Supercapacitors are among the coolest
of so-called passive electronic
components. Because they are ultra-
high-capacity capacitors, they can
function as batteries capable of being
very rapidly charged and briefly
powering many electronic circuits
and even small motors with bursts
of power. And they’ll endure many
more charge-discharge cycles
than conventional rechargeable
batteries. They’re great as backup
power for equipment during battery
replacement, and they’reideal for
providing long-term power for static
random-access memory (SRAM).
Rechargeable lithium, lead-acid, and
nickel-cadmium cells may require hours
to be recharged. But a supercap can be
recharged in a few minutes or even seconds.
MAKE A DIY SUPERCAP
While commercial supercapitors are best for DIY
projects, you can learn about their performance
by making one yourself. A very
simple supercap can be made with activated
carbon, aluminum foil, and lemon juice.
Figure
A
shows a DIY supercap made from
a single Tetra Whisper Filter Cartridge meant
for aquariums. Open the activated carbon pack,
pour the contents into one of the filter bags, and
seal the bag with a stapler. Next, cut two pieces
of heavy-duty aluminum foil slightly smaller
than the filter bag. Then sandwich the filter bag
between the two sheets of foil, making sure the
opposite foil sides do not touch.
Place the completed supercap in a shallow
container with a weight on top to hold it in place.
Or secure the layers together with tape, again
making sure the opposing foil sides don’t touch.
Finally, pour some lemon juice over the supercap
to provide an electrolyte.
The DIY supercap should be charged with 1.5
volts or less to avoid decomposing the lemon
juice. The one shown in Figure A was charged to
1.31 volts from a single AA cell. Figure
B
shows a
charge-discharge cycle of this supercap charged
to 0.9 volt and recorded by a 16-bit analog data
logger (an Onset HOBO 4-channel). The most
Getting to know
the super
fast-charging
supercapacitor
Badder
Than
Batteries
FORREST M. MIMS III
(forrestmims.org) an amateur
scientist and Rolex Award winner,
was named by Discover magazine
as one of the “50 Best Brains in
Science.” His books have sold more
than 7 million copies.
Written and photographed by Forrest M. Mims III
92 make.co
PROJECTS: Amateur Scientist
M74_092-3_AmSci_F1.indd 92M74_092-3_AmSci_F1.indd 92 7/16/20 11:46 AM7/16/20 11:46 AM
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