Using portable chargers

What is a portable charger?

A portable charger, which is often called a 'granny cable', allows you to charge an electric vehicle from a normal mains socket. These have some drawbacks though:

  • they only draw 10 amps (2.3kW) so charge your vehicle slowly, at a rate of 9-10 miles per hour (vs up to 30 miles per hour with an EV wall charger)

  • they aren't as safe as a proper EV wall charging unit

  • they aren't waterproof

More recently the use of portable chargers has been discouraged and are now sometimes classed as "occasional use" or "emergency use" chargers. This is really to encourage the installation of a EV wall charging unit. A proper wall charger is safer as it does not use your existing mains wiring and it also incorporates additional safety features and functions. However, with some common sense and care, portable chargers are safe and fine to use. Some EV drivers only use a portable charger to charge their vehicle, but as EV batteries have got larger in recent years, the slow charging rate means they are not a practical solution for batteries above 30kWh.

If you have recently purchased an EV, then you will use the portable charger as a temporary charging solution while you wait for your wall charger to be installed.

Portable chargers are very handy for:

  • Hybrid and small battery EV owners that have shorter charging times

  • Charging at home until your new wall charger gets installed

  • EV owners who have a second home or holiday home

  • Charging when away from home, such as visiting family or staying away

  • Charging at work or when on site

  • Emergency backup if your wall charger breaks

How to use a portable charger?

Using a portable charger is a simple as plugging into a mains socket one end, then into the car at the other end. Then lock the car and walk away. The car controls the portable charger and will turn it off once its fully charged.
It is best to plug it into the mains socket first and switch on the socket (i.e. make it live) before plugging the other end into the car. The plug on the car end isn't actually 'live', even though the portable charger is switch on, until it is properly plugged into the car.

Don't let the control box hang on the plug

You'll notice your portable charger has a short cable between the mains plug and the control box. If when its plugged in, the control box is left hanging on this cable, then you must either allow the control box to sit on something to take the strain off the cable or use the hook provided and hang it on a screw or hook in the wall.

We've seen many faulty portable chargers because users have left the control box hanging. Overtime, the weight of the unit stretches the mains cable and causes faults.

Using a portable charger in the rain

Portable chargers are not fully waterproof - they are only splash proof. It is the controller box near the mains plug which is susceptible to water damage and often the rubber grommets on the cable entry points are not waterproof. If this controller box is left exposed outside, then you could place an upturned bucket or large plant pot over it to protect it from the rain or the morning dew. Remember that it might not be raining when you plug it in, but it could get wet overnight.

The car end (i.e. the plug and charging socket on your vehicle) are fully waterproof and is perfectly safe in any weather.

No warranty claims will be honoured if water damage is the cause.

Charging on the street

While some EV drivers are charging their vehicles when parked on the street, using a portable charger from their house, this isn't a good idea due to crossing a public pavement. Some drivers have used cones, rubber cable protector or slung the cable overhead through trees, but crossing a public pavement is trip hazard and some councils are clamping down on this practice. If you have a rain channel or gully that can safely hide the cable, then that is better and some councils are now even able to install a channel to solve this problem.

Charging an EV from a terraced house using a portable charger. The driver has used the drain gully to cross the pavement so its not a trip hazard to pedestrians.

Using extension cables

You'll often find your closest mains socket isn't close enough to the parked car. You might have to run the cable through a kitchen window or through the letterbox into the hallway or under the garage door into the back of the garage. This is why we only stock the 10 meter versions at Go Green Autos. The standard is 5 metres. There is then a temptation to use an extension cable between the socket and the portable charger. The use of extension cables is not recommended and the portable charger should be plugged directly into a mains socket.

You might find that the portable charger will seem to work quite happily on an extension cable, but most extension cables are not up to the job and can overheat, melt or even catch fire. If this was in the middle of the night, the results could be catastrophic! This is also why the mains cable is so short on the portable charger itself.

While our message is DO NOT USE extension cables, we understand that some people do. So below is some additional information to help minimise the risks.

Most UK extension leads are rated at 10A or 13A. 10A leads will use 1.0mm2 cores. 13A leads will use 1.25mm2 or 1.5mm2 cores. You shouldn't use anything less than 1.5mm2 cable. The problem is that most retailers (and even the manufacturers) will not detail the actual cable size, so it is difficult to know what you are buying. Writing on the sides of the cable may tell you.

Also remember that the trailing socket on the end of extension cables are not waterproof either.

If you do use an extension lead, you must

  • Use one that is rated at 13 amps or above (i.e. thick cable)

  • Always fully unwind it

  • Use as short lead as possible

  • Keep an eye on it - feel the temperature

Don't take any risk. If you're unsure, get help from an electrician.

Always fully unwind extension leads otherwise they can melt and catch fire.

The maximum loading on an extension lead is greatly reduced when it is coiled up. For example, a 13A 4 metre lead unwould can take 3,120 watts. Yet when wound, this reduces to only 720 watts.

Be safe

The portable charger will be drawing 10 amps. In the UK, our ring mains, sockets and plugs are rated to 13 amps. So while this is comfortably within specification, the problems arise because charging an EV from a portable charger takes many hours. Drawing 10 amps constantly for 10+ hours can put additional stress on your existing wiring. There has been a few instances of electrical fires when charging EVs from normal mains sockets. These make the headlines because an EV was involved. But then there are thousands of electrical fires in UK homes every year which do not make the news. EV charging is safe, but only if your wiring, sockets and leads are sound and up to specification. Loose terminations are a common cause of fires, not from just EV charging, but from any appliance. Due to the length of time an EV is charging, this can show up existing problems with your wiring that didn't show before. The problem is that they are hidden behind sockets and you don't know until its too late. If you're unsure, get your wiring inspected by an electrician.

Plug your portable charger into a socket on the ring mains rather than a socket on a spur. A ring mains socket has two cables feeding it. A socket on a spur only has one cable feeding it. In almost all cases, your wiring will be buried in the wall, so you wont know. Normally all sockets in the house are on the ring mains and ok to use. Sometimes you might have just one socket in a garage or outbuilding and these are often on a spur feed. Try not to use these if you can.

British sockets are rated at 13A and therefore are fine with a 10A loading. However, some cheap sockets are poorly made and may not be able to come with a constant 10A load for many hours. This is why the electrical regulations changed on 1st January 2019 which effects the use of portable chargers. It introduced a new 'heavy duty' mains socket which is labelled as 'EV'. For further information see here. Therefore, if using a portable charger is your permanent solution, then you should maybe get your socket upgraded by an electrician. Or at least, make sure your socket is high quality and the screws are done up tight!

Do not add any other load on to the socket you are charging from. Do not charge from a socket that is also being used by other high current devices like a kettle, white goods, etc.

Don't overload leads or sockets. Use common sense or get advice from an electrician.

If your portable charger fails, or the error light comes on, or your vehicle will not charge properly, try plugging the portable charger into a different socket, ideally in a different room.

It is for all these reasons above why the installation of a EV wall charger is recommended and subsidised by the OLEV grant to encourage uptake. When these wall chargers are installed, a new dedicated 32A supply feed is installed from your consumer unit to the wall charger which takes away all the risks from using the existing wiring.