[OZAPRS] on small UPS for small vulnerable linux systems
Glen English VK1XX
glenlist at pacificmedia.com.au
Thu Feb 1 19:17:04 AEDT 2018
On small UPS
assuming you can get linux shutdown inside half a second, which I think
is quite easy,
With the droid consuming 2W, that's 2W for half a second, or 1 Joule
With a super capacitor, on the input side of the 12 to 5V switcher, half
of the capacitor voltage is usable, say 12 to 6V, and that is 75 % of
the energy storage utilized.
So for 1 joule delivered ,, we need 1.33 Joules stored, to use the cap
down to 50% volts.
now, energy = 1/2 C V^2, so that is 13.88 mF required. Which really
isnt too bad...
so, 5 of the smallest 2.7V caps in series will do it (with some parallel
equalizing R and Vz across them) .
ideally would keep the ESR below 0.1 ohm, so ...
so a little 2F one ,($1 each) , 5 in series to get the volts, would
provide 108 Joules or about a minute of run time.....
hmm it think that's right.
On 30/01/2018 10:03 PM, Matthew Cook wrote:
> All Good ! I'm running on a Asus Tinkerboard with an Rockchip RK3288
> (ARM Cortex-A17) which is no slouch and has onboard audio (in and out!)
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