# Help determining the size of my battery pack?

1086 Views 2 Replies 3 Participants Last post by  dtbaker
I did some calculations and wonder if I made any obvious mistakes.

The efficiency of 250Wh/mile multiplied by the range of 80 miles gives us a total energy of 250x80=25,000W or 25kWh. Since we already determined our voltage was 120V this means our Ah rating will be the total energy divided by the voltage. In this case 25,000W / 120V = 208Ah.

For Lithium batteries multiplying our Amp-hour rate 120V by 1.32(275 Ah).

how does this translate into what batteries I need?

thanks

Mason
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It's a compromise between what area you have to put them, how fat your wallet was and how quick you wish to accelerate. The max amps the motor requires matched to a C rating of the batteries is the one for battery cycle life. Even though TS and CALB quote 3C discharge capacity don’t confuse that with the 3,000 to 5,000 cycle rating, that's measured at 0.3C. No one has published the numbers for 3C cycle life but don’t expect to see triple figures. If you don't have the area for big capacity but need big amps then you are going to need Headway or A123 cells that are much dearer for equivalent capacity. So, a combination of peak amp draw and capacity will give the ideal pack, area to fit it and \$\$ to pay for it will start the compromise section.

T1 Terry
if you are assuming 250whr per mile, then that means a pretty small and aero car....

depending on speed, a 200ah pack at 120v might be enough. In the ballpark, but cutting it pretty close I'd guess if you are talking highway speeds where aero adds up fast, or cold weather running a heater, or dark with headlights.

to have some cushion you might consider a 144v pack of 200ah li.
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