Why Are Some Tesla Superchargers Slow & Can You Fix It Yourself?


Why Are Some Tesla Superchargers Slow

Tesla’s supercharger network is fast, convenient, and pretty darn reliable. Every day hundreds of thousands of Tesla’s, use that network to recharge on long road trips, top-up during the workday, or snag a little extra juice for an after-work errand.

Thanks to a very informative forum post on the Tesla owners Club of Western Australia and data from owners across Europe, it seems that Teslas software update appears to be throttling some Tesla Model S and X cars as much as 20 % compared to pre-update charge speeds. Charging is still far faster with a supercharger, but it’s still frustrating some owners.

In the last few months, we’ve seen Tesla increase the power capabilities of its supercharger network. Rolling out and switching on its first V3 supercharger stations can charge the newest Teslas at speeds in excess of 1,000 miles of range per hour.

Older vehicles have benefited from improvements to quick charging with V2 supercharger stations getting new firmware that improves their power output from 120-kilowatts to 150-kilowatts, or at least for cars with 100-kilowatt hour battery packs.

This rollout has not only meant that Tesla customers could charge their cars up to 25 percent faster on the V2 superchargers. It also means that more people can get through a busy supercharger site in an hour.

But many owners of older Tesla Model S and Model X cars are starting to notice that, instead of getting faster charge times, the latest over-the-air software updates pushed to their vehicles are causing those vehicles to do the opposite. Lengthening charge times instead.

These owners are more confused because some vehicles seem to be suffering from a slowdown in charge times, while others are not. And in the past week or two we’ve, had several people reach out and ask us why.

Of course, as is always the case with reports like this, we try to get to the bottom of the data, and we try and understand what’s been tried so far.

As usual, when there’s a story involving an automaker and a vehicle issue, we do try and reach out to the automaker in question when researching and writing a show so that they have a chance to give us an official statement.

As usual, we sent Tesla an email asking about this problem asking for an official response, but we have yet to receive one. If we do eventually get one, we’ll make sure to mention it.

Those who’ve experienced the issue seem to be tied with version 2019.16.1 or more recent and seem to focus on just 85-kilowatt-hour battery pack Teslas.

When applied, the software update appears to be throttling some Tesla Model S and X cars as much as 20 % compared to pre-update charge speeds.

Charging is still far faster with a supercharger, and those vehicles than it would be, say with a Chademo charging station and the Tesla to Chademo adapter, but it’s still frustrating some owners.

Interestingly, the slowdown appears to be happening throughout the charging session on affected cars, not just at the high or low end.

One owner, who supercharged before applying the update and then repeated the same experiment afterward, documented as much as a 17-kilowatt drop-in charge power at the same point in a charge cycle, in similar temperatures after they did the update

At this point, I should also note that Tesla’s battery management software is one of Tesla’s biggest assets, so it’s hardly surprising that Tesla keeps the actual operation of this piece of technology under wraps. But it is, I think, this system that’s responsible for the drop in charging power.

In May 2020, Tesla pushed a software update to its older vehicles designed to change some of the battery management subroutines related to charging and battery temperatures.

While Tesla didn’t go into any further detail, the software update was “out of an abundance of caution following an incident in which older Tesla Model S cars seemingly randomly caught fire while parked.”

It’s likely that the software routine monitors internal cell resistances inside the battery pack and then lowers charging power when the in-town resistance of cells is above a certain level.

When internal cell resistances are high, charging at high currents will lead to a much faster ramp-up in battery temperature than when the cells have a low internal resistance because the electrons can’t get into the battery fast enough.

It’s also easier to overcharge a battery with a high internal resistance when charging at a high current.

The cell’s voltage will rise dramatically towards the top end of its charge, potentially triggering a thermal runaway situation is bad.

The software update push by Tesla in recent months is likely the reason that some Model S and Model X owners with 85-kilowatt-hour battery packs are suffering a drop in charging current.

Those lower charging currents are being implemented to protect the cells in their car’s battery pack, either because the car’s battery management system has noticed the batteries are starting to show signs of aging or some other issue.

It’s an unfortunate side effect of having an older electric car, but let’s be honest, the good news is this. Your car’s battery pack still has plenty of years of life yet, even if supercharging might take a little longer.

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