andyb
Newbie
Joined: 23/10/2025
Location: United KingdomPosts: 1 |
| Posted: 02:43pm 24 Oct 2025 |
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Hi all, and thanks to Glenn for approving my account.
In a past life I worked in R&D at a small startup, writing firmware and doing basic prototyping for three phase inverters (mostly motor drives and some static power converters). Since then I've jumped ship from the R&D career (I'm now a repair engineer) and I'm just starting to rediscover power electronics as a hobby, which is where it all started. I built my first sinewave inverter about 20 years ago when I still lived with my parents - it was a very basic lashup with no protection or regulation of any kind, but powered various bedroom loads from an old UPS battery under my desk. Work took over, and the hobby died away.
Anyway, enough rambling. I've been lurking here for a few weeks now reading the DIY inverter build threads and thought it was time I joined up. By the way - massive hats off to the authors of the Warpverter and Ozinverter, that's some cracking work, and it's great to see DIY inverters gaining popularity!
Right now I'm working on a much smaller unit of my own design, for a very specific application - powering a chest freezer reliably in a shed or outhouse from a secondary small solar system, completely isolated from the house system. I hope to post more about this in the coming weeks, but for now here's a quick rundown of the spec and what I'm hoping to achieve:
1) 230VAC (I'm in the UK) ~150VA, 12V nominal input, with surge capability to start a fridge/freezer compressor (yes a tiny inverter but with a niche application)
2) Near zero idle power, achieved with automatic start-stop and load sensing (more on this later)
3) Basic protection - overcurrent and input undervoltage
4) A view to longevity, repair and easy replication in most parts of the world - off the shelf parts where possible, common parts, through-hole construction, etc.
More on the point of idle power, which is one of the key points here - I'm aiming to reduce the average idle power to practically nothing, simply by having the inverter power itself off completely when the thermostat in the freezer is open and not calling for cold. From this state the inverter powers itself on for 5 seconds every 15 minutes or so, checks for a load, and stays on if there is a load (i.e. if thermostat has clicked over) until the load disappears, then back to shutdown.
The basic topology as it stands is SPWM with amplitude control (multiplication done in software, sinewave lookup table generated in Excel), DDS frequency generation (for a tiny fraction of a Hz output adjustment, with a view to future grid tie development), single-level H bridge to LF transformer and filter, plus feedforward voltage control. All this is done in a basic low end 8 bit Atmel microcontroller with no floating point calculations. If there's any interest I can post more on how all this is achieved in such a low end controller.
Anyway, back to the workbench, cheers for now  |
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