January 29, 2010
about a year ago
For people experimenting with these super capacitors and using them to power equipment. Please keep in mind that a capacitor is not a battery. You do NOT “get” 7.5V by stringing 3 of them together as you would with a battery. A capacitor is basically “dead” until it is charged. And unlike a battery, it (mostly) linearly charges to whatever voltage it is supplied with by the end of its charge cycle. It has no charge of its own like a battery, so you don’t “get” voltage by putting them together. What you get is the capability to safely operate at the stated operating voltage. You could charge to any lesser voltage, and should certainly consider doing so as was mentioned in other threads. You would want at least 3 or 4 caps in series to safely operate at 5 volts, not 7.5. And charging is certainly important with these extremely high farad capacitors, as the capacitor is a virtual dead short when voltage is first applied. You need current limiting. Probably best to use a current-limited power supply which automatically reduces the voltage when rated current is exceeded. And through a suitable diode for safety of the power supply. This kind of power supply will operate in a “constant current” mode until the set voltage is reached at which time it will revert to “constant voltage” and continue charging, reducing the current supplied as needed.
And even though it’s tempting, avoid shorting the terminals of a fully charged capacitor. It could result in the discharge of thousands of amps. You know the flash tubes used for camera flash? A moderately powered one uses about a 250 or 300 MICRO-farad (.0003 farad) capacitor. When it flashes at full power, it dumps over 100 amps through the flash tube for about a millisecond or less. Imagine what your 10 FARAD capacitor will do when shorted. And the flash tube is by no means a direct short either.
It’s always fun to “play around” with electronic/electrical stuff. But do yourselves a favor and get some books on basic electricity and learn what it is you are playing with. My father instilled that principal in me over 50 years ago and I am forever in his debt (RIP).
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