krby
Solar Enthusiast
I've posted in other threads about a DIY UPS I have working. It's a collection of bought components (some I had on hand). It's an inverter, a charger, and a battery bank. Technically, this is an online double conversion architecture. The inverter is running full time. I've had this running since July, and recently added the "UPS monitoring over USB" functionality with an Arduino so my NAS is notified when AC mains goes away and will shut down gracefully (decreasing the load from 150W to about 55W).
Since this is a passion project, partially for fun, I'm now wondering about consolidating the converter/charger and inverter into a single "thing". An inverter/charger would be ideal, but it doesn't look like there is a big market for <1000W inverter chargers, or really anything that costs less than ~$900. This has me wondering how hard it would be to build a 350W (let's say 25-30A at 12V) UPS unit myself. What do I mean by "build a unit myself"? Anywhere from "design and get a PCB made" to "buy some components" (maybe the pure sine wave inverter, but things like the EGS002 board might make this ok to do myself ? and combine that with my own circuits and MCU and code.
To give some general background on my skillset (since I'm asking if this is "hard"):
I guess the hard requirements for the UPS are:
Since this is a passion project, partially for fun, I'm now wondering about consolidating the converter/charger and inverter into a single "thing". An inverter/charger would be ideal, but it doesn't look like there is a big market for <1000W inverter chargers, or really anything that costs less than ~$900. This has me wondering how hard it would be to build a 350W (let's say 25-30A at 12V) UPS unit myself. What do I mean by "build a unit myself"? Anywhere from "design and get a PCB made" to "buy some components" (maybe the pure sine wave inverter, but things like the EGS002 board might make this ok to do myself ? and combine that with my own circuits and MCU and code.
To give some general background on my skillset (since I'm asking if this is "hard"):
- Very experienced with coding in a variety of languages. Comfortable developing C or C++ on MCUs.
- I've built a 4.8Kwh / 3000W output "Yetti/Goal Zero" equivalent with the help of these forums. here.
- Self-taught/Amateur with electronics. I lack instincts like: "oh yea, you need a capacitor here to solve that problem." I know what the basic diode, resistor, MOSTFET, capacitor components are and what they do. Comfortable prototyping on a breadboard and prototyping PCB.
- Comfortable with batteries and charging of a variety of chemistries. Understand the safety concerns around various battery types (spent a ton of time in the RC hobby with LiPos)
- Comfortable soldering thru-hole. I've seen instructions for building a DIY SMD oven from a toaster oven. That seems totally within my ability.
- Very comfortable with CAD and 3D printing, and...embarrassingly I use CAD software for some wood projects, it helps me map out clearances and see how things will fit in the real world space they have to go.
- Comfortable with being safe working with 120V AC mains and DC up to 48V
I guess the hard requirements for the UPS are:
- Use my existing two 12V 200Ah AGM batteries, but with code or settings changes, be able to handle other chemistries (looking at existing multi-chemistry chargers, this doesn't seem hard). I have these wired in parallel now, because I had a 12V inverter on hand already. If it makes things easier, I could wire in series. I'm fine with not worrying about balancing them. They're SLAs, there are only two and they spend nearly all of the time fully charged.
- Ideally recharge the batteries from empty in no more than about 10hrs. So say 40A for a 12V configuration of 20A if I move to 24V.
- 300W of AC output. More is fine. I currently end up with a spike of about 250W if everything boots at once. Average power ends up being 100-125W.
- Pure sine wave inverter. I'm powering electronics in my home network rack with this. "modem", router, switch, NAS, etc.
- Double conversion or standby UPS architecture is fine, but the transfer time has to be fast enough to keep the electronics running. I was using a consume APC UPS before this and that was fine.
- Configurable/Controllable, and provide USB UPS monitoring to NUT. I've got the USB reporting working already. I assume I'll have an Ardunio-ish MCU and my own code to handle this. For simplicity, I'm start with hard coded settings for chemistry and various voltage and current settings for charge stages. Eventually, I would add a display and maybe an annoying 2-3 button menu interface.
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