by Richard Keech

2020-04-02

Here’s my quick and dirty method of powering some essentials in my home using my plug-in car, should that ever become necessary in a crisis.

The car

My car is a 2013 Holden Volt.  It’s a plug-in hybrid with a 16kWh battery pack.  It doesn’t come with any out-of-the box way of accessing that energy for use in the home.

The trick

Directly accessing the 16kWh battery in this car isn’t practical. So, the trick of getting energy for home is to get it via the 12V system.  Yes, EVs still have regular 12V batteries for the instruments and lights. The car’s 12V battery is kept charged from the main battery pack via a device called a DC-to-DC converter, rather than a motor-driven alternator.  So it turns the high-voltage DC from the drive battery into ~14.5V needed to charge a 12V battery.

The 12V supply from the battery can be used to drive a small inverter – the sort popular with camping, and 4WD folks.

The trouble is that the car needs to be started so that the 12V battery is kept charged.  While that’s not ideal, it isn’t a big problem. However, it does mean that, every now and again, the car’s internal-combustion engine may start and stop.

The wiring and plug

The 12V battery in the Volt is under the floor of the hatch at the back.  I’ve arranged a safe, quick-connect method plugging in by using a method described here.  There was a kit available in the U.S. for this, but I’ve put together the same thing from scratch.  The end result is a fused, easy-to-access plug and lead that’s normally tucked away discretely out of the way.

The plug used is a 120A Anderson plug which I got from Jaycar.

The inverter

To create mains-voltage electricity out of 12V DC I chose a 2000W pure-sine-wave inverter also from Jaycar.  The inverter, by itself, does not show the input or output voltages, so I’ve improvised using some bits and pieces at hand in my spares box.  I’ve mounted these items to a piece of MDF and screwed whole assembly to my garage wall.

In my case, I connect to the car using a heavy-gauge cable and another Anderson plug, run out the window of my garage.

Power delivery

It tests out OK. I don’t imagine ever pushing it to the inverter’s rated output of 2000W. However it could be capable of powering some lights and a fridge, and miscellaneous PC and utility devices.  So 20 – 100W continuous average power should be quite useful in a crisis.  And 13kWh of usable battery can power 100W for 130 hours.  The overhead of the car being turned on means that there’s a non-trivial consumption by the car being ready to drive, so the practical duration of backup power from the EV battery is reduced.

In a crisis, the car’s petrol engine would start automatically if required to maintain battery state.  So the potential for keeping useful amounts of power for a long time is considerable if the starting point is a full petrol tank and a full battery.

Obviously, this should only be done if the car is parked in a well-ventilated situation because the operation of the petrol motor produces fumes.

Keeping it safe

Keeping your electricals safe is obviously important. In this type of installation the main concern would be the need to avoid electric shock associated with the devices plugged in to the supply. In our homes we use safety switches. In this case I did the same thing with an an inline safety switch (RCD) from Jaycar electronics. I tested this will a few different load devices and I didn’t get any false activations of the safety switch. So I think a safety switch is a worthwhile for projects such as this.

Other cars

Other EVs and PHEVs can do this too.  Two EVs, the Hyundai Kona and Ioniq, provide for this very well by having a ‘Utility Mode‘.  This mode allows the 12V battery to keep charged without needing the car to be on and ready to drive.

DiY caveat

Note that this project does not involve or require working with or changing fixed mains-voltage wiring.  Any changes to your home’s mains wiring should strictly be left to an electrician.

For this project, all work on the mains-voltage side of the inverter is limited to plugging in un-modified extension cords, plug boards, and devices using normal mains plugs.

Non electricians are permitted to work on 12V wiring.

Conclusion

I haven’t seen this arrangement used ‘in anger’ yet.   But it seems prudent in uncertain times to have the means of powering basic devices during a crisis.