# Electric Vehicle Battery specification (very basic)

I have an concept electric car, i calculated it will need 15,000 Wh stored in batterys to operate over its required range (100 miles) on a certain drive cycle.

I am attempting to work out how many batteries i need

The motor it is powering has a voltage rating of 156 vDC specs here: http://www.azuredynamics.com/products/force-drive/documents/AC24LS_DMOC445ProductSheet.pdf

so does this mean that in Ah this is equivilent to 128 Ah? (P.t=IV.t = 2000 = I.156)

if i were using say, 3.3v batteries would this mean i need 48 (48x3.3=158)?

Also what are the effects of battery efficiency? If i have a 90% efficient battery does that mean my power is limited by 10% or is this just for the battery life?

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A typical electric vehicle can get 3 miles per kilowatt-hour, some can get 4 miles per kW-hr. You are designing for 5 miles per kW-hr, which is OK for a small light vehicle. For 156 volts and a 20 kW-hr battery, this is equivalent to 128 amp-hours (at full voltage). If each battery in the series is rated at 100 amp-hrs, then the entire battery pack is rated at 100 amp-hrs.

Bob S

I am not an electrical engineer by any stretch, but I can give you a little insight. First, batteries wired in series add voltages but not current; those wired in parallel add currents but not voltage. Multiple batteries can be wired using a combination of both methods to achieve the necessary combination of voltage/current.

The old EV-1 electric car had similar requirements and range that you are quoting, but used a 312 volt system instead of 156--exactly double. Therefore their motor current would be half of what you would be using, but the overall energy requirement would be the same, as the EV-1 also had a roughly 100 mile range. The EV-1 battey pack is quoted as follows:

"The Panasonic battery pack consisted of twenty-six 12 volt, 60 amp-hour lead-acid batteries holding 67.4 megajoules (18.7 kWh) of energy. The NiMH packs contained twenty-six 13.2 volt, 77 Ah nickel-metal hydride batteries which held 95.1 megajoules (26.4 kWh) of energy." (from Wikipedia).

Doing the math, I would assume that all of their batteries were wired in series to get the required voltage; in your case, you could do 13 (instead of 26), 12 volt/120-140 amp hour batteries in series to get the same overall power at 156 volts instead of 312. (Or, some combination of lower voltage batteries with similar amp hour ratings to get up to the required voltage.)

I hope that helped a little...

A typical electric vehicle can get 3 miles per kilowatt-hour, some can get 4 miles per kW-hr. You are designing for 5 miles per kW-hr, which is OK for a small light vehicle. For 156 volts and a 20 kW-hr battery, this is equivalent to 128 amp-hours (at full voltage). If each battery in the series is rated at 100 amp-hrs, then the entire battery pack is rated at 100 amp-hrs.

Bob S

Thanks Bob, though i recalculated and got 15Kwh for 100 miles now! I really cant see where i am going wrong if people think this is too low though. Drag is ok, rr is ok, force to accelerate is ok (though the drive cycle means accelerations are quite low). I have implemented motor eff but not any other at the moment.

If anyone looks up "Aptera 2e" you will see that it specifys 13,00 kWh for a range of 100 miles!

I hope that helped a little...