How To Power Your Home During A Power Outage With An Electric Vehicle

"Numerous power outages expected, likely prolonged." 

...reads the warning from the local Google Crisis Map warning for West Michigan as I compose this essay.  We still have power and internet at the moment, but it wasn't that way on February 7, 2019 when we lost power for nearly a full day.  The patchwork of power outages shown on the Consumers Energy Outage Map looked like a product of a quilting bee.

With just about everything in your home needing power to operate, even the controls and ignition of my gas furnace were affected.  I noticed that the house was getting a bit chilly in the 15°F outdoor temperatures.  While our comfort and access to a hot shower was a concern to me, ironically it was the 40 lbs of Michigan blueberries in my freezer being in jeopardy of thawing out that first popped into my head.

Note: if you prefer a quick video overview, I recorded this YouTube video.

Electric Vehicles to the Rescue

My Nissan LEAF with a Power Inverter Installed
The concept of Vehicle-to-Grid or V2G has long been promoted by Nissan (Nissan Using Vehicle To Grid Technology To Power US Operations), partially to draw attention to their CHAdeMO DC charging standard that has two-way electricity flow as one of its inherent features.  

Without the benefit of a V2G adapter, which to my knowledge is not yet easily available to the average homeowner, there's a relatively inexpensive and easy way to bring power to selected devices in your home during a power outage.  

12V DC to 110V AC Power Inverter

Batteries convert chemical energy to Direct Current (DC) electricity where electrons flow in one direction of the power circuit.  A typical car battery that runs your accessories like lights, heater blowers, wipers and electronics is a 12V DC system.  

Power Inverter
Image source:
The appliances in your home tend to run on Alternating Current (AC) where electrons move back and forth and at a higher voltage such as 110V in North America.  Without going into too much technical detail, they key to powering home devices is to convert 12V DC to 110V AC.  The device that provides this conversion is called a power inverter.  Inverters are commercially available at many retail outlets like auto parts stores, home improvement stores, and my favorite gadget store: Harbor Freight.

This setup works for internal combustion engine cars as well.  The reason this application is well-adapted for an electric vehicle is that you can keep the car powered up in the garage without creating exhaust gases.

How Much Power Do I Need?

My Gas Water Heater Connected
To The Extension Cord
Before you rush out to buy an inverter, you need to analyze how much power you want to run from your car.  Ideally, you would just throw a big switch to go from grid power to battery and go about your business of daily life.  Unfortunately, it's not that simple and running your whole house from a car battery is unrealistic.  

Wholesale Solar has an appliance power consumption guide for those who want to design a solar panel system.  This is a handy guide for looking up how much power each type of device uses.  You should check the actual use of the items based on their labels.  

The main things I want to operate in a power outage are my refrigerator and my gas water heater.  A refrigerator can run around 800 Watts when it's running, less if you have a newer more efficient unit.  I have a gas fireplace that heats my ground floor sufficiently, but I could also power my gas home heating system (see "Other Considerations" below).  While gas appliances get their heating energy from burning natural gas, they still have electronics, electric ignition systems as well as blower fans.  The blower fans will consume most of that energy and run 500-800 Watts.  

Appliances will often have a power surge when you turn them on and then stabilize to a smaller running power usage to keep them running.  Think of how a powering up a vacuum cleaner can sometimes dim your lights.  As a result, inverters are often rated for a continuous load and a peak load to absorb those surges.  

Add up the power rating in Watts of all the devices you intend to run simultaneously to get a maximum power rating for an inverter.  For me, I know I could keep it below 2,000 Watts.

Sample Harbor Freight coupon

The Selected Inverter

I decided a 2,000 Watt continuous / 4,000 Watt peak inverter from Harbor Freight would fit my needs, specifically a JUPITER - Item#63429.  The list price is $179, but you can often find coupons for this unit to bring the price down to around $129.  See example to the left.  This coupon may be expired by the time you read this, but Harbor Freight often run specials or have general percent-off coupons.  Just search for "Harbor Freight Coupons".

In addition to 3 110V outlets, it also features a 2.1 amp USB charging port and power use meter.  

Battery Cables
Image source:  eBay

Connection to the Battery

While some inverters come with integral clamp-on leads, the higher power units often have screw terminals, and you will need to purchase battery cables separately.  Because these cables could possibly carry such a large current at 12 Volts, they need to be an appropriate wire gauge to carry that much current.  The Jupiter inverter I purchase recommended 2-gauge wire cables.  Note that if you are not familiar with wire gauge, a smaller number indicates a thicker cable.  So you do not want to get a larger number gauge since that wire diameter will be too small and potentially overheat.  

Lug Terminal
Positive Battery
I purchased mine via eBay (see listing) and chose a set terminated with lug terminals.  A lug terminal has a loop that can be screwed on to the battery and inverter terminals for a secure electrical and mechanical connection.

Connect Cables to the Inverter First

Inverter Cable Connections
The inverter should have connection points for the battery cables.  On the unit I purchased, they were threaded rods with nuts.  Loosen and remove the nuts, then attached the red cable lug terminal to the positive lead on the inverter and the black cable lug to the negative terminal.  Replace and tighten the nuts.  The reason to do this first is that it's done while the unit is not yet connected to power.

Connect Cables to the Battery

Positive Battery Terminal with
Inverter Cable Attached
Ensure that the inverter is powered off.  The battery terminals are threaded rods with a nut.  The positive (red) terminal is shown here and the negative ground terminal (black) should be similar.  On the Nissan LEAF, a 13 mm socket will fit the nut.  Loosen the nut, remove it with you fingers so as not to lose it, connect the lug terminal wire, then replace and tighten the nut.  Be careful not to touch the exposed metal on the red cable to any metal parts of the car, which are grounded and could cause a short circuit with sparks.  Also, do not remove any existing cable from the battery, just the connection nut.  If you remove leads, you may lose power to the car, thereby resetting some on-board electronics.

Negative Battery Terminal with
Inverter Cable Attached
Similarly, remove the nut on the negative terminal, loop the interter cable lug over the threaded rod and secure the nut.  Again, don't remove any cables.  The final connection may cause a small spark on the battery terminal, but as long as the inverter is not already powered up or connected to a 110V load, this should not be significant.

All Systems Go

Green Power Light: Ready For Service
At this point, all the connections should be made and the inverter is ready to power up.  If there is power indication, turn on the inverter switch to see if you get a positive confirmation that you have power.  The unit I purchased has a green light indication that it has power.  

Turn On The Car

The 12V battery in your electric vehicle gets its power from the main vehicle battery (aka the "traction" battery) via a DC to DC converter.  In a combustion car, the alternator takes care of this function.  While the DC/DC converter function varies on different vehicles, it is mainly active when the car is turned on and ready to drive.  

I tried to use the LEAF's "accessory" function (hit power button twice without the foot on the brake) which powers up your infotainment screen, etc.  However a quick voltage check on the 12V battery showed it to be around 12V and thus not receiving power from the DC/DC converter.  When I powered up the car into drive mode, the 12V battery voltage shot up to over 14V, thereby ensuring the accessory battery was being charged.

If your 12V battery voltage gets too low, it cannot even power the electronics that run the car.  So you may have a full traction battery, but if the control computer can't run, the car is a brick!

Turn off your vehicle's climate control, headlights, and anything else that might draw power in the car to maximize battery life.

Ready for 110V Loads

At this point, I ran a properly sized extension cord into the house.  A cord rated for 15 A can safely run 1,800 Watts (15 A x 120V = 1,800 W), so again consider the total load you want to run continuously.  I first powered my refrigerator independently to make sure it could cycle the compressor and cool down.  I then connected my water heater which runs the control electronics and the exhaust blower.  Both cycled just fine and I kept my frozen blueberries and was able to have hot shower for the family.

Other Considerations

Monitor Your Car Battery

Periodically check your traction battery level to make sure it doesn't get too low.   My home power usage averages around 13 kWh per day in the winter, so even full usage should only drop the LEAF's battery level by 50% for 24 hours.  Assuming you would scale back your usage to only the essentials, you should be able to get several days if not a full week of use out of the car's battery.  

Potential Overload

In general, anything that uses electricity to provide heat will require a LOT of power.  That includes electric water heaters, electric ranges and ovens, space heaters, toaster ovens, and hair dryers.  Similarly, items with a large compressor like an air conditioner will require significant power.  Many of these devices would overload even a 2,000 Watt inverter.  

Another overload potential is the DC to DC converter itself.  While I have not found a definitive source for the maximum rating, the number 1,500 to 1,700 Watts is mentioned in this Reddit discussion of the LEAF DC to DC converter.  You'll want to double check this for your particular vehicle.  

Ability to Tie In

My gas home heater could likely be powered from the above inverter setup.  However, it's hardwired into my home breaker box and therefore, I don't have anywhere to plug it into the inverter.  I would need to have an electrician create a connection point to allow to me to run my heater from an inverter or other external source.  

Modified Sine Wave

Inverters use an artificial sine wave to create alternating current.  Most inexpensive units such as the one I purchased use a "modified sine wave" generator.  Rather than a true sine wave, they create a stepped wave that is good enough for most appliances.  However, some items are sensitive to this difference and may generate a high-pitched hum or not work at all.  Here are more details for the technically oriented:

Test Before You Depend On It

When it doubt, test your setup with the items you want to power before you need them.  You don't want to depend on, say, a CPAP machine or a medical oxygen concentrator, and then find out it won't work with an inexpensive inverter.

Removing the Inverter

Once you no longer need to use the backup power, you will want to remove the inverter.  Remove all loads from the inverter, unplug extension cords, and turn the power off.  Remove the positive (red) side nut that is holding the red cable lug, remove the inverter cable, then replace the nut.  Repeat for the negative (black) cable.  There's no need to remove the cables from the inverter.  This way you'll be ready for a future power outage event or another scenario where you can use 110V power from your car.  Tailgating anyone?

Why the LEAF?

Someone ask me the question about why I preferred to run the house power off the Nissan LEAF rather than my Tesla Model S.  The quick answer is accessibility of the 12V power.  The Nissan has its 12V battery easily accessible under the hood.  The Tesla would require me to remove the black nosecone to access the 12V terminals.  Here's a YouTube video that describes how to "jump start" your Tesla in case the 12V battery is dead which includes instructions on how to remove the nosecone. 

Warranty Considerations

Some vehicle manufacturers are not so keen on you cycling the battery on your car when it's not related to driving the car.  So please be aware of your vehicle's warranty language before using the car for home backup.  At least, maybe you don't want to advertise your backup use on social media unless your car, like my LEAF, is out of warranty.  See this Jalopnik article "Using Your Tesla To Power Your House Will Void Your Warranty" for more information.  



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