any advice for wiring an inverter and battery bank into my on grid home for backup purposes?

[cutlass1972]

My main question here is, does anyone here have any experience wiring this type of a system into an on grid home as a backup system? I have no illusions of being able to carry on like normal (television, stereo system, central air system, etc) all I am interested in doing basically is running my refrigerator and deep freeze and using the household wiring instead of running extension cords. I would think that I would be able to wire in a switch that would break the electrical connection to the grid and connect my inverter to the fuse box. Am I correct in my assumptions? Am I missing something?

[Nando]

You have an idea in your mind but NOT well detailed because no information about the "power inverter" capabilities and limitations, as well as, the loads specifications.

To get a GOOD assistance, good information should be supplied, always assuming that the "helper" needs to get all the facts accurately without any room for GUESSING.

The idea of using a car alternator to supply power to the Power inverter is going to be quite limited, around 0.5 to 1 KW, not enough power from the car alternator to drive refrigerator or freezer

It would be better to use the engine to drive a Induction Motor converted to Generator producing AC as needed with the limitations of the engine and the induction "generator" power.

Switching, between GRID power and Emergency power at the Grid entrance box, needs to be done quite carefully, all depending on the local arrangements -- I do not recommend it unless, good electrical background for the person doing the conversion to avoid probable short circuits.

Nando

[asheets]

You may way to read www.utterpower.com .  Several of his case studies deal with your subject.

[John II]

Your car alternator will need to feed several deep cycle batteries in order for you to have stable enough power to run your inverter.

The switch that you speak of is called a transfer switch. You never never want to accidently connect your inverter or generator to the live power line. To avoid this, you need to use a transfer switch.

Another method which I use. Just below my grid breaker box, I installed a bunch of outlets connected to the grid breaker box. Then I took most of my 15 amp cables that normally tied to the breakers in the grid breaker box and I attached 3' long short heavy flexible extension cords with ac plugs to them.. and brought them outside of the wall and pluged them into the boxes I had just wired into the grid braker box.

Then I also set up a bunch of outlets on the same wall connected to my inverter breaker box. Now I can take almost any house circuit and simply un-plug it from my grid breaker panel to my inverter panel. It gives a person a lot of flexibility, but you are limited to about 15 to 20 amps capacity on any one house circuit when you do it that way.

By using a Transfer Switch... it switches your complete house off of grid to an alternative source of power.

John II

Transfer switches.

http://www.northerntool.com/webapp/wcs/stores/servlet/NTESearch?storeId=6970&N=0&Ntk=All&
;Ntt=transfer%20switch&Nty=1&D=transfer%20switch&Ntx=mode+matchallpartial&Dx=mode+ma
tchallpartial

[srnoth]

A picture's worth a thousand words:

It sounds like I have something very similar to what you want to do. Basically, I have an 800w inverter connected to several truck batteries (12v bank), and I connect these to the car and use the car engine and alternator to charge them up.

The inverter is connected to that power transfer switch, which is basically just 2 2-way switches connected together so that they both swicth at the same time. It works great. I then have one circuit of my house plugging into that transfer switch. When power goes, I just flip that switch and turn on the interter. I can power several lights, a computer and the tv as long as there is gas in the car. You could do the same thing with a small engine and a car alternator. If you can you could use 2 alternators. They should be atleast 60amps each, so that is 120amps * 12v which is 1440 watts. Even with some lossed you would still be getting atleast 1kw. Then you just need a big enough inverter to power what you need.

You could disconnect one circuit from your house, put a plug on the end of it and connect it to a similar power transfer switch, but I found it was easier just to run a whole new circuit to the things that needed backup power.

Oh, and you should certainly be able to run your frige off a system like this. Friges have a high surge when they're first turned on, but once they're running they only use about 300w (mine atleast). So your idea should work.

Have fun,

Cheers,

Stephen.

[srnoth]

Here's the diagram for that switch:

I just tied the new output's ground to the house's ground since on most cheaper inverters there actually is not ground - there is nothing connected to it inside the inverter. It works fine this way.

Cheers,

Stephen.

[froggie]

I just tied the new output's ground to the house's ground since on most cheaper inverters there actually is not ground - there is nothing connected to it inside the inverter. It works fine this way.

I actually took my 150W inverter apart and found the earth and neural connected at the internal socket. The earth was connected to the chassis of the unit and that had a grounding screw at the back to connect to a true ground point if you were using it outside a vehicle. I think that may even have been connected to electrical "ground" negative on the 12V input, I never looked or tested that though.

I'm guessing it was done that way as it's an automotive inverter with a cigarette lighter plug and automotive "earth" is the car chassis anyway, as you're electrically insulated from the true ground by four big pieces of rubber and, you'd hope, a significant depth of asphalt

A friend of mine is a production audio and electrical engineer who does support work and repair for concert equipment for international bands (eg RHCP) and he offered to install an automatic load transfer switch for the internet cafe I was running

We had plans to install a diesel genset in case of extended outage, city centre power in my area wasn't too good back then.

froggie