge if the resistor was not included.

Pictorial Diagram

You can use thiscell phone chargerfor charging you cell phone during emergencies when there's no mains AC outlets, the circuit may be powered from any 12 volt leadacidbatteryor similar DC power source

Parts List

R1 = 5 Ohm, 2 Watt,C1, C2 = 10uF/ 25V,D1 = 1N4007,IC1 = 7805, mounted on a heatsink,Battery, any 12 volt automobile battery

Making a Multi-function Water Level Controller CircuitPosted bySwagatam MajumdarThe following multi-functionwater levelcontroller circuit post is based on the suggestions expressed by Mr.Usman. Let's learn more about the requested modifications and the circuit details.

The Suggestion:

"Hi Swagatam,

The conceptof this circuitlooks good. May I suggest a couple of otherdesirablefeatures?

1) To protect the motor from potential overheating (or as a safety feature) can u add an automatic shutdown timer? If the motor is running for one hour (or 1.5hrs or 2-hrs) and thewater leveldoes NOT reach the level-sensor, the motor should be automatically stopped. Of course, it can be re-startedmanuallyby pushing the start button again.

2) Can the motor bemanuallystopped at any time? For example, what if one wants to water the lawn (or wash the car) for a few minutes using high pressure water directly from the motor?"

Thanks very much!

Your suggestions are interesting!

I think I have discussed these issues in the following artricle:

http://homemadecircuitsandschematics.blogspot.in/2012/03/dc-motor-protector-circuit-over-voltage.html

However instead of a timer I have used atemperaturesensor circuit for tripping the motor if it starts getting hot.

The motor can bemanuallystopped by shorting the base of T3 to ground. This can be done by adding a push button across these terminals.

So the upper push button may be used for initiating the motor while the lower button may be used for stopping the motormanually.

Thanks Swagatam for a prompt reply. I've found another circuit on your blog (April 20th post) that is closer to what I have in mind.

http://homemadecircuitsandschematics.blogspot.com/2012/04/semi-automatic-water-level.html

I want a slightly different control logic in the above circuit:

Motor START Logic:Manual push button (already implemented)

Motor STOP Logic:1)Water levelreaches a pre-determined level (as implemented in April 21st post), OR2) A pre-determined time has lapsed (e.g. 30, 60 or 90 mins, this requires a long time-delay/counter), OR3) Manual stop (manual override), OR4) Power faliure (load shedding), this is implemented by default!

So I guess, the STOP logic (1, 2 and 3) can be configured to the base of T1 (in your April 20 post) and it should work. Pls comment, and if you have time maybe you can make a new post!

ThanksUsman

The Design:

Let's analyze the above requirements and check how they have beenimplementedin thefollowingdiagram:

1)Water levelreaches a pre-determined level: Point A and B may be appropriately fixed inside the tank for regulating this function. Since point B is situated at the bottom of the tank, remains connected withthe waterpermanently, now as the level rises and comes in contact with point A, the positive potential from point A connects with point B, which instantly reset pin#12 of the IC, switching OFF the relay and the entire system.

2)A predetermined time has lapsed: This feature is already present in the below given circuit. The timing outputs can be increased to any desired extents simply by increasing the values of P1 and C1.

3)Manual stop (manual override): This feature isactuatedby SW2, pressing which resets the IC pin#12 and the entire circuit.

4) Powerfailure(load shedding): During a possible power failure or instantaneous power "blinks", the IC needs to be supplied with the required supply voltage so that the timing does not get interrupted. This is very simply done by adding a 9 volt battery to the circuit.

As long as normal power is present, the cathode of D3 stays high keeping the battery switched OFF from the circuit. The moment power fails, the cathode of D3 becomes low, providing a way-in to the battery power which smoothly replaces the supply to the IC without causing any "hiccup" to the counting operation of the IC.

Parts list for the above explained multi-functionwater levelcontroller circuit

R1= 1M, 1/4 wattR3 = 1MR2, R6 = 4K7R4 = 120KR5 = 22KP1 = 1M preset horizontalC1 = 0.47uFC2 = 0.22uF disc ceramicC3 = 1000uF/25VC4 = 100uF/25VD1, D2, D3, D4 = 1N4007,Relay = 12V/SPDTSW1,SW2 = Bell push type of buttonIC1 = 4060T1, T2 = BC547TR1 = 0-12V/500mABATT - 9V, PP3

Water levelbuzzer indicator circuit

The following circuit of a water high level and low level indicator circuit was requested by Mr.Amit. Please read the comments given below to know regarding the exact specs of the requested circuit.

Circuit Description

The above shown water high and low level buzzer indicator circuit may be understood with the following points:

Point C which is connected to the ground or negative of the supply rail is kept immersed in the tank water at the bottom level such thatthe waterpresent in the tank is always held a logic low.

Point B is the low level sensor point which must be positioned near the bottom of the tank, distance may be set as desired by the user.

Point A is the high level sensor, which should be held somewhere at the top of the tank as per user preference.

When thewater levelreaches under the point B, point B goes high due to R6, making the output of N4 high and consequently producing a low at the output of N5....the buzzer B2 starts buzzing.

However in the meantime C2 starts charging up and once it's fully charged inhibits the positive potential at the input of N5.....the buzzer is switched OFF. The time for which the buzzer remains On may bedeterminedby the values of C2 and R5.

In an eventthe waterreaches the top level of the tank, point A comes in contact with the low logic fromthe water, output of N1 becomes high and the same process is repeated as explained above. However this time B1 starts beeping, only until C1 gets fully charged.

Five gates from the IC 4049 have been utilized here, the remaining one unused gate input should begroundedfor maintaining stability of the IC.

Parts List

R1,R6 = 3M3R3,R4 = 10KT1, T2 = 8550, or 187, or 2N2907 or similarC1,R2 = to be selected for setting up buzzer on timeC2,R5 =to be selected for setting up buzzer on time.N1---N5 = IC 4049B1,B2 = Loud piezo buzzers

This is my schematic design of a Pulse Width Modulator DC/AC inverter using the chip SG3524 .I have built this design and using it as a backup to power up all my house when outages occur.

If you like my work andintend to build the circuit don't forget to give me the 5 satrs :Dand subscribe to me by clicking on the "follow" buttonsoI know how many people benefit from the design, Thanks

Notes:

1>The schematic circuit design is for a 250 watt output, while the pics are of my 1500 watts inverter that i built, to increase the power of the circuit you have to add more of the Q7 and Q8 transistors in parallel, each pair you add will increase your power by 250 watts, ex: to get 750 watts of power from the inverter you need to add in parallel 2 of Q7 and 2 of Q8 to the original design.

2>If you increase the power transistors you have toenlarge the T2 transformer to match the new needs, the circuit's transformer is rated 25 amps to handle 250 watts of 220v, for every 1 additional amp you need on the 220v side you have to increase 10 amps on the 12v side, of course there are limits to the thickness of the winding so if you need more than 750 watts i recommend that you use a 24VDC supply instead of 12 volts:

DC voltage and Transformer "T2" winding recommendation:PowerSupplyWinding750w 12VDC P:24V "12-0-12" / S:220V1500w 24VDC P:48V "24-0-24" / S:220V2250w 36VDC P:72V "36-0-36" / S:220V3000w 48VDC P:96V "48-0-48" / S:220V3750w 60VDC P:120V "60-0-60" / S:220V4500w 72VDC P:144V "72-0-72" / S:220V5250w 84VDC P:168V "84-0-84" / S:220V*The transformer should be "center tapped" at the primary side.**You can make the secondary 110v if needed.***The transformer in the pic is a custom made (48V center tapped / 220v ) 2000 watts, weights like 10 kilos.

3>R1 is to set the PWM duty cycle to 220v. Connect voltmeter to the output of your inverter and vary VR1 till the voltage reads 220V.

4>R2 is to set the frequency to 50 or 60 Hz (R2 range is between 40Hz to 75Hz), so guys that do not have a frequency meter are advised to blindly put this variable resistor mid-way which should drop you in the range of 50~60 Hz.If you want you can substitue the variable resistor with a fixed resistor using the following formula: F = 1.3 / (RxC)in our case to get a 50Hz output we remove both the 100K and the variable 100K both from pin 6 and we put instead a 260K fixed resistor and we leave the 0.1uF (the 104 cap) as it is, this change should give out a fixed 50Hz as per the formula :1.3 / (260,000ohmx 0.0000001 farad) = 50HzBut in reality it will not exactly give 50Hz because the 260K resistor has a specificerror value marginso does the capacitor, that's why i recommend a variable resistor so that accurate calibration can be achieved.

5>Use either tantalum or polyester film "as in pic" for the 104 caps, ceramic disc caps change value once hot and this in turn changes the frequency of the inverter so they are not recommended.

6>Pin 10 of the SG3524 can be used to auto shut down the inverter, once apositive voltage isgiven instead ofnegative to pin10, the SG3524 will stop oscillating. This is useful for persons wanting to add some cosmetic makeup to their inverters like overload cutoff, low battery cutoff or overheating cutoff.

7>Wiring connections on the power stage side should be thick enough to handle the huge amps drain from the batteries. I marked them with dark black on the schema also I includeda pic so you see how thick those wires must be.

8>The design does not include a battery charger since each person will be building a custom version of the inverter with specific power needs. If you are ordering a custom made transformer you can ask them totake out foryou an additional output wire on the primary side to give 14v (between point 0 and this new wire) and use it to chargea 12vbattery, of course this needs a seperate circuit to control charging auto cut-off. But anyway this is not advisable because it will shorten the life of the transformer itself since using it as a charger will toast the enamel coating layer of the copper wires over time. Anyway .. YES can be done to reduce cost.

9>A cooling fan will be needed to reduce heat off the heat sinks and transformer, i recommend getting a 220v fan and connecting it to the output T2 transformer, when you power up the circuit the fan will start this will always give you a simple way to know that 220v is present and everything is OK.. You can use a computer's old power supply fan if you like.Note that the fan must suck air out from the inverter case and NOT blow inside, so install it the correct way or it will be useless.Also note how I fixed both the heat sinks and where the fan is,in a way that the fan sucks hot air fromlike achannel between the 2 heatsinks.

10>2 circuit breakers are recommended instead of fuses, one on the DC side and one on the AC side, depending on your designEx: for a 24vDC ( 1500 watts design ) put a 60Amp breaker on the DC side and a 6Amp on the AC side.For every 1amp of 220vAC you will be draining like 8 to 10 Amps from the 12v battery, make your calculations !

11>The 2 Heat sinks should be big enough to cool the transistors, they are separate and should NOT touch each other. "see the pics"

12>Important:If you're building a big design that uses more than 24VDC as power source, make sure not to supply the driver circuit with more than 24v maximum. (EX: If you have 4 batteries 4x12 = 48v ,connect the v+ supply of the driver circuit to the second battery's (+) terminal with a thin 1 mm wire which is more than enough. this supplies the driver circuit with +24v while supplies the power transformer with +48v)"see the batteries pic example"

13>"Optional" : Deep Cycle batteries are your best choice, consider them for best results ..read more

14>Be cautious when building this circuit it involves high voltage which is lethal, any part you touch when the circuit is ON could give you a nasty painful jolt, specially the heat-sinks, never touch them when the circuit is on to see if the transistors are hot !! I ate it several times :)

15>The optional "Low voltage warning" is already embedded in the PCB layout, you can disregard it and not install it's components if you do not needed. It does not affect the functionality of the main circuit.

16>The Motorola 2N6277is a durable heavy duty power transistor, it is used in many US tanks for it's reliability but unfortunately it is a very hard to find part,instead you can substitute each 2N6277 with 2 x 2N3773or any equivalent.

17>I've included an optional "Battery level indicator" circuit diagramthat has 4 LEDs, you can see it installed on the front panel of my inverter pic, it is functioning great and shows precisely how much juice the batteries still have. I have included a small relay that is powered by the lastLED to auto shutoff the inverter once last LED is off.

18>Also included anoptional "Overload circuit", it is very easy to build and can be calibrated tothe desired overload current threshold cutoff point through the potentiometer VR1.R1 is rated 5watts for inverters upto 1000 watts. For bigger versions of the inverter like1000to3000 wattsinverters, replace R1 (1 ohm, 5watts) with (1 ohm, 17watts) which should handle loads upto 10 VA.Make sure you installa proper relay to handle big current drains.

19> Please guys take your time to read and understand my notes, browse and read the posts and questions asked byothers because there are many useful information listed in replies. The main reason for menot answeringyour question is because it has already been asked before and answered upon.

20> It would be nice and inspiring for others if you take some photos and show us how you built your version, any additions to the circuit are mostly welcomed to be listed here, we can all benefit from them.

Adding a Soft Start to Water Pump Motors - Reducing Relay Burning ProblemsPosted bySwagatam MajumdarWhen heavy motor systems or high current motors are involved, initial switch ON current surge often becomes an issue. This surge tends to inflict huge sparking across the pump relay contacts causingcorrosionand reduction in its life due to stress, and wear and tear.

The sparking of the motor not only causes relay contact issues, butalsoaffects surrounding electronic circuits, causing them to hang or get disturbed due to large amount of RFinterferencegenerated during motor switch ON.

However safeguarding the costly motor relay becomes the main issue with such situations. Though there are many mechanical contactors available for controlling motor stress, these system are notefficientand are ineffective against the RF emissions.

The simple electronic circuit presented below hopefully is able to eliminate all issues concerned with heavy motor switch ON surge generation and relay contact protection.

The figure shows a simple dimmer switch circuit incorporating an ordinary triac and diac configuration, which can be very effectively used for adding a soft start to any high current, heavy AC motor.

Here the control pot has been replaced with a LED/LDR box. As we know that in normal dimmer switches, avariableresistance is used for controlling the fan speeds. Here the variable resistance isreplaced with a LED/LDRarrangement. It means now the speed of the motor, or in other words, current to themotorcan be controlled by controlling the intensity of the enclosed LED through an external trigger.

That's exactly what is done here. When the motor relay is switched ON, either by a switch or through an electronic control circuit such as a water level controller circuit, the LED of theattacheddimmer switch is also switched ON simultaneously.

The LED switches ON the triac and the connected motor.

Being a solid state device the dimmer switch acts a little faster than the relay and therefore the motor is first activated through the dimmer triac and just after a few milliseconds the triac gets bypassed by theconcernedrelay contacts.

The above process completely eliminates any sparking from the relay contact since the triac has already absorbed much of the current and the relay only has to softly takeover the already switched ON motor conduction.

Here the brightness of the opto-coupler LED is crucial,and mustbe set such that the triac is only 75% ON.

This adjustment will save the triac from initial heavy currenttransientand help the entire system to last for many many years.

The resistor R4 may be appropriately set for achieving an optimal glow over the LED.

Parts List

R1 = 15KR2 = 330K,R3 = 10K,Diac resistor = 100 Ohms,R4 = to be adjusted as explained,C1 = 0.1uF/400VC2, C3 = 0.1uF/250V,L1 = 10 amp/220V chokeTriac (Alternistor) = 10 Amp 400V,Diac = as per the above triac.

Simplified Version

A little inspection reveals that the circuitactuallydoes not require the opto coupler circuit at all. The circuit may be simply arranged in the following manner:R2 should selected suh that the triac conducts only 75% of the power.

When power isswitched ON, the triac provides a softinitialstart to the motor until within the next split second when the relay also conducts enabling the motor the required full power. This completely safeguards theactuatorcontacts from the initial current surges and sparks,

Much Improved Circuit

As rightly suggestedby Mr.Jim, an initial torque is imperative forinitiatinga motor optimally especially when it's loaded, if this initial torque is absent. the motor might stall with heavy loads under its belt and might start smoking withinminutes.

The following circuit is designed for solving both the issues together, it inhibits the initial surge current to the ON/OFF switch and yet allows the motor to start with a "kick" so that it initiates without problems even when it's loaded.

atThursday, September 27, 2012Email ThisBlogThis!Share to TwitterShare to Facebook