Battery Calculations

[Anical]

I am working on Line Maze solving robotic car. I am wondering how to select the battery. I talked to my lecturer he said for that I need to calculate how much is the overall power, voltage and current consumption. I did that yet i am not able to understand how to decide which battery i should be able to use. Can anyone guide me on how to choose the battery or the calculations assisting it?

 

[srizbf]

what is the power , voltage and current values you have calculated?

 

[d123]

Hi!

If you know the voltage, and the current draw of your robotic car, you need to consider the constant current draw, and then see which batteries actually have a good mA/h rating to match.

Example (from memory, excuse any errors, but roughly correct): I made a naff LED torch that can draw from 20mA to about 200mA or so on some settings.
My preference, due to size, was a standard rectangular 9V battery but it would have lasted 30 minutes at most, 12V (3 x 4.5V) battery instead should last 30 hours, so I opted for those - bulky, but longer lasting. 1.5V batteries AA or AAA have a better mA/h value than 9V batteries, which I imagine is why they are in so many battery operated devices. A tiny camera battery would last a few seconds...

It's good to browse online shops which provide datasheets for the batteries, or manufacturers, or check battery comparison webs, to get a better idea. In my experience it was not always easy to find what should be one of the first things a person would want to know about any battery.
Sorry I can't remember the formula for calculating A/h or mA/h. If I can find it I'll add it later.

 

[D.A.(Tony)Stewart]

Convert load to Watt-hours and decide on t in fraction of an hour, H and then size the battery based on cost and Watt-hours capacity using

power avail = Vavg*Ah

duration ~ Vavg*Ah / average load power [h]
~ Ah rating for similar duration divided by load current.

keep in mind that Ah drops in capacity from 20C to C to C/20 as ratings are often based on 20h loads