Most remote power systems are wired for 12 volts.
Some larger systems are wired for 24 volts. It's a delicate call
to make this decision in most cases. Even larger voltages are used
in some huge systems. The main advantage of 24 volt systems over
12 volts is that wire size is cut in half throughout the system.
Besides affecting battery bank wires, this includes solar panel, wind generator
and hydro plant wiring, too--if you have hundreds of feet of wire, this
cost can add up quickly. The disadvantages of using 24 volts are
that 1) you'll need an expensive, power-wasting transformer to run 12 volt
lights and appliances, and 2) if you want to buy a cheap, Chinese inverter,
they are only available in 12 volt versions. More expensive inverters
are available in different voltages.
Series and Parallel Battery Wiring
Lead-acid batteries always have 2 volt cells wired
in series to give the desired voltage. Some batteries have 3 2 volt
cells in the case, already wired together for 6 volts. Most battery
banks use a combination of series and parallel wiring.
Series wiring increases voltage but NOT amp/hour
capacity.
Parallel wiring increases capacity but NOT
voltage.
Series Wiring Example
Parallel Wiring Example
Typical remote power battery bank using 2 volt batteries
(series + parallel)
Typical remote power battery bank using 6 volt batteries
(series+parallel)
Battery Bank Wire Sizing
Batteries can put out a huge amount of power in a short time.
It is important to use big enough wire for your series and parallel connections
between the battery terminals (the interconnect wires) and to the inverter.
Note: We do not guarantee the accuracy of any of our information
regarding whether it meets NEC code or not!
For BATTERY INTERCONNECT wires, use #4 gauge if you have a 500
watt or smaller inverter. Use #2 gauge for an 800 watt inverter,
and go with #2/0 for larger inverters. If you can afford using #2/0
welding cable or can find a surplus deal on it (we did), we highly recommend
it for battery interconnects no matter what size inverter you have since
it is so flexible. Keep in mind that welding cable may not meet NEC
code, even though it is clearly the best and safest choice (because of
welding cables' flexibility, it puts little strain on the connection points)
for battery and inverter wiring. Go figure!
Buss Bars
It often saves a lot of trouble later to install + and - buss bars
directly off of your battery bank, connected with wire thicker than what
you need for your inverter (click here to jump to the inverters page for
the inverter wire sizing chart). These buss bars give you extra room
to hook up new windmills, solar panels, meters, loads, etc. Use rectangles
of at least 1/4" thick copper, drilled with extra holes. It's easy
to tap threads into copper, too--this will speed your hookup time (no nuts
necessary on the back side of the buss bar). If you have an amp/hour meter,
it's shunt should go between the - (negative) buss bar and the battery
bank so that all power collected and used is measured.
