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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?

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.

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.

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?

Lead foot? ;)

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.

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.

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

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).

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.

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.

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.

@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.

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.

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?


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

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

@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.

@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:

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

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!

@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".

Smartmeters are evil.

@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

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.

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 :))


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

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

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.


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