Batteries First

[twamaso]

Hello I am very new to this and not having a lot of luck. I have two 2600 watt wind turbins. I would like to charge a battery bank with those and then use the batteries to power much of my home. I do not want to grid tie. What I would like is a switch, inverter, or combination that would look at the batteries and when they were charged use them. If they are not charged then it would kick me back to the grid. So far all I can find are Auto transfer switches that work opposite of that. They look for grid power and when it goes down they kick you to battery or generator. I would really appreciate some help, any help, and please be as specific as is possible. Model #, name, whatever. I am looking at 4000 to 5000 watt inverter.

Thanks

[partsman]

I don't know if it will pass code anywhere so please check on this before trying!

I have limited experience with these switches for backup generators.

They are fairly expencive.

Seems like you could wire the switch backwards and run on inverter power as default

then when your inverter tripped out from low battery voltage the switch would switch to backup (grid) power.

[DamonHD]

I'm doing the same kinda 'backwards' thing on a much smaller scale (1%!):

http://www.fieldlines.com/story/2007/6/28/17204/5642

In your case you could use a battery monitor (with some hysteresis) to drive a large changeover relay or three to switch between grid/batteries when the batteries get low/high.

I'm still debugging my battery-level detector circuit right beside me on my desk...

Rgds

Damon

[rossw]

Just a word of caution on this "un-synchronised" transfer....

1. Make sure you use "break-before-make" switchgear, otherwise the results can be the release of large amounts of "magic smoke"
   
2. Its not quite as simple as may appear. Mains/grid supply, and your own locally generated supply (unless synchronised, somehow) have no known/fixed phase relationship meaning if you quickly change from one to the other, your sensitive equipment may VERY WELL be destroyed because of the very high "dv/dt" (change in voltage over change in time).
   
   

The reason is that lets say at the instant you change from local supply to grid supply, they are 180 degrees out of phase (as is going to be a "common" occurance). Instead of the mains cycle going smoothly and gently from say, -160V (120 RMS has a peak value around 160-170V), to the opposite +160 in the time it takes the relay contacts to change (ie, not long).

I've seen folks use TWO interlocked contactors to do the switching, with a delay between one opening and the other closing - but then your clocks, computers etc are all going to "drop out" when you switch from one to the other.

Of course, the "correct" way is to have your local inverter phase-lock to the grid, but thats a lot more complexity than 99% of inverters provide.

[partsman]

The transfer switches I have put in have had a 10 second delay so that the generator is not kicking on every time lightning flashes.

Could be a real pain if you switched on and off every day.

Plus if it only switched a couple times a month why not spend the money and effort going off grid all together.

This is probably why most aren't doing this type of system.

[jonas302]

How about a grid tied battery charger?

[JW]

Hi Twamaso,

 Try this link-

http://www.invertersrus.com/pwrups6000w.html

I dont know what to tell you about batterys but your going to need a whole bunch, and a genset.

JW