I'm a noob. I have asked another question in this forum, but in component level. As the answer of that question says to use 12v and 5v relay. I reached out to local electroni6c market. But for covid-19 everything is shutdown in Bangladesh, local online electronic suppliers also stopped their services. So I need another solution. Any help would be great.

I have a 4g modem with WiFi hotspot. As my main home router doesn't support sim card, so I have to use this in some situations, but not all the time. But now I also need this to work during the load shedding. So I tried to modify it. But for not having the skills required to do all this, I couldn't.

Here is my existing setup:figure 1 figure 2

Numbers in blue are the parts number:

  1. A 12V 1A power supply.(I'll replace this with a 12V 3A power supply in few days)

  2. A IR RGB LED controller with maximum output of 3A. But I have connected only 0.2 meter LED strip instead of 1 meter.

  3. A 12V to 5V 2A buck converter. This circuit bord is actually from my car phone charger.

  4. A desktop fan to keep everything cool, specially the router. Cuz it gets so hot that after working for 30 to 40 minutes without fan, it stops working.

  5. The router.

So to make it work during the load shedding, I added a 5V 1A power powerbank circuit. Which doesn't support pass through charging. So I had to add that like this:

figure 3

But it creates more problem then it solves. Because, I found out that, connecting the both input and output line in parallel of the powerbank circuit will fry the chip in the powerbank circuit. Also I was about to add the 12V fan line to the powerbank. But, I couldn't. So during the load shedding even if I separately run the router from the powerbank, it's gets hot due to no cooling fan. (I can add another fan parallel to the router, but it will spin all the time instead of only when the power bank is powering)

Even if I connect desktop fan parallel to the router, this will blow the chip in powerbank, 12V buck converter and the router as this will bypass the 12V to 5V buck converter. As the purple colour 1 marked red line shows this in the below photo:shot circuit

This is only my DC circuit problem. I also want to add a feature exactly like intelligent LED lights. Where if I cut the AC line via switch, everything should turn off, like the router, fan, LED driver. But if the switch is on but no AC power due to load shedding. The fan and router should be on and consume power from the powerbank.

Finally the question is over as I thik I have explained everything. But if you have any questions please let me know. Also any suggestion regarding improvement of the question would be appreciated.

Note: I could have just used the intelligent LED light circuit I had bought, but It is a very low quality circuit with a 4V lead acid battery. It didn't had any battery protection ic. So I searched for better LED light with li-on battery and minimum protection circuit. But in my area all electronics shops only keep this as they are cheap.


1 Answer 1


You can try adding Schottky diodes on both input and output +V lines of your PB (6).


simulate this circuit – Schematic created using CircuitLab

D1, D2 should be Schottky. Not the best solution, but it might work as a "poor mans" backup power solution. Better solutions involve more complex schematics so I'm not sure if you can find parts for them in the current situation.

Or if your PB (6) supports both charging & powering output at the same time you can disconnect your router (5) from DC-DC (3) and connect it only to the PB (6) output. That way it will work as a simple UPS. Some power banks can support this mode.

  • \$\begingroup\$ Thanks for the answer, bought a mi power bank with pass through charging. So this problem is solved. But I'm looking forward for any relay alternative. \$\endgroup\$ Apr 6, 2020 at 8:13
  • \$\begingroup\$ @ShohidulAlam I've updated my answer with a schematics on what I've meant on another solution. \$\endgroup\$
    – NStorm
    Apr 6, 2020 at 9:08

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