A while ago, I highlighted a design in my homelab where I kept core services running on a low power core to get longer runtimes on my UPS. I talk about it in this post, and that setup worked well for a long time.

But as my network grew and more things became important, I started to lose some of the runtime of that UPS. Recently, I’ve upgraded my NVR to a full Unifi NVR appliance, added a TV antenna and amplifier, and a few other gadgets that I’ve deemed also critical infrastructure, so the wattage has increased and the UPS was only able to do about 20 to 30 minutes now. This is in part due to its aging batteries, but also the increased load.

I sought out to fix this, and landed in the category of Lithium power stations. These are self contained units that contain a Lithium battery and an AC inverter, and are intended for things like camping, RV’s or even backup power like we’re using here. Jackery, Bluetti and Ecoflow are major brands in the space, if you can’t picture what I’m talking about.

How I Justified This

When looking at power stations vs Lithium UPS units (or even larger lead acid units), these power stations looked really appealing. When making my comparisons to traditional UPS systems, these are the points I considered.

  • Cost - Both in upfront cost and maintenance. Lead acid units will need a new set of batteries every few years, so buying a large unit used for cheap would still require several hundred dollars of batteries. New UPS units were several thousand dollars at a minimum, so even more expensive.
  • Utility - These power stations accept solar panel input and are moderately portable (smaller ones more so), so I could take the unit out of the rack and use it on a trip or elsewhere. In a longer outage, some solar panels would be enough to keep things like my fridge going for much longer.
  • Safety - A lot of folks have hacked together battery strings for UPS units that exceed the design capacity of the UPS. Some units can handle this, but others aren’t designed to run the inverter at high load for hours at at time. Changing battery chemistry from lead to lithium also seemed like a bad idea without more knowledge than I have.

Features Needed To Make This Work

I went with a Bluetti AC70, but a lot of stations should work. There are a few features you need to look for though:

  • Rated Power - This needs to well exceed the wattage of the devices you plan to run. Unless you’re running your entire rack, this shouldn’t be an issue. Don’t look at things talking about X-Boost or other tricks, as they won’t work for electronics.
  • Rated Capacity - Expect to get about 80-90% of this value, but this will govern the runtime of your gear. For example, if you have 250 watts of load and 750 watt hours of capacity, divide 750 / 250 to get about 3 hours of runtime.
  • LiFePO4 Battery - Most stations use this chemistry now, but some don’t. This will withstand lots of charge / discharge cycles and is very stable and safe.
  • Passthrough Charging or a UPS Mode - Different brands call this different things, but this allows the station to output power as it’s charging. When AC Power is present, it’s passed to the output and the battery is only switched on when no AC input is present. Some units have slow chargers that don’t allow this, so be sure to check.

Other features, like app control, are all immaterial.

Wait, But What About Clean Shutdowns?

So you’re buying this and now you’re asking “How will my machines know to shutdown?”

The answer is the lead acid UPS we’ll run inline after the power station. I plug my lead acid UPS into the output of the power station which seems silly, but has benefits.

First, you’re free to take your power station elsewhere and not lose the only UPS. I use mine on trips at times or once the power is out and my generator running. I’ll free it from the rack and use it elsewhere in the house where my generator can’t reach.

Second, this solves all the problems with communication. In an outage, the power station will transfer to its internal battery and power the other UPS and the load. Once the power station is dead the lead battery will take over and report a normal grid outage to whatever software you use. Once those batteries are low, you can trigger a normal shutdown as you did before.

If your power station outputs a pure sine wave, the lead UPS will only trip for a second while the power transfers from the grid to the power station’s battery (if even that). After this, it should continue to run as if on grid power until the power station runs out.

A Few Odds and Ends

One thing that I also purchased was a cord like this one. This takes the IEC power cable coming from the wall and lets you either plug it into the power station’s input port or bypass the power station and power the UPS directly off the grid again. If you take your power station out of the rack, this makes the change over much easier.

(On the above, keep in mind my setup is only drawing a few hundred watts, and only one output of that cord is used at at time. Don’t be dumb and overload cheap cords, you’ll burn things down.)

You’ll also want to adjust the charging speed of the power station. Many can vary from a few hundred watts to 1KW+. When there’s grid power and the battery needs charged, this value gets combined with whatever your load is using for a larger total draw. If you have 500 watts of gear and charge at 1KW, you’ll pull 1.5KW and you may start tripping breakers for the circuit. I keep mine charging at only a few hundred watts, so at worst the setup draws < 500 watts.

Also make sure to discharge the battery at times to keep it healthy. I’m not sure how much damage is done by keeping things charged to 100% all the time, but I go down every month or so and let the power station discharge most of its battery. Check the manual for your power stations in case it has more guidance.