Building a DIY UPS using off-grid solar inverters

[gcs8]

So, I use to have two APC SMT3000RM2U that I had modified with an external 100AH 48VDC SLA battery but after years of service the charge controllers in them died. So I started looking around for a set of replacements and was looking at the APC SRT3000RMXLA-NC on eBay, the price was a bit high for my taste, but not out of the question, the bigger problem being that it used a 96VDC battery pack and the extended runtime battery packs were expensive and you did not get a lot of run time for the cost.

So I started looking around for alternatives, so down the internet rabbit hole I went, I looked at things like the AIMS Power PICOGLF120W48V240VS, but that was kinda too heavy for me to mount to the wall by myself. I looked at some of the Victron Energy stuff, neat ecosystem, but a bit rich for what I was looking for. Then I found two candidates for what I wanted, the MPP Solar PIP-LV-MK SERIES – ZERO TRANSFER TIME inverters and the Growatt 3kW Stackable Off-Grid Inverter | SPF 3000TL LVM-ES.

Now I had narrowed down my inverter options I started looking at batteries, everything from Battle Born Batteries, SOK, Big Battery, and EG4. It seems like there is a pretty decent community around the different battery companies, but I ultimately went with the EG4-LL Lithium Battery | 48V 100AH battery for its BMS and built-in precharge resistor. The warranty was nice also, the shipping on it sucked though. (read expensive)

So going with the EG4-LL kinda pushed me to the Growatt SPF 3000TL LVM-ES inverter for its ability to talk natively to the BMS on the battery vs the MPP Solar inverter that was a bit harder to find an online community around, but it was a good backup plan to have to incase the transfer time on the Growatt was not fast enough for my equipment. For some context, the Growatt’s transfer time is ~10 (average)-20 (max)ms compared to the 4(average)-8(max)ms that an APC UPS is. I also did a bit of research and found that most of my gear has a hold-up time of ~17ms, so I thought I would be pretty safe, but there is no telling how something will perform in the real world vs on paper.

So I ordered everything through Signature Solar and then played the waiting game, the inverters came in 2-3 days via FedEx and the battery came about a month later (it was a pre-order, they sell out fast). While I was waiting on the battery I started a gsheet of all the different supplies and what not I would need. ( Whole Home UPS - Google Sheets ) I already had some knukonceptz Power Cable from my car audio days, so that was a nice little savings.

Once I get everything in, I started the project on the first free weekend I had, I am hella outta shape from covid times and never leaving the house so it took me longer than I want to admit to get it all done, but it is done and working as intended and now I have ~2.65 hours of battery backup for the rack and room to grow. The inverters are setup in a split-phase arrangement so I can power 120VAC and 240VAC stuff, might put the HVAC on this at a later date or I was also looking at a 48VDC mini-split I could power directly off the battery pack, you can put like 16? of these batteries in parallel with the BMS comms and they will work as one cohesive unit.

I am open to any and all questions, here are some ugly pictures.

[gcs8]

@wendell this may be of interest to you from your last UPS video.

[MadMatt]

Very nice! … have you tried to cut power and see what happens?
Every datasheet I see for these inverters have a warning saying they are not a true UPS (e.g. it may take them too much to switch from AC to battery inverter when AC fails) …
I have been looking into getting a similar setup, but based in Italy, so 220 AC single phase and much more batteries to power the whole house but the EG4 and SOK batteries here are a no-go and the only option is Pylontech, of which availability is very scarce …
I also have 6KW worth of solar panels to charge the batteries for free about 7 months per year …

[gcs8]

@MadMatt yeah, I have cut the power several times under load, seems fine, I am waiting on some real-world power disruptions to see what happens.

If you are worried about it, check out the MPP Solar Inc » PIP-MK Series might be more your speed.

[MadMatt]

@gcs8

If you are worried about it, check out the MPP Solar Inc » PIP-MK Series might be more your speed.

I am not worried the plan is to use the Inverter UPS circuit to feed a proper UPS (I dont’t have a rack yet, but I do have 3A@220V worth of various electronics) and some other appliances for which the time switch will be driven by a contactor anyway.
The plan is to have the UPS line of the inverter to be connected to some of the house loads normally connected to grid, with a contactor to operate the switch in case grid goes down.
When grid is up I am going to be using the ability of the inverter to monitor power draw after the solar panels and eventually feed ac to the whole house when needed…
Now I only need 10K eur wort of batteries and 2K eur worth of electrician and paperwork, so that I can then claim a 50% tax deduction on it …
Probelm here in Italy is that between the scarcity of product and all the tax deduction because ov covid restoration plans I can’t find a freaking contractor that can do it in the next 1-2 years , so they say
I am completely fed up of this bllshit, but prices here have been inflated because of tax deductions, so a 4.8KW Pylontech 5000 can be preorderd for 1700EUR+VAt (23%) that means 2200USD plus shipping, and I would like to have at least four of them … from march to september my PV array produces 30-40KWh/day worth of energy, and the house consumption is 10-20 during the day, depending on wether we charge our PHEV renault …

[gcs8]

@MadMatt ah, yeah, glad I can do my own electrical work, but I also have a buddy who is a licenced elechiken if I had to permit something.

Sorry you have to pay vat.

UPS after the inverter is probably a pretty safe way to go if you are worried about the transfer time, it should be a better sign wave than the grid in most cases so it should not piss off the UPS.

I use ~90-100KWh/day here, so the most I would probably do is ~30KW of batteries as I don’t have a real basement or anything.

[MadMatt]

@gcs8

Sorry you have to pay vat.

Amen
also, that is the best price ordering from an unknown place in the Netherlands … in Italy I have been trying to find a supplier but nada

I would be perfectly able to do the electrician work, but because of the contactor and the on grid/off grid it needs to be done by someone with an official license, and in order to do the tax deduction a contractor needs to buy the goods and re-invoice (with a surplus) … it’s the proverbial crock of s**t if you ask me

[rcxb]

@gcs8

might put the HVAC on this at a later date or I was also looking at a 48VDC mini-split I could power directly off the battery pack

That sounds… crazy… unless you have a huge solar PV installation. It would almost certainly be cheaper to run such heavy loads directly from a generator rather than battery.

Have you figured out how much each KWH of power from your batteries costs you, factoring in the number of charge/discharge cycles and the purchase price? It is not going to be cheap.

[gcs8]

yeah, that sounds like suck all around.

[gcs8]

@rcxb No PV, HOA won’t let me, the same thing with a Genset.

~$340/KWh for the battery, it’s warrantied for 7000 cycles 80% DoD and I am not cycling it every day, maybe a few times a year depending on power. I don’t really care too much about the cost, it’s cheaper and more flexible than an APC UPS, In theory, I could run the whole house off of the setup as it stands right now, though I would probably need a 2ed battery to feed the full 62.5A per inverter at full load, the BMS is only good for 100A each.

[abacusns]

Hey, question - that image looks like a Grafana dashboard. I was under the impression that it wasn’t easy to get data off of the Growatt (at least out of their monitoring site) - is that the case? Otherwise, how are you feeding your dashboard?

[frzn]

@gcs8

APC SMT3000RM2U that I had modified with an external 100AH 48VDC

I’m about to do this. I got a SMT3000RMI2U from a recycling bin for free. Do you know what killed yours and if there’s anything that you would recommend I do to protect mine?

Hard to find a good EU supplier of lifepo4 batteries as well that isn’t incredibly expensive

[MadMatt]

Something along these lines?

GitHub - johanmeijer/grott at 2.7-(Beta)

I ended up finding and buying a 10kwh lifepo bundle from a local supplier, a rebranded sofar model. Had to binary parse the data it was sending out to feed my mqtt/nidered/openhab/emoncms local setup …

GitHub - serek4/node-red-sofar-inverter: node-red server/proxy for sofar...

[gcs8]

I am using https://iotawatt.com/ to just take raw CT data off the input and output. Here is an updated dashboard.

[gcs8]

I am guessing mine probably went tits up due to two charge controllers on the same battery pack, but they made it 2-3 years like that before I had 1 battery fail and that is when it started to cascade into issues. I think if you keep a 1:1 relationship you might be just fine. Just make sure you get SLA AGM and you probably want to use 4awg for the battery links, my 8ga copper wire was definitely too thin for what I was doing with it.

I would also probably recommend going with a unit that can take external battery packs that are meant for extended run times, the units I was using were definitely not designed to run as long or as hard as I was running them.

[MadMatt]

@abacusns I am using a combination of open source components to collect and store my sensor data and manage my home automation

This is how the PV production and Battery storage ended up being installed:

Left to right:

• 6KW Solaredge inverter
• 3KvA UPS, dedicated to my home office/homelab- it provides battery backup and straightens power grid signal/makes sure voltage is always at 220V

• Sofar ME3000SP (RETROFIT ZST-3000SP) - Retrofit inverter that can charge/discharge10Kwh (in my configurazion, up to 25KwH if it makes sense) worth of batteries at 3KwH max
• 2xWeco4k4Pro LifePo 5Kwh batteries, dept of discharge set at 80%
• Viessman Gas burner

The retrofit inverter monitors PV production and house consumption and decides whether it’s time to cherge/discharge the batteries according to its state, tracking works pretty well
This is an example of one day (one month ago, northern Italy in late october does not have as much solar irradiation) where the battery was charged by 3PM, while the PV array was also providing power to the house, and then the battery provided part of the evening/night consumption until it discharged …

The PV inverter, the battery inverter and the whole house are connected using this electrical panel (consumer unit in UK parlance):

I have sectioned out each part (PV,Retorfit Inverter, House, and also sectioned further house circuits and use modbus power meters to monitor energy production/consumption/flow between sections (the eastron units in the photo)
I also use the EPS output from my Retrofit battery inverter, that can provide AC power from the battery when the main grid is down. By law in Italy this must happen on a completely separate circuit from the rest of the house. In my case, I connected this backup output to an ATS (Automatic Transfer Switch - the one labeled SH&ZG) that can switch between grid and backup power automatically, and connected that output to my UPS and a dedicated set of wall plugs (freezer/things that needs to stay powered on even in case of blackout). I have a total of 10 power meters (some of them are in other consumer units) and collect data from them using a raspberry pi 1 through RS485, and feed the data to a mosquitto server running in a container on my NAS

I then use the mqtt feeds to push the data to an emoncms instance (emoncms is an open source monitoring solution that is specialized in collecting time series data in general, energy related ones specifically) where it is collected and displayed through different views:
The data is collected in inputs, divided by node instances
This is a modbus power meter node:

This is a node that collects data from my gas burner (using another raspberry, connected to the burner optoserial interface directly):

The process step has a lot of pre-baked functions for converting energy and power related entities:

Inputs can be manipulated using various logic and mathematical constructs as needed - this is a process that collects the power feed from the battery inverter, logs it and then applies some logic to decide whether the battery is charging or discharging, and it logs it appropriately to separate feeds: it is used in the graphical display at the top of the page to determine how much energy was sent to the battery and how much energy came out of it at any given time:

These processes create feeds, that are separate time series streams of data, that can be combined and displayed graphically as needed:

And you can combine this data in custom dashboards:

I also run a grafana/prometheus/influxdb stack on my nas to collect data from various other components, mostly non-energy related like parts of my homelab/home network and/or stuff that provides prometheus exporter compatible metrics:

DSL modem:

Starlink data:

Proxmox Epyc Server:

I am also using LibreNMS to collect more detailed data regarding my network components and servers

![Screenshot 2022-11-01 at 21.51.28|720x495]

so, if we ever end up creating the 1 year sensor data hoarder challenge or something like that I think I would automatically qualify. I have data in emoncms from about 2012, when I started collecting bits and pieces of sensor data to try and understand how much power I was using. Back then the data was collected via CT clamps to an arduino and sent via RF signals to the same raspberry I am using now …

[cdoublejj]

OP, any pics of the batteries?

[gcs8]