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I'm interested building my own battery pack using a series of super capacitor, something like this : http://youtu.be/z3x_kYq3mHM

I plan to use it as a power backup solution for my laptop. Based on what i've been reading on the internet, using super capacitor to store energy are much more faster compare to using lithium battery and it weights more lighter than the lithium. After discovering that idea, that made me really interested in building one to be used as power backup for my laptop.

Now I can just charge the battery pack separately (by regular outlet or solar) and when I'm low with battery for my laptop I can charge my laptop again using that battery pack.

I really don't know how efficient is this idea and if this is viable to be used for a laptop battery pack. I'm also not sure how long will the battery pack last once it's hooked to a laptop (eg Macbook Pro) and if I series a bunch of super capacitor will it still weight light enough to be carried along with a laptop.

I'm interested to hear your thoughts.

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    \$\begingroup\$ Energy density† - Li-Ion: 800 KJ/Kg; Lead-Acid: 170 KJ/Kg; Supercapacitor: 20 KJ/Kg. († OK, "specific energy") \$\endgroup\$ – RedGrittyBrick Aug 14 '13 at 19:18
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    \$\begingroup\$ It's not entirely clear what you mean. Do you mean you want to replace your laptop's internal battery with supercaps? Or do you want an external module of some kind, to charge the batteries from? \$\endgroup\$ – Stephen Collings Aug 14 '13 at 19:32
  • \$\begingroup\$ An external module to charge the battery. Basically I need that module so i can charge stuff when i'm outside and charge the module when there is an available power outlet or maybe from a solar panel \$\endgroup\$ – Pennf0lio Aug 14 '13 at 19:36
  • \$\begingroup\$ @Pennfolio, you may wish to consider accepting one of the answers. It's an important part of the process. \$\endgroup\$ – Stephen Collings Jan 8 '14 at 16:25
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As RedGrittyBrick pointed out, the biggest problem is energy per volume. Batteries of pretty much any sort store far more energy than ultracaps for a fixed volume. Caps have definite advantages, such as lifetime (a good ultracap should be functional long after a battery won't hold a charge any more) and power density (peak current out of an ultracap module can be thousands of amps!). But for energy storage, batteries win, hands down.

That doesn't mean it's not an interesting idea! It just means you need to know what to expect. Assuming you want to replace your internal battery entirely, your operational lifetime will be cut, probably down to maybe 5% of what you had, if you're lucky. Now, for some applications, the difference between four hours and ten minutes is a killer. For others, all you really need is enough time to travel between power outlets. So even the reduced lifetime isn't really a deal-breaker.

Also, if your goal is to replace the internal battery, your new module will need some brains to talk to the BIOS properly. Otherwise, the PC may not think it has a battery at all. To avoid that complexity, you might be better off bypassing the internal module connections and plugging into the laptop's DC input. The PC would think it was running on external power, so you'd have no software indication of how much power you had left. Again, depending on the application, that may not be such a big deal.

Now, if you plan to leave the internal battery in place, and just charge that off the external ultracap, I'd suggest that's not worth doing. The amount of energy stored in your standard internal battery is, oh, let's say something like 160 kJ. (Rough estimate, 90W power supply, 30 minute charge time.) An ultracap to hold that much energy is much bigger than a car battery, and outweighs your laptop by probably a factor of twenty.

In summary, this is probably only worth doing if you replace the battery entirely, and don't care about reduced runtime. And even then, probably only as a fun project, and not as anything practical.

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  • \$\begingroup\$ I didn't say caps have higher energy density. I said they have higher power density. Entirely different metric. As for guessing energy content, I wasn't wrong. I said it was a rough estimate. If I'm anywhere within 50% of the actual value my point us still valid. That's the point of a rough estimate. And I get the volume comparisons by working with maxwell and ioxus ultracapacitor modules daily. \$\endgroup\$ – Stephen Collings Jun 7 '15 at 9:28
  • \$\begingroup\$ Also, redgrittybrick gave 2.5% energy density if cap vs battery. My 5% was generous to the idea. Where did you get 11%? And I got the idea that the asker might want to charge the battery from an ultracap from his comment saying as much. \$\endgroup\$ – Stephen Collings Jun 7 '15 at 9:34

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