capacitor battery?

[daguuy]

yesterday i went to a store called gateway electronics (it has everything you wouldn't find at radioshack plus more) and in the capacitor isle i saw a bunch of 15000 uf 16v capacitors for really cheap. i didn't need them at the time so i didn't get any but i think they might be a good battery for a future portable that can be charged really fast an infinate amount of times. what's the equivelant to 15,000 uf in amp hours? i think if you use some of those in parrallel and a switching regulator (and a bunch of electric tape so you don't kill youself). would these give me a good amount of play time if i used 6 of them in parrallel (90,000 uf) and charged them to a little less than 16v and used a switching regulator?

[Kurt_]

http://www.hackaday.com/entry/1234000383070996/

It would work. He used a 10f (I THINK that's 10,000uf) capacitor to make a 9V battery. If that lasts 2-3 hours, you should get about 1000mAh (that's my out of the blue guess) on one of them. Get some, and try it. Supercaps are cool.

Mind you, the discharge curve is a little less linear, but it's nothing a TI regulator can't handle. Just make sure it has a big range of VIN.

[timmeh87]

youre off by an order of magnitude. micro is 10e-6. 10,000uF = .01F

also, a normal 9v battery has a capacity of about 150mAh

C= Q/V

where
C = capacitance
Q = electric chage
V = potential difference

so

.015(16) = .24C of charge

using the calculator here, http://www.unitconversion.org/unit_conv ... harge.html

(.24) coulomb = 0.000066667 ampere-hour

im not sure if i did this right, please correct me if its wrong..

[JAY]

10F is 10*10^6uF, or 10,000,000uF. If he got 2-3 hours out of that, then 90,000uF wouldn't last very long.

Edit: darn you, timmeh; you squeezed it in before me!

[Gamelver]

hell, it'd take a 63F cap just to get 2.8 or so amp hours....

and I believe 1F caps are like the size of cans of coke, only skinnier and taller......good luck powering something with caps .

[superdeformed]

youre off by an order of magnitude. micro is 10e-6. 10,000uF = .01F

also, a normal 9v battery has a capacity of about 150mAh

C= Q/V

where
C = capacitance
Q = electric chage
V = potential difference

so

.015(16) = .24C of charge

using the calculator here, http://www.unitconversion.org/unit_conv ... harge.html

(.24) coulomb = 0.000066667 ampere-hour

im not sure if i did this right, please correct me if its wrong..

Not sure where you're getting your numbers from, but I believe most 9V batteries have a capacity of ~500-700mAh. 150mAh sounds about right if you're talking about rechargables though.

In the case of that 9V cap battery, I came up with:
charge = 10F * 2.3V (voltage of the cap) = 23 coulombs
then with that unit converter 23 coulombs = 6 mAh

Obviously that's not going to get you very far being used as a normal battery.

and I believe 1F caps are like the size of cans of coke, only skinnier and taller......good luck powering something with caps

The 10F cap in that 9V battery is 10x30mm . Usually the really big capacitors are high voltage ones.

[Triton]

yea like the ones used at www.powerlabs.org they are EC caps and about a foot tall and mebe 4-6 inches diameter!

[Kurt_]

I read off the hackaday .pdf that capacitors discharge exponentially...
That would make them even worse.

[timmeh87]

well yes, i was using the number off of my rechargable 9v battery, we dont usually talk about alkalines around here

and i took the other numbers from dagguys original post. and the equation from wikipedia.

--

now curious, i did a quick google search. the highest capacity reghargable i found was 270mAh, the only listed capacity for a alkaline was 600mAh, and i found a lithium 9v with a 1Ah capacity!

http://www.engineeringtalk.com/news/sjp/sjp102.html

----

this is avaliable at digikey for $350:

http://www.epcos.com/inf/20/35/ds/B49410B2506Q000.pdf

5000(2.5) = 12500C = 3.47Ah @ 2.5v.

not to shabby. its also huge.

[Gamelver]

@ superdeformed: yeah, er, I just heard my ECE teacher say that last year ....it is probably just the high voltage caps that are big...and he probably meant that when he told us .