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Active Contributor

Join Date: Jul 2009
Posts: 11

### Battery Capacity and Battery Cells - Serial and Parallel

07/26/2009 7:43 AM

I read in a textbook that Battery Capacity is the amount of current Drawn over time (Ampere Hour rating). Now suppose we take a cell of 4V . To increase its Battery Capacity or current drawn over a period of time we can increase its size so that more matieral is there(more electrons avalible) . My question is I hope I am right about this concept of how to increase Battery Capacity Now the main question is If we can increase battery capacity by increasing size of mateiral used Then Why Cells are connected in series (Fron +ve terminal of one cell to -ve terminal of other) to increase the Voltage say two cells of 4V each are connected to get 8V. So what is the purpose of Using 8V (cell in series) Instead of single 4v cell when our basic requirement of increasing Battery capacity can be met by using 4 voltage cell but large in size...

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Guru

Join Date: Jan 2008
Location: NY
Posts: 1119
#1

### Re: Battery Capacity and Battery Cells - Serial and Parallel

07/26/2009 11:33 AM

Same reason AC power is transmitted at higher voltages. Lower current (higher voltage) usually provides lower I-squared-R losses per unit of power used.

You can design a system (e.g. motor and controller) to run from a 4Vdc 1200A (4.8 kW or ~6.4 hp) source OR you can design a system to run from a 120Vdc 40A source (4.8 kW or ~6.4 hp).

Considering wire size and controlling electronics, which system do you think would be easier/cheaper to build and more efficient to operate?

Anonymous Poster
#2

### Re: Battery Capacity and Battery Cells - Serial and Parallel

07/27/2009 3:50 AM
Power-User

Join Date: Aug 2008
Location: West Virginia
Posts: 185
#3

### Re: Battery Capacity and Battery Cells - Serial and Parallel

07/27/2009 9:25 AM

Except for the wire size, its also a matter of preference. If you use an inverter, its always easier to build them to run at higher voltages. This becomes more of a factor at higher capacities. The other issue is granularity. How expensive is it to replace one cell if it fails? Eg... A single cell that's much bigger because you went for low voltage high current instead of high voltage low current for the same Watt hours of capacity.

If you're using the juice directly, motor size shrinks as the voltage increases also.

Associate

Join Date: Sep 2006
Posts: 54
#4

### Re: Battery Capacity and Battery Cells - Serial and Parallel

07/27/2009 10:46 AM

Basically connecting cells in series increase the voltage of the cell. connecting them in parallel increases amperage (amp hours ) of the cells. So if you have let say 9 3.2V cells (A123 LIFe cells) w/ 1 Amp Hr capacity and you connect 3 of them in series you get a 9.6V battery Battery w/ 1 AmpHr Capacity, now if you do this with the other cells and get 3 9.6V batteries, and connect then in parallel, you would get a 9.6V 3AmpHr battery ( I wish this allowed me to draw diagrams to show it better ). but I think you get the idea HLG

Guru

Join Date: Jan 2009
Posts: 997
#5

### Re: Battery Capacity and Battery Cells - Serial and Parallel

07/27/2009 12:06 PM

Livagain1,

Jon

Associate

Join Date: Sep 2006
Posts: 54
#7

### Re: Battery Capacity and Battery Cells - Serial and Parallel

07/27/2009 8:43 PM

YUP

Guru

Join Date: Jan 2009
Posts: 997
#10

### Re: Battery Capacity and Battery Cells - Serial and Parallel

07/28/2009 12:26 AM

Livagain1,

And this:

Jon

Power-User

Join Date: Mar 2006
Location: Valdosta, GA
Posts: 361
#6

### Re: Battery Capacity and Battery Cells - Serial and Parallel

07/27/2009 1:48 PM

Connecting cells in series is not used to increase capacity. The purpose of connecting cells in series is to arrive at the voltage needed to power a particular circuit. You can connect batteries in parallel to increase capacity and leave the voltage alone. This has the same effect as increasing the size of the cell by 2 times if 1 additional battery is used and so on.

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Active Contributor

Join Date: Jul 2009
Posts: 11
#8

### Re: Battery Capacity and Battery Cells - Serial and Parallel

07/27/2009 11:26 PM

Thank you so much for your replies ...no space left for any doubt!! thanks

Guru

Join Date: Jan 2009
Posts: 997
#9

### Re: Battery Capacity and Battery Cells - Serial and Parallel

07/27/2009 11:58 PM

Key,

Indeed. nicely stated.

Jon

Anonymous Poster
#11

### Re: Battery Capacity and Battery Cells - Serial and Parallel

08/10/2009 12:01 AM

Thanks above answers.If you need cheap laptop battery , http://laptopsbattery.us and http://www.lenovo-batteries.com is good chose .

Member

Join Date: Jan 2010
Posts: 5
#12

### Re: Battery Capacity and Battery Cells - Serial and Parallel

01/03/2010 9:08 PM

Battery connecting in serial will get more voltage but same capacity.

Battery connecting in parallel will get more capacity but same voltage.

So, answer to you question is that, you have to connect the battery in parallel to get more capacity.

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