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In India power cut is often. And most houses are installed with Inver-battery, for backup till the power comes back. But since all inverters don't behave as ups, there occour a little gap between the power switching i.e. from main power to battery power. Gap is roughly lasts for 1-2 seconds. And during that gap my router turns off for obvious reason. Can i do something to cover this gap and prevent it from turning down? I've tried using two 220uF capacitors in paralled to power supply input in router but nothing noticable happened. Power supply for router is of 12 V 0.5 A. Please help.

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    \$\begingroup\$ Your capacitors are many orders of magnitude too small for this task. It is possible but it would probably be preferable to find a true 12v UPS. Unfortunately much of what is sold under that term is more in the realm of an "overgrown powerbank" than something actually intended for that use. Generally speaking electronic usage questions are off topic here, and if you were going to design something you would preferably target the router internals rather than its power input connector. Have you considered a small AC mains UPS? \$\endgroup\$ – Chris Stratton Nov 1 '18 at 14:37
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    \$\begingroup\$ +1. Buy a UPS. Safest and easiest solution. \$\endgroup\$ – Adam Lawrence Nov 1 '18 at 14:42
  • \$\begingroup\$ +1 on what Chris said. A USB power bank and a 5 to 12 V converter is probably your best option. \$\endgroup\$ – winny Nov 1 '18 at 14:43
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    \$\begingroup\$ @winny the problem is that most powerbanks aren't actually designed to work as a UPS, even though in trying to buy a DC UPS you'll be flooded with product listings for powerbanks \$\endgroup\$ – Chris Stratton Nov 1 '18 at 14:50
  • \$\begingroup\$ Unless you know what you are doing ; DON"T play with big capacitors... at the very least a shock will hurt, or it won't hurt ever again... \$\endgroup\$ – Solar Mike Nov 1 '18 at 15:16
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Something a little cheaper than a mains voltage UPS is like:-

ups

which you can read about here. It does what you want without the inverter/step up components to produce mains level voltage.

The problem with your capacitor only solution is that the capacitors need to be pretty large, and commonly you'd use super capacitors. That then leads to huge inrush current management. And since most super caps are 2.7V, some form of voltage equalisation when you stack them up to increase voltage. A practical, safe and reliable circuit quickly gets complicated.

If you want a project, there are many DIY circuits on line for this exact scenario. If you simply want a solution, buy one of the above like thingies.

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  • \$\begingroup\$ Brilliant! How much are they? \$\endgroup\$ – winny Nov 1 '18 at 16:40
  • \$\begingroup\$ @winny Looks like they go for ~£25. \$\endgroup\$ – Paul Uszak Nov 1 '18 at 17:02
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    \$\begingroup\$ Thanks for suggestions. Actually i got to know about these before but thought that it will be a waste of a powerbank to use just for filling 1-2 seconds gap. But as it is the only feasible solution, I'll go for it. Thanks again. \$\endgroup\$ – Rishabh Nov 2 '18 at 4:11

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