Maximizing DIY Battery Pack Capacity: Understanding Amp-hours vs. Watt-hours

[CasVS]

Hi,

I am a university student in the Netherlands and I just got the assignment of building a robot on a budget. Because of this budget I would like to make the battery pack that powers the 2 servo motors and 2 electric motors myself.

I did some research and found out it would be best to connect multiple AA Alkaline (1.5 V 2700 mAh) batteries. I know my basic physics as the current will stay the same and voltage adds up, though what about the capacity? I understand how this battery works but now my question was if I connect for example two batteries do I get a battery pack that can deliver 3.0 V with 5400 mAh, or just the 3.0 V with again a capacity of 2700 mAh.

Thanks in advance!

 

[Bystander]

two batteries do I get a battery pack that can deliver 3.0 V with 5400 mAh, or just the 3.0 V with again a capacity of 2700 mAh.

Think about it ... a little bit more and you will have answered your own question.

 

[CasVS]

Think about it ... a little bit more and you will have answered your own question.

You sound like my physics tutors haha! I calculated the amount of Watts and think it is silly to assume that both the capacity and the voltage gets doubled. So from this I will assume that the battery pack would have a 8.1 W output with the 3.0 V and 2700 mAh!

Thanks

 

[Bystander]

Ta-da.

 

[jim hardy]

See ? You new all along !

 

[CraigHB]

That's a pretty common source of confusion. Charge capacity in terms of Amp-hours does not change with the number of series cells, but energy capacity in terms of Watt-hours multiplies with the number of series cells. For a load that consumes a constant amount of power run time will double, for an ohmic load where power consumption goes up with voltage run time will not increase.