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What is the current state of things when it comes to super capacitors and batteries? Are super caps anywhere near rivalling LiPo's in capacity?

I've often heard people talking about super caps as being a viable replacement for batteries, in that you can charge virtually instantly and recharge millions of times, but is this just a pipe dream?

SamGibson
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Thomas O
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    What characteristics do you want? You've mentioned capacity, but there are a lot of other categories with which to make the comparison: Charge time, internal series resistance, voltage, storage, durability, effects of temperature, cost, availability, size, toxicity...the list goes on. What's important to you? – Kevin Vermeer Oct 25 '10 at 21:02
  • It's a curiosity thing, I'm not planning to make a product that uses either. – Thomas O Oct 26 '10 at 09:23
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    FWIW: in another question about batteries vs capacitors (no, I can't find it back right now) I noted that PCB mounted batteries require manual soldering as wave soldering would short them. Hand-soldering is expensive. – stevenvh Jul 13 '11 at 07:37

4 Answers4

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I would say, anything that you would consider a coin cell battery for you can "start" to consider a supercap.

The other aspect is that in devices that need current in spurts (like a wireless transmitter), you can use a supercap to provide the short bursts of power needed and then slowly charge them back up from your battery. This method extends the life of your battery.

Kellenjb
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    The charging a supercap and then using it for transmitter power is done by cell phones. – Kortuk Oct 25 '10 at 21:22
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    Re: replacing coin cells, really? Even for long life, low voltage uses like a PC bios battery? Wouldn't leakage reduce usefulness? – naught101 Sep 27 '13 at 13:51
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Some ballpark figures I remember from a year or two ago:

  • Batteries have 10 times the energy density of supercaps.

  • Supercaps have 10 times the power density of batteries.

So for the same size you can store a lot more energy in batteries, but draw much more power from supercaps.

That's why some trams use supercaps and not lithium batteries.

SamGibson
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starblue
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10

Supercaps can be worthwhile if you'll be doing energy harvesting. They're much easier to charge/discharge than batteries. If you have lots of incidental power coming in short bursts it makes sense to store it in a capacitor instead of a battery immediately. They don't match batteries for energy density yet (and they're certainly not as cheap joule for joule). If you plan on having this sit around a long time without any power coming in to charge it and expect it not to have lost any charge I don't think you'll be happy. You're better off with a high-resistance battery if it has to sit a long time and not source a large amount of current. The exact determination depends on what you're doing but I think you'll be happier with batteries.

AngryEE
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5

Super caps are lower voltage (1.2V or so each), so need to be wired in series and parallel combinations to be able to get accessible voltage from them. You will generally need a buck boost converter on the output side to adjust the voltage dependent on the charge left in the super capacitors.

Compared to a Lion battery where you can get a much linear voltage over a smaller range in relation to charge, so generally a buck converter will suffice.

So as a replacement for battery not really, there are too many issues with them. As a complement to a battery use. Do you want to the device to remain powered after power lose? for a reasonable time to change batteries and the like? then super caps may be the answer.

smashtastic
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    Hmm... not sure about low voltage, you can get 2.5V, 2.7V and 5.5V supercaps, LiPos are 3.7V, Ni-MH 1.2V, they are all in the same ballpark. – Thomas O Jan 02 '11 at 01:27