Wiring the cabin

Updated 7-6-10

See also this page for more information. 

First we should have a little bit of background on designing a low voltage circuit, especially a direct current (DC) system. Think of your circuits as a tube with marbles in it (just like our friend Ted Stevens description of the internet). 

The marbles flow only in one direction in direct current. The rate of flow of the marbles (amperage) is dictated by the size of the tube and the supply of current. All the current in the world won't do any good if the tube is too small.

 Therefore, the larger the tube, the faster the marbles will flow. Too small of a tube will cause friction and a loss of the marbles' energy to friction. So, the larger the tube, the less loss of energy there is. Put in electrical terms, the larger the wire in a low voltage solar system, the less loss of current you will have which is why you see massive wiring in solar panel installations that produce high currents. 

Current is important because that is what you use for charging a battery bank and/or powering equipment. Having a million volts at 0 amps is useless. Having 14 volts at 50 amps is something you can use. A diode is a little thing that is a one way valve in our tube of marbles. It allows the marbles to move in one direction (negative to positive) but not the other way. 

A solar electric system has at least one diode somewhere in the system, whether it be in the solar panel, the wiring or the charge controller. 

Some of the inexpensive solar panels (like the Harbor Freight kits) have no diodes at the solar panel. 

Here's a description of my wiring and my charge control system with costs (2008 prices):

PV wiring

• Panels wired to low voltage junction box (Lowe's, $2.99), bonded together with stainless bolts. This is a decidedly low tech solution to bonding the feeds from the solar panels. Other solutions are available however are more expensive. Since we move the panels around a lot, add to the system and reconfigure it for testing, a simpler way was called for.

• Panel negative and ground bonded together. Ground is a 6 foot ground rod driven into ground. Second ground is located 35 feet away bonded to negative side of system at that end.

Grounding

• 1 ground rod ($20) at east end of cabin, 100 amp service ground cable.

• east rod bonded to 12 volt negative.

• 1 ground rod ($20) at west end of cabin, 100 amp service ground cable.

• west rod bonded to 110 volt neutral / ground.

PV to charge controller

• 10 gauge solid wire (low voltage orange) purchased at Lowe's home improvement, 30 foot run.

Charge controller

• Xantrex C-12 charge controller/12 volt distribution panel ($82).

• Bulk setting at 14.3, float at 13.3, auto equalization off.

Generator

• 2500 watt 110 volt, 12 amp 12 volt outputs ($495).

Battery Charger

• Schumacher battery charger ($80) with bulk/float. Used at 30 amp setting.

• Uses 110 of generator output for power.

Battery bank

• Bank #1: 3 group 31, 110 amp hours each, 330 total amp hours. Approx 75 cycles on bank 

• Bank #2: 2 East-Penn group 31, 119 amp hours, 238 amp hours total, 10 cycles on bank as of 7-6-10

House wiring

• Square D QO (12 volt, 110 volt rated) distribution panel ($79).

• 3 circuits used. Circuit one is bedroom, circuit 2 is outdoor lights, circuit 3 is living area.

Inverter

• Xantrex 350 watt modified sine wave inverter.

• Bonded to 110 volt panel feed.

• Neutral successfully bonded to 110 grounding.

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