Welcome to Tesla Motors Club
Discuss Tesla's Model S, Model 3, Model X, Model Y, Cybertruck, Roadster and More.
Register
  • The final cut of the 9th episode of the Tesla Motors Club Podcast, featuring Chad Schwitters, the former president of Plug In America, is now available. You can watch it now on YouTube or listen to it on all major podcast networks.

Average MPH on 13amp UK plug

arg

Active Member
Supporting Member
Aug 22, 2012
1,838
1,853
Cambridge, UK
6-7mph is about right for Model S in the UK. Model X should be at least 5. If you were hearing 2mph, that may have been from the USA with 120V power (and even then would need other unfavourable conditions to get it that slow). Alternatively, it could have been someone who plugged in to a 13A socket and looked at the MPH on the display straight away, without leaving enough time for it to settle on the final figure. In general, the charging mph on the display is highly misleading and you are better to look at the power figure and make your own estimate of how that turns into miles.
 
  • Like
Reactions: Fellsteruk

cizUK

Member
Mar 13, 2017
316
296
UK
13A * 230V = 2990W = 3kW
259 (NEDC) miles / 75kWh = 3.5 miles / kW
3kW * 3.5 miles/kW = 10.5 mph

237 (EPA) miles / 75kWh = 3.2 miles / kW
3*3.2=9.5 mph

213 (realistic) miles / 75kWh = 2.8 miles / kW
3*2.8=8.5 mph

Of course, you may have to account for losses, I don't know how significant it is.
Have I got the calculations right?

But Tesla's plug must only have a 10A fuse to get 2.3 kW
 
Last edited:

arg

Active Member
Supporting Member
Aug 22, 2012
1,838
1,853
Cambridge, UK
Have I got the calculations right?

The calculations are correct, but some of your assumptions are optimistic.

Although a "13A" plug, experience dictates that they aren't suited to continuous operation at that current, and manufacturers of EVSE (including Tesla with the UMC) have adopted 10A as the safe limit.

The NEDC range is hopelessly optimistic and no use for practical purposes. On the other hand, you are assuming that a "75" has 75kWh of usable battery, when in fact a portion of that capacity isn't available for use, so your "realistic" calculation is actually pessimistic. I use 333Wh/mile (or 3 miles per kWh) as a rule of thumb - it's an easy figure to work with, and actually matches very closely to my lifetime average shown in the car. I have the displays in the car set to "typical" rather than "Rated"(=NEDC), and I believe the "typical" calculation uses a slightly lower figure, about 300.

There is an overhead on charging - a (quite small) percentage overhead on the power conversion, but also a fixed overhead for running all the computers/cooling systems/etc that have to be powered up to enable any kind of charging. As a round number, deducting 1A for this (230W) is about right.

So:

Actual current drawn from 13A socket: 10A
Deduct 1A for fixed overhead: 9A
Convert to watts at 230V: 9 * 230 = 2070W
Convert to MPH at 333Wh/mile = 2070/333 = 6.2MPH
Convert to MPH at 300Wh/mile = 6.9MPH
 
  • Informative
Reactions: Rocky_H

cizUK

Member
Mar 13, 2017
316
296
UK
The calculations are correct, but some of your assumptions are optimistic.

Although a "13A" plug, experience dictates that they aren't suited to continuous operation at that current, and manufacturers of EVSE (including Tesla with the UMC) have adopted 10A as the safe limit.

The NEDC range is hopelessly optimistic and no use for practical purposes. On the other hand, you are assuming that a "75" has 75kWh of usable battery, when in fact a portion of that capacity isn't available for use, so your "realistic" calculation is actually pessimistic. I use 333Wh/mile (or 3 miles per kWh) as a rule of thumb - it's an easy figure to work with, and actually matches very closely to my lifetime average shown in the car. I have the displays in the car set to "typical" rather than "Rated"(=NEDC), and I believe the "typical" calculation uses a slightly lower figure, about 300.

There is an overhead on charging - a (quite small) percentage overhead on the power conversion, but also a fixed overhead for running all the computers/cooling systems/etc that have to be powered up to enable any kind of charging. As a round number, deducting 1A for this (230W) is about right.

So:

Actual current drawn from 13A socket: 10A
Deduct 1A for fixed overhead: 9A
Convert to watts at 230V: 9 * 230 = 2070W
Convert to MPH at 333Wh/mile = 2070/333 = 6.2MPH
Convert to MPH at 300Wh/mile = 6.9MPH
Yes, that makes sense, although Tesla still says 2.3kW when you are saying 2.07kW
Anyway, it all gives very similar figures
 

Products we're discussing on TMC...

About Us

Formed in 2006, Tesla Motors Club (TMC) was the first independent online Tesla community. Today it remains the largest and most dynamic community of Tesla enthusiasts. Learn more.

Do you value your experience at TMC? Consider becoming a Supporting Member of Tesla Motors Club. As a thank you for your contribution, you'll get nearly no ads in the Community and Groups sections. Additional perks are available depending on the level of contribution. Please visit the Account Upgrades page for more details.


SUPPORT TMC
Top