Specifications
AT 49
A deep cycle battery’s lifespan is also affected by
how it is recharged – it is possible to overcharge
a battery, thereby reducing its lifespan or
destroying it altogether. Each different
battery technology has a preferred method of
recharging to maintain an optimum lifespan
(delivering that preferred method is one of the
roles of the charge controller/regulator).
As with all things in life, rechargeable batteries
are not 100% efficient. Deep cycle batteries
are typically 90% efficient, which means that
10% of the energy used to recharge the battery
is lost in the recharging process – this must
be considered when choosing solar panels to
recharge the battery.
The charge controller/regulator serves two
purposes. As a charge controller, it ensures the
energy from the solar panel is used to recharge
the battery correctly (a switch or menu item
selects the appropriate battery technology). As a
regulator, it ensures the DC voltage supplied to
the inverter from the battery and/or solar panel
remains constant.
The more expensive charge controller/
regulators include metering to show all input
and output voltages and currents. Apart from
monitoring the overall performance of the
system, this is invaluable for fine-tuning the
position of the solar panel(s) for optimum
conversion of solar energy.
The inverter takes the DC voltage from the
charge controller/regulator and converts it
to the 240V AC required to power our audio
technology.
Lower cost inverters produce an output that is
described as a ‘modified sine wave’, which is
essentially a poorly filtered 50Hz square wave.
These are not recommended for audio work
because the output voltage contains many odd-
order harmonics of 50Hz (e.g. 150Hz, 250Hz,
350Hz, 450Hz, etc.) that can bleed through the
power supplies of audio technology and create
a buzz in the signal – especially if you’re using
budget audio technology that isn’t expecting
anything higher than 50Hz from the mains
power and therefore has poor rejection of those
higher frequency harmonics.
The more expensive inverters produce a ‘true
sine wave’ or ‘pure sine wave’; this is the type
of inverter required for audio work. With less
than 4% total harmonic distortion, the power
supplied by most true sine wave inverters is
cleaner than that supplied by the mains, which
typically has 5% total harmonic distortion.
(When you add to that the audio frequency
tones superimposed on the mains to control
off-peak hot water services and so on [look up
Zellweger/Decabit ‘ripple control protocol’ for
more information], ‘wireless’ home intercom
systems that use the mains wiring as a signal
path, and any other electrical trash picked
up on the journey from the power station to
your house, the mains power itself ought to be
condemned as an audio hazard!)
While inverters add the convenience of mains
power compatibility, there is always a slight loss
of power involved in the process of converting
DC to AC. This loss defines the inverter’s
efficiency, which is typically around 90% (e.g.
10W of power from the battery will produce
9W of power from the inverter). This efficiency
loss must be considered when choosing the most
appropriate battery for the system.
Do you need an inverter? If all of your
equipment is capable of operating from +12V
DC (e.g. a location sound rig for film and
television work), you could avoid the expense
and efficiency loss of the inverter and power
your equipment directly from the charge
controller/regulator. But if you want the
convenience of connecting your equipment
directly to the solar power system as if you were
connecting it to mains power, you’ll need the
inverter.
An important word about electrical safety: the
inverter produces an output voltage of 240V AC,
and therefore requires an earth connection to
maintain electrical safety. This is not something
to be taken lightly – the 240V AC output of a
solar power system can kill you just as easily
as the mains power. So always consult with a
solar power equipment supplier about the most
appropriate earthing method for your situation.
Most inverters have a single power outlet socket,
so you’ll need a power board if you want to
connect more than one item to the solar power
system. Make sure you choose one with enough
sockets to power all of your equipment, and
allow extra space for any overly-wide AC
adaptors that block access to adjacent sockets.
It is worthwhile writing ‘solar power’ in clearly
visible letters on the power board, not only for
identification purposes but to prevent someone
from inadvertently plugging a heater or iron
into the system and flattening your battery.
A power board with in-built UPS
(Uninterruptible Power Supply) is a smart
investment, because it will provide back-up
power to your equipment in the event that
your battery runs flat and you want to keep
working. A UPS contains a small rechargeable
battery and a simple inverter that only come
into action when there is a loss of input power. It
requires some electrical power to run its internal
monitoring circuitry and keep its battery
charged, but it’s not significant.
The UPS sounds an alarm to let you know
when it is no longer receiving 240V AC (some
+12 to +17V DC
+12V DC 240V AC 240V AC
Solar panel(s)
Charge
controller /
regulator
Rechargeable
‘Deep Cycle’
Battery
Inverter
Powerboard
with UPS
Figure 1.
Laptop
Interface
Monitors
Hard Disk
Studio A at London’s ‘The Premises’ is an entirely solar-
powered recording/mixing studio featuring an SSL
AWS900 console, a ProTools HD2 TDM system running
from a G5 Macintosh, ATC SCM100ASL and Genelec
S30 active studio monitors, a healthy collection of
microphones, and a host of outboard from
API, Neve, Summit Audio, Thermionic
Culture, Lexicon, TLA, Drawmer
and TC Electronic. You
can read about it here:
www.premisesstudios.
com/studio-A.html
Earth