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I'm trying to find a small supercap for an energy harvesting application, but I can't seem to find one after hours of googling. Loads of pdfs say "Capacitance, 1mF to 100F" or something, but I can never find anything under 5mF. I actually only need about 600uF, but the more the better.

The constraint is that it has to be as small as possible, preferably a coin cell type thing no taller than 2mm, although I imagine that might be pushing it, although maybe not because this one (http://www.farnell.com/datasheets/2024570.pdf) is a good diameter, but is 5mm and 10mF. Non-radial ones are fine, they just have to fit inside a 20mm diameter circle. Thanks for any ideas!

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    \$\begingroup\$ You're not finding a 1mF capacitor because usually they're labeled as 1000uF. \$\endgroup\$ – DerStrom8 Mar 25 '16 at 1:32
  • \$\begingroup\$ Voltage rating is the primary driver of size in capacitors. What voltage rating do you need? \$\endgroup\$ – Dan Laks Mar 25 '16 at 2:07
  • \$\begingroup\$ It only needs to be charged to about 1.8-1.9V \$\endgroup\$ – BeB00 Mar 26 '16 at 12:24
  • \$\begingroup\$ I also tried searching for 1000uF but nothing really came up \$\endgroup\$ – BeB00 Mar 27 '16 at 2:06
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You don't need a supercap, you need a few ordinary MLCC capacitors. Looking at Farnell I can find 220 µF X5R, 6.3 volt in 1206 packages, 1.6 mm tall and they are surprisingly cheap (Murata GRM31CR60J227ME11). You can get them with a lower maximum voltage if you don't need that high.

Three of these and you have your capacitance, but add a few extra because X5R is sensitive to DC bias voltages. As you can see, there are room for quite a few, even if you take the courtyard into consideration.

enter image description here

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  • \$\begingroup\$ That does look pretty good, although I guess the pcb thickness needs to be taken into consideration and the extra manufacturing steps. I might be able to squeeze them ont the existing pcb though I guess. Do you know, is this the most capacitance-dense type of capacitor available in such a small package? \$\endgroup\$ – BeB00 Mar 26 '16 at 12:28
  • \$\begingroup\$ @BWalker I'm pretty sure they are. I browsed around on Murata's website, and they seem to beat every other technology for such a constrained height. They also brag about having the world's thinnest supercaps, but even they are 3.5 mm thick. \$\endgroup\$ – pipe Mar 26 '16 at 16:00

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