# Will this DC UPS with off the shelf components for home network and laptop work?

I am trying to build a DC UPS to power modem, router which have power requirements of 12V 2A and a laptop which has power requirement of a 20V 3.5A.

I am planning to use a AC to DC SMPS which is capable of 24V 20A which is connected to a solar charge controller via step down (buck) converter (21V ~20A).

A 12V 46AH SLA Battery is connected to the output marked for battery in the charge controller which means it takes care of trickle current and float current to charge the battery.

A modem, router is connected directly to the output marked for connecting DC load in the charge controller. Output is 12V and max 30A current.

In parallel to the modem and router a step up/boost converter is connected to the charge controller. It steps up the voltage to 20V to meet the requirements of a Laptop. Max current for the laptop is 3.5A.

I am more of a software developer than a electrical engineer. I have come up with this design using off the shelf components with the knowledge available to me by means of other DIY DC UPS in Youtube.

I would like to know if this would work? If any flaws in the design or any heating problems that I should anticipate.

edit: Updated diagram:

Old diagram:

Off the shelf parts listed below Battery Charger 20A: https://www.amazon.in/gp/product/B07SSS5CKZ/ref=ox_sc_act_title_3?smid=A2VYJQQSTF1WW0&psc=1

• Probably work, but a bit overkill and low efficiency to do it in that many steps. Can’t you find a battery charger instead? Then you just need a low voltage cutout somehow like the one your solar controller would provide. Aug 29, 2020 at 7:45
• @winny Yes, I have now found a battery charger. High current ones are hard to find. amazon.in/gp/product/B07SSS5CKZ/…. Should I update the original question?, since based on it there is an answer given.
– rej
Sep 1, 2020 at 8:50
• Something like that, but regulated output voltage. Here is a better one: mouser.in/ProductDetail/MEAN-WELL/… As long as your buck and boost converters have undervoltage lockout (UVLO) available and set to about 11 V to prevent damange to your battery, you should be good to go. If not, you need to provide it externally. Sep 1, 2020 at 14:13

A solar charge controller isn't ideal for managing the battery.

A basic controller like that works by alternately connecting the panels directly to the battery, and disconnecting them. This is only OK because the solar panels are a current source. The solar controller isn't capable of floating the battery, so when the bulk charge is finished it just squirts in a bit of high current every now and then.

The buck converter you show is actually capable of current limiting, so it won't blow up.

But the battery will take a beating, being alternately charged and discharged every second or two, as it supplies the loads, then the voltage drops, and the charge controller connects the 20 A current source, only to find the voltage shooting up again.

The way you usually make such a UPS is like this:

15 V DC source -> diode -> load
15 V DC source -> linear charger -> battery