[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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