Variable output from Power Bank (24W = 12v * 2A and 5.4W = 9v * 0.6A)

Question

I started with trying to find 2 UPS for 2 of my routers with the following input specifications:

1. 12v 2A
2. 9v 0.6A

I realised that buying 2 power banks will be economical than buying 2 UPS for the AC power source.

I started searching for the power banks with the output specifications which matches my routers' input specifications. I did not have issues finding the 9v 0.6A. However, I am unable to find the 12v 2A, except for car jump start power banks (which are very costly and I am not sure if they allow charging while connected to the router at the same time).

I thought of building one by stacking sufficient Lithium-ion 18650 batteries should not be difficult with configurable output voltage and amperes.

I came across these instructables

1. 8v 0.6A
2. 12v (Amps not mentioned)

But none of the above matches one of my router's input specs (12v, 2A)

I also checked other questions on StackExchange, but not very helpful, example:

1. Powering 12V 2A device from high-power USB portable charger - No conclusive answers.
2. Creating a Li-on backup for a 12v router - Good schematics and answer but the output specs does not match mine.

So, I landed up here to understand how this can be built. I am based out of Bangalore in India and I would prefer to procure materials available here.

My requirements:

1. Build a power bank which can charge itself and also power the router at the same time (work as an UPS)
2. Display output voltage and current preferably
3. Configurable unit on the built device which can moderate the output voltage and current.
4. Battery overcharge protection unit
5. Under and over voltage protection
6. Cost effective - I am ok to sacrifice point 2 from the above to cut down on cost! I can always use a voltameter to check the output specs manually ;) Fine with leaving behind point 3 as well and have a fixed output instead of variable one, however, I would love to have point 3 covered!

This is what I can think at the moment from requirements perspective, is there anything else I should consider?

I am very naive at electronics but very much interested to learn and build :) Looking forward to lots of fun and education from the community and a fruitful product!!

Answer 1

You may want to consider using a standard 12V gel-cell or AGM lead-acid battery and charger for your 12V 2A load. Ensure the charger can supply more than 2 Amps while at the float voltage output of (about) 13.5 Vdc.

This is far less expensive than using a custom Li-Ion battery and charger /with cell balancing. As a bonus, you get far longer run time for far less money.

Consider purchasing your 12V gel-cell from an alarm company supplier. In Canada, my alarm-company supplier sells 12V 8AH batteries for less than Can $20. A suitable charger costs much more than that but the local automotive stores have suitable chargers.

If both units are located close to each other and can share the same power source, you can add a buck DC-DC converter to run the 8V device.