Tesla Model 3 and Supercharger

Tesla Model 3 and Supercharger

First some background on charging speed.

Charging speed can be stated in different ways:

First, there’s C rate which is the time to reach 100% charge. C rate of one means the battery can be charged to 100% in one hour. C rate of 2 means the battery can be charged to 100% in 1/2 of an hour. C rate of 3 means the battery charges to 100% in 1/3 if an hour. Other chemistries have higher C rates but may not have the energy density and may cost more than Tesla’s NCA chemistry. Lithium titanate (LTO) is a chemistry that can be charged at very high C rates. In general though, Tesla automotive batteries charge at a C rate of about 1.

Tesla's 100D premium offering equal to Model 3 when it comes to charging?

Tesla's 100D premium offering equal to Model 3 when it comes to charging?

A second way of stating charge speed is power (kw) that the battery can take during charging. More power means more energy (kWh) can be pushed into the battery in a given amount of time. Obviously more power means faster charging when measured in miles per unit time.

A third and most important way to state charging speed is in miles per unit time. Miles per minute of charging is really is all the consumer needs to know. If it is X miles to the next charging stop then this measure of charging speed tells the consumer how long he has to wait at the super charger before heading out to the next destination.

Miles per minute charging speed is the product of two variables: charging power times vehicle energy efficiency or miles per kWh. In other words how far will the car go on 1 kWh of energy.

If you want to maximize charging speed you can do it by increasing charging power and/or vehicle efficiency.

Here in lies the secret to why Model 3 can charge as fast as a P100D. It is very energy efficient. It goes much further on 1 kWh of energy than the Model S or X. The new Model 3 with big battery appears to return an MPGe of 126 while my 2012 Model S has an MPGe of only 89 a whopping 41% increase!

But I digress. How do we know that the model 3 charges as fast as the 100D?

First some simple math and a video by Bjorn Nyland of the P100D charging tells us.

P100D Charging (via <a href=Bjorn Nylund)" draggable="false">

P100D Charging (via Bjorn Nylund)

In this video we can see that the P100D charges 50% in 30 minutes. Range of the Model S 100D is 335 miles. 50% of 335 is 168 miles. Essentially the same as Tesla’s Model 3 specs on super charging speed of 170 miles in 30 minutes for model 3. Implicit in these calcs is the assumption that a Model X P100D in Bjorn’s video and a Model S 100D will charge at the same C rate.

Second we have a quote from Tesla’s Q2, 2017 earnings call courtesy Seeking Alpha.

Question from Colin Langan UBS Securities:

“And what about, just as a follow-up, the charge time? I know Porsche has said that they could charge in 15 minutes. Do you think that's possible in the future? And is the charge time on the 3 the same as the S? I wasn't sure in some of the release.”

Elon Reeve Musk - Tesla, Inc.

“It's about the same. It's comparable to the high-end S. The recharge rate of how many miles per hour you recharge is sort of a function of the battery pack size. So, like a 100 kilowatt-hour pack, because charge rate is a function of percentage of pack – think of 3 and a high end S as being similar in charge rates.”

So there you have it. The Tesla Model 3 charges as fast as the Tesla Model S 100D.

170 miles in 30 minutes

Add this to the fact that the Tesla Model 3 has nearly the range of the Model S 100D and you have quite an impressive product for less than half the price.

References: Transcript of Tesla earning call courtesy Seeking Alpha Hat tip JeffK at Tesla Motors Club

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