What is battery ?
Batteries are a collection of one or more cells whose chemical reactions create a flow of electrons in a circuit. All batteries are made up of three basic components: an anode (the ‘-‘ side), a cathode (the ‘+’ side), and some kind of electrolyte (a substance that chemically reacts with the anode and cathode). for more information about battery visit Sparkfun official site
Understand battery terms
You can take any batteries it has some common parameters like voltage, current, temperature ratings, etc. let us look at the terms we see in batteries
Voltage
The battery voltage is mentioned on the battery body, normally it rated in V (volts) something like this >> 3.7V, 9V, 12V. It indicates that the battery can able to provide the voltage it stated on the label. For example, the 12v battery can able to supply 12V until it gets a discharge.
Current
Current in the battery is given in Ah or mAh an ampere-hour (abbreviated Ah, or sometimes amp hour). let see this term by an example.
you have a battery and is rated as 12V and 1.3AH. here we can view two technical terms voltage and current. As we understand that the term voltage referred to as max voltage that the battery can able to supply until it gets a discharge. Now lets come to the point another term called current in Ah or mAh it can be called as amp-hour or milliamp-hour. we know that the current is the flow of electrons and hour is referred to the time. So your 1.3Ah battery can able to drive 1.3A load for one hour.
How to calculate charging time of the battery
Battery Charging
Charging a battery is a process of filling the electronics in side the battery and creating the chemical reaction that holds the potential of electronics and discharge it whenever needed to the circuit when we connect closed circuit.
we can charge the battery in several methods either by charging circuit just like a mobile phone charger or by using the dc power supply just like a battery to battery charging. or by other power sources like solar etc.
the main motive of charging the battery is to fill the electrons inside the battery in any way using DC power supply. okay, here we have a question what is the voltage and current rating for charging the battery?
as we already saw battery voltage is the voltage level where the battery charger should supply. no more than that or lesser than that voltage should supply to the battery. if the lesser voltage is applied then the battery will not get charged fully. if overvoltage is applied to it, battery plates may get damage and battery may lose its capacity and some unexpected things also may happen.
Battery charging current is the current rating battery should charge and charger should limit the current. how do we know battery charging current? simple, charging current should be 10% of the Ah rating of the battery.
Battery Charging Time and Battery Charging Current Formula for Batteries. (With Example of 120Ah Battery).
Below is a simple battery charging current and battery charging time formulas with a solved example of 120Ah lead acid battery
Here is the formula of charging time of a lead acid battery.
Charging time of battery = Battery Ah / Charging Current
T = Ah / A
Where,
T = Time hrs.
Ah = Ampere Hour rating of battery
A = Current in Amperes given by charger or charging circuit
Example:
Suppose for 120 Ah battery,
we calculate charging current for 120 Ah battery. As we know that charging current should be 10% of the Ah rating of battery.
Therefore,
Charging current for 120Ah Battery = 120 Ah x (10/100) = 12 Amperes.
But due to some losses, we may take 12-14 Amperes for batteries charging purpose instead of 12 Amp.
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, it has been noted that 40% of losses occurs 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
Putting the values;
168 / 13 = 12.92 or 13 Hrs ( in real case)
Therefore, an 120Ah battery would take 13 Hrs to fully charge in case of the required 13A charging current.
Normally in electronics practical and ideal will have great difference. it is because of the environment and the device properties with respect to age.
Battery Discharging time
We have seen the battery charging time and now we have a battery fully charged right ? lets talk about how long will be the battery can supply the power to the circuit ? to understand this concept we should know the concept of load current.
Load Current
What is Load ? An electrical load is an electrical component or portion of a circuit that consumes electric power. every components we use in electronics or electrical consumes power.
how do we know the Load current ?
Simple !! It is given in the device datasheet. say for example you can see any electrical appliances in the home it has a power rating in watt same as every motor, microcontroller, led, etc., has power ratings. and if you can’t understand let us make it too simple let us take LED and it normally rated 20mA so it is called the load current. The load current is the current needed to drive components. The component may be a Motor or Microcontroller or anything maybe. the current needed to drive the device is called load current.
Calculate Battery Discharge time
So we know what is Load current right? ok in system number of components going to be present and they are all going to consume power. so if you want to find the battery discharging time first calculate the entire circuit power consumption. get the datasheet of each component and note down the current rating of every component and finally add it you will get the load current.
another step to find the load current connect the ammeter in series to the circuit while it drives.
In the above picture, we have bulb replace your circuit positive and negative end of bulb connection to find the total current drawn by the circuit
Okay we know the system load current then lets do the math now
Lets take an example that your circuit contain microcontroller which consume 500mA and you have dc motor that also consume 500mA then totally you have 1A load current. Assume that you use 5Ah Battery. formula for battery discharging time is
Battery Discharging time (in hours) = Battery capacity in AH / Load current or(current drop of the circuit)
Let’s apply it in the formula
Battery discharging time = 5Ah / 1A
5 Hours
If you use 5AH battery and 1A load your battery will supply the rated voltage up to 5 Hours.
This is ideal result in practical it may get vary.
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