Cell & Battery

Cell

A cell is a very basic source of electric energy to drive small electrical load. A simple cell is of 1.5volt which we use in day to day life. These are usually one time usable, generally we use in torch or small toys. There are other cells also which comes in different voltage range like 1.2Volt and 3.7Volt. These are mostly rechargeable cell used in digital cameras, remote controlled toys like cars, planes and drones etc. We also have button cells mostly used in small watch or wearable, computer motherboard etc. Unit of voltage is ‘V’ or mentioned as ‘Volt’ also. When a small bulb is connected to the cell some current flows through the bulb hence it glows up. The current is denoted by symbol ‘I’. One connector of cell is Positive (+) and other connector is Negative (-). Correct polarity should be used in circuit, i.e. positive and negative connector should be connected correctly as per circuit diagram. Else circuit may burn or will not work.

Battery (Cells in Series)

If four cells of 1.5volt are connected in series, the total voltage is 4 X 1.5V = 6.0V.  Please note that in series connection positive terminal of one to the negative terminal of other and so on. The voltage of each cell gets added in this type of connection. If we connect positive terminal together or negative terminal together, both cell will oppose each other and net voltage will be “ZERO”. In series connection the voltage increases but the current delivery capacity remains same.

Battery (Cells in Parallel)

And if any number of 1.5V cells are connected in parallel, the voltage remains same i.e. 1.5V. Here the net voltage remain same, but the current delivery capacity adds up. In parallel connection also, please note that similar terminals are connected together. The net voltage is same as voltage of each cell. In parallel connection we should connect same type of cell in group, if we connect a 1.5V cell in parallel to 3.7V, then due to potential difference both cells, current from 3.7V will push to 1.5V cell trying to charge it. This will continue till voltage of both cells become equal. But in this case 1.5V cell will overcharge and may burst. Also its important not connect opposite polarity of two cells in parallel connection, else it will create a short circuit and may harm you.

mAh or Ah Rating

So, one specification of cell or battery is its voltage rating and the other is “Ah” or “mAh” rating. This specifies how long the battery will sustain if specific amount of current is drawn from it. It is the product of Current (mA or A) and Hours(H) For example if the mAh rating of any battery is say 2000mAh, means if we connect any load on this battery which draws 2000mA current, then this battery will sustain for 1Hr. If we draw lesser current it will lasts longer. So, if we draw 1000mA from same battery it will last for 2Hrs. So, we can calculate this using formula mAh rating = Current in mA X time in Hours. So time = mAh / mA. So time for this battery if we draw 1000mA, we can calculate it as 2000mAh / 1000mA = 2Hrs.

For bigger batteries used in cars or home inverters, rating is normally in “Ah”, so a 140Ah battery will last for 1hrs is we draw 140Amps. Similarly if we draw 1Amp, time = 140Ah / 1A = 140Hrs.

Other rating is the maximum current what we can draw from battery; some batteries provide high current (in Amperes) like Li-Po (Lithium Polymer) batteries used in drones or RC planes and helicopters. On the other hand small torch batteries are capable of delivering very low current in milliampere to small bulbs or LEDs (1Ampere = 1000 milliamperes).

For rechargeable batteries we use standard charging current of 10% of AH or mAh rating. So for 140Ah battery the charging current should be 10% of 140 i.e. 14Amps.

There are two more specifications of any battery. One is deep discharge voltage and full charge voltage. If a battery is rated as 3V deep discharge limit, then we should ensure that using this battery, it should not be discharged more than 3V, else may not charge again or may work improperly. 

The other specification of full charge voltage indicates that any battery should not be charged above this voltage else it may heat up, swell out and will go defective. So almost all good quality charges keep checking the battery voltage while charging and once this full charge voltage limit is reached, the charger stops charging to protect it from over charging.

So, that’s all about cell and battery, keep reading more for other components.

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