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Simple Li-Ion Backup for wifi and routers and other small 12V systems

The idea is to backup all sorts of small electronic wifi routers and ethernet boxes in my home
this way we can still be online, in case of a power failure.
Here is a simple and cheap way to make a little backup unit for this usage,
it will run 2-4 hrs on the battery size as shown
Li-Ion cell taken from defective computers, so they are for free.
The large double schottky diodes come from PC powersupplies, the 3.3V or the 5V output has the best, so they are for free too

The schematic and parts.
D1-D2 is inside ONE diode, since they are double. D3 is the other diode, parallel both of them.
R1 sets the charge current. The white LED and 100 over each cell is used for BALANCE, make the 3 voltages equal,
The white leds also indicate if all cells are charged, Green LED show input charge voltage is available.

No charge input, green led off.

Charge input, Green LED on.


more detailed assembly puctures of another one i also made.

I glued the diodes and resistors to the case using a thinn layer epoxy, good for heattransfer,
since I could not wait for the epoxy to cure, I added heatmelt glue :-) this way i could continue the work,
Note the batt, in, and out points, and how the diodes are connected.

The final product with cables. And mounting plate for wall screw.


Thomas Scherrer OZ2CPU 2017
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