The advent of rapid charging technology has revolutionised the electric car industry. Instead of waiting for hours to recharge, cars like the Nissan LEAF, Mitsubishi i-Miev, Volkswagen e-Golf and Tesla Model S, can be charged from empty to full in well under an hour, making long-distance trips in an electric car possible for the first time in history.
Regardless of the car and the type of charger, most automakers and news outlets — including this one — tend to quote a headline 30 minute ’empty to 80 percent full’ rapid charge time when talking about any quick charging capabilities. That’s partly because most plug-in cars on the market today — with the obvious exception of the Tesla Model S — charge at between 30 and 50 kilowatts from a DC quick charger and have a useable battery capacity of around 20 kilowatts, give or take twenty percent.
But while theory is great, the reality of everyday rapid charging isn’t as clear-cut as the quoted figures might at first seem. External weather conditions, the age of the battery pack and even the individual charging stations themselves can affect how quickly a car charges.
And since questions about rapid charging times are fairly common from our readers, we’ve decided to give you a few quick pointers to help you understand why the reality of rapid charging isn’t as simple as the headlines suggest, which we feel ties in nicely to a more general article we penned in November on the subject. (If you’re new to the subject of Rapid Charging, we recommend you go back and read that article first to get a general background before reading this article.)
If you’re already familiar with the basics, read on, and we’ll detail what can slow down your charging times.
This is the biggest factor for any rapid charging experience. If your car’s battery pack is under or over temperature, it will take longer to charge it than if it were at a normal, temperate (read room-temperature) level.
In fact, as Nissan details in its own owners’ manual for the LEAF electric car, the difference between charging at sub-zero temperatures and charging on a comfortable summers’ day can be as much as 60 minutes.
Taking the LEAF as an example, Nissan says less than three bars illuminated on the LEAF’s battery temperature gauge can result in a charge time of more than 90 minutes, reducing to approximately 30 minutes when 6-7 of the temperature bars are illuminated. If the LEAF’s battery pack gets any warmer, the time starts to lengthen again, taking more than 60 minutes if more than 10 segments are illuminated on the LEAF’s temperature gauge.
While cars with active thermal management are less prone to suffering massive changes in rapid charging times due to weather, there’s still a difference, since the car still has to ensure that its battery pack doesn’t get too hot or too cold.
Just like internal battery temperatures can affect charging times, so too can outside temperatures, since most rapid charging stations are located outside.
As a consequence, you may find rapid charging times reduced when a rapid charging station starts to overheat, either through extreme outside temperatures, or constant use.
Since most rapid charging stations are more than capable of handling a wide range of temperatures however, this shouldn’t be a problem unless you live somewhere where temperatures regularly exceed 30 or 40 degrees Celsius.
Charging from ‘reserve’ charge levels
On pretty much every electric car we can think of, the last ten or twenty percent of the car’s battery pack is essentially a ‘reserve’ charge level. While the car still operates normally at the top-end of this, the car will enter into a reduced power mode if you drain the battery too far.
In order to prevent damage to the battery pack, you’ll find that charging from really low state of charge levels will add as much as ten minutes to your rapid charging time. And while we often detail rapid charging times from ’empty to 80 percent full,’ most automakers refer to the low-battery warning as being the marker of ’empty’ rather than a complete draining of the battery pack.
As a consequence, being less than the low battery warning marker for your car will result in your car taking longer than the quoted 30 minutes to charge — and we should also note that trying to charge your car beyond 80 percent full will equally extend your charging time dramatically.
Charger power levels
While they may all look similar, not all charging stations are created equal. While some DC rapid charging stations may have the on-board capabilities to manage power levels in excess of the power levels your car can handle, others will top out at a lower-then-expected power level.
This could be due to the charging station using lower-cost components to offer a lower-rapid charging rate, or it could be caused by the physical limitations of the wiring and power supply at the rapid charging location.
It’s also worth noting that sharing a rapid charging station with another car — be it a Tesla Supercharger or a triple or dual-head rapid charging station — could restrict the power to each car, resulting in both cars being allowed to charge but at a reduced rate.
Tip: if you’re at a Tesla Supercharger, you’ll find the actual stalls will be split between one or more chargers located nearby. By looking at the number on the stall, you should be able to associate the stall with its appropriate charger by looking for a number and letter on the stall itself. If there’s someone else there already, charging at stall 1b, for example, try to pick an empty stall with a different number prefix, since any stalls with the same number (1a, or 1c, for example) will be powered by the same charger.
The final big influencer of rapid charge times will be the actual health of the car’s battery pack. That’s because the car’s on-board battery management system is the one in control of the rapid charging process — not the charging station — and it won’t allow a high rate of charge if the car’s battery pack isn’t at peak health.
As batteries age and the pack as a whole becomes more unbalanced (a term which refers to individual cell voltages within the pack deviating from the modal cell voltage within the pack) the pack’s on-board battery management system has to work harder to try and keep the battery pack healthy.
This results in a slower charging time overall — and a much lower rapid charging current that can safely be applied to the battery pack.
With rapid charging becoming more widespread and demand for rapid charging much higher due to increased electric cars on the road, we advise anyone thinking about making a trip which includes rapid charging to take the following precautions to ensure that you’re not caught out when rapid charging.
- Plan at least twenty extra minutes for your charging. As well as ensure you can get the level of charge you need, planning extra time into your charging cycle means that you’ll be less likely to get stressed if there’s someone in the charging queue ahead of you.
- Try to arrive with more than the minimum ‘charge now’ warning for your car. It’ll speed up your charging experience, and put an end to that horrid range anxiety that comes with driving near the end of the pack.
- Be aware of the weather! If it’s really hot or really cold, be prepared for the extra time it takes to charge.
If you’ve got any tips for new rapid charger users — be they CHAdeMO, DC CCS, or Supercharger — leave them in the Comments below.
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