4
As well as powering single components the solar panel can also be
used to power complete circuits, such as the transistor project
board (code: ELE 062a) or an LCD clock.
USING A SUPERCAPACITOR WITH THE SOLAR PANEL
A supercapacitor looks much the same as a regular electrolytic
capacitor but is able to store a much higher charge. Unlike regular
capacitors, which use conductive foils and a dry separator, the
supercapacitor has special electrodes and electrolyte. The type
supplied has a 10 Farad capacitance - more than 2000 times greater
than a 4700
µ
F capacitor!
A fully charged supercapacitor will power an electric motor for a
couple of minutes or a small LED for several hours. One way to
charge a supercapacitor is to connect it to a battery for about 10
seconds (or longer for a full charge). Alternatively it can be ‘trickle-
charged’ using a solar panel, as shown in the illustration below.
Note the use of a diode to prevent current ‘leakage’ from the
capacitor.
Supercapacitors cannot be overcharged - when they are full they
stop accepting charge. Charging time will depend on the level of
light, but can be reduced by connecting additional solar panels.
Once charged, the supercapacitor can be disconnected from the
solar panel and is ready for use. The addition of a double pole
double throw (DPDT) switch makes it easy to switch between
charging mode and running mode.
INPUT
SENSOR
D1
R3
OUTPUT
C
B
E
R2
OUTPUT
PROCESS
INPUT
R1
TRANSIS
TOR
PRO
JEC
T BR
D
+
diode
+
LED
solar
panel
capacitor
DPDT
switch
WARNING
Do not charge the
supercapacitor beyond 3V.
5
Automatic switching circuits are more complex. One solution
makes use of a light dependent resistor and a transistor, as shown
below. In good light conditions the transistor is switched off and
the solar panel charges the supercapacitor. When the light level
drops the supercapacitor provides the power. The transistor
switches on and the LED lights up.
The supercapacitor provides exciting opportunities in the context
of product design and rechargeable products. Possibilities include
the design of robots, buggies, torches, warning devices, motorised
tools, toys, etc.
USING THE SOLAR PANEL AS A SENSOR
The solar panel can be used in light sensing circuits as an
alternative to a light dependent resistor. This is useful where high-
power devices need to be activated by light. The panel is
connected to a transistor such as a BCX38B, as shown in the
diagram below.
INVESTIGATIONS USING THE SOLAR PANEL
There are several interesting experiments that can be undertaken
quickly and easily with the solar panel. Several of these require
measurement using a multimeter (code: MET 001).
+
+
b
e
c
+
output
+V
0V
10k
OFF
V
600
200
A
200µ
20m
V
2000µ
200m
10
600
200
20
2000m
200m
2000k
200k
20k
2000
200
Ω
hFE
10A DC
VΩm
A
COM
600V max
CAT II
600V
0.2A max fused
10A max
unfused
TEACHING
RESOURCES
DT-830B
NPN PNP
E
B
C
E
E
C
B
E
collector (c)
base (b)
emitter (e)
BC548 transistor
