الاثنين، 9 نوفمبر، 2015

How to Calculate the charging Time and Charging current for battery Charging?

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Easy Battery Charging Time and battery Charging Current Formula for Batteries. ( with Example of 120Ah Battery).





Battery Charging Current and Battery Charging Time formula
Here is the formula of Charging Time of a Lead acid battery.
Charging Time of battery = Battery Ah / Charging Current
 T = Ah / A
 

Example,
Suppose for 120 Ah battery, 
First of all, we will calculate charging current for 120 Ah battery. As we know that charging current should be 10% of the Ah rating of battery.
so charging current for120Ah Battery = 120 x (10/100) = 12 Amperes.
but due to losses, we can take 12-14Amperes for charging purpose.
suppose we took 13 Amp for charging purpose, 
then charging time for 120Ah battery = 120 / 13 = 9.23 Hrs.
but this was an ideal case…
practically, this is noted that  40% of losses ( in case of battery charging)
then 120 x (40 / 100) = 48 …..(120Ah x 40% of losses)
therefore,  120 + 48 = 168 Ah ( 120 Ah + Losses)
Now Charging Time of battery = Ah/Charging Current
 
168 / 13 = 12.92 or 13 Hrs ( in real case)
Therefore, an 120Ah battery would take 13 Hrs for completely charging ( with 13A charging current).
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Analog-to-Digital Conversion

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Analog-to-digital conversion is the process of sampling and then converting an
analog signal, usually a voltage, to a multi-bit digital number that is proportional to
the amplitude of the analog signal. Analog-to-digital conversion is used in many
applications ranging from encoding of voice-generated signals in
telecommunication systems, to data acquisition and control systems.
 Conversion is initiated by activating the ‘Start Conversion’ input of the converter. At completion of the conversion process the ‘Conversion Complete’ output of the converter will change logic state. This signal is used to notify the controlling device that data conversion is complete, and valid data can now be read.




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الاثنين، 2 نوفمبر، 2015

What is the difference between fault current and overload current?

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The major difference between the two is the magnitude and duration of the fault current. In a short circuit, an extremely large current is experienced by the circuit in a short duration. But in an overload, the normal load current is greater than the circuits rating. for example a circuit rated at two hundred amps, is loaded to 250A.
Under a short circuit condition, the circuit breaker and circuit experiences a massive current leading to a large induced magnetic force in the device. This will trip the circuit breaker in it's magnetic setting, clearing the fault. Under an overload condition, the cable and circuit breaker will experience excessive heating due to the overload, this will trip the circuit breaker in it's thermal trip.
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Why we use a capacitor in an electric fan?

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. Capacitor is used for both starting the electric fan and improving power factor
. The voltage taken by the fan during running has lagging power factor and in order to run the fan we need leading power factor. The capacitor increases the power factor. So we use capacitor in fan to increase its power factor
. to give a quick start-up for any instrument, capacitor is used in electronics, by using capacitor in the start-up there is a charge accumulation in between the plates of capacitor, which is discharged again and gives a quick start to the instrument otherwise we have to use a very high voltage to the instrument.
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What Are Real-Time Embedded Systems?

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 Real-time systems are computer systems that monitor, respond to, or control an external environment. This environment is connected to the computer system through sensors, actuators, and other input-output interfaces. It may consist of physical or biological objects of any form and structure. Often humans are part of the connected external world, but a wide range of other natural and artificial objects, as well as animals, are also possible.
The computer system must meet various timing and other constraints that are imposed on it by the real-time behaviour of the external world to which it is interfaced. Hence comes the name real time. Another name for many of these systems is reactive systems, because their primary purpose is to respond to or react to signals from their environment. A real-time computer system may be a component of a larger system in which it is embedded; reasonably, such a computer component is called an embedded system.
Applications and examples of real-time systems are ubiquitous and proliferating, appearing as part of our commercial, government, military, medical, educational, and cultural infrastructures. Included are
    • vehicle systems for automobiles, subways, aircraft, railways, and ships
    • traffic control for highways, airspace, railway tracks, and shipping lanes
    • process control for power plants, chemical plants, and consumer products such as soft drinks and beer
    • medical systems for radiation therapy, patient monitoring, and de fibrillation
    • military uses such as firing weapons, tracking, and command and control
    • manufacturing systems with robots
    • telephone, radio, and satellite communications
    • computer games
    • multimedia systems that provide text, graphic, audio, and video interfaces
    • household systems for monitoring and controlling appliances
    • building managers that control such entities as heat, lights, doors, and elevators.
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Current Transformer

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Current Transformers (CT’s) are instrument transformers that are used to
supply a reduced value of current from bus bar or cables to meters, protective relays,
sensors, and other instruments. CT’s provide isolation from the high current
primary, permit grounding of the secondary for safety, and step-down the magnitude
of the measured current to a value that can be safely handled by the instruments.
CT ratios are expressed as a ratio of the rated primary current to the rated
secondary current. For example, a 300:5 CT will produce 5 amps of secondary
current when 300 amps flow through the primary. As the primary current changes
the secondary current will vary accordingly. With 150 amps through the 300 amp
rated primary, the secondary current will be 2.5 amps (150: 300 = 2.5: 5).
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الاثنين، 19 أكتوبر، 2015

Different starting methods 4

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Softstarter

A softstarter has different characteristics to the other starting methods. It has thyristors in the main circuit, and the motor voltage is regulated with a printed circuit board. The softstarter makes use of the fact that when the motor voltage is low during start, the starting current and starting torque is also low.
During the first part of the start the voltage to the motor is so low that it is only able to adjust the play between the gear wheels or stretching driving belts or chains etc. In other words, eliminating unnecessary jerks during the start. Gradually, the voltage and the torque increase so that the machinery starts to accelerate.

One of the benefits with this starting method is the possibility to adjust the torque to the exact need, whether the application is loaded or not. In principle the full starting torque is available, but with the big difference that the starting procedure is much more forgiving to the driven machinery, with lower maintenance costs as a result.

Another feature of the softstarter is the softstop function, which is very useful when stopping pumps where the problem is water hammering in the pipe system at direct stop as for star-delta starter and direct-on-line starter. The softstop function can also be used when stopping conveyor belts to prevent material from damage when the belts stop too quickly.
























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Different starting methods 3

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Frequency converter

The frequency converter is sometimes also called VSD (Variable Speed Drive), VFD (Variable Frequency Drive) or simply Drives, which is probably the most common name. The drive consists primarily of two parts, one which converts AC (50 or 60 Hz) to DC and the second part which converts the DC back to AC, but now with a variable frequency of 0-250 Hz.

As the speed of the motor depends on the frequency this makes it possible to control the speed of the motor by changing the output frequency from the drive and this is a big advantage if there is a need for speed regulation during a continuous run.
In many applications a drive is still only used for starting and stopping the motor, despite the fact that there is no need for speed regulation during a normal run. Of course this will create a need for much more expensive starting equipment than necessary.
By controlling the frequency, the rated motor torque is available at a low speed and the starting current is low, between 0.5 and 1.0 times the rated motor current, maximum 1.5 x In.
Another available feature is softstop, which is very useful, for example when stopping pumps where the problem is water hammering in the pipe systems at direct stop. The softstop function is also useful when stopping conveyor belts from transporting fragile material that can be damaged when the belts stop too quickly. It is very common to install a filter together with the drive in order to reduce the levels of emission and harmonics generated.



























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Different starting methods 2

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Star-delta start

This is a starting method that reduces the starting current and starting torque. The device normally consists of three contactors, an overload relay and a timer for setting the time in the star-position (starting position). The motor must be delta connected during a normal run, in order to be able to use this starting method.

The received starting current is about 30 % of  the starting current during direct on line start and the starting torque is reduced to about 25 % of  the torque available at a D.O.L start. This starting method only works when the application is light loaded during the start. If the motor is too heavily loaded, there will not be enough torque to accelerate the motor up to speed before switching over to the delta position.
When starting up pumps and fans for example, the load torque is low at the beginning of the start and increases with the square of the speed. When reaching approx. 80-85 % of the motor rated speed the load torque is equal to the motor torque and the acceleration ceases. To reach the rated speed, a switch over to delta position is necessary, and this will very often result in high transmission and current peaks. In some cases the current peak can reach a value that is even bigger than for a D.O.L start. Applications with a load torque higher than 50 % of the motor rated torque will not be able to start using the start-delta starter.


























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