SuperCap 9V Battery

9V batteries are often found in devices that aren’t used very often. If you use a NiCd rechargeable battery you may find it completely discharged by the time you need it. Capacitors on the other hand can maintain their charge for years. This circuit uses a 10F cap with a switching voltage regulator to increase the voltage from 2.3V to 9V. With a light load the cap will last up to 3 hours and once discharged it can be recharged in less than 20 seconds. Warning: PDF link.

[thanks nullset]

94 thoughts on “SuperCap 9V Battery

  1. to m56:

    Super caps are not much use (yet) for audiophiles (except for backing up your presets) as they have a very large Equivalent Series Resistance (ESR).

    The aluminum-electrolytic caps (those monsters used for car audio) have an ESR of ~.01 to .0001 ohms which allows them to dump their energy quickly to boost the current available form the battery to make those huge bass notes possible.

    a super cap on the other hand has an esr many times higher than that; this cap can only provide 9a, almost nothing compared to the thousands possible with electrolytic caps.

    btw, elliot can we got rid of the Weblogs, Inc. Customer Service from the post activation e-mails?

  2. I like the wireless mouse comments above. My thought would be to add the old school ball& rollers to an optical mouse and use the rollers as a charging circuit then even light movement would provide some kind of charge.

  3. Good hack idea for powering the suitable devices.

    It stores little energy compared to batteries, it won’t power an LED very long, and isn’t practical for a digital camera. E = 0.5 * C * (V ** 2) = 0.5 * 10 F * (2.5V ** 2) = 31.25 Joules Compare this energy to a typical 9V battery: 9V * 0.1 AH = 9V * 0.1 AH * 3600 Seconds/Hour = 3240 Joules, greater than 100 times the energy!

  4. I know this is a really old post, but I’m a n00b to electronics and have a project that I have been working on for a few weeks that involves this circuit. What I’m attempting to do is build this little sucker and use it to power a single apple pro speaker, the 10W harmon kardon globes. Basically, I’m trying to run a contact mic directly to the speaker and use this circuit, attached to some solar cells, to power it. I’m totally unfamiliar with all of the equations that are posted above, however it seems like this may not be the option for me. I was wondering if someone would be gracious enough to help me out with this. I can provide more details if needs be.


  5. #52: ESR = effective series resistance

    This is the same as “internal resistance”, because a supercapacitor is modeled electrically as a capacitor in series with a resistor. Keep in mind that the ESR does vary with temperature, and directly affects charging voltage.

    For instance: the Maxwell PC-10 is rated at 2.4V, but with the ESR figured in, you would have to charge it (measured across the terminals) to 2.55V.

  6. You’d need about 10,000f to hold the juice of a single AA battery. There are cool applications for this 9V “milli-battery”, but battery replacement in general isn’t it. Now if those brainiacs at MIT are able to produce their carbon-filiment capacitor as hoped, we’ll have 10,000f caps in a AA form factor. THAT will be the cat’s pajamas!

  7. Great circuit. Remember if you use typical 2N2222’s for the transistors, put a 200 volt or greater rated diode across the collector-emitter of the transistors connected to the inductor or you will blow the transistors. Also, you can just use a 9 volt zener in place of the one transistor with no connection to it’s collector.

  8. As mike, “…” and others have already pointed out: the energy a supercap holds is nowhere near that of a battery. You can use it however as backup power for things that use almost no energy (memory, some microchips on standby) or for something that runs intermittent. If parts are matched properly, a cap needs very little (read none) in charging circuits:
    A small solar cell (6V for a 5V cap) can charge a cap directly. The cap will pull down the voltage and the voltage rises as the cap charges. Once it reaches 5V, you have to start using the cap, so the voltage doesn’t rise higher, or have a bypass zener.

  9. BTW, with SMT PWM and some finagling, you should be able to get 2 of those caps in there, for 2x the run time, which means very close to the same as the 9V battery it is replacing.

  10. Maxwell’s stuff is quite pricey. The smallest BC series at 350F is $72 today at a popular online distributor….. I can go through an awful lot of alkaline 9V batteries for that.

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