February 2012 Archives

News Flash: Electric Cars Like to Be Plugged In

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Today's big news flash is that if you leave a Tesla Roadster sitting for a long time without being plugged in, it can ruin the battery.

In other news, if you never change the oil in a Ferrari and drive it until the engine seizes, you're out of luck on warranty and insurance coverage.

port_renfrew_charging.jpg
To put this issue in context...

In January of 2010, we were away from home and left our Roadster sitting for 26 days. Before we left, I put the Roadster in Storage Mode and plugged it in. Storage mode tells the car to charge only when needed to keep the battery at the ideal, safe charge level to best preserve battery longevity, something like 20% of capacity.

While we were gone, the temperatures dropped down into the 20's. (We were glad to be in Hawaii.) I'm sure our garage stayed above freezing due to waste heat from the furnace keeping the house at minimum temp.

The Roadster battery pack was at 68% when we left and at 55% when we returned. That's a nice even 0.5% loss per day. The logs showed that the car never charged. This was confirmed by our wall meter not moving (less than 0.1 kWh). Since it never charged, I could have left it unplugged and it would have made no difference.

This means I could drive the Roadster 100 miles to the airport, running the charge down to 50%, and leave it sitting for nearly 80 days and still be above 10%. Obviously, if I wanted to leave the car parked at the airport for over two months, I'd park it in a pay lot that would let me plug it into power, even a normal 120V outlet, to keep it charged while I was away. But even if they messed up, the car would be fine in this case (assuming moderate weather).

In a hot environment, where the car might need to actively cool the battery pack, being plugged in is more of a concern.

In normal situations, this is a total non-issue. Even in extreme weather, or if the car is driven to a low state of charge, or left in storage for months, the owner just needs to follow the directions and plug it in. Pro tip: before leaving, make sure the car can charge to verify the cord, the outlet and the car are all happy with the situation.

It's not difficult to plug in an electric car. The photo above shows us charging from a 120V outlet at a yurt 40 miles from the nearest gas station. If we can find out an outlet there, you'll be able to find an outlet if you ever need to leave your electric parked for several weeks.

Gas cars have similar vulnerabilities, they are just more familiar. Never change your oil: kill your engine. Fill your radiator with water: break your engine block when it freezes. Drive over a rock, puncture your oil pan: kill your engine. Pay someone to change your oil and not tighten the plug: kill your engine. Have a neighborhood prankster dump something in your gas tank: kill your engine. Never service your transmission: buy a new transmission.

Electric cars have a lot less that can go wrong, it's just not the same things that will kill a gas car.

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