# Grid Tie Inverters - backup power from car to house



## Salty9 (Jul 13, 2009)

Not exactly what you were asking about, but similar: http://blogs.scientificamerican.com/guest-blog/2011/10/27/vehicle-to-grid-technology-electric-cars-become-power-grid-batteries/


----------



## StanSimmons (Sep 3, 2011)

Jack R. is using one as a load for battery testing. http://www.projectooc.com/evtv/index.php?showid=84#84

The most common converters are grid-tie, which will not operate if the power grid is down. These will work fine if you want to load a battery pack for testing, but won't do you any good if power is out in your area.

An off-grid converter can be used to power your house from your battery pack during an outage. You will want to get an electrical panel interlock of some sort so that you don't feed back power to the grid and kill any linemen working on the outage. The problem with off-grid converters is that most of them are 12-24VDC not 120-180VDC. A MPPT charge controller could step down the voltage to handle that.

Just throwing the main breaker and backfeeding thru an outlet will work... but is illegal in the US and most of the world. If you do it, you will want to backfeed thru a 220/240 outlet (dryer/stove outlet), otherwise you will find that half the plugs in your house will not be powered.


----------



## charliehorse55 (Sep 23, 2011)

This thread may of interest: http://www.diyelectriccar.com/forums/showthread.php/120-230v-ac-mains-64643.html

Didn't find anything of that high wattage for such low input voltage requirements, if you wanted high wattage (say 7kW), you'd need to go to much larger battery voltages.


----------



## PZigouras (Jun 5, 2010)

gdirwin said:


> Has anyone researched off-grid inverters (or grid-tie inverters) to take power from your EV into your house?
> 
> Ratings:
> DC Volt: 120-180VDC
> ...


Some controllers, like the one from AC Propulsion use what's called "V2G technology" for vehicle-to-grid connectivity. It's probably a lot easier for them to do it, since the inverter runs the car's AC motor to begin with. 

It's probably a lot more work to add something like this to a DC controller. You may be better off just buying a large, standard inverter and running it as a stand-alone off the car.


----------



## ElectriCar (Jun 15, 2008)

gdirwin said:


> ...I would manually open the main breaker to my house, connect this through an AC plug and back-feed my house ...
> 
> It would be nice if it could self-limit current, but not essential.
> 
> All info appreciated!


That is a serious code violation as it's a safety issue and a very risky one. Should you forget your car is connected somehow and energize the main once the power returns, you will likely have some serious excitement. If not you, someone else could do the favor for you and blow up your expensive new gear and batteries. 

However if you're convinced you can not make a mistake with this, install a breaker in your panel for the amperage of the inverter you use if one isn't built in or even smaller for a little cushion. Connect the inverter to the terminals of the breaker. Turn the main breaker off first, turn on the new breaker and you're in business.


----------



## StanSimmons (Sep 3, 2011)

ElectriCar said:


> That is a serious code violation as it's a safety issue and a very risky one. Should you forget your car is connected somehow and energize the main once the power returns, you will likely have some serious excitement. If not you, someone else could do the favor for you and blow up your expensive new gear and batteries.
> 
> However if you're convinced you can not make a mistake with this, install a breaker in your panel for the amperage of the inverter you use if one isn't built in or even smaller for a little cushion. Connect the inverter to the terminals of the breaker. Turn the main breaker off first, turn on the new breaker and you're in business.


An interlock of some sort really is needed. One of the simplest is a metal plate that blocks the mains when the backup breakers are active and blocks the backup breakers when the mains are active.

My father uses the following one for his genset backup. http://www.interlockkit.com/index.htm


----------



## adamj12b (May 4, 2009)

ElectriCar said:


> That is a serious code violation as it's a safety issue and a very risky one. Should you forget your car is connected somehow and energize the main once the power returns, you will likely have some serious excitement. If not you, someone else could do the favor for you and blow up your expensive new gear and batteries.
> 
> However if you're convinced you can not make a mistake with this, install a breaker in your panel for the amperage of the inverter you use if one isn't built in or even smaller for a little cushion. Connect the inverter to the terminals of the breaker. Turn the main breaker off first, turn on the new breaker and you're in business.


The really scary thing is probably 50% or more of the people in the New England area that are running generators right now, are powering their home in this way. 

Yesterday I heard of at least 3 people having their generator either blow up or are back feeding the neighborhood and will be blown up if they dont catch it.

-Adam


----------



## ElectriCar (Jun 15, 2008)

Well accidents happen. It's easy to forget to do something in order and poof its' gone or worse someone gets injured. But to do it properly it's a little more expensive. That's what I do and it can get pretty expensive depending on how large it is and how much you want to power. 

One thing about doing it this way is you can overload the generator and possibly damage it. By code it's supposed to be that the generator can handle anything connected to it. Powering the entire panel doesn't comply with that.


----------



## charliehorse55 (Sep 23, 2011)

I think the best way is just to run an extension cord to you car and run any appliances you want to directly off of it. Don't use your home's wiring at all.


----------



## Ziggythewiz (May 16, 2010)

I would second Charlie's approach. It's hard to track down vampire loads across the whole house and in an emergency you don't want to be powering any more than what you really need. Also, unless you live somewhere with frequent outages it doesn't need to be a really convenient system. Just hook your exetnsion cord to the fridge or whatever and run it to an inverter on one of your batteries; switch batteries every 4-8 hours.

I hope no one lives somewhere where outtages are frequent enough that a full home UPS is necessary.


----------



## StanSimmons (Sep 3, 2011)

I disagree with the extension cord method. Extension cords are generally smaller gauge wire than what is in your walls and that can cause problems for long runs. Extension cords are also prone to damage if they are pinched in a door or window, leading to a potential fire. You won't be able to run your furnace blower off of an extension cord, and if your power is out in the winter, you just might need your furnace.

My recommendation is to have a system professionally installed, but failing that, install a mechanical lockout yourself. Have all of the breakers properly labeled and turn off any that aren't needed during an outage. Anyone who can convert a vehicle to electric can easily handle installing a lockout kit.

I know several people that have external gensets that plug into a weatherproof dryer outlet or a permanent hardwired connection. A few have automatic switches, most have mechanical lockouts, and a few have mechanical lockouts and have the genset only power a sub-panel with only the minimum needed circuits on that sub-panel hot.

Ziggy, there are a lot of folks that live where power outages are common, and often long lasting... and in the case of a disaster, very long lasting.


----------



## Sunking (Aug 10, 2009)

To be code compliant you would have to have either an Automatic Transfer Switch or Manual Transfer Switch installed at the service entrance where the meter is. Typically you would use a Generator Snorkel made by Appleton at the switch, and use an umbilical cord of appropriate size for the current involved.

But if you are really serious the best option both economically and operationally is to install a pad mounted emergency generator fueled by either LPG or diesel fuel. No gasoline.

EDIT 

Now that I stop and think about it, there would be no code compliant way to use an EV as emergency power as it is not listed for that purpose.


----------



## charliehorse55 (Sep 23, 2011)

Sunking said:


> To be code compliant you would have to have either an Automatic Transfer Switch or Manual Transfer Switch installed at the service entrance where the meter is. Typically you would use a Generator Snorkel made by Appleton at the switch, and use an umbilical cord of appropriate size for the current involved.
> 
> But if you are really serious the best option both economically and operationally is to install a pad mounted emergency generator fueled by either LPG or diesel fuel. No gasoline.


Even if you already have an electric car with a 30kWh battery? As for the weak extension cords, I was thinking to use a thick 30A rated cord. I have it sitting in the garage anyways, it would work.


----------



## StanSimmons (Sep 3, 2011)

Sunking said:


> To be code compliant you would have to have either an Automatic Transfer Switch or Manual Transfer Switch installed at the service entrance where the meter is. Typically you would use a Generator Snorkel made by Appleton at the switch, and use an umbilical cord of appropriate size for the current involved.
> 
> But if you are really serious the best option both economically and operationally is to install a pad mounted emergency generator fueled by either LPG or diesel fuel. No gasoline.
> 
> ...


Why would it matter if your battery bank is housed in a battery cabinet hung on the wall or on four wheels? If you use a commercial off-grid converter and an approved interconnect lockout system you should be golden.


----------



## Sunking (Aug 10, 2009)

charliehorse55 said:


> Even if you already have an electric car with a 30kWh battery?


Does not matter. Electrical code is very specific in that anything that is connected to the premisses wiring shall be listed and approved for the purpose. 

You can certainly connect your charger to take power from the premissis wiring because it is listed and approved for that purpose, but not the other way around. 

It is a technicality, but if you were to install a transfer switch with a generator snorkel to code and inspected, the AHJ is not going to know you intend to use your EV as the source. Being plug-n-cord connected is a gray area, but the code would treat it as a Emergency Generator

The real challenge is finding a battery inverter to work with your battery voltage. We use a lot of commercial inverters made to operate at 140 VDC, 290 Vdc and up to 600 VDC but they are pricey.


----------



## charliehorse55 (Sep 23, 2011)

Sunking said:


> Does not matter. Electrical code is very specific in that anything that is connected to the premisses wiring shall be listed and approved for the purpose.
> 
> You can certainly connect your charger to take power from the premissis wiring because it is listed and approved for that purpose, but not the other way around.
> 
> ...


Right, but what about just using an extension cord? There's no way that's against code, since it wouldn't even tie into your homes electrical system. 

Also, how expensive is expensive? Even just a ballpark would be great. I'm trying to find a unit for the range of 300V-450V DC input 120VAC output to use on my conversion. It would also be acting as a backup for my house so I am willing to pay for a quality unit (it would also run the AC and the DC/DC converter while the car is operational).


----------



## Sunking (Aug 10, 2009)

charliehorse55 said:


> Also, how expensive is expensive?


The ones I am referring to are those used in large scale UPS system which means around the $3/watt mark. Let me look around a bit, but I would need a specific nominal battery voltage.

Something along these lines is what you are looking for.


----------



## Ziggythewiz (May 16, 2010)

StanSimmons said:


> Ziggy, there are a lot of folks that live where power outages are common, and often long lasting... and in the case of a disaster, very long lasting.


In terms of 'common' I mean more than daily. Any less and you shouldn't need a full home UPS. That's an uninterruptible power supply. Does your home's power need to be uninterruptible? It's not that tough to go throw a few levers to accomodate manual lockouts.

As for long lasting...how long is your EV going to power your home furnace? 2 hours? 2 days? Certainly not 2 weeks. The point of the extension cord approach is to use emergency means to maintain the essentials (such as a window AC or space heater in 1 room instead of powering the entire house), not to maintain your usual standard of living.


----------

