Specifications

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However if the best form of charging circuitry is to be available for use in the project
more than just the multi-stage charging system must be looked at. Another method
available for use is to utilize what is known as maximum point power tracking or MPPT
for short. Initial research showed that at first look the maximum point power tracking
system is a great deal more complex than other multi-stage charging systems. Price to
is also much higher than other conventional forms of charging circuitry. At first look the
use of maximum point power tracking did not offer very much appeal however that was
soon offset when its‟ efficiency rating was determined compared with other charging
circuitry. Compared to other charging circuits a maximum point power tracking system
has an average efficiency rating above ninety five percent, a good thirty percent more
than other charging systems.
In order to maximize efficiency a maximum point power tracker does exactly what its‟
name implies the electronics inside the charging system track the maximum output
coming from a voltage source and also track the voltage across terminals of the
charging battery and determine what is the best voltage that should be supplied to that
battery to efficiently charge it. Without the use of a maximum point power tracking
system the power available to charge the battery can only be determined by the voltage
currently across the battery terminals.
An example of this would be if you had a depleted battery and the voltage across its‟
terminals was ten and a half volts if a turbine was supplying over twenty volts and a
current of ten amps only ten and a half of those twenty volts could be used to supply a
charge to the battery supplying only one hundred and a half watts out of the potential
two hundred available to the battery. The use of a maximum point power tracking
system would be able to raise the inputed voltage and current supplied to the battery to
deliver around one hundred and four watts instead of the initial one hundred and ten
watts without a maximum point power tracking system. That gives an efficiency rating
for the maximum point tracking system to around ninety seven percent efficiency. The
relationship between output of an example pv array battery charging system and the
wasted power involved in the power transfer can be seen in the table below.
Figure 13 - MPPT Characteristic Graph
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