SuperCap 9V battery

supercap 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]


  1. ... says:

    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. Gray cube says:

    Where do I find the ESR on the spec sheets – is that “Internal Resistance”?

    I was reading Maxwell’s UltraCap FAQ and they claim to have a much lower ESR than other super or ultra caps, but I’m not sure were that is specified on their spec sheets…

    Here is their FAQ:

    Here is their 10f small ultracap:

  3. LUKE says:

    Well at least projects like this can serve as learning project for those who are just learning electronics. Lets see more of the same in the future to make learning exiciting.

  4. livejasmin says:

    yes, more of these kind of projects, and of course great article

  5. bjheu says:

    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.

  6. Lawrence miller says:

    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!

  7. the0ne says:

    a while back i came apon another hackaday episode, a usb charger. could you possibiy solarly charge the capacitor, to run the usb charger?

  8. Unchain says:

    Now that’s what I call a capacitor!

  9. jake Biggs says:

    If only there was one for a PSP… time to get the soldering iron heated.

  10. dellpickel says:

    I wonder how well this will work with that diy usb charger at

    if it would work than for fun put on one of those tiny calculator solar panels!

  11. Chris says:

    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.


  12. direavenger says:

    #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.

  13. drwho says:

    Does anyone have this article? The link is no longer valid.

  14. Chickenman says:

    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!

  15. duongga says:

    tui muon hack per fect

  16. john says:

    Hey! where the heck did the .pdf go?!

  17. yaleman says:

    Just in case someone’s looking for the PDF – I’ve found it here:

  18. john mcc says:

    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.

  19. Mark says:

    The link to the PDF article is a broken link…

  20. emmanuel says:

    i want to try this but i don’t know where to buy

  21. james says:


  22. Ed Ianni says:

    I can’t find the schematic for the “Supercap 9v Battery” by Eliot Phillips anywhere. Has it been removed. Thank you. Ed

  23. tantris says:

    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.

  24. spuffler says:

    The PDF file link is giving an error.

  25. spuffler says:

    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.

  26. spuffler says:

    Ah I see yaleman posted the link on Decc 13 2007, use your browser find function.

  27. spuffler says:

    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.

  28. Anton says:

    The link to the PDF article is a broken link

  29. Anton says:

    Now that’s what I call a capacitor!

  30. Robert says:


    Meh, probably not… Though, the circuit diagram is there…

  31. Michael F. says:

    Impressive GET! Where do ya get your iPhone news? :) My hat is off for you.

  32. Shiekh says:

    “Capacitors on the other hand can maintain their charge for years”
    Super-caps discharge faster than batteries

    One can get an array of 6 large super-caps (each 2500F 2.5V) for around $55

    and I put one in a UPS; so fast so good. Run time is short, but enough to cover glitches, and shutdown gracefully.

    I found that at 13.6V they did not need balancing.

  33. voronin says:

    I so want to stick my tongue to the end of that!

  34. Anonyoymsoyms says:

    Link to the circuit (PDF):

    Go go «Resurrect Pages» for Firefox! :3

  35. Pedro Lever says:

    This is so awesome. I can’t wait until this kind of technology is used in electric cars.

  36. Haseeb ul Hassan says:

    Where is the PDF link??

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s


Get every new post delivered to your Inbox.

Join 96,468 other followers