Application Note AN-MX921-003
© 2004 Spectra Engineering Pty Ltd Ver1.0 Page
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MX921 Option T46
INTRODUCTION
The MX921 has been design around low power
consumption, to maximize operation time when used
in conjunction with battery(s) powered sites. To insure
maximum efficiency of the radio and to insure
maximum efficiency from your Battery system, we
have developed option T46, Low Loss Solar
Regulator and intelligent Battery Manager.
Typical other types of battery managers have high volt
drop due to there design or the necessity of a diode on
the solar panel. With the T46 option we have removed
all the unnecessary volt drop caused by diodes and
employing an efficient Switching mode regulator
system to achieves 99% charging efficiency. This
technique is virtually lossless and disconnects the
Solar Panel from the Battery when the end float
voltage has been reached. It has the added advantage
of not generating any electrical noise.
The intelligent Battery Manager automatically stops
the solar panels, wind generator or other power source
from charging the battery when the battery is fully
charged.
Special features
•Plug and Play installation with MX921.
•MX921 Front panel power on\off control.
•LED readout to show the status of the
solar charging system and batteries.
•User Adjustable Control Settings for
different types of batteries systems.
•Very low voltage loss. Using extremely low
resistance FETs, the voltage drop across the
controller from the Solar Panel to Battery and
from Battery to MX921 is much lower than
other third party controllers
•Over Volts protection.
•Over Charge protection.
•Deep discharge protection
•Reverse Polarity protection
Operation information
To maintain a long battery life, it is desirable to use
only a small part of the total battery(s) capacity before
recharging. Each time the batteries are run down and
charged up, the batteries undergo a charge/discharge
cycle. If more than half the battery's stored energy is
discharged before it is recharged, this is called 'deep
cycling'. Solar systems normally do one shallow cycle
per day, but during 'low sun' periods may undergo
much deeper discharges (system dependent). For
maintaining a long battery life, the shallow cycle
should be less than 20 per cent of battery capacity and
the deep cycle less than 80 per cent.So when
choosing your battery(s) insure you take this into
account.
It is possible to damage batteries by overcharging
them. Some solar panels have an output voltage which
is claimed to be low enough to stop charging above 15
volts and to be 'self regulating'. However, because
their open circuit voltage is still +18 volts or so, they
will actually continue to charge with a much reduced
current. Most conventional panels will deliver full
power up to about 18 volts and therefore an external
Low Loss Solar Regulator and intelligent Battery
Manager (option T46) is required.
The Loss Solar Regulator and intelligent Battery
Manager continuously monitors the battery voltage
and will disconnect the load if the voltage is higher
than 15V in the factory default position. This is Over
Volts protection. Like wise when the voltage reaches
higher than 13.8V in the factory default position the
solar panel is disconnected. This provides over
charging protection.
When the battery is below 11V in the factory default
position the battery manager will hold the battery
system disconnected for a period of 2:30min. This is
done to prevent oscillations in the circuit due to
battery(s) voltage recovery.
When the Battery’s voltage is below the set voltage
point, the Solar Panel is connected to the Battery via
the low loss switching FETs. During the charge
process the terminal voltage will slowly rise until the
voltage rises above the switch point, at which time the
Solar Panel is disconnected.
In normal operation, the Batteries terminal voltage
will hence cycle between the hysteresis points of the
controller. The default setting is to stop charging
when the Battery terminal voltage reaches 13.8 Volts
and charge below 13.3 Volts.
