Your electric vehicle was supposed to transport you around town and beyond. The problem is range and charging station availability. With enough public charging stations, electric cars can drive any distance. Unfortunately between the 80-120 mile range of most electric cars, and that insufficient public charging, we face serious limitations. But does that mean we must be limited to traveling a short distance from home?
Electricity is everywhere in these modern times. What's lacking is the charging connectors at charging stations that are required for charging.
If we only charge at home, we're limited to driving within a circle around our home. When we charge at public charging stations, our driving range is limited to areas with charging stations. Why should we allow either of these to limit where we can drive? Electricity is everywhere, why not access that electricity to drive anywhere?
Successfully electric car travel over long distances, at this time, means having the flexibility to use any power outlet you find, and the equipment to maximize the charging rate. You must develop the skills understand some simple rules for safely using (and maybe building) extension cords and adapter cables matching any power outlet.
Currently (2017) the public charging station network isn't enough to let us freely drive our electric vehicles anywhere we want. Most cities have public level 2 and even fast charging, but the inter-city charging network is weak. Even though electricity is everywhere, the electricity has to be adapted into a charging plug for recharging the car. The good news is we don't have to be limited to the public charging station network. There are plenty of high power electrical outlets available, and with the right equipment we can snag a 6 kiloWatt charging rate for a fairly reasonable charging time.
The car manufacturers provide a 120 volts 12 amps (1.2 kilowatts) line cord charger with each car. That unit is better than nothing, since you can always find a compatible power outlet.
The outlet shown to the right, a NEMA 14-50 outlet, is the primary objective for full-speed 6 kiloWatt electric vehicle charging away from both home and the public charging network. This, and other 240 volt 40 amp outlets, will let you charge at 6 kiloWatts continuous power. That's enough for 25 miles of range per hour of charging. (see Understanding charging rates and effective trip speed) Many RV parks have these power outlets, making them potential informal charging locations opening the door to driving into areas lacking public charging infrastructure.
Is it safe to use extension cords and adapters to charge an electric car? Yes, with care. Can you charge an electric car from a dryer outlet? Yes, with care. The short answer is to use a good quality extension cord with thick wires and beefy plugs. In the lists below we show several choices for 120 volt 10 gauge extension cords that are safe for use with a line cord charger, and several 240 volt 40 amp extension cords safe for use with higher power charging stations. Further, a J1772 extension cord is completely safe due to cords and connectors built for the purpose.
WARNING: Vehicle manufacturers universally warn against using an extension cord to extend the reach of the supplied line-cord charger. Please, exercise caution in reading what is written here.
The general principles are:
Where does the heat come from in a substandard situation? A skinny cord, frayed wiring, bad power socket, acts like a "resistor" or "heating element". Sending too much current through a bad connection acts like a heater. Say your car is pulling 6 kilowatts, a 10% loss from a bad connection means 600 watts being dissipated as heat, or about the same as a typical hair dryer. That's a common cause of electrical fires.
Avoid violating Electrical codes Smart electricians and electrical engineers have spent decades cooperatively developing the electrical code. Their recommendations were won through hard work and the occasional electrical fire. It's easy to create adapters to connect a 240 volt 50 amp device to a receptacle rated for 120 volts 20 amps. That's obviously not going to work terribly well, because running 6+ kilowatts through a 120 volt 20 amp plug is going to cause a problem. The device for which you create such an adapter must accommodate dual voltages and automatically adjust its power.
Your fate is in your hands - this is for educational purposes. I am offering this for education, and you are responsible for your actions. Applied incorrectly this can cause electrocution or fire. Take care, be smart and educated, and you'll be okay.
Your best bet is using approved charging stations and approved on-board chargers - but we often have to "make do" with whatever electrical outlet we find. The manufacturers have spent megabucks developing a safe charging system. BUT, unfortunately, we cannot always charge through approved charging stations, and we often are faced with normal power outlets. High power portable charging stations do exist, and success with means understanding what kind of power outlet to use.
The need for safety: Done badly, it's possible to cause damage. The warning against extension cords isn't a whimsy, they're rightfully concerned about safety. Carefully done, you can safely ignore that warning, but you must know what you're doing. There have been multiple fires from electric cars being charged through substandard wiring. How? Bad wiring can easily cause enough heat to raise surrounding materials to the ignition point. This isn't a new issue since electrical fires have happened for as long as we've used electricity. Careful use of good quality extension cords and power outlets is the way to avoid an electrical fire.
We bought our electric vehicles to, for example, help the climate. Getting on the evening news by causing an electrical fire negates the gain you might have achieved.
The electrical code isn't an arbitrary set of nanny-state rules. It was developed through decades of experience and application of electrical engineering principles. Let's have a brief summary, and for many more details see Electric car charging within electrical code and power outlet limits
The "80% rule" says that continuous power through a plug/socket has to be 80% of the rated value. Electric car charging fits the definition of a continuous load, and therefore we must constrain ourselves by this rule. Hence for a "50 amp" power outlet, the charging rate must stay below 40 amps.
Ampacity is the measure of the maximum safe current (amps) we can use in a wire of a given thickness. Generally, the thicker the wire the more current it can carry. Wire thickness is measured in "gauge", and you may have seen this number used. A typical home extension cord is 14 gauge, for example. That wire gauge is completely insufficient and unsafe for the line-cord charger that comes with electric cars.
The 120 volt line-cord charger usually runs at 12 amps, and requires a 10 gauge extension cord. The 6 kiloWatt charging stations run at 32 amps continuous, and requires a 6 gauge extension cord.
The most correct electric car extension cord solution is to extend the J1772 connection. The J1772 extension cords (see the next section) are built to handle the load, with beefy wires and connectors.
That won't always be feasible, however.
With the 120 volt line cord charger it's quite feasible to use a 25 foot or 50 foot length of 10 gauge extension cord. A couple of these are listed below that are excellently built. The bright yellow color helps mitigate any tripping hazard.
For higher power there are several choices meant for 240 volt high power loads. The NEMA 14-50 cords should be used with the 6 kiloWatt charging stations, while the 6-20 and L14-30 cords should be used with lower rate stations. You will almost certainly need adapters - since the 6 kiloWatt charging stations universally use a NEMA 6-50 plug. A couple NEMA 6-50 to 14-50 adapters are listed below.
If you cannot find a suitable manufactured adapter, it's relatively easy to build an adapter.
What happens is gasoline car owners, whether unwittingly or on purpose, sometimes park in front of EV charging stations. See Charging station etiquette - effectively sharing limited resources
Rather than get stuck unable to charge, wouldn't it be useful to pull out a J1772 extension cord? That's the thought behind these two products. You'd have a J1772 extension cord, with all the necessary safety features built in (thick wiring and beefy plugs), that you can use to extend the reach of the charging station.
These extension cords can also be used at home. Say your charging station has a prescribed location, but your car has to park far away? The charging station might come with a 25 foot cord that doesn't reach the parking spot. What do you do? Use the J1772 extension cord.
The JLong 40 amp J1772 extension cable, from Quick Charge Power, and the De-ICEr 40 Amp 20 Ft J1772 Extension Cord for EV Charging Stations, from Electric Motor Werks, are both properly designed J1772 extension cords supporting a 40 amp continuous electrical load. Other J1772 extension cords max out at 32 amps, meaning the components aren't as high a quality. By supporting 40 amps, the wires are thicker, and the connectors more robust, making either a safer choice than the others.
I own a JLong, and am impressed with how solid and robust are the connectors. The cable is flexible enough to easily loop into a small bundle that's easy to carry in the trunk. Finally, there's a small but important detail - the charging handle can be locked using a simple padlock. This means your car won't be unplugged unexpectedly or at the very least the JLong won't be stolen.
J1772 extension cords are useful any time the charging cord isn't long enough to reach your car. Maybe you've been blocked from a charging station, but can park a couple stalls down. A J1772 extension cord like the JLong or De-ICEr gives extra reach.
The JLong isn't the only electric car extension cord choice. You can also safely extend the other side of the charging situation connection using a more traditional extension cord. This must be done with care, using extension cords meant for heavy duty usage. Fortunately these do exist.
120 volt cords for the line cord charger Every electric car comes with a 120 volt line cord charging station. Generally these run at 12 amps 120 volts, meaning the extension cord must be capable of running that much current continuously. Scroll down to the bottom of this page and you'll find a few such choices. If you're looking at extension cord packages in the store, study the writing carefully. It'll say the cord is rated for 10 amps, 15 amps, whatever, and that the cord is 12 gauge, 14 gauge, or whatever. The smaller the gauge number the thicker the wire - 10 gauge is the minimum recommended for this purpose. Again, scroll down to the bottom of this page and you'll find several extension cords meant for contractors.
240 volt 20 amp extension cords Several 3 kiloWatt charging stations are available in a tiny package that are easy carry around at all times. The Aerovironment TurboCord has the advantage of supporting both 120 volt 12 amp and 240 volt 16 amp. Scroll down to the bottom of the page and you'll find NEMA 6-20 extension cords that will work perfectly with the TurboCord.
240 volt 40 amp extension cords For higher power 6+ kiloWatt charging stations, you'll need a heavier-duty extension cord. Scroll to the bottom and you'll find several NEMA 14-50 or NEMA 6-50 extension cords. These handle 40 amps continuous and will do what you need. Most (all) of the charging stations shown here come with NEMA 6-50 plugs rather than 14-50 plugs. That means buying a NEMA 6-50 to NEMA 14-50 adapter, several of which are shown below, or else replacing the NEMA 6-50 plug from the charging station cord with a NEMA 14-50 plug.
The following are some useful extension cords.
NOTE CAREFULLY: When in the store looking at extension cords, read the label carefully and look at the thickness of the wire. For charging an EV, we want at least 10 gauge thickness.
Some of these have a molded plug on one end, and bare wire at the other. That makes them excellent starting points for building adapter cords. It's also possible to buy an extension cord, cut off the ends, and attach other plugs, to build a custom adapter.
Charging an electric vehicle is almost certainly going to happen outside. It might be raining. Water and electricity is of course a bad idea. GFCI plugs are designed to make it safe.