I have a LED strip and 12v LED TV and I run them on 220v to 12v power supply but my 220v ac is cut off daily for hours and back again so I bought a 12v battery. I built the following relay circuit that helps me in switching power when 220v is gone and back to 220v power supply when its back.

The main problem is that this circuit run effectively when it switches from 12v battery to the power supply and all the devices are still running. But once it switches from the AC power supply to the 12v battery the TV switch off and the LEDs switch off for seconds and back again.

So, I need to edit this circuit so it will never affect the TV and LEDs behavior on any switching case.

enter image description here


They actually make devices for this; what you want is called an uninterruptible power supply, or UPS. They usually only output line voltage, but you can plug things into them in exactly the same way you would plug it into the mains. The only problem is, if it's for several hours, you're unlikely to get one that can operate for the full time until the power comes back on, at least not cheaply.

If you want to continue to use the simple circuit you have.... Depending on the requirements of the TV, you might be able to get away with putting a large capacitor across its terminals. Even better, what type of battery is it? I think that if it's a lead-acid battery, you could have it always connected across the TV, and the external power supply would keep it charged when not being used (though 12V is not enough to fully charge a "12V" lead-acid battery; they go up to around 14V when fully charged). At that point, you wouldn't even need the relay, though it's still a good idea to stop it from trying to feed power back into the power supply. Could just use a low-Vf diode for that, though; no need for the complexity of the relay. You'd need one anyway, in that case, to stop the battery from keeping the relay on.

  • \$\begingroup\$ No, i want and edit for this relay as using transistors \$\endgroup\$ – user3498298 Apr 23 '17 at 23:41
  • \$\begingroup\$ @user3498298 I've expanded the answer to include this. No need for transistors; simple rearrangements of your existing design can do it if your battery is the right type. \$\endgroup\$ – Hearth Apr 23 '17 at 23:49
  • \$\begingroup\$ Can you do this rearrangement on the photo i will be greatfull to you \$\endgroup\$ – user3498298 Apr 23 '17 at 23:52
  • \$\begingroup\$ Well, what you want to do depends on your power demands. I recommend reading the answer I gave, thinking about the options, and trying one. Be careful, though; if your battery is a lithium-ion one, or just not rechargeable, sticking it directly to a 12V supply is likely to cause catastrophic failure (i.e. battery on fire). \$\endgroup\$ – Hearth Apr 23 '17 at 23:57
  • \$\begingroup\$ Incidentally, I came across this question which might provide all the information you need. \$\endgroup\$ – Hearth Apr 23 '17 at 23:58

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