# Charge electric car from dryer plug?

#### MTurner

Hello, I was surprised to read today that one of the bigger impediments to electric cars coming to market is the fact that the 'quick' chargers require installation of a seperate power line. Why? Every house, apartment, condo, etc in America pretty much has a 220 plug for the dryer. Why can't those be used to quick charge electric cars? It's not like people are using their dryers 24/7. I asked around a bit and basically the main reason a seperate line has to be run is because of the danger of 220, but I don't see electric cars becoming commercially viable if everyone knows they have to get a seperate line run at their own expense, and repeat it every time they move. Also, what about all the people in apartments, condos, etc? Is there not some type of system that could be devised that could securely fasten to the 220 plug with pass-through for the dryer, and run a cable up to 70 ft for hookup to a vehicle? It just doesn't seem like that would be something that is too hard for us to make...any ideas?

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#### russ_watters

Mentor
I saw the article and ran the math and I was pretty confused by the issue too. Here's what the CNN story says:
Electric cars like the Nissan Leaf and Chevrolet Volt ideally use special "quick chargers" that have to be hardwired directly into high-power lines.

Installing the chargers is not like putting in a ceiling fan. The equipment has to be fully approved, installed by a competent professional, and in most cases, a city or state inspector will have to approve it all.

You could plug your car into an ordinary wall socket, but not if you're in a hurry. Charging a Nissan Leaf would take up to 16 hours, and charging a Volt would take eight.
http://money.cnn.com/2009/12/11/autos/electric_car_charging_challenges/index.htm?cnn=yes

So lets look at the math:

The Wiki in the Volt has a 16 kWh battery, with 8 kWh useable (it is a plugin hybrid.
The Wiki on the Leaf just says a 24 kWh battery.
The Wiki on the Mini-e says a 35 kWh battery.

The National Electric Code says a branch circuit can't be designed more than 80% full, which for a typical residential circuit is 120Vx16A=1920W. I'm not sure if that is a the real maximum for a single device on a multiple outlet circuit, though, since the biggest draws you ever see for household devices are 1500W. But lets go with it...

For the Volt, that means the 8 kWh capacity takes 8/1.92=4.17 hours assuming 100% charging efficiency.
For the Leaf, 24/1.92= 12.5 hr
For the Mini-E, 35/1.92 = 18.2 hr

Now the Mini-E and Leaf have 100+mile ranges, so they go beyond what a "commuter car" should be expected to do. But yeah, if you want to drive 80 miles each way to Grandma's house for Thanksgiving, you may have an issue. As a 40 mile a day commuter car, it wouldn't be an issue.

Now lets say you use a dedicated 40A, 220V circuit (actual draw, 32A, 7.04 kW). The new numbers are:
Volt: 8/7.04=1.1 hr
Mini-e: 35/7.04=5.0 hr

The downside, of course, to these is that you do need somewhat special circuits, so your options for where to charge would be limited.

Now what about the phrase: "hardwired directly into high-power lines"? The words don't really have a lot of meaning to me. "Hardwired" may mean there is no plug, that you wire the charging device directly to the circuit. That's not necessary and not how I would design it, but it may actually be that way. "High-power lines" is a completely meaningless phrase. I don't know what they intended by it, but every normal residence in the US has 220V.

A bigger issue, not discussed, is that not all residences will have that much extra power available. It isn't uncommon for a single family house with electric hot water, dryer and cooking (plus an air conditioner....) to have a 100A service. That's 4 devices up to 32 A apiece. You can use some diversity and not assume they are all running at full capacity all the time, but still, there may not be any extra capacity on such a house to add another 220V/40A circuit. And upgrading your service is very expensive.

In any case, though, yes you do need an electrician to add a 220V/40A circuit (almost certainly not an inspector). If the wiring is easy, it should cost <$500. #### MTurner Thanks for the math on that. I'm assuming those timeframes are to take a vehicle from 0-100% charge with a dedicated line. The question, however, was whether it would be feasible to simply use the 220 plug almost all housing units have available to charge an electric vehicle. Yes, you won't get the same timeframes as you would from a dedicated circuit, but most homes are not running at the capacity of their circuit a majority of the time. Most people just need a simple easy way to plug their cars in overnight for the next days commute, or to go back out that evening. So why not make it as simple and easy as using the dryer plug when circuit capacity is available (when ac is off etc)? Is there any reason NOT to? Does the current cause too much heat meaning special heat shielded cables are needed (if so, why don't dryers have them)? Can it not be transmitted across 70 ft easily? What are the logistical reasons it can't be done? #### russ_watters Mentor Except that you might need a really long cable to go from your dryer to the garage, no, there shouldn't be any problems with that. #### mgb_phys Science Advisor Homework Helper The question, however, was whether it would be feasible to simply use the 220 plug almost all housing units have available to charge an electric vehicle. Yes it's perfectly reasonable to charge a small plugin electric from a 220v/16A dryer outlet (in the US) or a normal 230V/13A outlet (in the Eu). in Europe you could also run a separate 32A or 50A 230V circuit as you would for an immersion heater or electric shower. As russ worked out. You would want slightly heavier cable than a regular extension cord just because of the handling it will take, being dragged out to the car every day, stepped on and driven over. You might also want to wire it into the dryer supply rather than use a regular dryer plug, but thats easy enough. The demand for fast charge is for commercial operations. If you don't have a garage near the house you might want to charge up like you would at a gas station. Since even with custom power supplies it's going to take 15-30min to recharge just because of the limits of battery technology. The guess is that places like parking garages will offer pay-for recharge while you park, or supermarkets/malls will offer free recharge while you are shopping as a draw. Last edited: #### gmax137 I think it's just a matter of safety. They are pretty high currents. So why not make it as simple and easy I think that's the concern - too easy. Expect to read about some fool who buys a$0.99 cheap extension cord at the discount store & then grafts on the plug & socket from an old dryer cord... When the wires melt and his house burns down he's going to sue Chevvy

Can it not be transmitted across 70 ft easily? What are the logistical reasons it can't be done?
Seems like dragging a 70 foot cord up from the basement to the driveway every nite is kind of an inconvenience. I would sure rather have a dedicated line, with a self-winding retractable feature. Take a look at the kind of "shore power" cables that boats use to hook up power at marinas. Heavy cables prevent overheating & unnecessary voltage drop.

#### dr dodge

if you consider that you will be trying to charge your car after work, and your wife will be trying to get laundry done after work (our fam of 5 meant laundry every nite) then the shared plug gets "busy". during the 8 summer months in the south the AC unit will be running all day long, then with the dryer, hot water heater, home accessories, and electric car, I would bet that the 80% rule would get very close to the total load the house can safely handle. now add all the houses in the subdi-land, and added grid draw is gonna go up. maybe what they really ment was the grid would need upgraded.

and I an not sure which I rather have, a way to work, or a clean shirt when I get there

dr

#### russ_watters

Mentor
Yes it's perfectly reasonable to charge a small plugin electric from a 220v/16A dryer outlet (in the US) or a normal 230V/13A outlet (in the Eu). in Europe you could also run a separate 32A or 50A 230V circuit as you would for an immersion heater or electric shower. As russ worked out.
Actually, electric dryers tend to run on 40A circuits, not 20A circuits and nominal in the US is 240V, not 220. Here's a pretty standard electric dryer that's 240V, 26A: If the entire world's population were infected
You would want slightly heavier cable than a regular extension cord just because of the handling it will take, being dragged out to the car every day, stepped on and driven over. You might also want to wire it into the dryer supply rather than use a regular dryer plug, but thats easy enough.
The cable would be nowhere close to a regular extension cord. Neither the wire size nor the receptacle configuration would be typical.

#### mheslep

Gold Member
I saw the article and ran the math and I was pretty confused by the issue too. Here's what the CNN story says: http://money.cnn.com/2009/12/11/autos/electric_car_charging_challenges/index.htm?cnn=yes

So lets look at the math:

The Wiki in the Volt has a 16 kWh battery, with 8 kWh useable (it is a plugin hybrid.
The Wiki on the Leaf just says a 24 kWh battery.
The Wiki on the Mini-e says a 35 kWh battery.

The National Electric Code says a branch circuit can't be designed more than 80% full, which for a typical residential circuit is 120Vx16A=1920W. I'm not sure if that is a the real maximum for a single device on a multiple outlet circuit, though, since the biggest draws you ever see for household devices are 1500W. But lets go with it...

For the Volt, that means the 8 kWh capacity takes 8/1.92=4.17 hours assuming 100% charging efficiency.
For the Leaf, 24/1.92= 12.5 hr
For the Mini-E, 35/1.92 = 18.2 hr

Now the Mini-E and Leaf have 100+mile ranges, so they go beyond what a "commuter car" should be expected to do. But yeah, if you want to drive 80 miles each way to Grandma's house for Thanksgiving, you may have an issue. As a 40 mile a day commuter car, it wouldn't be an issue.

Now lets say you use a dedicated 40A, 220V circuit (actual draw, 32A, 7.04 kW). The new numbers are:
Volt: 8/7.04=1.1 hr
Mini-e: 35/7.04=5.0 hr

The downside, of course, to these is that you do need somewhat special circuits, so your options for where to charge would be limited.
Great post Russ.

Now what about the phrase: "hardwired directly into high-power lines"? The words don't really have a lot of meaning to me. "Hardwired" may mean there is no plug, that you wire the charging device directly to the circuit. That's not necessary and not how I would design it, but it may actually be that way. "High-power lines" is a completely meaningless phrase. I don't know what they intended by it, but every normal residence in the US has 220V.
Yes I believe that's a crudely put way (by Money) of saying the quick chargers are probably 440V, i.e. service not typically available in residences.

A bigger issue, not discussed, is that not all residences will have that much extra power available. It isn't uncommon for a single family house with electric hot water, dryer and cooking (plus an air conditioner....) to have a 100A service. That's 4 devices up to 32 A apiece. You can use some diversity and not assume they are all running at full capacity all the time, but still, there may not be any extra capacity on such a house to add another 220V/40A circuit. And upgrading your service is very expensive.
A very good point. Not only is the upgrade to a large service expensive, the power utilities would push back if it was requested on a large scale. If 6/10 residences in a neighbourhood all wanted to bump from 100A to 400A, and use it, they'd have to upgrade the local transformers, at least. Essentially the residential neighbourhood would start looking like a commercial/industrial load to them, which is fine, but I expect they'd want to charge accordingly to handle the distribution upgrade.

#### mheslep

Gold Member
...I would sure rather have a dedicated line, with a self-winding retractable feature. .
I believe that self-wind is an important oversight now in most of the curb side, on the street chargers being installed. None of them have/support such a feature. The car driver rolls around with the cable, pulls it out to plug in. No retraction means at large scales means either a) cables have to be annoying short for street side parking maneuvers, or b) we all trip and drive over the slack in long cables.

Edit: looks like coiled cable is the proposed answer.

#### mheslep

Gold Member
Couple examples:

Last edited by a moderator:

#### mgb_phys

Homework Helper
Those look a bit 'design concept'
There is already a couple of proposed standards, Europe and Japan look like they are all going to agree on the Merc system.
The US could go with a different plug because people don't often drive into America from another country (except Canada which doesn't count ;-)

#### gmax137

thanks for the photos, mheslep

I don't see why the concept has the cable provided by the driver... I can see people unplugging the car end, go inside to pay or get a coke, and drive off leaving the cable behind. If I pulled into a gas station and found a just a hose fitting on the pump, I'd be pretty surprised ('what do you mean, you didn' bring your hose...'

I suppose there's a simple explanation that makes sense

#### hamster143

Yes I believe that's a crudely put way (by Money) of saying the quick chargers are probably 440V, i.e. service not typically available in residences.
Okay, we have to be careful here. There seems to be some confusion:

- Quick chargers mentioned by the article are 440V and up to 50 kW. No one is going to be installing those in personal residences. At first, there will be maybe 50 of those per state installed in major cities and on major freeways (e.g. between Los Angeles and San Francisco).

- Home chargers installed for owners of Leaf and Mini will be substantially less powerful, they will draw 10 kW tops, possibly much less.

- You don't need to run a separate circuit, you may be able charge from the dryer outlet. You do need a basic piece of hardware that plugs into the dryer outlet and a proprietary cable (SAE J1772) that runs from that hardware to the EV. That way your EV would be able to negotiate the current without burning out or blowing the fuses. The connector cable is designed with a number of safety features. For example, it is automatically depowered if it's not plugged in, or it's damaged (maybe because you ran it over while backing out of the garage the previous night).

#### Averagesupernova

Gold Member
Okay, we have to be careful here. There seems to be some confusion:

- Quick chargers mentioned by the article are 440V and up to 50 kW. No one is going to be installing those in personal residences. At first, there will be maybe 50 of those per state installed in major cities and on major freeways (e.g. between Los Angeles and San Francisco).
50 KW (actually KVA) transformers with single phase 240 volts is not at all uncommon in rural areas. If someone has the need and is willing to buy that amount of power, the supplier will see to it that the equipment is put in place to do so.

#### russ_watters

Mentor
Also, the power company is required by law to provide you with a service to your house that meets any reasonable request. What is "reasonable" is defined by the law. So if a 400A service doesn't currently fit the definiton, the law could always be changed to occommodate this.

#### Averagesupernova

Gold Member
Also, the power company is required by law to provide you with a service to your house that meets any reasonable request. What is "reasonable" is defined by the law. So if a 400A service doesn't currently fit the definiton, the law could always be changed to occommodate this.
I would also like to point out that what is "reasonable" as defined by the law will likely vary from location to location. I don't doubt one bit that there are locations where a single phase 240 volt 50 KVA transformer at a residence would be above and beyond "reasonable".

#### mheslep

Gold Member
Also, the power company is required by law to provide you with a service to your house that meets any reasonable request. What is "reasonable" is defined by the law. So if a 400A service doesn't currently fit the definiton, the law could always be changed to occommodate this.
400A is common, I have it.

#### mheslep

Gold Member
... At first, there will be maybe 50 of those per state installed in major cities and on major freeways (e.g. between Los Angeles and San Francisco).
50 quick charge stations per state? I doubt it. Maybe in California. Look at the details: A Leaf quick charge is supposedly 80% of ~25kWh (100miles) in 30 mins, i.e. ~40 kW per charger. Half an hour wait means a rest station has to be built or collocated - bathrooms, food. Then nobody will tolerate waiting in line for a charge at a "quick charge" station, so 5-10 chargers have to be installed. Parking, etc. If the batteries improve in charge rate - to say 10 minutes ( LiFePO technology doesn't support this yet), then we have a 150kW charger required, per vehicle charge point. Further into the future, with say 200 mi/ 50kWh, 5 minute charge batteries, the service is 600kW per charge point!

What's needed is some kind fast battery exchange mechanism. There's a Berkely study showing wide spread acceptance of EVs in 10 years IF battery lease and exchange can be made to work, twice that time if not.

#### dr dodge

I am wondering who is gonna pay for all the "charging pods" and who will stand good for the power bill. also, those connectors and cable don't look like they'd be any fun in parts of the world that have harsh winter conditions. Ice and snow packed into the connector on your car, then some "brainiak" gets out his truck key to dig ice out of the end and (insert the smell of bacon here)
people are scarey enough with gasoline

I say a lady "pressure wash" her trunk lid with about a gallon trying to muscle the hose to the wrong side of her car.

a "full service" fueling infrastructure would be much better (for in town) as it would control access and help with a minimum level of safety

dr

"Charge electric car from dryer plug?"

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