Powering A Laptop With Supercapacitors

What do you do when you find a small horde of supercapacitors? The correct answer is a spectrum of dangerous devices ranging from gauss guns to quarter shrinkers. [Rinoa] had a less destructive idea: she’s replaced the battery in a laptop with a bank of supercapacitors.

The supercaps in question are 2.7 Volt, 500 Farad caps arranged in banks six for a total of about 3 watt-hours in each bank. The laptop used for this experiment is an IBM Thinkpad from around 1998. The stock battery in this laptop is sufficiently less advanced than today’s laptop batteries. Instead of using a microcontroller and SMBus in the battery, the only connections between the battery and laptop are power, ground, and connections for a thermocouple. This is standard for laptops of the mid-90s, and common in low-end laptops of the early 2000s. It also makes hacking these batteries very easy as there’s no associated microprocessors to futz around with.

With all the capacitor banks charged, the laptop works. It should – there isn’t a lot of intelligence in this battery. With one bank of six supercaps, [Rinoa] is getting a few minutes of power on her laptop. With a stack of supercaps that take up about the same volume as this already think Thickpad, [Rinoa] can play a few turns of her favorite late-90s turn-based strategy game. It’s not much, but it does work.

Check out [Rinoa]’s video below.

21 thoughts on “Powering A Laptop With Supercapacitors

  1. At the start he says something about a charging circuit built into the capacitors (so that he doesn’t have to worry about over charging the capacitors)?! Now, I don’t know much about caps, but I’ve never heard of them needing a charging circuit. Reverse voltage, or over voltage, I know that is a problem, but over charging? Hmm…

    1. Unlike electrochemical batteries, you can constant-current charge a capacitor all the way up to full. Obviously, however, this will involve raising the voltage above the maximum rated voltage near the end of the charge cycle. You’d need some sort of cutoff to ensure you don’t explode them.

      You can’t really use a plain old voltage source, since, when empty, they look like a dead short, and, when near full, they charge abysmally slow. It WORKS, if you limit the current sufficiently to avoid damage to anything, but it’s far from ideal.

      1. >”Unlike electrochemical batteries, you can constant-current charge a capacitor all the way up to full. ”

        What do you mean “full”? Capacitors are never full – at some point they just exhibit dielectric breakdown and explode.

        1. I assume he’s talking about the capacitors rated working voltage. If the manufacturer says “Don’t go above this voltage, or shit will go down!”, then I would say that is a fair approximation of a level to call “full”.

          Don’t be such a smart arse.

          1. Put a bottle on a tap and fill it, now put it on an air line and tell me when it’s full… :D
            Either way given enough pressure it will rupture. The rupture point is however, somewhat below the saturation point. Be that electrons or not

          2. Oh I get the concept OK, never said it was wrong. I just meant that “FULL” in this example could be reasonably regarded as what the manufacturer dictates. Seems like a logical idea, they will know better than you or I what the capabilities of their product are. Full and Empty are both somewhat arbitrary concepts anyway, as neither is technically correct – even a “vacuum” *isn’t*…

            Hell even my O2 tank has a dial marked “Empty” to “Full”, and just because I *can* cram in a few more atmospheres of pressure, doesn’t mean it is a good idea to try. I think for the sake of exploding pressure vessels, I will regard what the manufacturer calls “full” as being so. ;)

    2. Those supercaps are 2.7V each. When you arrange them in 5V or 12V bank you need balancing circuit because they’re connected in series, just like 18650 cells in laptop batteries. Balancing circuit is quite simple, it just keeps individual caps from overcharging.

  2. IIRC, an MC34063 can be set up as a constant current with voltage limit.
    With supercaps they can indeed be charged up quite fast (IIRC tens of amps) but only from a regulated source.
    Neale used some for a project and used a bench power supply set to the max voltage, with a series load (piece of wire) to further limit the current, LM317T with heatsink also works.

    I’ve also found out that the ones from old balance boards can be used, this is a very cheap source if you find one at a charity shop or recycling centre. The trick is to explain that you want to use it for parts only :-)

  3. This might be a good way to ensure folks don’t wreck their laptop batteries by leaving them plugged in all the time.
    I once found that my x520 had lost 25% of its capacity overnight, yet when cycled and left in the BIOS with screen brightness turned down a few times to “train” the battery it mostly came back.
    (does anyone have a broken unit there please, need a USB PCB urgently!)
    Also putting “suspect” capacitors on a slow charge at Vmax 2.7V sometimes reforms them so this is worth the attempt.

  4. Seems like it a good design for a UPS. You should only need it to work long enough to do a shutdown. Some super caps, an inverter, and the SBC of your choice and you should be good.
    Or you could make it a UPS for an Pi and have the pi manage it all.

      1. It actually looks like the s/replace this/with this/ grammar goes back to at least the “ed” editor…I’ve never fully looked into it before, and Wikipedia isn’t clear on how qed was used. But it’s a broader thing than vi, certainly. (I learned it just by lurking around Slashdot as a teen, before I’d ever used any of the tools that understand that)

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