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Wednesday, November 12, 2014

Electrical Wiring for Building – Standard and Code

Here is an article discuss on Electrical Wiring Standard and Code as used to provide power in buildings and structures, commonly referred to as building wiring.

The international standard wire sizes are given in the IEC 60228 standard of the International Electrotechnical Commission. This document and its precursors were created due to a need for a standard definition of cable conductor size. However, this standard is not written in such language that it can readily be adapted as a national wiring code.

Get more information regarding the Electrical Wiring Standard and Code here (reference: scribd.com)

Monday, October 13, 2014

Latest new Oxygen Sensor Simulator Oxygen Simulator Sensor

The schematic diagram for the simulator. Closing the switch engages the simulator. Turning the knob clockwise simulates a lean condition, turns the LED off, and the car should start running rich to compensate. The big "V" is a digital voltmeter (not shown in the pictures). Using a smaller value for C1, perhaps 4.7 uF, will make the circuit oscillate faster and might be more like a real oxygen sensor (a new sensor switches more often than an old one).

The schematic diagram for the simulator. Closing the switch engages the simulator. Turning the knob clockwise simulates a lean condition, turns the LED off, and the car should start running rich to compensate. The big "V" is a digital voltmeter (not shown in the pictures). Using a smaller value for C1, perhaps 4.7 uF, will make the circuit oscillate faster and might be more like a real oxygen sensor (a new sensor switches more often than an old one).

The schematic diagram of the adapter cable and oxygen sensor. Note the heater is shown as a resistor, mine measured about 7 ohms.

Friday, September 26, 2014

Temperature Sensor Circuit for Remote Distance Applications

The circuit shows a temperature sensing device which can be used to indicate at a remote point when the temperature passes through a certain value or to give an alarm when this occurs.
The sensing unit itself contains a 2N930 transistor. The base-emitter voltage of this device appears across R1 and (as the base current is far less than the collector current) the voltage at the upper end of R2 will be the emitter-base voltage multiplied by (R2 + R1)/Rl.

The base emitter volt· age changes with T a temperature coefficient of —2.2mV/°C and this change is multiplied by the same factor before being applied to the LM339 circuit. The potential at point A is set by the resistors R3 and R4. As _the temperature of the sensor transistor rises, the voltage at point B falls. At the time this voltage falls below that at point A, the output of the LM339 voltage comparator will go high. lf, however, the input connections to the LM339Aare reversed, the output will go low when the temperature of the sensor falls below the preset point.

The LM339 contains four separate voltage comparators in one package; only one of these comparators is used in the circuit shown. The other three comparators could be used with another three temperature sensing transistors so that an indication is given when the temperature passes through three other preset values. The`value of R5 should be chosen so that the current passing through the remote sensor unit is about 10pA. lf the temperature range over which operation is required is narrow, the ratio R2/R1 may be large so that the system is- very sensitive to small temperature variations. A potentiometer may be substituted for R3 and R4 so that the temperature at which the comparator switches is variable.

The voltage at point B is,highly linear over a very wide temperature range (about -65°C to +150°C) and there- fore the potentiometer which replaces R3 and R4 can be given a linear calibration. A feedback resistor may be connected from the output to the non- inverting input to provide a small amount of hysteresis (so that the temperature at which the output changes when the temperature is rising is different from that when it is falling); one then has the basis of a thermostat. ‘ The output current has a maximum value of about 15mA.

Tuesday, September 23, 2014

Automotive 12V to 20V converter for audio amplifier

The limitation of car supply voltage (12V) forces to convert the voltages to higher in order to power audio amplifiers.
In fact the max audio power x speaker (with 4 ohm impedance) using 12V is (Vsupply+ - Vsupply-)^2/(8*impedance) 12^2/32 = 4.5Watts per channel, that is laughable...
For powering correctly an amplifier the best is to use a symmetric supply with a high voltage differential. for example +20 - -20 = 40Volts
in fact
40^2/32 = 50 Watts per channel that is respectable.
This supply is intended for two channels with 50W max each (of course it depends on the amplifier used). Though it can be easily scaled up or the voltages changed to obtain different values.

Overview - How it works
It is a classic push-pull design , taking care to obtain best symmetry (to avoid flux walking). Keep in mind that this circuit will adsorb many amperes (around 10A) so take care to reinforce power tracks with lots of solder and use heavy wires from the battery or the voltage will drop too much at the input.
The transformer must be designed to reduce skin effect, it can be done using several insulated magnet wire single wires soldered together but conducting separately. The regulation is done both by the transformer turn ratio and varying the duty cycle. In my case i used 5+5 , 10+10 turns obtaining a step up ratio of 2 (12->24) and downregulating the voltage to 20 via duty cycle dynamic adjust performed by the PWM controller TL494.
The step-up ratio has to be a little higher to overcome diode losses, winding resistance and so on and input voltage drop due to wire resistance from battery to converter.

Transformer design
The transformer must be of correct size in order to carry the power needed, on the net there are many charts showing the power in function of frequency and core size for a given topology. My transformer size is 33.5 mm lenght, 30.0 height and 13mm width with a cross section area of 1,25cm^2, good for powers around 150W at 50khz.
The windings , especially the primary must be heavy gauged, but instead of using a single wire it is better to use
multiple wires in parallel each insulated from the other except at the ends. This will reduce resistance increase due to skin effect. The primary and secondary windings are centertapped, this means that you have to wind 5 turns, centertap and 5 windings again. The same goes for the secondary, 10 turns, centertap and 10 turns again.
The important thing is that the transformer MUST not have air gaps or the leakage inductance will throw spikes on the switches overheating them and giving a voltage higher than expected by turn ratio prediction, so if your voltage output (at fully duty cycle) is higher than Vin*N2/N1 - Vdrop diode, your transformer has gap (of course permit me saying you that you are BLIND if you miss it), and this is accompanied with a drastical efficiency reduction. Use non-gapped E cores or toroids (ferrite).

Output diodes, capacitors and filter inductor
For rectification i preferred to use shottky diodes since they have low forward voltage drop, and are incredibly fast.
I used the cheap 1N5822, the best alternative for low voltage converters (3A for current capability).
The output capacitors are 4700uF 25V, not very big, since at high frequency the voltage ripple is most due to internal cap ESR fortunately general purpose lytics have enough low esr for a small ripple (some tens of millivolts). Also at high duty cycle they are feed almost with pure DC, giving small ripple. The filter inductor on the secondary centertap furter increases the ripple and helps the regulation in asymmetrical transients

Power switch and driving
I used d2pak 70V 80A 0.004 ohms ultrafets (Fairchind semiconductor), very expensive and hard to find. In principle any fet will work, but the lower the on-resistance, the lower the on-state conduction losses, the lower the heat produced on the fets, the higher efficiency and smaller the heatsinks needed. With this fets i am able to run the fets with small heatsinks and without fan at full rated power (100W) with an efficiency of 82% and perceptible heating and with small heating at 120W (some degrees) (the core starts to saturate and the efficiency is a bit lower, around 75%)
Try to use the lowest resistance mosfet you can put your dirty hand :-) on or the efficiency will be lower than rated and you will need even a small fan. The fet driver i used is the TPS2811P, from Texas instruments, rated for 2A peak and 200ns. Is important that the gate drive is optimized for minimal inductance or the switching losses will be higher and you risk noise coupling from other sources. Personally i think that twisted pair wires (gate and ground/source) are the best to keep the inductance small. Place the gate drive resistor near the Mosfet, not near the IC.

Controller
I used the trusty TL494 PWM controller with frequency set at around 40-60 Khz adjustable with a potentiometer. I also implemented the soft start (to reduce powerup transients). The adjust potentiometer (feedback) must be set to obtain the desired voltage. The output signals is designed with two pull-up resistors on the collector of the PWM chip output transistor pulling them to ground each cycle alternatively. This signal is sent to the dual inverting MOSFET driver (TPS2811P) obtaining the correct waveform.

Power and filtering
How i said before the power tracks must be heavy gauged or you will scarify regulation (since it depends of transformer step up ratio and input voltage) and efficiency too. Dont forget to place a 10A (or 15A) fuse on the input because the car batteries can supply very high currents in case of shorts and this will save you face from a mosfet explosion in case of failture or short, remember to place a fuse also on the battery side to increase the safety (accidental shorts->fire, battery explosion, firemen, police and lawyers around). Input filtering is important, use at least 20000uF 16V in capacitors, a filter inductor would be useful too (heavygauged) but i decided to leave it..

Final considerations
This supply given me up to 85% efficiency (sometimes even 90% at some loads) with an input of 12V because i observed all these tricks to keep it functional and efficient. An o-scope would be useful, to watch the ripple and gate signals (watching for overshoots), but if you follow these guidelines you will avoid these problems.
The cross regulation is good but keep in mind that only the positive output is fully regulated, and the negative only follows it. Place a small load between the negative rail and ground (a 3mm led with a 4.7Kohm resistor) to avoid the negative rail getting lower then -20V. If the load is asymmetric you can have two cases:
-More load on positive rail-> no problems, the negative rail can go lower than -20V, but it is not a real issue for an audio amplifier.
-More load on negative rail-> voltage drop on negative rail (to ground) especially if the load is only on the negative rail.
Fortunately audio amplifiers are quite symmetrical as a load, and the output filter inductor/capacitors helps to maintain the regulation good during asymmetrical transients (Basses)

FOR FIRST TESTING USE A SMALL 12V power supply and use resistors as load monitoring switches heat and current consumption (and output) and try to determine efficiency, if it is higher then 70-75% you are set, it is enough. Adjust the frequency for best compromise between power and switching losses, skin effect and hysteresis losses

Bill Of Materials
=================
Design: 12V to 20V 100W DC-DC conv
Doc. no.: 1
Revision: 3
Author: Jonathan Filippi
Created: 29/04/05
Modified: 18/05/05

Parts
2 R1,R2 = 10
4 R3,R4,R6,R7 = 1k
1 R5 = 22k
1 R8 = 4.7k
1 R9 = 100k
2 C1,C2 = 10000uF
2 C3,C6 = 47u
1 C4 = 10u
3 C5,C7,C14 = 100n
2 C8,C9 = 4700u
1 C12 = 1n
1 C13 = 2.2u
1 U1 = TL494
1 U2 = TPS2811P
2 Q1,Q2 = FDB045AN
4 D1-D4 = 1N5822
1 D5 = 1N4148
1 FU1 = 10A
1 L1 = 10u
1 L2 = FERRITE BEAD
1 RV1 = 2.2k
1 RV2 = 24k
1 T1 = TRAN-3P3S

author: Jonathan Filippi
e-mail: jonathan.filippi@virgilio.it
web site: http://www.cool-science.tk

Monday, September 22, 2014

Automotive 12V to 20V converter for audio amplifier descriptiona and circuit diagram

Circuit diagrams

Bill Of Materials
=================
Design: 12V to 20V 100W DC-DC conv
Doc. no.: 1
Revision: 3
Author: Jonathan Filippi
Created: 29/04/05
Modified: 18/05/05

author: Jonathan Filippi
e-mail: jonathan.filippi@virgilio.it
web site: http://www.cool-science.tk

Saturday, August 30, 2014

Video Switch for Intercom System Wiring diagram Schematic

Simple and easy Video Switch for Intercom System Circuit Diagram. Nowadays a lot of intercom units are equipped with video cameras so that you can see as well as hear who is at the door. Unfortunately, the camera lens is perfectly placed to serve as a sort of support point for people during the conversation, with the result that there’s hardly anything left see in the video imagery. One way to solve this problem is to install two cameras on the street side instead only one, preferably some distance apart. If you display the imagery from the two cameras alternately, then at least half of the time you will be able to see what is happening in front of the door. Thanks to the video switch module described here, which should be installed on the street side not too far away from the two cameras, you need only one monitor inside the house and you don’t need to install any additional video cables.

Circuit diagram :

Video Switch for Intercom System Circuit Diagram

Along with a video switch, the schema includes a video amplifier that has been used with good results in many other Elektor projects, which allows the brightness and the contrast to be adjusted separately. This amplifier is included because the distance between the street and the house may be rather large, so it is helpful to be able to compensate for cable attenuation in this manner. The switch stage is built around the well known 4060 IC, in which switches IC2a and IC2d alternately pass one of the two signals to the output. They are driven by switches IC2b and IC2c, which generate control signals that are 180 degrees out of phase. The switching rate for the video signals is determined by a clock signal from an ‘old standby’ 555 IC, which causes the signals to swap every 2 seconds with the speciﬁed com ponent values.

Naturally, this schema can also used in many other situations, such as where two cameras are needed for surveillance but only one video cable is available.

http://streampowers.blogspot.com/2012/06/video-switch-for-intercom-system_11.html

Wednesday, August 27, 2014

Solid State Switch For Dc Operated Gadgets

This solid state DC switch can be assembled using just three transistors and some passive components. It can be used to switch on one gadget while switching off the second gadget with momentary operation of switch. To reverse the operation, you just have to momentarily depress another switch.

The schema operates over 6V-15V DC supply voltage. It uses positive feedback from transistor T2 to transistor T1 to keep this transistor pair in latched state (on/ off), while the state of the third transistor stage is the complement of transistor T2’s conduction state.

Initially when switch S3 is closed, both transistors T1 and T2 are off, as no forward bias is available to these, while the base of transistor T3 is effectively grounded via resistors R8 and R6 (shunted by the load of the first gadget). As a result, transistor T3 is forward biased and gadget 2 gets the supply. This is indicated by glowing of LED2.

Solid-State Switch For Dc-Operated Gadgets Circuit diagram :

Solid-State Switch For Dc-Operated Gadgets Circuit Diagram

When switch S1 is momentarily depressed, T1 gets the base drive and it grounds the base of transistor T2 via resistor R4. Hence transistor T2 (pnp) also conducts. The positive voltage available at the collector of transistor T2 is fed back to the base of transistor T1 via resistor R3. Hence a latch is formed and transistor T2 (as also transistor T1) continues to conduct, which activates gadget 1 and LED1 glows.

Conduction of transistor T2 causes its collector to be pulled towards positive rail. Since the collector of T2 is connected to the base of pnp transistor T3, it causes transistor T3 to cut off, switching off the supply to gadget 2) as well as extinguishing LED2. This status is maintained until switch S2 is momentarily pressed. Depression of switch S2 effectively grounds the base of transistor T1, which cuts off and thus virtually opens the base-emitter schema of transistor T2 and thus cutting it off. This is the same condition as was obtained initially. This condition can be reversed by momentarily pressing switch S1 as explained earlier.

EFY lab note. During testing, it was noticed that for proper operation of the schema, gadget 1 must draw a current of more than 100 mA (i.e. the resistance of gadget 1 must be less than 220 ohms) to sustain the latched ‘on’ state. But this stipulation is not applicable for gadget 2. A maximum current of 275 mA could be drawn by any gadget.

Author : Praveen Shanker - Copyright : EFY

Tuesday, August 26, 2014

Supper Deluxe Charge Rate Limiter for Small Capacity NiCad Batteries

Here is a deluxe version of the simple charge rate limiter, using the same idea but with the ability to charge two packs simultaneously from a single wall charger. For schema description and parts list, see the simple charger page. Since wall chargers provide about 55mA, you should not use this dual schema to charge batteries at rates greater than 27mA (for a total of 54mA).

Saturday, August 23, 2014

DC fan control circuit for power amplifier

DC fan control circuit for power amplifier .Variable speed DC fanThis series of works based on the input signal. Speed / fan rotation depending on size of the input signal coming from speaker lines. If there is no signal then the fan will spin slowly according to the setting VR1.Input supply can be taken directly from the main transformer power amplifier, 12V CT 12V, so no need to increase the transformer again.

Circuit Schematic Electronics | CSE

This circuit has been tested and do not cause buzzing.correction: the lowest R: 560 ohm

Tuesday, August 19, 2014

Frequency Meter for AC line Wiring diagram Schematic

There are specific gauges are of little use for most areas of electronics, but some are expensive and hard to find even Brazil. An example is the frequency meter AC line, it really is a measuring instrument of little or no use to most of us. We can use a frequency common adapting a cable, but for anyone working with inverters, UPS and generators, this is a primary tool.

Frequency Meter for AC line Circuit Diagram

Here a schema meter AC line frequency super simple and easy construction that can measure the frequency of 10Hz to 100Hz at a voltage of 110 V to 240 V.
This schema converts the sine wave output of the square wave 100k watt resistor and zener diode 1 watt 6.8V which may be a 1N3829A.

The medium is directly proportional to frequency, so it can be read in a 100mA ammeter (M1).
To calibrate the use of 60Hz known home network, set the pot VR1 to read 60mA.

Tuesday, August 12, 2014

Best Electronic Crowbar Wiring diagram Schematic for AC or DC lines

This is Best Electronic Crowbar Circuit Diagram for AC or DC lines. For positive protection of electrical or electronic equipment, use this against excessive supply voltage. Due to improper switching, wiring, short diagram, or failure of regulators, an electronic crowbar schema can quickly place a short schema across the power lines, thereby dropping the voltage across the protected device to near zero and blowing a fuse.

The triac and SBS are both bilateral devices, the schema is equally useful on ac or dc supply lines. With the values shown for Rl, R2, and R3, the crowbar operating point can be adjusted over the range of 60 to 120 volts dc or 42 to 84 volts ac. The resistor values can be changed to cover a different range of supply voltages. The voltage rating of the triac must be greater than the highest operating point as set by R2, II is a low power incandescent lamp with a voltage rating equal to the supply voltage.

Best Electronic Crowbar Circuit Diagram for AC or DC lines

It may be used to check the set point and operation of the unit by opening the test switch and adjusting the input or set point to fire the SBS. An alarm unit such as the Mallory Sonalert may be connected across the fuse to provide an audible indication of crowbar action. (This schema may not act on short, infrequent power line transients).