Dc inverter power feedback into home on blackouts

hpcre
hpcre Registered Users Posts: 3
in Grid Tie and Grid Interactive Systems #1
Hello guys, I'm new to this forum. I have a question about some inverter wiring needs.
I have a ups inverter, which means it has an AC input and an AC output.
Input is for battery charging and current sensing (mains). Output is for providing AC feed when the mains suffer a blackout.

I need my inverter to provide power to my entire home (barring some high usage equipment), but I'm not sure how I can connect the input and output lines to the same power outlet in the house without creating a big problem for the inverter since power will flow from the house to the inverter when mains power is present.
How can I stop the power from flowing back into the inverter when mains power is present.
I want a somewhat automated solution, not needing me to switch on and off a few switches to get the inverter hooked up every time there is a blackout.

Thanks for the help guys. Sorry for the long post
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,639 admin
    #2
    Re: Dc inverter power feedback into home on blackouts

    There are a lot more to discuss, but you basically make a subpanel for your"protected loads".

    Power the sun panel with the inverter ac outlet.

    Connect the inverter ac input to your main panel.

    The ups should manage the ac main power and battery power to keep your protected loads working.

    If it does not, then you don't have a ups but something else.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • hpcre
    hpcre Registered Users Posts: 3
    #3
    Re: Dc inverter power feedback into home on blackouts

    Thanks for the suggestions. But this requires me to make a big change in my home electrical wiring and install another panel, which i don't have a place for.

    I was hoping for a more simplistic solution to adjust whats already installed, instead of re-wiring everything. My protected load is everything in the house, which means i need inverter AC to run through the same wires that mains AC run on, except i need only one of them to run at a time.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
    Re: Dc inverter power feedback into home on blackouts

    Reasons why you shouldn't do what you want to do here:

    1). Back-feeding the whole service panel means you will energize everything connected to it, including the wires that go outside to your utility. Without some kind of safety interlock to prevent the main breaker from being on when the inverter is energizing the panel this is dangerous and unlawful.

    2). If your inverter outputs only 120 VAC then it will only energize the half the panel it is on, except for Voltage traveling through any 240 VAC devices (such as hot water heater) which will result in partial Voltage on the second half. Another danger.

    3). Unless it is a really big inverter it is not going to handle all the household loads. It will easily fault out when things are turned on.

    If you really need to run everything when the grid goes down, buy a large generator and connect it to the service panel via transfer switch. There is no cheap, easy way to do this and be safe.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,639 admin
    #5
    Re: Dc inverter power feedback into home on blackouts

    There are two commerical methods available (that I am aware of) to do "minimal" amount of work to add in back up power sources to a home's existing wiring.

    The first is a transfer switch where you wire in two wires per circuit to the main panel. One wire connects to the branch circuit breaker--This goes to the "transfer switch". The second comes from the transfer switch and is wire-nut connected to the branch circuit. These transfer switches are available in a wide variety of sizes.

    http://www.electricgeneratorsdirect.com/stories/3-How-to-Pick-the-Perfect-Manual-Transfer-Switch.html (don't know anything about website or product)

    Attachment not found.

    You can then wire up your genset/UPS/etc. through the manual transfer switch. There are probably automatic transfer switch versions too.

    A second is a special genset adapter that goes under the main utility meter. Will allow you to plug in and run a genset (or off grid inverter). I do not believe you will have any access to utility power--Only manual transfer possible (you have to plug in genset cable or remove genset cable):

    Attachment not found.

    http://www.mjmec.coop/content/generator-transfer-switch-installation
    http://www.generlink.com/about_generlink.cfm

    Otherwise--Yes, you are looking at a major electrical re-wiring job to (safely, code) wire in a protected subpanel (as far as I know).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • hpcre
    hpcre Registered Users Posts: 3
    #6
    Re: Dc inverter power feedback into home on blackouts

    Thanks guys for the great help. I'll research the possibility of a transfer switch, as it seems the only solution to what i need.

    I'm in 240V country, so i dont have three phase input like in the US. and I'll be energizing only the lights in the house, other heavy load devices are on separate switches which will be isolated.
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