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i am looking to run a 60mm by 60mm 12v 0.22A fan for 2 to 3 mins with no power after it is shut down. It is needed i case of a power failer. What is the best way? Also want to run fan after shutdown to cool element

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    Probably more appropriate in electronics stack exchange
    – Ecnerwal
    Oct 10, 2014 at 0:05

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A capacitor or a battery will both work. The idea is to maintain a device that stores electrical power to be delivered after a loss of the main power.

My first attempt would be to use a rechargeable battery. An appropriately sized 12V battery, or combination of lower voltage batteries connected in series, will be able to power the fan. Your fan only requires 0.011Ah to run for the 3 minutes stated. Most batteries should be kept above 50% discharge. So plan for 0.022Ah or larger.

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  • Capacitor is unlikely to hold enough power. Note that if you want the fan to start before the battery runs flat, you'll need a timer circuit of some sort. This is more appropriate in the Electronics discussion, since it's not quite trivial.
    – keshlam
    Nov 13, 2014 at 23:32
  • A capacitor can store enough power. It simply depends on the voltage and capacitance of the capacitor chosen. I haven't done the math, but it's likely to require a rather high capacitance which would make it unrealistic in both cost and size.
    – rjbergen
    Nov 14, 2014 at 4:54
  • OK; a reasonable capacitor can't. Supercapacitors could, but they'd cost more than could be justified for this application.
    – keshlam
    Nov 14, 2014 at 5:01

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