Author Topic: Connecting backup power to the house  (Read 7707 times)

jens

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Connecting backup power to the house
« on: January 13, 2008, 11:53:42 PM »
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« Last Edit: December 26, 2009, 09:24:39 AM by jens »

mike90045

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Re: Connecting backup power to the house
« Reply #1 on: January 14, 2008, 12:53:51 AM »
Recharging flooded lead acid batteries is about 80% efficient.  AGM batteries are about 90% efficient, but if overcharged, you cannot add water.  ( to get 100 watts out, you need to charge with 120 watts - 80%)  Holds true for any voltage.

If you have a DC source (generator) and it is running, it's power would be directly feeding the grid-tie inverter.  The batteries may be "on-line", but in an idle state, or preferably, in "float charge".

for 4,000 watts (33.3A@ 120V), I would suggest as high as possible DC voltage as you can locate inverter/charger for.
96V : 41.6A
72V : 55.5A
60V : 66.6A
48V : 83.3A
because of copper losses in the wires.

30A household circuits require 10 ga wire (USA)  more ampreage requires even thicker wire, both for safety and low resistance losses.

Of course, you will need proper DC rated fuses and circuit breakers, conventional AC ones will not work for DC, as the DC arc does not self exinguish.

If you are looking for something solar, to feed the grid, and reduce your electric bill, Grid tie can't be beat, as modern high voltage inverters  [ 300 - 600VDC ] run about 96% efficient.  I will use a generator for the rare blackouts.  Eventually, as I move out of the city, I will have a grid-tie system again, and because of likelyhood of extended blackouts, a generator & modest battery bank.
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mike90045

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Re: Connecting backup power to the house
« Reply #2 on: January 14, 2008, 12:56:35 AM »
I would have seamless power.

To get a seamless transition, you need fairly expensive parts,
(grid tie/standalone inverter, battery bank, charge source) and a auto-start generator.

To stay alive, you can use a more manual system.

Doug

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Re: Connecting backup power to the house
« Reply #3 on: January 14, 2008, 01:14:28 AM »

Of course, you will need proper DC rated fuses and circuit breakers, conventional AC ones will not work for DC, as the DC arc does not self exinguish.


You need to be more specific and say the protection device needs to be rated to interupt DC.
Many Common molded case breakers are rated for DC and as far as I know any modern HRC class II fuse will easily deal with low voltage DC. But these are things you need to consult with the equipment data sheets to be sure of.

Lastly above about 400 Vac arcs are no longer self extinguishing, that is what we use things like form 2 fuses especialy with todays high values of available fualt currrent.

A Small DC bank at home can also generate some significant values of fault current. You actualy need to find this sort of things out if your going to build your own system. A modern CB in your home panle for example is designed to interupt 10,000 symetrical AC amps, that does not mean it can do the same for DC but a proper fuse could.

Doug
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rmchambers

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Re: Connecting backup power to the house
« Reply #4 on: January 14, 2008, 01:21:56 AM »
There are multiple brands and types within brands and each do something differently.  I only have experience (hands on) with the Trace-Xantrex DR series which I have one of in the basement.

It is NOT a grid tie inverter.  In the normal state of affairs it takes power from the grid, and pushes it through to the load and takes a little to float charge the batteries.  Grid fails, batteries kick in and the computers and such stay online.  Grid comes back, inverter monitors for a bit, likes what it sees, goes back to grid power and dumps a lot of charge at the batteries bulk then absorbsion then float.

The SW series from Trace have a grid tie option, they also have generator auto start and I believe will acknowledge battery feed coming in too high (like power from solar or wind) and will invert that and send that to the load.  If you use in the house less than the solar and wind are generating then it pushes the excess out to the grid.  The SW also has generator start and programmable quiet times where if the grid fails it won't autostart the generator and wake everyone up unless it's a dire need.

How it works on the other brands (outback etc) I can't say but all the manufacturers have PDF's on their respective sites.

As for metering, it all depends on the meter now.  If your meter is the mechanical one with the spinning wheel and analog dials then feeding power to the grid will slow down and stop the wheel and run it backwards hence unwinding your KWH usage numbers.

I have a digital meter at my house so I don't know how that would react to me feeding the grid, but since my inverter isn't a grid tie it's not much of an issue.  In order to do it legally you need to get all the work done and signed off on and enter into an agreement with the power company.  If you did it on the quiet and your power production did not equal or dwarf your home consumption then the power company probably wouldn't even notice.

Robert

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Re: Connecting backup power to the house
« Reply #5 on: January 14, 2008, 01:40:32 AM »
  This is the best of the emergency power transfer panels, the others require lengthening the circuit wires to reach from the old panel to the new panel. The Generac doesn't.
  Generac Guardian Automatic Transfer Switch 16 Circuits
   Item number: 260202647484   

  The whole service transfer switch is preferred in many situations. Generac makes an excellent 200AMP service rated auto transfer unit but I'm at a loss to find the unit on the site at this moment.

Tom

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Re: Connecting backup power to the house
« Reply #6 on: January 14, 2008, 02:40:13 AM »
I have a Trace SW2512 Inverter and it will do everything you want and do it automatically too. The inverter has input connections for shore power, generator power and battery power. The inverter will automatically transfer from shore to battery power when a failure occurs. If the batteries get low it will start the generator and recharge the batteries. If the shore power comes back on before the batteries get low it will recharge them from shore power. If you are on batteries and need more power than the inverter can deliver it will start the generator, synchronize with it and give you the combination of the 2.

Is there any combination of things I missed?  :o
Tom
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mike90045

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Re: Connecting backup power to the house
« Reply #7 on: January 14, 2008, 03:31:50 AM »
Trace/Xantrex SW series have been discontinued, and dealer stock is dwindling .

The replacement line XW series, is not fully ramped up into production.  The XW series is as capable as the SW was,
and has more capability for bells & whistles. (costs more too)

diesel guy

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Re: Connecting backup power to the house
« Reply #8 on: January 14, 2008, 03:45:16 AM »
Tom,

There is also a Equalizing Batteries Mode to keep your battery bank in top condition. Also, there is a Selling Power - From a DC Source Mode, my 5548's had them not sure if your 2512 has it. It enables the battery bank to stay fully charged and sell the excess power from an engine driven DC/solar/wind/hydro source, back into the grid. It also has a Selling Power - Stored in the Batteries Mode, to sell what power was produced that day, back into the grid. I loved the Trace inverters with all their options, what I didn't like is that, they don't last long before needing repair. I went through 2 sets of 5548's before I gave up on the Trace product line. Some love them and some don't. When they work they are great. I hope yours last along time.

Diesel Guy

Doug

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Re: Connecting backup power to the house
« Reply #9 on: January 15, 2008, 01:16:56 AM »
Just for laughs I looked up the rating for a common fuse for you guys...

An amp trap J fuse ( specificaly the AJT25 for my Petteroid electrics )
 200,000 A at 600 vac and 100,000 at 500 dc

I think that answeres any question about a proper fuse's ability to interupt DC
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Tom

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Re: Connecting backup power to the house
« Reply #10 on: January 15, 2008, 03:15:56 AM »
Diesel Guy,

I've heard that a lot about the SW5548. I was going to buy a set, but went for the Outback inverters instead. Not to many bells or whistles, however the have been no glitches after the first month in operation.
Tom
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diesel guy

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Re: Connecting backup power to the house
« Reply #11 on: January 15, 2008, 03:53:47 AM »
Tom,

In my opinion, you made a wise choice. Outback inverters are well made and the military uses them for their small systems. They don't like all the bells and whistles, the more basic an inverter, the more reliable.

Outback inverters are expensive per watt, but they spend the money on good quality internal components and they are beating Trace at their own game. That is one of the reasons for their loss of market share over the past few years. You’re going to get years of trouble free service from those units, good luck.

Diesel Guy

Andre Blanchard

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Re: Connecting backup power to the house
« Reply #12 on: January 15, 2008, 02:42:28 PM »
Outback inverters are expensive per watt, but they spend the money on good quality internal components and they are beating Trace at their own game. That is one of the reasons for their loss of market share over the past few years. You’re going to get years of trouble free service from those units, good luck.

Diesel Guy

The group of engineers that started Outback did so after leaving Trace. ;)
Often means they had some ideas they wanted to try but management was not willing to listen, usually means bad news for the old company.
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Andre' B

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Re: Connecting backup power to the house
« Reply #13 on: January 15, 2008, 07:54:50 PM »
Andre Blanchard,

That's interesting, I didn't know that and it make scene.

Diesel Guy

Tom

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Re: Connecting backup power to the house
« Reply #14 on: January 16, 2008, 03:44:20 AM »
Thanks guys for all the good info. One thing the Outback inverters have, that Trace does not, is an available load balancing transformer which allows all the current from both inverters to go to either leg of the service. Unfortunately I didn't know if this was standard or optional when I ordered the system and didn't get one.
Tom
2004 Ashwamegh 6/1 #217 - ST5 just over 3k hours.