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Model S charging efficiency

Took delivery of my Model S, 4 days ago and can’t stop raving about the car. I have a 85 kWh battery with single charger. When plugged in to the wall via mobile connector into a NEMA 14-50 plug on a 240V/ 50 amp circuit the car shows it is drawing 235-240V and 40 Amp but is only charging at a rate of between 20- 25 miles/hr not the 31 miles/hr Tesla advertised. Outside temperature while charging has been between 50-60 degrees. Have others had similar experiences or do I have a problem?

It's pretty standard.
I haven't seen over 28 miles/hr, most of the time it's about 26.
The efficiency is about 65% or so, i.e. if it shows you've used 10kwh expect to use over 16kwh to charge.

First, I think the 31mi/hr rate is based on ideal miles, not rated miles, so if you convert that drops it to 27 or so. Then, I think the overall charging efficiency is around 87% (I haven't measured it carefully with the Model S, but that is what I get on the LEAF and I assume it is similar), and that brings it to 23. Finally, the charge rate is slower as you get near full, so if you are just topping off the battery it will be lower (though I am not sure there is that much effect at lower rates, but it definitely won't charge at 80A near full).

In my 3 days of driving, I am replenishing about 40mi of driving so it is near the top end of the range, and I see a charge rate of 22mi/hr on my car at 40A, so that fits in line with expectations.

One thing to be clear about is whether you're talking about rated miles or ideal miles. 31 is ideal miles, which is equivalent to about 27 rated miles.

Tesla Energy Screen should give us accurate Wh/miles drived. However, Does it take into account the charge lost when car is resting/sleeping?

Next month, I will take my PG&E usage (I added a 2nd meter, expensive!), and compare the PG&E watts used vs what the Tesla used. I am guessing charge effiency would be 90% or less.

Multiply rated miles by 0.72 is my realized miles.

Life time average 370 Wh/mile. Car is 5 weeks old (was out of town for 10 days), 810 miles driven since delivery. 1/3 local driving, 2/3 highway, Bay Area.

Model S: regular 85KW, 19" wheels (for safety and mileage), almost all options except premium sound & rear seats.

Terrain is hilly near my house. I seem to average about 420 Wh/mile in neighborhood and town driving. Temperate has averaged about 50 the past month. Climate set on low fan, 72 degree, 70% screen brightness, seat heat #1. Car always charged to 240 rated miles late at night, but lower by 7 am, ranging from 230-238, does not seem to matter if it is plugged in or not.

Seem to average about 350 Wh/mile in Highway driving, a mixture of 70 miles/hour and congested commute traffic when the average speed can slow down to 15 m/hr, stop and go. When going 70 m/hr, seems about 370 Wh/hr, which is worse than the Tesla graph, but Tesla graph is ideal. In general, car is not driven hard, except when "showing" family and friends :)

Other: I believe the Energy screen statistics of Wh/mile is overstated because (1) the car does use energy when parked if screen is on,(2)Charging is not 100% efficient. I estimate 90% charge efficiency, but I can't back up my claim scientifically yet. (3) The car loses miles just sitting there, even when the car is sleeping, even with 4.1.

Thanks guys, you cracked part of the code. Charging rate is directly tied to how you have the car set to report range ideal vs rated. My car had been set to rated when I switched to ideal and plug the car in it reports a charging rate of between 30 - 31 miles/hr just as advertised.

On the charging info page it says (*assumes 250 V circuit). I'm guessing in order to charge @ the rates advertised will require "optimal" conditions and power supply.

Does anyone know the charging efficiency difference between J 1772 and NEMA 5-20R? There is a site on my route that has both of these and I just wondered if the NEMA 5-20R would give me more charge per hour if I stop there instead of the J 1772. Then I would have to see if I can buy the adapter if it is more efficient.

It depends on the amperage of the J1772, but most of them are at least 30 amps, whereas the NEMA 5-20R is 20 amps, not much better than your standard household current. Plus the J1772 adapter comes included with the Model S.

Does anyone know if charging efficiency is better when starting from a depleted battery vs a nearly full battery? I know the rate slows as the battery becomes full, but does efficiency also worsen? I use about 30-40 miles of rated range per day; so is it more efficient to top off every night to 240 miles rated range or am I better off to let the battery go down to ~40 miles of remaining range and charge every 5th night? In other words, does it require more kwh input to top off 30-40 miles every night then adding the same rated range every 5th night? There is a separate question on what is best for battery life.

A second question is whether charging efficiency differs between a standard 110v12amp plug vs a NEMA 14-50 plug with 240v50amp service. I get about 3 mph with a standard plug which should cover my daily usage with an overnight charge. I also have installed a NEMA 14-50 plug.

Bump.

Just did my first normal commute today, a 144 mile roundtrip with MS85/twin chargers/NEMA 6-50 (HPWC on order). According to the Tesla website calculator, it should take about 4.5 hours on a 40A circuit, actual forecast is 5.5. hours. it charges at 234 +/-1 Volts, 39/40 Amps, or about 25-26 mi/hr. Won't be able to check on charge slow down towards the 80% full mark, as I will emitting lots of zzzzs. Still plenty fast for an overnight charge, have not the slightest of worries.

Can anyone explain why with a 110V 15A supply the rated charging miles are 3 and when doubling it to 220V 15A the jump is to 8

5 miles per 110V at 15A (nominal) (115V 12A actual) at a rated usage of 300W per mile is in the ball park of 5 mph. (115V * 12A =1,380W which divided by 300W = 4.6 mph of charge).

So why on a 110V 15A the rated charge is only 3 mph? I find it hard to believe that the vampire loads would take a whopping 600W per hour (the missing 2 miles per hour at 300W each).

In fact I can confirm that it is not the case as I have monitored the usage drop when I stopped charging and the charger was not drawing anything.

Does anyone know the answer?

@againgone - I don't know any specifics in the Model S, but some energy is wasted in the rectifier and voltage regulator. I wouldn't be surprised that more energy is wasted at a lower voltage depending on the design, and clearly it would be optimized for 240V rather than 120V if a tradeoff had to be made.

Could be there's some constant load being deducted from the feed. Algebraically,

110 - c = 3 (1)
220 - c = 8 (2)

220 - 2c = 6 (-2x(1))
___________
c = 2 mi/hr being expended for battery resistance/heating, or whatever, while charging.

I'll have to add a sensor on those two hots and see what happens while the car is not charging.
I'll post back.

@agiangone, did you get a chance to measure?

I am also charging at 110 and I'd like to understand why Tesla advertises 5m/h even though it seems that most using 110 get 3m/h - as I do. I'd based some decisions on 5, and while 80% of that was quite workable 60% is cutting it close enough that it weighs on my mind and I find myself "warning" people about (my) reality. That can't be good for Tesla.

Hmmm...

@david.cheney,

I am purchasing a Model S 85. Based on Tesla's calculator, it would take me 12 hours to charge for just my 50 mile round trip commute. Since I don't get home until about 7pm and leave in the morning around 8am, I would barely recoup my commute mileage. That doesn't factor anything else, like the occasional detour for food, meeting friends later, etc. I suppose everyone's schedule is different, but it would be extremely difficult to make my life work around a minimum 12 hour charge time.

At least in my case, I don't think I would get much fun out of the car if I had to limit myself to a 110v outlet.

@david.cheney - same answer here as the other thread, which is you are comparing ideal miles (ie, 300mi/charge) and rated miles. If you set your display to ideal miles you should get about 5mi/hr, but you will probably have difficulty achieving that range unless you drive very conservatively.

@Amped, looking around I find that the 110v self limits to 12A, so it charges at effective 3m/h and your 50m drive takes 16+ to recover. Totally unworkable.

@Jat, clearly my research was insufficient. If I'd only done my homework I would have discovered that an "ideal mile" is 3168 feet.

/end_sarcasm

Seriously, I simply read the Tesla page: "MILES OF RANGE PER
HOUR OF CHARGE" = 5. ANd yes, I know its more complicated than that. I suppose I thought they would use an average ("expect 4-6") rather than "ideal", whatever that means.

Tesla defines ideal range of 300mi as a constant 55mph on flat ground with no HVAC. If you want your charging to be 5mi/hr, simply change the display setting to show ideal miles rather than rated miles. Good luck making your driving match that, but no single number is going to reflective of everyone's driving style or even the same person at different times in different conditions.

Your gas car also varied gas mileage as much or more, but you didn't notice or care much.

You might be able to use a doubler, plugs into 2 outlets. If they are separate circuits you can get double voltage and amperage. http://www.teslamotorsclub.com/showthread.php/7977-220-charger-from-110-...

@plinz:

Just don't count on being able to drive the car the number of ideal miles it says if you have the system set to display ideal miles. You can get ideal miles, but you would need to be on cruise control at maybe 25-50 MPH. Any realistic driving uses charge that corresponds more closely to rated miles. And driving at speeds of 65-70 uses more charge than rated miles.

@BrianH, ty.. perhaps from the neighbors attached garage :)

@plinz, miles/charge is of course very important.. and of course very different than rate of charge.

I bought a 40 knowing that would make this a local car. My commute is 20m round trip and with a nice 20m buffer I am gonna drop by maybe 40-50 miles (factoring in some not-"ideal" on top of my own 100% buffer).

Charging rate is at the core of this thread, and AFAIK the issue applies regardless of battery size or power supplied. It has most to do with what Tesla is claiming, as some - like me - will not only base their decisions not only on the claim but also - like me - not be well positioned to upgrade their power.

Tesla's page here - select adapter guide says simply this: "110V / 12A 1.4kW 5 MILES OF RANGE PER HOUR OF CHARGE" (their CAPS). They do not use the word IDEAL nor qualify the 5 in any fine print.

Here's how their claim affected me. Given the numbers above, at 5 m/h charge I can pull into the garage at 9pm and leave at 7am and always have it "full" for the occasional joy ride (followed by some painful down time). However, at 3m/h I am suddenly in the 13-17 hour range and I am always playing catch-up. Anything beyond my commute suddenly moves the needle somewhere between "concerning" and "can't be done".

I am reduced to hoping I can live mileage down 40% from what I had expected - but customers "living with" 60% of claim is NOT gonna build your market.

I am seeing more explanation for why my trust was misplaced than demand that Tesla correct or at least clearly qualify their claimed rates of charge.

No doubt such an adjustment would be painful - but clearly people who experience what I am are not going to go away otherwise.

I stepped up and out big time to buy this car because I am so excited by all that it is and can be, and I'm most disappointed of all that my excitement is so tainted by something as mundane - yet real - as "but I can't use it as they had told me I could". :(

Is this an apartment garage or something where you can't install a 240V?

I did some 110V calculations before I got my car, incase my 240 wasn't installed in time. Basically, I did a full charge and then charged as much as I could each night, which wasn't enough to get back to full, but it gave back some mileage throughout the week and on the weekend it would have to charge for a looooong time to get back to full.

Well worth the investment, if you can install a 240. Even an apartment complex might be open to allowing it to be installed if you pay for it. Just sell the fact that it's "EV ready" for the next tenant.

IMO, buying an MS with only 110V power available is a triumph of hope over intelligence.

@ BrianH,

I'm more inclined to believe it a triumph of hope over practicality.

You really really need a 240 V outlet. 110 "works" but it doesn't make sense as a regular means of charging.

On the current limits: the National Electric Code requires that EV charging be treated as a "continuous load". And it requires that any continuous load may only go up to 80% of the circuit breaker setting for the circuit. So a 15 amp circuit is required to go to 12 amps max. And the 240V/50A recommended configuration has to be limited to 40 amps by that same rule.

(For that matter, the high power wall mount charger allows circuits up to 100 amp circuit breaker, which means it can go up to 80 amps.)

It's cruel to starve a MS to death.


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