maximum available and varies significantly with changes in sun level, motor speed and
load.
The DC to DC down convertor means the unit takes in DC power and converts it to DC
power at a lower voltage. The voltage out of these units is always lower than the input
voltage.
How is this all done?
All the units function in a similar manner. They store energy from the solar panel in a
small capacitor (the capacitor behaves somewhat like a small battery) this capacitor is
charged by the panel until it reaches the voltage that the electronics unit has previously
been set to. (Just below the panels maximum power voltage). The electronics unit then
switches power to the motor on till the capacitor discharges slightly (typically by about 1
volt) it then switches power to the motor off till the capacitor charges up again, when the
capacitor has charged to the set voltage the unit again switches power to the motor on till
the capacitor discharges. This switching process continues.
The output section of the electronics unit includes an inductor and an electrolytic
capacitor for energy storage and smoothing of the nominal square wave DC being sent to
the motor. There is also a diode or field effect transistor in this output section which
allows the current to continue to flow in the motor during the time the electronics unit has
switched off and is waiting for the input capacitor to recharge. It is the action of this
inductor, capacitor, field effect transistor or diode that enables the current in the motor to
greatly exceed the panel current but at a lower voltage.
There are detail differences between units which effect their operating efficiency and
ease of set up and operation. I strongly suggest you check data from the manufacturer for
specific details of any particular unit.
NOTE: In late 2010 the Automax unit became available, it automatically selects and
tracks the maximum power point of the panel making adjustment unnecessary. This unit
has identical electrical performance to the Easymax III unit.
9 Steering
Many cars seem to perform very well without steering. However a car without steering
will be dragging the wheels sideways on the corners and consequently wasting some
energy. Tests performed at Box Hill High School indicate that for a 1200 gm car with
aluminium wheels and no steering there is an additional drag force of 0.25 Newton while
cornering. This translates into about an extra 1.2 seconds race time in full sun on a car
capable of a 20 second race.
We expected a car fitted with plastic wheels which have a lower coefficient of friction
than aluminium would have lower drag losses.
Another car without steering was tested. This car has standard R & I Instrument Gear
Company wheels and guides made from acetal, only the drive wheel was aluminium. Its
car weight during these tests was 2500 gm. The test was performed on the Box Hill High
School track by pushing the car around the corner and measuring the force required to
just keep it moving.