System wiring

See also this page for an in depth explanation of low voltage systems.

Updated 7-5-10

Wiring for off grid homes is a lot like wiring for a grid powered home. Obviously, you have to follow codes, etc. (unless you're really, really out in the sticks and there's no inspectors around but it's still a good idea to follow safety protocols!). 

Most times unless you are a real diehard off gridder, there will be TWO separate systems involved, a low voltage DC system (at least one set of wires is needed to charge a battery bank; the wiring from the solar panels (or wind/water turbine) and the normal 110 AC wiring. 

If you power anything using the battery bank, then another set of wires is needed. 

Careful planning is important. Draw everything out either on paper or using a computer program (Paint or even PowerPoint are handy for this) . Use orange wiring for your 12 volt DC wiring. If you are doing this for the first time, label virtually everything you hook up, connect or use. Trust me, shorting out a battery bank that has over 1,000 amps of power is not a good thing to do.

The 12 volt side is treated differently than the  110 volt AC side. It sounds opposite of what you would think but lower voltage systems (especially DC) requires larger wire (lower gauge number) because of resistance. As an example, we have a 25 foot wire run from the solar panel distribution panel to the battery bank and the charge controller. For that we use 10 gauge wire (which conveniently is orange to indicate low voltage) for as little loss as possible. Measured at the output of the wire, we have .02 amps of loss to resistance - quite acceptable. The 10 gauge wire feeds into the Xantrex C12 charge controller (once we get the two new 60 watt of panels made - see the diary entry - we'll have many more amps than the C12 can handle so we'll need a new one).

The PV system (and wind turbines) need to be grounded using approved connectors (national code states that they have to be of a certain metal and have at least two threads of screw contact). Read the article link at the top of each page here at the site or use this link. So does the output side of the system. 

As a side note, we had a television antenna at the shack that I forgot to pull down when I left once. The lightning strike burned part of a wall, a curtain and blew out most of the AC side of the wiring. Grounding is important.

For getting the power from the battery bank around your home or cabin, there are options that you need to consider. First is appliances. 12 volt DC or 110 AC? The market for 12 volt lighting and appliances is absolutely exploding right now. There are 12 volt real fridges, freezers, AC units, ovens, toasters and coffee makers. Let's not forget about televisions. 12 volt electric blankets? No problem! The best place I've found for purchasing these is roadtrucker.com. Check them out.

If you decide to use 110 AC, then you need an inverter which come in two flavors, modified sine wave and pure sine wave. Modified sine wave works with most stuff but causes noise on radios and shouldn't be used for appliances. Pure sine wave inverters are more expensive. You can use normal household wiring from your inverter.

For getting the power from the inverter to the home wiring you can hard wire it (if the inverter has that option), use a transfer box or use what is called a suicide cord (that's an extension cord with two male plugs). NOTE: SUICIDE CORDS ARE DANGEROUS AND MAY BE ILLEGAL WHERE YOU ARE. IF YOU ARE CONNECTED TO THE GRID, NEVER, EVER USE A SUICIDE CORD. Plus if you grab the live end you get to find out why it's called suicide cord. So, hard wire it if you can.

In a system of this type you have two basic choices for your battery bank, series or parallel wiring.

ah=amphours (capacity - volume, if you want - of the battery)

Briefly, in a series circuit, you're taking batteries of a lower voltage and connecting the positive to negative throughout the bank to get the voltage that you want.

Example: 6volt/20ah + 6volt/20ah = 12volt/20ah

Your flashlight is an example of a series circuit. 

What you are doing is increasing the voltage. This can be good because your longer life batteries (robust design, long life) are usually a lower voltage. This is because large batteries (both 2, 6 and 12 volt) are made up of 2 volt cells. Obviously, if the battery case is the same size, a 6 volt battery is going to have much larger 2 volt cells than a 12 volt battery of the same size so it would follow that the capacity (volume) is higher.

In a parallel circuit, you're taking batteries of a higher voltage but lower capacity (volume) and connecting them positive to positive and negative to negative to get more capacity.

Example: 12volt/20ah + 12volt/20ah = 12volt/40ah

While not directly relating to this, your home wiring is an example of parallel wiring.

There are benefits and drawbacks to each system.

Some prefer series connections because you can use high capacity golf cart batteries to get a wicked large capacity bank. This is a definite advantage. However, if you lose a battery you lose voltage and have to find a golf cart battery and possibly be down for days unless you happen to have a supplier nearby.

In a parallel connection, you use higher voltage but less robust (usually) batteries to create a wicked large capacity. However, the batteries don't last as long. If you lose one of the batteries you lose capacity (volume) not voltage and go to Wal-Mart and buy another battery. 

Parallel connections of  can cause all kinds of problems in large battery banks. The batteries in the strings with the main connections (in my case the inverter connection) take all the current load while the middle of the string contribute voltage and a little bit of current to try to balance out the bank capacity.

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