high current UPS ish design

This is my latest attempt to try building a ups ish system for my 3D printer the printer is custom-designed with 5 meters (no, it's not a typo) on each axis.

we use MKS Gen v1.1 with custom marlin core.

this board can handle 12-24v.

with our calculation, our current draw is 20 to 60 amps when bed and nozzle are heating up.

so a commercial UPS is not affordable.

I came up with the following circuit as our power source.

I could use some tips to optimize it.

simulate this circuit – Schematic created using CircuitLab

I know it's not pretty

My charge controller is Arduino Mega with the following algorithm:

if the battery voltage drops below 11.5 the relay is connected to charge the battery up to 13 volts then the relay is disconnected.

V1 is a power source with 80 amps capacity.

V2 is 3 car batteries connected in parallel. (to handle the sudden current shock)

There is a backup generator behind V1 which starts if V2 drops below 11.2.

There are other loads on the printer side that are mission-critical and can not be turned off even for 1 second.

P.S: I was thinking about adding a capacitor to smooth out the voltage but I could use a bit of help to calculate its capacity.

P.S2: we are planning to add solar panel as V3 later this year...

P.S3: I know, I know its idiotic, but we are tight on budget and cannot afford a big UPS we are pretty much out of money and this printer is our income source ...

( it took me around 35 days to build this printer, speed is 3mm/min, it's huge )

• Could you state the question more clearly? Jul 25, 2019 at 18:19
• @DmitryGrigoryev I need some optimization on my circuit to lower any risk, if possible Jul 25, 2019 at 18:21
• Optimization requires to define criteria and constraints. E.g. optimizing for max current with limited cost will give a different result than optimizing for min cost with a minimum required current. Jul 25, 2019 at 18:28
• @DmitryGrigoryev I'm looking for optimization in terms of clean voltage and clean current with cost in mind to minimize any possible damage to the printer. I'd sleep better if I could keep the voltage on 12v Jul 25, 2019 at 18:30
• And why do you need an UPS? There are plenty of off-the-shelf power supplies for 12..24V. 60A is a high current but not unheard of. Jul 25, 2019 at 18:37