Reply #26: it takes hours to charge an electric car, even at full power [View All]

[krispos42]

A dedicated 230-volt single-phase circuit from your house can only output about 10 horsepower or 7 kilowatts. Assuming that an electric car can go 250 miles at 55 miles per hours with pretty slick aerodynamics, a level road surface, and no parasitic electrical use needs a net output at the wheels of 9 horsepower. So, taking in to account things like A/C and blowers, radios, lights and lighting, cruise control, and car monitoring software, plus inefficiencies and friction losses, the draw on the battery might easily be 15 or 20 horsepower.

So assuming 15 horsepower for 5 hours is 75 horsepower contained in the batteries. That's a 7.5 hour recharge time assuming the battery can absord energy at a sustained rate.

And it gets even longer if we start making electric SUVs and minivans and such, because they have both larger surface areas and lesser coefficients of drag and would need more charging power to replenish their larger battery packs.

It's a lot of juice to shove back into a battery. Using a home charger at night during off-peak usage makes a lot of sense, but you would have to reorganize your life.

It is this kind of problem that kept interest in the electric car down, especially when gasoline was cheap. I would note that modern lithium-ion batteries have had their development greatly advanced by the demands of cell phones, iPods, Palm Pilots, and the like. Ten years ago the batteries would have been nickel-metal-hydride, which carry much less charge per unit weight than lithium-ion batteries. Even the vauted Prius is still using, I believe a NiMH battery pack. Twenty years ago we'd be stuck with nickel-cadium battery packs.