Building a DIY UPS using off-grid solar inverters to support my server rack.

[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 2 ) 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.

 

[Heliian]

Absolutely horrifying.  

 

That open electrical panel with all the wire bunches coming out of it is an electrocution and fire hazard.  

 

I applaud your use of a backup system and your DIY spirit but I don't condone such dangerous installations. 

 

 

 

[leadeater]

1 minute ago, Heliian said:

That open electrical panel with all the wire bunches coming out of it is an electrocution and fire hazard.  

 

I applaud your use of a backup system and your DIY spirit but I don't condone such dangerous installations. 

I'm pretty sure that will be for photo taking so we can actually see how it's being done.

[Heliian]

4 minutes ago, leadeater said:

I'm pretty sure that will be for photo taking so we can actually see how it's being done.

This one? It looks like the mains panel.  

[leadeater]

Personally I just attached a bunch of our replaced DC VLRA batteries to my UPS, 24x 120AH ones with 8 year design life and actually still rather new and also never discharged by more than 80% while they were used at work 

 

Just put a proper set of isolation diodes, the correct kind for this application, between each battery string and the UPS input also then brought a custom 76V (88.2V charge) battery charger.

 

Works a treat and have about 12 hours of battery run time.

[leadeater]

1 minute ago, Heliian said:

This one? It looks like the mains panel.  

Yes, you're assuming that's how it will stay, I doubt it. It's also not the only tidy up that needs doing but getting it system tested and knowing it'll actually work helps a lot before finalizing cabling and access panels. If this is a known and standardized install sure different story, do it all from the start.

[gcs8]

33 minutes ago, leadeater said:

Yes, you're assuming that's how it will stay, I doubt it. It's also not the only tidy up that needs doing but getting it system tested and knowing it'll actually work helps a lot before finalizing cabling and access panels. If this is a known and standardized install sure different story, do it all from the start.

Na, the panel is always like that, no good way to pass all the CT wires out of it, the CTs are not a fire hazard, several electricians have looked at it and other than it bothering their OCD for being neat, have agreed it's a non issue. The CTs give me all this data that I feed into InfluxDB and display with Grafana. 

[gcs8]

47 minutes ago, Heliian said:

Absolutely horrifying.  

 

That open electrical panel with all the wire bunches coming out of it is an electrocution and fire hazard.  

 

I applaud your use of a backup system and your DIY spirit but I don't condone such dangerous installations. 

 

 

 

lol, people are always afraid of the unknown, none of the wires that are white and black carry any high voltage, they are the data lines for the CTs to the iotawatts. None of this is dangerous unless you are stupid enough to jam your hand into the panel, it's been like this for years and years, and will probably stay this way for years to come until I move out. 

[gcs8]

45 minutes ago, leadeater said:

Personally I just attached a bunch of our replaced DC VLRA batteries to my UPS, 24x 120AH ones with 8 year design life and actually still rather new and also never discharged by more than 80% while they were used at work 

 

Just put a proper set of isolation diodes, the correct kind for this application, between each battery string and the UPS input also then brought a custom 76V (88.2V charge) battery charger.

 

Works a treat and have about 12 hours of battery run time.

yeah, that's a pretty sweet setup, what UPS are you running?

[leadeater]

2 hours ago, gcs8 said:

yeah, that's a pretty sweet setup, what UPS are you running?

Eaton 9130 3kva

[leadeater]

2 hours ago, gcs8 said:

Na, the panel is always like that, no good way to pass all the CT wires out of it, the CTs are not a fire hazard, several electricians have looked at it and other than it bothering their OCD for being neat, have agreed it's a non issue. The CTs give me all this data that I feed into InfluxDB and display with Grafana. 

lol I would have still cable managed them and used cable cutouts and put a cover on but eh w/e 

[gcs8]

11 hours ago, leadeater said:

Eaton 9130 3kva

neat

[gcs8]

11 hours ago, leadeater said:

lol I would have still cable managed them and used cable cutouts and put a cover on but eh w/e 

I might if I replace the whole panel, that's still up in the air, my electrician buddy says he will replace the whole panel for a case of beer, the current panel is from ~1983 and I am not a huge fan of it, I also want to drop a SPD in the panel. Just not a fan of doing drywall work.