How Rating is Done? | How Battery is selected for a Project?

How Rating is Done? | How Battery is selected for a Project? 

1. Rating Calculation

First of all, we will find the rating of all the components we are using in this part for our case the maximum power consumption for the L298N motor driver _[4] is 20W, and the input voltage range is 3.2V to 40V DC. Another device is 4 DC motors which will be power up from the driver itself so don’t need to mention the rating of these motors in the power management phase. A servo motor is consuming a maximum of 4.8W of power and its voltage range is 4.8-6V.

While seeing to above voltage ranges, there are two ranges that are the 3-40V range and 4.8 – 6V range if we are power both from the same source then we will need a power supply of voltage rating that is the intersection of both ranges that 4.8-6V, for that case, we will definitely select 5V because it is easily available. But in this case, we will power the servo motor from the 5V output pin of the L298N motor driver to avoid less voltage range and to power for a longer time span.

Also, the maximum power rating of the controlling part is

20W+4.8W=24.8W

But in case we are powering the servo motor from the L298N driver then no need to include it in power management all the power will be adjusted by the hero i.e. the L298N driver, thus

Total power consumption = 20W

As

Power=Voltage x Current

Then

 

For one hour of surveillance, the battery rating should be 

Capacity Rating =Current x 1 hour = 2 x 1=2Ah or

Capacity Rating = 2000mAh

This means if we are getting 2A of current constantly then will lead the battery to be fully discharged after one hour of time. But this should not be the case in reality battery should not be completely discharged for its long period of life. Thus, if we consider that battery should only be discharged for 50% of the total charge then we need to double the rating let take it to 4000mAh, or else we need to use two such batteries in an hour.

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2. Battery Selection

For battery selection, we are using 6 cells (AA 555 china cells) in series. Each AA 555 china cell has 1.672V and a capacity rating of 2600mAh, making it in series of 6 cells the voltages of every cell adds up to approximately 10V, that’s why we right the 10V in the above current formula. For 50 % discharge of the battery for one hour of a lifetime, we need to make two series of 6 cells and make both in parallel to add up its capacity rating to 5200mAh and 10V, as the voltages add up in series and capacity adds up in parallel see the above figure.  Roughly we have used only 6 cells for the project controlling part, as the using of pair of 6 cells (12 cells) will be weighty and may affect the system performance because of the high load. 6 cells are enough for this project and we will use it as it has a high capacity of 2600mAh.