Hello community,
I want to create a DIY 12V UPS for my NAS by using an MPPT 75/15, a LiFePo4 battery and a laptop power supply instead of a solar panel.
Now I have discovered that the MPPT cannot be powered by the connected battery. This means that in the event of a power failure, the MPPT switches off. Is this normal?
What is the difference if a solar panel does not provide power at night?
Thank you in advance
Hello @Stopbit
the role of an MPPT is to load a battery from PV. It swtiches on as soon as thereis enough PV to power it. It swtiches off if PV isnot availabe.
If the MPPT is part a VE-Network (VE.direct connetion to GC device) qand there is no PV, than it will continuue to communicate but switch off the chartger.
To create 230V or 110V AC you need an inverte. Most people use a MNultiPlus 2 inverter / charter. Though a system that can do both. Charge from grid and create a grid.
Whole system consists of:
The hwole is also named ESS Energy storage System and can run grid parallel or as USV in beweteen the grid on AC_in and the critical load on AC_out_1.
You will need at least a 19V and 300w laptop charger. I recommend a 75/10 so you don’t need such a powerful laptop supply but you can also adjust the charge current from the controller. For a UPS, I would also look at AGM and see if you can use the load terminals on the MPPT to shut off when the voltage is too low so you won’t damage the battery. Lithium does not like being at 100% and will degrade rapidly when used for UPS. There are also sodium batteries now that handle the 100% charge better. You will need a 24V laptop charger to get the 16-odd volts to charge the sodium. It sounds like a fun project.
Thank you very much for your support. I know Multiplus, Cerbo, etc., I have installed them in my motorhome. I have no experience with the MPPTs from Victron.
I definitely don’t need 230V alternating current, as the NAS, the router and a SoHo switch run on 12V direct current. Together they need a maximum of 4A.
What surprises me is that the MPPT switches off completely when there is no power supply, in my case via a laptop power supply. This means that even though the battery is connected and full, I no longer have any power at the load terminals and my devices crash.
If you connect the MPPT to a DC bus bar as well as the battery and the load, than the MPPT can be switched off and the load get served from battery.
Maybe you can draw your setup.
I started the project with a no-name PWM. It worked as expected. However, I had no way of accessing it remotely. That’s why I wanted to switch to Victron. I specifically chose an MPPT with a load output. I didn’t expect that it wouldn’t output anything without PV voltage and it doesn’t make sense to me. Is the device perhaps defective?
I’ve already thought about the possibility of connecting the load in parallel to the battery, but then my consumers would have to deal with the higher charging voltages.
Here is a picture of my experimental setup.
Is programmable. The default ls are mention in the manual
I think this is all needlessly complex. The load output of the solar controller isn’t regulated, so you’re not gaining anything by connecting loads to it rather than the battery - your loads are still going to be seeing higher charge voltages.
Why not just connect an AC-to-DC charger to your battery bank, and connect your loads to the battery bank?
If you want a regulated 12v flat output for your loads, you’d want a DC-DC converter, not a solar charge controller.
I’m not sure that your use case warrants using the load output? I’m 90% certain that the load output voltage is the same as the battery voltage. What is the concern of connecting your equipment directly to the battery?
If you need a steady and specified voltage for the NAS, then a DC-DC converter or regulated power supply might be a better approach.
Hi guys, I’ve been out and about with the motorhome for a few days now.
Sometimes it’s not a bad idea to get some distance and, it’s almost a bit embarrassing, the reason why the MPPT deactivated the load output when there was no PV was a defective fuse in the battery cable. Unbelievable, my mistake!
Now everything is working as I hoped.
The best thing, contrary to some assumptions, is that the load output is regulated, 12.5V under load. Perfect.
I still have to research whether, as mentioned, a permanent float is not good for the LifePO4 batteries. If necessary, I simulate “night” with a smart plug (Shelly or Tasmota).
Thanks to everyone for the tips!
Happy holidays
You already have the batteries so use them. The float voltage will be fine, which should be 13.6V. Check the capacity once a year to see if they are degrading and stop using them when they get to 80% of the original capacity.
