Page 7 - PS Battery Guide May 18

Battery guide For PowerSpout

Battery specifications explained

Voltage
The nominal voltage of the battery is a fundamental choice that determines the
compatibility with related equipment (Power conversion equipment or PCE).
Very small systems may use 12V batteries. Most larger systems are 48V.
Sometimes a 24V battery makes sense if you home AC loads do not exceed about
3kW. These voltages are nominal, which means that the actual voltage of your
battery will be constantly changing with varying state of charge and
charge/discharge currents at that moment.

You can use any smaller size unit to build a battery bank of any voltage by
connecting several in a string. For example you can connect 8 x 6V batteries in a
string to make a 48V nominal battery.

Connecting positive to negative like this is called a series connection and it builds
up the voltage. (Take care to read the safety instructions before you start to
actually handle batteries.)

Amphours
The second most important parameter is the Amphour (Ah) capacity that
specifies the amount of current the battery can deliver multiplied by the hours
for which it can sustain this current. For example 100Ah indicates that a battery
can deliver 10A for 10 hours. But there are complications:

Rate
The amphours rating is conditional on the number of hours. The
abbreviation is for example C10 for the "10 hour rating" whereas C20
would be for 20 hours.
A battery might deliver 10A for 10h = 100Ah at C10
but it might deliver 6A for 20h = 120Ah at C20

Percentage Depth of Discharge (DOD) duty
No battery is very good at delivering 100% of its rated Ah capacity on a
regular basis without wearing out. In practice the number of cycles that a
battery can survive within its warranty period will depend on the depth
of discharge (DOD). With Lead Acid batteries for example the optimum
duty will often be only 50% cycling to obtain useful number of cycles
whereas deeper cycling may drastically reduce the number of cycles
available. Other battery types may be good for much higher DOD, but
there is usually a recommended limit that is less than 100%.

© 2018 EcoInnovation Ltd (NZ) Page 7
Last reviewed 19/6/18