TIME REQUIRED:
1–2 Hours
DIFFICULTY:
Easy
COST:
$10–$20
MATERIALS
» Aluminum foil
» Activated carbon Regent Aqua-Tech or Tetra
Whisper Filter Cartridges, from aquarium store
» Lemon juice bottled or fresh
» Clip leads (2)
» Tray
» Battery, 1.5V or less AA, AAA, C, or D size
TOOLS
» Stapler
» Voltmeter (optional)
obvious feature is the nearly instantaneous
charge time, which is far faster than typical
conventional capacitors.
You can charge a DIY supercap to a higher
voltage by stacking multiple layers. In Science
and Communication Circuits and Projects
(sparkfun.com/products/11132), one of my
RadioShack Engineer’s Mini-Notebooks, I
describe how to make a multi-cell supercap by
stacking 5 layers of premade activated carbon
sheets purchased at an aquarium store. The
sheets are separated by slightly larger sheets
of paper towel. Bare, copper-clad PC boards
are placed on opposite sides of this 5-layer
sandwich, which can be charged to 3 volts or
more. This DIY supercap will power a red LED
for several minutes or longer.
COMMERCIAL SUPERCAPS
You’ll need to use a commercial supercap for
practical applications. Many are available, and
their prices have dropped significantly since they
were first introduced.
Page 92 shows an NEC supercapacitor that
can be charged to 5.5 volts. It has an incredible
capacitance of 4.7 farads! This means you can
charge this supercap from an active USB port
and use it to power many low-power circuits.
Figure
C
shows the charge-discharge cycle
of this supercap when connected across a 470-
ohm resistor. While the discharge is faster than
might be desired, the charge time is only about
10 seconds.
GOING FURTHER
You can perform many experiments with DIY
supercapacitors. Try stacking them to increase
their capacity, or substituting the lemon juice
with other electrolytes. How does the charge-
discharge cycle change when vinegar is
substituted? Or when salty water is used?
The electrolyte substrate used here is the
filter bag provided with the activated carbon. But
you can also use a paper towel or fabric.
Finally, you can experiment with the physical
configuration of DIY supercaps. For example,
you can roll your sandwich of foil/carbon/foil
into a cylinder. Insert the cylinder into a pill
bottle and pour in some electrolyte.
93
makeprojects.com
A
0.8
0.6
0.4
0.2
0
0 200 400 600 800 1000 1200
Volts
Seconds
DIY Supercapacitor Charge-Discharge
1
4
3
2
1
0
0 200 400 600 800 1000 1200
Volts
Seconds
NEC Supercapacitor Charge-Discharge
5
B
C
M74_092-3_AmSci_F1.indd 93M74_092-3_AmSci_F1.indd 93 7/16/20 11:50 AM7/16/20 11:50 AM
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