For some time now, owners of the Tesla S -- particularly in colder climates -- have been complaining about a vampire load on the car which can suck as much as 20 percent from the batteries overnight. This is a serious problem if you’re traveling and have to spend the night in a hotel that doesn’t have charging stations (those that do are the extreme exception). Tesla has been working on the problem but folks continue to complain so should you be concerned?
The core issue that this all stems from is that charging is still not as easy or prevalent as filling stations are, and while the electricity is a lot cheaper that cost doesn’t yet overcome the extra price paid for an electric nor the inconvenience. Batteries, particularly Lithium Ion batteries, need to be managed so they have a full useful life, and given that the battery pack on a Tesla is nearly a third of the car’s cost, making sure that battery pack is well taken care of requires a number of practices.
One is that you neither fully charge nor fully discharge the battery cutting the actual range of the car substantially from its advertised range. Two is that, like gas, the harder (faster/more aggressively) you drive the less range you have. And third, Lithium Ion batteries don’t work well when too hot or too cold.
Managing their temperature, particularly heating them, can take substantial power and that is likely why the Vampire Power reports appear to be coming from colder states. And if the battery overheats, driving range drops dramatically (which is one of the reasons you won’t see a Tesla S, or any electric, on a race track in a race any time soon). While the batteries apparently aren’t heated at night they are heated when you first start the car and the car will report a reduction in range (thus the loss in available range).
Why I think this is being reported more on Teslas then in Nissan Leaf cars or Chevy Volts is that the Tesla has a much larger battery then either and doesn’t have a gas engine to supplement it like the Volt does.
No Easy Fix
The problem goes to the core of the power storage technology. Lithium Ion batteries, while substantially lighter and more effective than lead acid batteries, still have to be managed, and unless you can either improve the batteries substantially or replace them with something better, much like Lithium Ion replaced lead acid for vehicle propulsion, you’re going to have to use power to maintain the batteries and take a particularly large hit if the car is parked outside off power on a cold winter’s night.
While there are new Lithium Ion formulations coming that improve capacity and new battery technologies like Lithium Air that are more advanced, the greatest hope comes from Supercapacitors which could eliminate the battery problem entirely. Supercapacitors can charge close to load limits, which could take the time needed to charge an electric car like the Tesla S down to minutes if not seconds (it will likely depend on just how much current the DMV feels is safe to handle). They can be fully charged and discharged without additional wear, and can be built into the car. For instance, they can be broken down into small components and put underneath the body and because they don’t wear out they don’t require a battery pack which should make the car far easier to balance and far lighter.
Supercapacitors, unlike Lithium Ion, don’t contain a fuel source so they don’t burn themselves. They can discharge far faster than Lithium Ion though, which creates a greater risk of electrocution or extreme heat as a short could dump their entire capacity to ground. However you could put in a safety solution that isolated the Supercapacitors from each other and/or intentionally dumped them to ground in a controlled short to eliminate most of the risk.
Overall the Vampire loads being reported by Tesla drivers are part of the growing pains for what is still a relatively new technology when compared to internal combustion engines. We are simply more used to the problems with gas and don’t take the fact that the vapors are explosive, or liquid caustic and cancer causing as serious. We’ve long since accepted the problems with gas and while electric cars are potentially far safer, problems with them are new and thus they stand out more simply because the car itself is different. For instance, folks focus on the number of Tesla fires rather than the lack of Tesla deaths, the more important statistic. You can replace the car.
Perhaps to be treated fairly that last part will need to change and, I expect, when we finally perceive electric cars like we do gas cars we’ll be able to do a more balanced comparison. When that happens, I expect, gas cars will be done. Until then anticipate more unique problems with electrics as we learn more aspects of what makes them different.
President and Principal Analyst, Enderle Group
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