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  • Capacitor storage

    I checked the old forum threads and nothing's been added about super capacitors since 2013, so I thought I'd resurrect the subject.
    Been checking Youtube about capacitor storage and once you get past the "We want to sell you" and the plain BS claims there are a few people who are actually developing the technology and putting it to practical use. Look up Robert Murray Smith on Youtube and you will see what I mean.
    I'm going to order a few with the idea that my panels can charge them and when I turn on something like a pump that has an initial very high starting surge current draw the capacitors can discharge and stop the inverter from shutting down.
    So is anyone on the forum using or experimenting with super capacitors for energy storage?

  • #2
    Originally posted by NeilTheCop View Post
    So is anyone on the forum using or experimenting with super capacitors for energy storage?
    Energy storage - no. Just too small to be worthwhile.
    Power storage - yes. (i.e. the example you gave) If all you need is a short burst of power to start something and do some filtering, they're great.

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    • #3
      What jflorey2 said.

      Supposedly a car maker or two have been using them for a couple years now in start-stop hybrids doing exactly that.
      (See for instance the 2016 Cadillac ATS.)
      Nice that they've found a market niche, I hope they can expand to bigger applications.
      Last edited by DanKegel; 12-15-2016, 05:34 PM.

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      • #4
        Originally posted by DanKegel View Post
        What jflorey2 said.
        Stop answering questions, you have no clue.

        MSEE, PE

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        • #5
          There is no way Super Caps will ever be used for energy storage. They are not capable of doing that period. Look the Specific Energy of SC's range from 1 wh/Kg to 30 wh/Kg, about half that of lead acid and 1/5 that of lithium. Makes them worthless for energy shortage.

          Can it work to bridge a a very short term power gap? Yes if you can afford it. In your case less expensive to just size the battery properly to begin with. Super Caps have the following limitations and prevents them from being used as Energy Storage not to be confused with Power Storage.

          Low specific energy; holds a fraction of a regular battery

          Linear discharge voltage prevents using the full energy spectrum

          High self-discharge

          Low cell voltage; requires series connections with voltage balancing

          High cost per watt

          Now here is something Dan and the public are completely clueless about which will prevent any kind of capacitor from ever being used for any Energy Storage and the only thing you ever need to know about Super Caps. If everyone knew this, the question would never be asked. Nor would have so many people be conned out of investment money.

          A Super Cap has a working voltage of roughly 2.5 to 2.7 volts. That means you would have to arrange the Caps in series to get any useful voltage up to something useful. That does not sound like a problem right? I mean that is how we deal with batteries. Well you would be dead ass wrong. When you arrange capacitors in Series, the capacitance DIVIDES unlike battery capacity adds. Take 2 1-Million Farad capacitors, put them in series and you now have 1/2 the capacity. Add a 3rd in series, and you now have 1/3 the capacity of a single capacitor. The more you have, the less you have. Capacitance is like debt, not something you want more of. The only way to make Capacitors add is in parallel. About the only thing you can do with 2.7 volts is run a LED.

          Speaking of LED's is one of the few applications Super Caps are used for. Some new models of Emergency Egress Lighting Use Super Caps to store power and used to power a LED when power goes out so you can see your way out of the building . They also have some industrial uses like Power Factor Correction and smoothing. But energy storage, never.

          If you ever hear the name EEstor, run, do not walk away.
          Last edited by Sunking; 12-15-2016, 01:48 PM.
          MSEE, PE

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          • #6
            Originally posted by Sunking View Post
            A Super Cap has a working voltage of roughly 2.5 to 2.7 volts. That means you would have to arrange the Caps in series to get any useful voltage up to something useful. That does not sound like a problem right? I mean that is how we deal with batteries. Well you would be dead ass wrong. When you arrange capacitors in Series, the capacitance DIVIDES unlike battery capacity adds. Take 2 1-Million Farad capacitors, put them in series and you now have 1/2 the capacity. Add a 3rd in series, and you now have 1/3 the capacity of a single capacitor. The more you have, the less you have. Capacitance is like debt, not something you want more of. The only way to make Capacitors add is in parallel.
            While it's true that capacitance of two capacitors in series combines like that of two resistors in parallel, that doesn't mean that connecting supercapacitors in series is necessarily a bad idea.
            The total theoretical energy stored remains the same whether they are in series or parallel. E = 1/2 C V^2, so if you halve C but double voltage, you get the same energy as if you double C but keep voltage the same.

            That part I remember from back when my Dad taught me electronics. More practically, a little googling found that
            Murata's supercapacitor technical note mentions that connecting them in series requires voltage balancing,
            and that supercapacitor manager chips like TI's BQ33100 can do this for a stack of five small supercapacitors in series.

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            • #7
              Originally posted by Sunking View Post
              A Super Cap has a working voltage of roughly 2.5 to 2.7 volts. That means you would have to arrange the Caps in series to get any useful voltage up to something useful. That does not sound like a problem right? I mean that is how we deal with batteries. Well you would be dead ass wrong. When you arrange capacitors in Series, the capacitance DIVIDES unlike battery capacity adds.
              Two batteries gives you twice the energy storage that one does - even though the AH capacity does not go up if you connect them in series. Two capacitors gives you twice the energy storage that one does - even though measured capacitance goes down if you connect them in series. Simple 5th grade math.


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              • #8
                Originally posted by jflorey2 View Post
                Two batteries gives you twice the energy storage that one does - even though the AH capacity does not go up if you connect them in series. Two capacitors gives you twice the energy storage that one does - even though measured capacitance goes down if you connect them in series. Simple 5th grade math.
                Me thinks you need to go back to school.

                Substitute Farads for AH so a 5th grader can understand. Say a 2.5 volt 1 AH battery has 2.5 Watt Hours of capacity. By your misplaced logic if you put two in series you should have 5 watt hours. Wrong answer. You would have 5 volts @ .5 AH with two in series.The exact same 2.5 watt hours. You failed 5th grade math. The only way to make the power add in a capacitor Is in PARALLEL. A first year electrical student would know that first semester. Two 1000 Farad capacitors in series = 500 Farads every day of the week. Are you sure you are an engineer.? Even an Electrician knows this.


                I think you need to go back to school and learn capacitors start here. Here is your first lesson When you connect capacitors in series, the result is that the effective plate surface area decreases, thus capacity loss. When you add batteries in series or parallel, the plate surface increases. Now go back to your college and get a refund.

                Besides even if what you said were true, you cannot access all the energy. At best only 50% without some complicated Boost converter circuitry . Think about that a while.
                Last edited by Sunking; 12-16-2016, 12:52 AM.
                MSEE, PE

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                • #9
                  Originally posted by Sunking View Post
                  Substitute Farads for AH so a 5th grader can understand. Say a 2.5 volt 1 AH battery has 2.5 Watt Hours of capacity. By your misplaced logic if you put two in series you should have 5 watt hours. Wrong answer.
                  Let's see:
                  2.5 volts at 1AH = 2.5 watt-hours.
                  5 volts at 1AH = 5 watt-hours. Twice the energy.
                  Easy peasy. Looks like your 5th grade teacher owes you a refund.
                  Two 1000 Farad capacitors in series = 500 Farads every day of the week.
                  That's right. But then you took a little knowledge, misapplied it - and you fell flat on your face. But don't believe me - let's do the math.

                  Take two of the popular Maxwell BCAP0350 caps. 350 farad, 2.7 volt. You want 5.4 volts so you connect two together. Lo and behold, it is now good to 5.4 volts, but their new capacitance is only 175 farads! Why? Ctot=1/(1/C1+1/C2+1/C3 . . .)

                  "Ha!" says SK. "That's half the energy."

                  But then you continue to do the math. You remember that the ENERGY stored (you know, the thing measured in units like watt-hours you mentioned above) is 1/2CV2. And one capacitor can store 1275 joules (or watt-seconds.) That means two capacitors in series must store. . . half that? Or the same?

                  So then you apply that formula to the new capacitor formed when you put both in series. 5.4 volts at 175 farads is . . . .2550 joules, exactly twice what a single cap is!

                  You scratch your head. "How can that be?" you wonder. Then you notice that while the capacitance has decreased by a factor of two, there's a mysterious little tiny "2" at the end of the energy equation after the voltage term - why, that's an exponent! It means you square the voltage - so the doubling of voltage has led to a quadrupling of stored energy. Take half the energy, quadruple it - and you get twice the energy with twice the number of capacitors. Easy peasy.

                  Maybe you didn't learn how to square a number in fifth grade. Like I said, get a refund.

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                  • #10
                    http://flexgenpowersystems.com/ Definitely not for home use but used in oil and gas applications to provide surge load at drilling sites. Drilling sites usually have very large generators that mostly idle but are needed to cover surge loads. The Flex Gen unit provides short bursts of power to deal with the surge. It means they can get by with much smaller generators.

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                    • #11
                      Originally posted by Sunking View Post
                      Say a 2.5 volt 1 AH battery has 2.5 Watt Hours of capacity. By your misplaced logic if you put two in series you should have 5 watt hours. Wrong answer.
                      Uh, right answer for batteries. Ah's aren't cut in half because batteries are placed in series, they just don't add. Is jflorey2 on the SK hit list now too? It's a little out of control here moderators.

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                      • #12
                        SK is having a little trouble with math / EE, and doesn't trust me or jflorey2. J.P.M., can you help him out with the math? Maybe he'll listen to you.

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                        • #13
                          Originally posted by DanKegel View Post
                          SK is having a little trouble with math / EE, and doesn't trust me or jflorey2. J.P.M., can you help him out with the math? Maybe he'll listen to you.
                          Dan, I'm pretty sure I forgot more math than you'll know for some time, if ever if your current antics were to stop and you were to attempt something productive.

                          As for any input I may have to this thread: In general, I try to stay out of contributing to discussions unless I think I have something cogent to contribute/add based on knowledge or experience I think I may have. Since I believe in equal opportunity as well as equal responsibility from all, I'd say that applies to your input as well. Therefore, IMO, this forum would be a better information exchange without your input. You post above is a one of many examples why I have that opinion.

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                          • #14
                            J.P.M., are you saying my math is wrong? Or are you just saying you'd rather die than admit that I'm right about something?
                            Last edited by DanKegel; 12-16-2016, 09:07 PM.

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                            • #15
                              SK: Your math is leaving out the fact that the stored energy in a string of capacitors is (1/2)CV2. The square is important.

                              One cap, C, one volt gives .5Joules.
                              Two caps, C/2, two volts, gives 1.0 Joules, twice that of a single cap even though the capacitance has been cut in half.

                              And, BTW, SK, were you trying to troll DK with a false fact or were you just thinking AH and saying WH?
                              Substitute Farads for AH so a 5th grader can understand. Say a 2.5 volt 1 AH battery has 2.5 Watt Hours of capacity. By your misplaced logic if you put two in series you should have 5 watt hours. Wrong answer. You would have 5 volts @ .5 AH with two in series.The exact same 2.5 watt hours.
                              I am pretty sure that two 2.5W-h batteries in series do store 5.0W-h of energy.
                              The problem with substituting Farad for AH is that for a battery Energy = V x AH (no square there). And AH is unchanged by putting two identical batteries in series.
                              Last edited by inetdog; 12-16-2016, 10:40 PM.
                              SunnyBoy 3000 US, 18 BP Solar 175B panels.

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