Ultra Capacitors

Discussion in 'General Electronics Chat' started by salty9, Jun 29, 2009.

  1. salty9

    Thread Starter New Member

    Jun 8, 2009
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    A couple of years ago I read an article about ultra capacitors and their potential for energy storage. Does anyone here have any later info? The article was talking about multi-farad capacitors which seemed implausible to my general physics knowledge of electricity.
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    I like to have one of those at my backyard

    Rifaa
     
  3. Externet

    AAC Fanatic!

    Nov 29, 2005
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    In real life, things are somewhat different.
    Part of my troubleshooting tools is a 250 F at 2.5V (>500 Coulombs; >1KJoule) capacitor bank, the size of a cigarette pack I use to blow hair fine solder splashes in circuits manufacturing. Some internal layer shorts vaporize too.
    It does have a punch effect, but charge after half an hour is not impressively held any more.

    As current technology, they are leaky. They do not hold their charge as a battery. For 'short' term storage, they are useable. A car battery could get away replaced with 150F, but likely will not start next day.

    Miguel
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
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    Wikipedia has this - http://en.wikipedia.org/wiki/Supercapacitors

    Notice that the critters are quite limited as to voltage, meaning stacking any number of them for a voltage source. And, unlike batteries, the charge begins to fade as soon as energy is used in a load.
     
  5. DC_Kid

    Distinguished Member

    Feb 25, 2008
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    you would need perfect insulators and all terminals would need to be insulated from the environment (needs to be in a vacuum). makes it kinda impractical.
     
  6. steveb

    Senior Member

    Jul 3, 2008
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    There is a new type of super capacitor called the lithium ion capacitor. They also operate at low voltage 2.2-4.2 VDC. Capacitance are now up to over 4000 F in a thin rectangular package the size of a circuit board. There are many advantages including low ESR and very low leakage allowing only 5 % drop in voltage over 3 months. Also, 1 million charging cycles is possible.

    See the following link and note the graph that shows a comparison with fuel cells, batteries and standard super caps.

    http://en.wikipedia.org/wiki/Lithium_ion_capacitor
     
  7. steveb

    Senior Member

    Jul 3, 2008
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    I need to correct this voltage spec. I was going from memory, but when I checked I found I was a little off. The voltage range is 2.2-3.8 V for some JSR devices I'm familiar with.

    See attached PDF for a comparison of these new caps with the older super-cap technology.

    Also, the approximate cost of these devices is 10 cents per Farad.
     
  8. DC_Kid

    Distinguished Member

    Feb 25, 2008
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    are those specs right? a 2k F electrolytic fits in 373ml volume ??? must be using atom thick insulator and foils...???
     
  9. steveb

    Senior Member

    Jul 3, 2008
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    Yep. As crazy as it sounds to some of us old timers, we are talking thousands of Farads in a very thin flatpack. New devices are now over 4000 F. That 2200 F cap shown is 4 inches by 5 inches by 1/3 of an inch.
     
  10. steveb

    Senior Member

    Jul 3, 2008
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    Note that the volume was actually 124 ml for the 2200 F Li-ion device.
     
  11. beenthere

    Retired Moderator

    Apr 20, 2004
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    I recall a 750,000 uF 70 volt capacitor that was about 4" in diameter and about 10" tall. We all marveled at the amount of damage it did when it blew up.
     
  12. DC_Kid

    Distinguished Member

    Feb 25, 2008
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    sounds like more hype than real applications.

    searching around i found this:
    They need to work on the weight and price here. A quick calculation suggests a lead-acid deep-cycle battery has an energy density of about 10.5 Wh/kg packaged into a final product? And it would take about 286 ea 2200F capacitors to provide equal capacity?? 8360 Coulombs capacity (3.8V) => 1A for 8360 secs at 1.9V avg => 1.9 * 8360 / 3600 = 4.41 Wh/cell lead acid = 12 * 105 = 1260 Wh Need 1260 / 4.41 cells = 286 286 * 2200 * 0.10 = $62,920 Need to cost reduce by a factor of 1000 - No deal. I'll wait for portable nuclear fission.
    source:http://www.edn.com/blog/1470000147/post/1110030711.html
     
  13. steveb

    Senior Member

    Jul 3, 2008
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    There are real applications, and the cost will come down eventually. These are very new. In engineering there are always cost/performance tradeoffs and new technology is usually expensive initially.

    The revealing thing about the calculation you quoted is that this capacitor has higher energy density 14 Wh/kg than the lead acid battery 10.5 Wh/kg. That's pretty amazing. This is the first time in history a capacitor has surpassed the old standby lead acid battery in this specification.

    Sure the cost is higher, but the thing that was not factored in to the cost calculation was that the capacitor has 1 million allowed charging cycles. How many does a lead-acid battery have? Probably 1000 to 5000 depending on the charge depth. So, if you need to have 100% charge depth, the cost of the capacitor approach is potentially cheaper right now (in some applications), since there is no replacement labor cost, and the device can be built fully sealed with no need for batter access.

    Let's see, how long has the lead-acid battery been around? - 150 years I think. The Li-ion capacitor? Hmmm ... Do you still think it's hype? Probably the better question is; will something even better come along before the Li-ion capacitors finds widespread use?
     
    Last edited: Jul 1, 2009
  14. Tesla23

    Active Member

    May 10, 2009
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    The current commercial applications of super caps in consumer electronics that I am aware of is more to to with power delivery than energy delivery. For any device that consumes energy in bursts there is a potential benefit to simply placing a super cap across the battery. Efficiency improvements are of the order of 10% or so. Current applications include TDMA phones (e.g. GSM), cameras and notebook computers.

    The improvement comes about as a capacitor relies on charge transport, whereas a battery relies on a chemical reaction, so the capacitor typically has a shorter response time. So the super cap charges slowly between power bursts, and supplies most of the power during the burst (when the battery voltage would sag).

    Here is an example app note (http://www.cap-xx.com/resources/app_briefs/ab1012.pdf) that gives an example of a super cap increasing the number of shots in a digital camera by 40%. This was just the first I found - shows the idea.

    Ultimately they may/will get super caps to have comparable energy densities to batteries and that will expand their application. The Q=CV relation is a bit of a challenge for the power supply though.
     
    Last edited: Jul 1, 2009
  15. DC_Kid

    Distinguished Member

    Feb 25, 2008
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    weird, they only get 22 pics on fresh batteries?? what type of digi camera is it??
     
  16. steveb

    Senior Member

    Jul 3, 2008
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    The application you mentioned is the one I see mostly. However, I heard that military/police flashlights are one new application. The benefit is that the structure is sealed and very durable. There is no need to change batteries or wait for batteries to charge. Charge time is a few minutes and much faster than rechargeable batteries.

    See the attached chart. Energy density is already comparable. Li-ion supercaps are better than some batteries and within an order of magnitude of the newest battery technologies. Also, note that power density is better than all batteries!

    For applications that require steady voltage, the current solution for the annoying Q=CV relationship is to use a DC/DC converter. The 2.2-3.8 VDC range can be converted to a steady 3V, 5 V or 6 V with 90% efficiency. Higher voltage is obtained with stacking cells, just like battery cells. Note that batteries also have voltage variation (although less severe), but also more source resistance which drops the voltage under load.
     
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