A world of super capacitors

[tadam]

Hello all,

I've been inspecting datasheets of 50 F supercaps of Panasonic (goldcap) and Cooper Bussmann (x times more expensive).

Both are officially rated at 1000 hours at 60 or 70 ° C. When applying the arrhenius formula that would give you a 2-3 years guaranteed life at 15°C.

That is one part of the datasheet. They also show "typical data" where they seem to operate up to 10 years with only 30% decrease in capacitance. Highly acceptable, but how should I interpret this data?

What could be the difference in price between these two manufacturers (is it different technology??). I would like my cap to last 5-10 years in parallel with a battery through a series resistor (the battery itself cant be discharged higher than a couple 100 mA).
Also Cooper-Bussman lists "hybrid battery pack" under applications, not so Panasonic, this I find suspicious.

Thanks
J.

 

[Sceadwian]

I don't think they've really been tested to that extent. The manufacturing processes are so new.. Their MTBF are just guesstimates.

 

[Boncuk]

You need a lot of supercaps connected in series when connecting to a battery.

Their nominal (max) charging voltage is 2.5V.

You might also read the datasheets of the WIMA SuperCaps (up to 1,200F).

Boncuk

 

[Sceadwian]

Boncuk, he said he wants the super caps in parallel with the battery, and a current limit resistor not in series, and typically speaking, super caps aren't run in series, not sure why you would do that, and how many you need in series dpeends on the battery pack and the exact supercap you're using. the Superstor 1F ones that I have are 5V rated. Their more broad ranging models are 2.5v.

 

[tcmtech]

When they come out with 250 volt super caps in the 10000F range then I will take some serious interest. (55 gallon barrel sized most likely)

But just think what that could do to your buddies screwdriver end!

 

[amitie30]

Regarding supercap price and life things

Hello,

I'm working at VinaTech, manufacturer of supercapacitor based in Korea.

* As for 2.7V 50F, market price for some massive q'ty is set around $3.
I can also see that some makers or online sellers offer over $10 in case of sample basis...

* Life : You'd better see simply cycle life of supercap(room temperature condition). Most of supercaps, also VinaTech, offer over 500,000 cycles(from rated 2.7V down to half 1.35V charge/discharge). You are to get a real data about cycle life.

* Regarding Arrehnius calculation, I also referred to this, but I guess the condition is "continous loaded at rated voltage", without one time cut off power over the whole life, similarly accelerated high temperature testing for 1000 hours at 70 C or 2000 hours at 60C. The real application of supercaps is not like that...I'm not so sure about arrehnius. Anyhow, I think it is better to see cycle life instead.

If you have further questions to make clear, you are freely to contact at my email, jkim@vina.co.kr or hycap@vina.co.kr

 

[tadam]

No Boncuk is right, I need 2 in series. And then you have to watch out for balancing, but I have calculated that I can get away without balancing resistors.

Ive been told goldcaps exist since the 80ies, its not so new then?

Do you think I will be able to keep leakage current in the uA range? Last time I measured over a 24 h period it was 30 uA but that seems to come down over time.

 

[Sceadwian]

tcmtech, you're an experimenter, you should try to make some of your own super caps. Get some large tin foil rolls and stretch film from an industrial supplier and wind some really big non-polar poly caps =) Juuuust for fun. Always wanted to do it, at the very least they could be used for motor run caps.

 

[tcmtech]

I have seriously thought about it many times being things like motor start and run caps are rather pricey for bigger ones.
I just dont know where to find the exact specs for which insulator materials and what thicknesses relate to what voltages and what capacitance per square unit of aria. I have some formulas some place for making HV glass plate capacitors but none that relate to paper or any types of plastics materials.

Being I have my lathe, setting up the roll holders and the proper pretensioning systems for making very large capacitors would be all that hard. And I have several suppliers that carry about any type of plastic film needed already on rolls.
I just need some proper design specs formulas!

And what exactly makes up a super capacitors materials anyway?

Yea, I know. Just Google it.

 

[Sceadwian]

Buy the thickest poly wrap you can find, and high quality film is a must. Don't buy that sticky thin stretch film for cheap skid wrapping that is very common. Basically what you want is just good old plain basic constant thickness plastic wrap, no plasticizers, not adhesives nothing. Check out a few places near you I'm sure you'll find something that looks to you like decent plastic film (not stretchy gooey crap) find out where they get it and buy a roll. The foil is just the thickest aluminum foil you can find.

As far as super caps go the only thing that makes them different is the surface area per unit volume. You can make a 'super cap' out of 'normal' materials... you just gotta make it bigger =)

If you can find a supplier for some kind of wrap that you think would be okay, find out what thickness's they offer it in and what the material is, it's easy to look up the dieleectric constant and from the thickness determine the voltage that's safe, but as long as it's not chincy film you should be able to get 100+ volts out of it safely. I won't say more than that simply because the film itself is the really important part, and keeping it intact and even throughout construction is a must. You will have inductance and conductance problems with larger rolls though because winding the coil adds inductance and the longer the roll (diameter) is the more resistance the metal is going to have regardless.

Also, just for fair warning, most plastics that you'll find have a relatively high dielectric absorption, which means especially with a higher value cap if you discharge it fast and then disconnect it, it can regain some of it's previous voltage. The 80u 180V electrolytic flash caps that I've used before will discharge from 200 volts down to 0 almost instantly, but when you disconnect them they'll recharge to up to 80 volts from the electrons that were trapped in the dielectric material.

 

[Boncuk]

Boncuk, he said he wants the super caps in parallel with the battery, and a current limit resistor not in series, and typically speaking, super caps aren't run in series, not sure why you would do that, and how many you need in series dpeends on the battery pack and the exact supercap you're using. the Superstor 1F ones that I have are 5V rated. Their more broad ranging models are 2.5v.

Hi Sceadwian,

even a 5V supercap can't be connected in parallel with a battery (even with a current limiting resistor). If a 5V cap is charged by a 6V battery it will blow up when exceeding the max allowable voltage.

A 1F cap is not really a supercap (seems to be a gold cap). Supercaps start at a minimum of 400F.

According to WIMA info it's not advisable to charge a supercap beyond the rated voltage because of the possibility of destruction.

Using supercaps for supply power backup > 2.5 or 5V respectively I don't see any other way than connecting the appropriate number of caps in series to stay within limits.

Of course this measure reduces the total capacitance drastically.

Regards

Hans

 

[Sceadwian]

even a 5V supercap can't be connected in parallel with a battery (even with a current limiting resistor). If a 5V cap is charged by a 6V battery it will blow up when exceeding the max allowable voltage.

Okay, how about a 1.2, 2.4, 3.6, or 3.7 volt battery? That to me logically says that you can use 1-3 NiMh/Nicads or a Lithium cell with a 5V super cap directly with no worries.
I've run 5V super caps in parallel with lithium, and in replacement of NiMh one two and three packs before.

Supercaps have no starting value what you consider it to be the starting point of the definition of a super cap is irrelevant and non-technical.

Using supercaps for supply power backup > 2.5 or 5V respectively I don't see any other way than connecting the appropriate number of caps in series to stay within limits.

<gasps> 2 2.5v's for a 5 volt system or use 2 5V's for a 10V system. NO WAY! Yes capacitance divides at that point, but that's why you're supposed to understand your power requirements and what super caps can do for you in the first place rather than make these broad reaching statements.

 

[Boncuk]

No Boncuk is right, I need 2 in series. And then you have to watch out for balancing, but I have calculated that I can get away without balancing resistors.

Ive been told goldcaps exist since the 80ies, its not so new then?

Do you think I will be able to keep leakage current in the uA range? Last time I measured over a 24 h period it was 30 uA but that seems to come down over time.

Hi tadam,

I'm almost right. Here is a WIMA SuperCap of 110F and 14V nominal voltage. If 110F don't suffice check page2 of the sheet. There is a 200F/14V SuperCap.

You might connect that one in parallel with the battery. Don't forget to add a diode to prevent discharging of the cap into the battery when it depletes.

If you need assistance translating the datasheet to English please feel free to PM me.

Regards

Boncuk

 

[Boncuk]

Hi tcmtech,

if you want to experiment with supercaps I suggest using silicone oil as insulator.

A friend of mine built a high voltage cap (100KV) using that oil. It is normally used in foam cutting machines and shredders to prevent sticking of the material to the hot knifes.

I probably used the wrong term for "foam". It's the kind of foam used for upholstery of furniture. The shredded foam (including the crust) is used for cheap pillows, and "spaghetti" type foam is used for high quality pillows.

In large factories they use tons of that oil and knocking the door with the feet (hands full with two sixpacks) you'll certainly get the desired amout free.

Regards

Boncuk

 

[Boncuk]

Supercaps have no starting value what you consider it to be the starting point of the definition of a super cap is irrelevant and non-technical.

Please forgive me my ignorance.

I should have written that this my personal opionion about caps.

A cap (from my understanding) is a cap ranging from nF to µF, a cap-cap is in the low F range, and a supercap is in the hundreds (or thousands) F-range.

 

[tcmtech]

Hmm. Silicon oil?
I think I still have a gallon or two of that around anyway. If not I know where I can get it cheap! (and legal)

Any idea what capacitance something the size of a 5 gallon bucket would have at 250 volts or less?

What type of insulator material do they use thats not hard to find?
I can get many different plastics and types of paper easily enough.

I can get the poly sheet stuff like sceadwain mentioned. But I have seen many capacitors that have different types of paper like material saturated with oil in them as well.

 

[Sceadwian]

I would think you're missing a really big section there Boncuk =)
I would say a cap is generally in the range of nf to maybe 100u
I would say a large cap is generally 100u to 10000u
very large to super cap would be up to the 1F range to perhaps 50F. Anything larger than that I would call a large supercap, or an ultracap. There really is no set range or language definition. But think you're short changing what should be called a super cap because it's not so much about the farrad rating of hte cap but the overall energy density. I have 1F 5V supercaps that are smaller than 6 volts 10,000u caps.

 

[tadam]

"As far as super caps go the only thing that makes them different is the surface area per unit volume. You can make a 'super cap' out of 'normal' materials... you just gotta make it bigger =)"

-> So you dont think theres a difference in technology then between Panasonic which are "organic" supercaps and Cooper which are "aerogel" supercaps.

OK I'm talking about 50 - 100 F range, you dont seem to consider that as "supercaps"

About voltage ratings, pay strict attention to them. For my application I need 3V, so that would be 2 x 2.3 V rated capacitors in series. That halves the capacitance, doubles the ESR value. AND you have to pay strict attention to balancing: what would happen if one cap in series is at one extreme of the cap rating, say +20%, and the other is -20%, would they still be within tolerable limits then...

WIMA seems to make interesting products, too bad the voltage rating is always so low...

 

[Boncuk]

WIMA seems to make interesting products, too bad the voltage rating is always so low...

I suppose a voltage rating of 14 is sufficient for many applications unless you want to use them with a 24V truck battery.

If you want higher capacitance you might connect them in parallel.

 

[mmmalmberg]

I have used the carbon aerogel 2.5V 10F supercaps (and others) in series with resistors or 2.5V zeners to balance. Put those stacks in parallel with batteries. That works fine... They have low esr and seem to stack well. I think the spec on the cooper aerogels I remember reading listed something like a million cycles.