Home Built Uninterruptible Power Supply (UPS)

A UPS can be a valuable tool to protect your electronics against power surges, brown outs, and black outs. I’ve always tried to use and maintain one at home for my own equipment. But they can be expensive and the batteries don’t seem to last long (duration of charge and overall lifetime). So I decided to build one of my own.

WARNING: I did some research online and it seemed pretty simple to build one. I’m by no means an expert in electronics so use this information at your own risk. There is danger in working with these types of electronics. You can potential start a fire or short out your equipment if you wire things improperly.

A few tips before we start:

  1. If you don’t understand completely what you are doing please stop
  2. DC wiring must never be reversed (positive to negative). This will usually destroy electronics. AC is different as it alternates in voltage both ways.
  3. Be sure your equipment is off when working on it. Use a multi meter to test it. Be sure to be set to AC or DC.
  4. Be very sure to use the correct gauge wiring when connecting components. Wires that can’t handle a high load will short out and burn up. This can cause a fire.
    1. Use online resources like wire guides to figure out what gauge you need
    2. The length of the wire is very important too. Short and direct runs are best.
  5. Don’t trust all information you see online. Including what you are reading now. This is a learning experience for me and I’ll be upgrading my UPS as I find flaws.

I decided on a pure sine wave inverted as I had issues with one that wasn’t a pure wave, it was a simulated sine wave. The difference is that some electronics don’t handle how quickly and sharply the voltages go up and down on the AC side. I had purchased a 2000 watt inverter and had issues powering up an old computer. It also had trouble with a electric fan. The fan is a great example showing how AC motors need the smooth sine wave increase and decrease in voltage to start and stop. (Think of moving a car with block wheels versus round wheels)

Parts List:








Wiring Diagram:

This system is pretty easy to build. You use the power inverter to power all of your AC equipment. The Iota 55 amp charger will charge the battery and power the inverter as long as it has power from the power grid. The battery is big enough to output enough amperage for the inverter (1,000 watts / 12 volts = 83 amps). The iota charger can’t supply enough power to the inverter if we have the maximum load on the inverter but this was OK with me as my power load is pretty small.


I’m using about 110 watts powering a few HP switches, cable modem, 2 PoE access points, a 4 disk enclosure, a Intel NUC, as well as a raspberry pi. I’m able to measure this with my bayite display. Then I was able to measure the load from my iota charger with a kill-a-watt AC power measuring device. The kill-a-watt came out to about 150 watts. So I’m seeing some loss in the conversion of AC to DC and this is normal. I’m sure there is even more loss from AC to DC and back to AC through the inverter. But this is the cost of a system like this.


Knowing my usage I estimated I would get about 8 hours of run time. A 100 amp/hour battery can output 100 amps (at 12 volts) for 1 hour or 10 amps for 10 hours. Since I’m using about 8 amps and you don’t want to discharge too low, i’d estimate 8 hours.


I did purchase a deep cycle battery. The difference between a regular sealed lead-acid battery and a deep cycle sealed lead-acid battery is the deep cycle will allow for a larger discharge and go down to a lower voltage without ruining the battery. If I remember correctly you don’t want to go below 10.8 volts charge on a lead-acid battery otherwise you will damage it. Speaking of this the iota charger had a separate accessory that can help keep batteries maintained properly. I had purchase this and installed it to help maintain my battery.


As for expansion I can add another battery to my setup to double my run time. You would want to connect it in parallel, not a series. In parallel the voltage stays the same and in a series it would double (this could cause damage to the inverter if it can’t accept much over 12 volts).


The gauge of the wire i used was very important. The lower the number the more amperage it will support but keep in mind the length is very important too. Too long and you can cause the same issue as having to thin of a wire. I tried to keep everything under 3 feet.



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