2.3kWh LiFePO4 Solar Energy Storage System / Double Conversion UPS

[VagueDirector]

The aim of developing this was to make an ultimate system to power my electronics under all situations. The system is able to make use of any solar input that is available, with the remaining power requirements made up from the AC input. The AC charger is set to 13.2V, which keeps the battery from going below ~50% state of charge. That way there is always power available, even when the AC grid is not available and solar is insufficient. The unit is 80-85% efficient as a double conversion UPS, with ~94% efficiency on the AC charger and ~90% efficiency on the inverter. When solar generation is greater than load requirements, excess energy is stored in the battery for use later in the day/night. This system took a long time to design and build, everything was planned out in Fusion360 beforehand to ensure I was happy with it before purchasing components.

Features:

• Battery: LiFePO4 4S2P 12.8V 2.3kWh (using 90Ah cells)
• AC Input: 240V 400W
• Solar Input: 100V 400W
• AC Output: 240V 1000W
• DC Output: 12V10A Cigarette Port x2, USB 5V2.1A x2, USB QC3.0 x1, USB Type C PD3.0 18W x1
• Temperature controlled, always running silent fan with dust filtered air intakes
• Coulomb counting state of charge meter
• Detachable active cell balancing module
• Portable with wheels, mass ~30kg so it can be lifted up stairs
• Monitoring displays for Battery, AC Output, AC Input and Solar input.
• Battery is lightly compressed using additional ETFE sheets between the cells.
• Threaded rods redistribute much of the battery weight to the case walls, also greatly improving rigidity of the battery and case.
• Over/under temperature protection for the battery.

Related resources:

• Cell terminal covers / shrouds: https://www.thingiverse.com/thing:4567648
• Battery management system display: https://github.com/vagueDirector/ArduinoXiaoxiangSmartBMSDisplay

3D Model in Fusion360: System electrical diagram: AC Inputs & Outputs: Monitoring displays: DC Inputs & Outputs: Inside: The cells on the bench: 3D Printing cell holders / shrouds: Thermal image when under 800W Inverter load: Thermal image when AC input is at maximum (400W):

 

[gnubie]

We have some really talented people on this forum!

 

[Supervstech]

it is a thing of beauty!

I want one!

 

[Supervstech]

thermal image shows your conductor is too small through the switch though.

 

[VagueDirector]

thermal image shows your conductor is too small through the switch though.

Yes I have noticed that. It isn't from the cables though, the hotspot there is from having the main fuse and switch very close together (both of which get warm under high load). The switch is supposed to be 100A or 200A rated (depending on where you look), but I'm keeping an eye on it as I suspect it may be underrated/chinesium. Doesn't seem to be that much of a problem though, it's nowhere near the temperature where things start to melt.

 

[Supervstech]

Yes I have noticed that. It isn't from the cables though, the hotspot there is from having the main fuse and switch very close together (both of which get warm under high load). The switch is supposed to be 100A or 200A rated (depending on where you look), but I'm keeping an eye on it as I suspect it may be underrated/chinesium. Doesn't seem to be that much of a problem though, it's nowhere near the temperature where things start to melt.

Oh, I agree there, just minor gripe.
It looks like you have #2 or 33mm2 from the battery, and #6 or 13.3mm2 through the switch.

 

[VagueDirector]

Oh, I agree there, just minor gripe.
It looks like you have #2 or 33mm2 from the battery, and #6 or 13.3mm2 through the switch.

The main conductors from the battery to inverter are all 25mm^2 copper. I've marked wire sizes on the electrical diagram.

 

[SolarOhio]

Very nice! Does it have any sort of grounding for the inverter or charge controller?

 

[VagueDirector]

Very nice! Does it have any sort of grounding for the inverter or charge controller?

The mains earth conductor from the AC input is connected to the AC charger, the solar charge controller and the inverter (green/yellow wire). The AC output is an I.T. earthing system with a floating neutral. I thought about adding a N-E link on the inverter along with an RCD, but read that it doesn't necessarily make the system safer than leaving it floating. This is the same configuration as my cyberpower desktop UPS. The electrical diagram shows exactly how it is wired.

 

[Leaking Acid]

That is truly inspiring!