Power draw while charging

Power draw while charging

A recent AP article hit the papers a couple of days ago claiming that "Plugged into a socket, an electric car can draw as much power as a small house." The article reports that utility companies are planning upgrades of transformers and other equipment to prepare for this huge power demand. Of course, they only discuss the "mass-market" cars that are coming out and specifically focus on the Leaf and Volt, but they also refer to Toyota later in the article and make no distinction between the power demand of the current electric cars and those due out in 2012 (no mention of Tesla at all). How factual are these claims and do they apply to the Tesla vehicles? I remember something about the draw being like plugging in a laptop. If this article does not apply to Tesla it would be nice if Tesla could publish a rebuttal. Can anybody insert some facts here?

Timo | 1 dicembre 2010

EV draws just as much power as you allow it to do. It doesn't draw anywhere close as much energy than small house, but power it can draw. There is a difference between the two.

If you drive, lets say, 40miles/day average and charge every day you use approx 9kWh/day to charge (applies to any typical passenger EV, not only Tesla). Usual 230V@10A is enough to charge that in about 4 hours, which is enough if you just plug it in for night in your garage.

To put that in right context just TV&associated electronics (300W) + PC&monitor(400W) run about 13 hours/day uses that same.

So, nowhere close to energy need typical small house uses. OTOH you can make that charging using L3 charger and charge using around 50kW power, which is quite a lot more than typical small house use at any moment.

Steve | 30 novembre 2010

See–-tesla-evs-and-grid for a discussion of transformer limitations.

Especially for a Tesla HPC charging station that can draw 70A continuously while charging for 3.5 hours, that 70A draw is quite likely to be as much or more than would be drawn by a small house most of the time.

Regarding the total amount of energy, in our house when we had one EV it accounted for about 1/3 of our total energy consumption. Now we have two EVs.

Timo, my experience is that the EV energy consumption as measured by the AC power going in is more in the range of 300-400 Wh/mile (measured with GM EV1, Toyota RAV4-EV, Ford Ranger-EV, and Tesla Roadster). Therefore 40miles/day is more like 12-15 kWh/day. That is comparable to the power my wife and I use in our home in one day, separate from the EV, but I only commute 13 miles/day.

Timo | 1 dicembre 2010

For Roadster that 300-400Wh/mile equals around 70-85mph average speed. Pretty high for 13 miles a day. How did you calculate it? Are the charging losses big enough to explain that?

Jaffray | 1 dicembre 2010

Lead foot? ;)

SteveU | 1 dicembre 2010

Timo, I agree with Steve based on my experience charging my Roadster over the last two years. The wall-to-wheel use of energy is higher than the battery-to-wheel. It isn't a lead foot, but charging inefficiencies. I get between 320 Wh/mile and 390 Wh/mile wall-to-wheel for the same driving (distance and speed). The variation is roof (on is better than off) and outside temperature (cooler is better than warmer because the battery coolant pump uses power all day while parked on a hot day). (Roof makes about a 20 Wh/mile difference and warm weather about 50 Wh/mile.) I'm never over 65mph and often under 50mph, by the way.

SteveU | 1 dicembre 2010

I neglect to answer your question about how I calculated this. I had a meter installed on the dedicated circuit for the car and I have recorded the mileage and charge for every charge my car has had.

Timo | 1 dicembre 2010

I guess that means charging losses are quite a bit higher than I expected. Can you give an estimate on how much that is?

dubaty | 1 dicembre 2010

So getting back to the AP article, their claim is accurate if using the dedicated hard wired charger, but less accurate if simply charging via a typical socket (of course they didn't make that distinction). It seems that the drain on a utility company's transformers would only become significant if there were several EVs in the same area - optimistic on their part (they are seeing this as a big increase in revenue).

Timo | 1 dicembre 2010

Well, plugin hybrids count as EV:s for charging and I guess their portion of the main fleet will increase rather rapidly. It doesn't need to be pure BEV to cause that same strain, so it is better to be safe than sorry in this case. Like Steve above PHEV Prius would be enough for him to have almost pure electric range for his average commuting.

It is true that this change will not be instant, but it is coming and power companies are better be ready for it, so I guess it is not entirely just for money, even that this probably is part of the reason they are doing it now, and not later.

Brian H | 2 dicembre 2010

Particularly since most of the delivered power will be in normally slow hours, it's mostly gravy for them. I'm sure they're quite happy with it.

qwk | 2 dicembre 2010

I wouldn't count plug in hybrids as an EV. Most are only able to charge 120v/12a, so the strain on the grid is like running your vacuum.

SteveU | 2 dicembre 2010

@Timo: I haven't kept a record of the battery-to-wheel energy usage, mainly because I didn't care (I felt the point was how much energy I was using, regardless of where it is going). My general sense based on the driving range I get is that 250 Wh/mile is about the battery-to-wheel usage. I assume the 70 Wh/mile variation I've seen mostly flows through to the battery-to-wheel numbers (that is most of this isn't during charging) although on hot days the charging cost of cooling the battery is undoubtedly higher.

SteveU | 2 dicembre 2010

From contact with other owners I know that at least three transformers in California have been destroyed due to overload caused by too many Teslas charging at the same time. At least one of these was at night. So... there are at least some definite weak points in the current distribution system.

Rrroger | 4 dicembre 2010

In reference to SteveU, can an older (1960s) removed 30amp electric company mechanical wheel meter survive an in-line hook up similar to what SteveU is talking about? The meter that I saw at a junk yard for sale, had two line in legs, and two supply legs(connection screws). Would that only be 15amp per leg, and would it work to study, and save charging data by reading the dials, or would it burn up from too much current?

qwk | 5 dicembre 2010


I dont know if it is a good idea to use anything that old from a junkyard near these expensive cars.

ob1 | 5 dicembre 2010

it will be a good idea to incorporate some sord of dynamo to keep the battery charging wile the car are runing or have a second battery charging in the same car and switched when needed.Bein a tesla electric car it will be nice to have a self sustain energy power sorce like tesla's dream

Steve | 5 dicembre 2010

@Rroger: Old mechanical wheel meters are fine, but 30A is not enough. I'm surprised it is that low. I would expect any incoming panel meter to be at least 100A.
You can get such meters reconditioned from a company like Hialeah Meter Company for a low price. That is where I got mine for an installation like SteveU's.

ChristianG | 6 dicembre 2010

@ob1 and what about a dynamo wich is running on the dynamo that runs on the wheel, so we get twice as much energy?

What you're talking about is called regenerative braking and will of corse be used in the Model S as it's already used in the Roadster and most hybrid cars.

Here's a blog:

Timo | 6 dicembre 2010

@ob1: generator is a brake. Figure it out.

Rrroger | 6 dicembre 2010

Thanks for the info, Steve, about Hialeah Meter Company in Florida. Their reconditioned meter prices are great. I expected
to have to spend $220 or more, so the 30 amp $30 junk yard meter seemed the only possibility, but $17.50 for 100amp reconditioned meter with $10.50 mounting bracket may work for me!

Steve | 8 dicembre 2010

@Rrroger, I think that is even less than I paid about 10 years ago. I suspect that the market is being flooded now by all the old meters that PG&E and others are removing to install "SmartMeters".

Brian H | 8 dicembre 2010

Smartmeters are evil.

ob1 | 8 dicembre 2010

@ChristianG and timo Regenerating-braking uses power n return back some of the power.Iwas thinking of a self-powering open electrical power system extracting their electrical energy directly from the active vacuum and readily scalable in size and output,or a iteractive phase conjugate retroreflective systems wich passively recover n reorder the scattered energy dissipated from the load n reuse the energy again n again. Fpr example a KAWAI cop>1.0 magnetic motor with clamped feedback powered themselves n their loads.yes n i try to figure it out lol

Brian H | 10 dicembre 2010

words fail me, much as sense fails you. That's some of the most incoherent nonsense ever written on this site, and you've had some stiff competition.

Timo | 10 dicembre 2010

I was quiet because I just couldn't find anything to say from my amusement of that "incoherent nonsense". Reference that came to my mind was ST "particle of the week" (if you don't know what that means, you are not geek enough :))

Samuel H. | 10 dicembre 2010


Exactly WHAT ARE YOU TRYING TO SAY? (in real geeklogic please)

Vawlkus | 13 dicembre 2010

He wants the Zero Point Module from Stargate Atlantis -.-

searcher | 13 dicembre 2010

ob1, Been there and done that buddy, I am part of the stiff competition,ha. My suggestion would be to locate mechanical or electrical engineer who speaks in your native language and discuss all with him directly and not on this site. At least do this first, and if you get it understood by him and he is in agreement and can see your point. Then I suggest "go get a patent buddy". These guys are really sharp and a little sharp tounged to,ha. No offense anyone,ha. If it works out then you can come back and have a little fun.

Samuel H. | 15 dicembre 2010


Timo | 15 dicembre 2010

Spicy little things those zero point modules, aren't they? Too bad that only one in Earth is in that "research facility" in Antarctica.

Tesla 940 | 16 dicembre 2010


How does your dedicated electric meter compare to the charging history displayed in the car?

I've logged most of my recharges but have no idea of what the energy loss is between what is going through the house electrical circuit and the car's charging history.


searcher | 17 dicembre 2010

spicy little things huh, timo. Guess you think the John Hutchinson guy who you would probably consider a fraud as many others do. You know the guy I mentioned who was working on free energy etc with german companies. Well it turns out that he has done some DOD work and recieves Christmas card from Presidents Bush and Clinton, so maybe not altogether a fraud. I can almost gurantee you that Nikola Tesla was considered the proto type mad scientest in his day, and of course all his stuff didn't pan out but has yours or do you have any stuff or you just sitting on the sidelines critiqueing others and leading this merry little inner circle on this website. Sorry for uncharitistically prickly mood, not having a particular good morning, very low patientece level this morning. "Spicey little modules" very cute.

SteveU | 17 dicembre 2010

@Tesla 940: Initially there was a significant and consistent difference between the amount of power used according to the meter and the amount of power used according to the car. If I remember right, the difference was about 10%. A fairly early in the life of the car update to the firmware fixed this and now they track exactly. (With rounding the measures may be off for a single change, but over time they are the same.)

Tesla 940 | 18 dicembre 2010


Thanks for the information.

dubaty | 20 dicembre 2010

Sorry, been away from this thread for a while. Point of clarification about an earlier post. I believe the Tesla Roadster (and presumably the Model S) do not use regenerative braking; rather they regenerate when you ease off the accelerator. The cars decelerate and regenerate without braking. The brakes are just regular brakes and are only needed during the last 5 mph to completely stop the vehicle. I just drove a Roadster this weekend and it was quite an experience. The ability to control the speed that much from just one pedal was odd at first, but it quickly feels right. If someone thinks I have my facts wrong, please let me know.

Douglas3 | 20 dicembre 2010

I think you're getting a bit confused by the terminology. The Tesla Roadster does regenerative braking when you lift off the accelerator pedal. You don't have to change the name just because you don't use the brake pedal.

Brian H | 21 dicembre 2010

Yes; regenerative braking IS deceleration whenever power is not being applied. No car requires use of a pedal to activate it.

searcher | 21 dicembre 2010

Kudo's to great job of informative posts by Douglas3 and BrianH. Not that you needed my cheers of course.

ggr | 23 dicembre 2010

Brian, I'm afraid you're partly wrong. The Prius only does very small regenerative braking when you back off the throttle pedal. When you do put on the brake pedal, the first part just increases the regeneration, then as you press harder actually engages brakes. One of the things claimed in the lawsuit against Toyota about "unintended acceleration" is that sometimes the Prius' brake system will actually completely disengage for a second or so, as regen moves over to brakes.


Tesla 1233 | 1 gennaio 2011

Some houses still have an electrical service under 100 Amps at 240V. 100 Amp is probably typical today; although I suspect 200 Amp is typical for new construction today.

The Tesla 70 Amp high power charger requires a 90 Amp breaker so I think it is fair to say that it can draw as much or more than a small house (at peak loads).

I recently purchased a Clipper Creek 70 Amp high-power charger from Tesla and am currently waiting for a PG&E representative to come over and discuss installation. They already told me that they will need to upgrade the transformer. If I only charge at night, I suspect replacing the transformer is over-kill, but I suppose it is possible that some hot summer afternoon I may want to do a quick charge.

My sales advisor said that many Tesla owners serviced by PG&E that converted to smart meters found that it cost them as much or more for power than if they had kept the original meter. I suspect that is true, however PG&E will install a second meter so you can take advantage of the off-peak rate of about 5 cents per KWH for charging the EV and leave everything else as is. Effectively, that means installing a 100 Amp service along side my existing 200 Amp service. I think that is the way I will go, but I first I need to find out what PG&E will charge, if anything.

AlfredG | 2 gennaio 2011

Tesla 1233: Make sure you do not install more power at home than you are likely to need.
- How often will you return home nearly empty and have to refill in a a few hours to leave again?

I found that at home I can make do most of the time with an ordinary 230V/10A household connection. For a full overnight charge already 230V/16A is sufficient. Only if I return at 22:00 and wanted to leave again at 07:00 I need 230V/30A for a full charge and for both cases the "Universal Mobile Connector" is more than adequate (rated at 40A).

Those fast charges would be really convenient somewhere underway near a decent restaurant to stretch your daily range.

If I get home after a three hour drive, the last thing I normally aim for is leaving home again the same day for another long drive.

- Alfred

Tesla 1233 | 2 gennaio 2011

I understand that at home I will not need a fast charge most of the time. I already have a spare 240V dedicated circuit in the garage. If it were 30 Amp it would be sufficient but it is only 20 AMP. If the wiring was in a conduit I could easily replace it with a larger diameter but it is not. I decided since I will need to run conduit, the incremental cost to go to 70 Amp is worthwhile. (I have always tended toward over-kill and found that it often pays). Besides, I can always charge at a lower rate when desirable.

It is possible that some Tesla owners passing along CA 4 will want to stop by for a visit and a quick charge. If so, I will be able to accommodate them.

Thank you for your comment Alfred.

Steve | 2 gennaio 2011

Tesla 1233: Some care is necessary when talking about electricity meters. I think what the Tesla sales advisor really meant was that some owners found they paid more when taking service under the E-9 tariff, which charges different rates by time of use, rather than the more common E-1 tariff that is a constant rate at all times. It is true that one needs a more complicated meter to handle the ToU tariff, but it does not need to be one of the "SmartMeters" that PG&E is phasing in now across their whole customer base. Even people on the E-1 tariff have SmartMeters installed. In fact, although all my neighbors who are on E-1 have SmartMeters, I am on E-9 and I did not get one yet because I also have solar panels and am on a "net metering" tariff in combination with E-9 so I can sell power during the day and buy it back at night. I do have a smarter-than-average meter, but it must still be read monthly by a meter reader. It is not one of the new SmartMeters that report back usage over the network on an hourly basis.

Because I have solar power, the E-9 ToU tariff is a good deal for me. In the summer, I sell power at $.30 per KwH in the afternoon, then I buy it back at $.05 after midnight to charge my car. So long as I can shift a large enough fraction of my electricity usage to the mignight-to-7am period, I come out significantly ahead compated to the E-1 tariff. My lifestyle without kids is also more flexible regarding afternoon and early event usage so the E-9 tariff is not inconvenient for me and my wife.

Also, having two meters like the PG&E person mentioned does not require having two service lines to your house. There is a dual-meter adapter that plugs in where the one meter usually goes. One meter feeds the existing panel, and then there is a tap off the side of the adapter that can go to a new, small panel for special circuits, for example, the charging circuit for your car.

Steve, Tesla 33

Tesla 1233 | 2 gennaio 2011

Thank you for the clarification on the term "Smater Meter". What I was trying to convey is a varying rate structure based on time of use vs. my current rate, which has an escalating price structure based on monthly consumption. The point I was trying to make and that the PG&E representative agreed could be the case is that the use of a single meter billing at the E-9 rate could be more expensive than my current rate structure. Use of a second meter would permit me to use their E-9B rate for charging the Roadster.

When I spoke to the PG&E representative she indicated that I would need to install a second service panel for the second meter and provide a gutter (or sealed termination) connection between the existing panel and the new panel to connect to the new panel to the existing service line. She did not say (and I did not intend to imply) that a second power line drop would be used. However, she did imply that a larger diameter service line might be required since my total load could approach 300 Amps (the sum of the two main breakers) and that I might be billed for that work. My point was the possibility of being changed to upgrade the service line, not to install a second service line.

She did not mention the possibility of using a multi-meter panel, which I do see mentioned on their web site at

However, based on the diagram in the above document I would need to replace my existing panel with a multi-meter panel. That would be more expensive for me than adding a sealed termination enclosure and a new 100 Amp panel next to my existing panel.

A multi-meter adapter is not an option for me. See Item 7 on page 2 of the above referenced document which states:

Dual meter socket adapters are not approved for use.

Steve | 4 gennaio 2011

Tesla 1233: The escalating price structure based on monthly consumption (that is, tiers 3 - 5) applies to the E-9 tariff just like it does with E-1. With E-9A (single meter), the baseline allowance is the same. Until fairly recently, the incremental cost between tiers was also the same across all ToU periods and it was the same for E-1 and E-9. Now, though, the increment between tiers is less during the off-peak period (midnight to 7am) as further incentive to move EV charging to that period.

When EV1 customers began taking service under the E-9B tariff around 1999 or 2000, there was a problem that they got the usual baseline allowance applied to their main meter on the E-1 tariff, and the second meter for the EV charging on the E-9B tariff got a baseline allocation of zero. That meant all of their consumption of power for EV charging was charged at the Tier 5 rate (over 300% of baseline) because the baseline was zero! That was clearly a bug in the charging algorithm. However, it would also not have been fair to give those customers two baseline allocations. If you are considering E-9B, you should ask how the baseline allowance is managed now.

Tesla 1233 | 7 gennaio 2011

The initial information I had from PG&E listed only one rate for
E-9B but upon further seraching I see that it too has a tiered structure.

Thanks for pointing that out, I will push them hard for complete information.