DIY Inverter

Roswell Bob

Solar Enthusiast
I am interested in leading an effort to design an inverter. If anyone else is interested in this then maybe it could happen. I am semi-retired after 40 years of power conversion engineering. I spent 30 of those years doing nothing but industrial inverters. The last 10 years I have been doing Military/Aerospace designs. Recently I did a high frequency 2kW design for the army. I have all the test gear and software necessary to pull this off. LeCroy, Spice, Mathcad, Pads, Altium and thermal design software as well. If the management would like to suggest or create a folder I will begin.
 

rin67630

Solar Addict
I am interested in leading an effort to design an inverter. If anyone else is interested in this then maybe it could happen. I am semi-retired after 40 years of power conversion engineering. I spent 30 of those years doing nothing but industrial inverters. The last 10 years I have been doing Military/Aerospace designs. Recently I did a high frequency 2kW design for the army. I have all the test gear and software necessary to pull this off. LeCroy, Spice, Mathcad, Pads, Altium and thermal design software as well. If the management would like to suggest or create a folder I will begin.
It is always good to have experts on board.
What could your inverter offer that commercial ones won't?
 

Roswell Bob

Solar Enthusiast
It is always good to have experts on board.
What could your inverter offer that commercial ones won't?
The DIY experience. Beyond that I have no idea. I think a reasonably complete paper design could be done in a short amount of time. That would include all design equations including semiconductor junction temperatures, thermal designs, costed BOMs and so forth. The initial paper design could be a simple inverter with 4 switches. A specification would be a good place to start. Down the road comparisons between LF & HF designs could be made. I am especially interested in HF designs as I'm certain they will take center stage over the net few years. If the design gets to the point where it makes sense to build a few then that is certainly do-able. There are some experienced guys here who I am sure could help with this effort. PCB prototype costs could be spread over a few people to make it more palatable. I ran another interesting project like this, over the web, 20 years ago and the results were very positive. If there is any interest in looking at a DIY inverter then I (or anyone else) who would want could project engineer the development effort. If no interest then that is fine too.
 

rin67630

Solar Addict
Frankly, if your design cannot beat commercial devices on a specific feature, I can hardly imagine that it would have been worth doing it yourself.
It will be more expensive anyway buying all the parts... The Chinese sell some finished modules for less half your price of purchasing the BOM.
Assessing, correcting, improving them could be IMHO more valuable.

Tinkering with inverters is definitely not somewhat for rookies and it can be life threatening.
But it could have been for lawyers, if something gets wrong!

I am currently working on a low-power MPPT SCC, just because all commercial devices have too much own consumption, stealing for themselves most of the scarce power on dark winter days.
If I could have purchased one that fits, it would have been much easier.
 

rin67630

Solar Addict
P.S. I am an engineer too and in my company, they used to cut the cables with chainsaws and a megawatt was not really worth mentioning....
Now I find it extremely interesting to explore the other side and tease the milliampere.
 

Roswell Bob

Solar Enthusiast
P.S. I am an engineer too and in my company, they used to cut the cables with chainsaws and a megawatt was not really worth mentioning....
Now I find it extremely interesting to explore the other side and tease the milliampere.
You prove my point. There is no lack of talent on this page. I'll throw some kind of vague spec together and see where it goes. I am member of Ray Ridley's page on FB. I've had some conversations with Ray and he believes it is possible to design/build a high frequency inverter here in USA that could compete with any of the off-shore stuff landing here. That is an ambitious project which I'm sure you know requires an incredible amount of engineering time and $$$. I have other projects that eat up most of my time so that I am not interested in that kind of a battle.
 

Roswell Bob

Solar Enthusiast
P.S. I am an engineer too and in my company, they used to cut the cables with chainsaws and a megawatt was not really worth mentioning....
Now I find it extremely interesting to explore the other side and tease the milliampere.
Can I ask you who you work for? I am curious.
 

svetz

Works in theory! Practice? That's something else
Staff member
Moderator
What did you think of 99.5% Efficient Inverter Design?
I am interested in... design an inverter. If anyone else is interested...

I'm always interested to read what others are doing. There are a few folks on the forums designing/experimenting their hearts out ... (from playing with battery chemistry (e.g., My adventures building a Zinc-Bromine battery by @danielfp248 to designing new BMSes (e.g. DIY BMS design and reflection by @BiduleOhm ). The more the merrier! As you can see from those threads, you won't lack for feedback.
 

rin67630

Solar Addict
I can propose 100%.
Most of our current devices labelled "100V-240VAC" have a switching power supply on-board anyway.
They rectify AC to DC, just to chop it to high frequency pulsed DC, transform and rectify to DC again.

It you run batteries e.g. at 96V, your 100V devices will happily run from their DC voltage as well (slightly out of range since they expect 120V peak, but they all work well according to my experience.
The only caveat is that 96VDC is not trivial to switch, most ON-OFF switches/relays are not designed to cut the spark, you need DC breakers.

By the way: telling that "sensitive electronics need pure sine" is absolutely bullshit.
They run at best with mod sine.
 
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Roswell Bob

Solar Enthusiast
What did you think of 99.5% Efficient Inverter Design?


I'm always interested to read what others are doing. There are a few folks on the forums designing/experimenting their hearts out ... (from playing with battery chemistry (e.g., My adventures building a Zinc-Bromine battery by @danielfp248 to designing new BMSes (e.g. DIY BMS design and reflection by @BiduleOhm ). The more the merrier! As you can see from those threads, you won't lack for feedback.
I am a little bit familiar with that type of design. I will say that the efficiency gains are real when switching at these very slow rates. They will probably remain a laboratory curiosity for a good while. The difficulty I think is maintaining some kind of balance between complexity and waveform. Filtering at 60Hz is near impossible especially considering the efficiencies expected - so that the sine needs to be fairly accurate. The voltage steps have to be rather small to get accurate sinewave to start. Interesting concept.
 

DerpsyDoodler

Solar Enthusiast
If I could make a suggestion, what about creating an open source inverter design or mppt controller design whose spec could be given to a mfg and asked to make it? Imagine a world where no more “is this brand also this brand and that brand but they’re not mfgd by any of those names?” Rather it would be more like “is this identical to the open source spec xyz? Yes? Done.” Creating a spec for a quality piece of material that anyone can get so long is they can mfg or source the mfg would set a baseline by which all inverters or whatever product can be compared; and, who knows, maybe even force a quality baseline for “cheap” inverters.
 

Roswell Bob

Solar Enthusiast
I can propose 100%.
Most of our current devices labelled "100V-240VAC" have a switching power supply on-board anyway.
They rectify AC to DC, just to chop it to high frequency pulsed DC, transform and rectify to DC again.

It you run batteries e.g. at 96V, your 100V devices will happily run from their DC voltage as well (slightly out of range since they expect 120V peak, but they all work well according to my experience.
The only caveat is that 96VDC is not trivial to switch, most ON-OFF switches/relays are not designed to cut the spark, you need DC breakers.

By the way: telling that "sensitive electronics need pure sine" is absolutely bullshit.
They run at best with mod sine.
 

MattiFin

Solar Enthusiast
Some random thoughts:
Biggest pain in the butt for DIY SMPS projects are always the transformers/magnetics.
Probably best way to go is the same as the chinese hf inverters: several smaller transformers in parallel-series confiquration.
You avoid the need for exotic core sizes, no need to try to source and wind with copper foil, less hassle with proximity losses on windings etc etc.

DC-DC topology?
push-pull is the "classic" choice but bit prone to go up in flames and you have to deal with hard switching and body diodes.
2-transistor forward: hard switching but IMO most bulletproof topology. At 2kW power level I'd probably opt for interleaved 2-phase solution.
ZVS full-bridge: hard to archieve soft switching at low loads
LLC full-bridge: ?
 

Roswell Bob

Solar Enthusiast
Some random thoughts:
Biggest pain in the butt for DIY SMPS projects are always the transformers/magnetics.
Probably best way to go is the same as the chinese hf inverters: several smaller transformers in parallel-series confiquration.
You avoid the need for exotic core sizes, no need to try to source and wind with copper foil, less hassle with proximity losses on windings etc etc.

DC-DC topology?
push-pull is the "classic" choice but bit prone to go up in flames and you have to deal with hard switching and body diodes.
2-transistor forward: hard switching but IMO most bulletproof topology. At 2kW power level I'd probably opt for interleaved 2-phase solution.
ZVS full-bridge: hard to archieve soft switching at low loads
LLC full-bridge: ?
Good comments. Yes, the magnetics are the difficulty. We've been doing planar designs for a few years now and that takes a lot of the grief out of winding. We're in the middle of a 2.8kW design now. I think transformer is 16oz copper. I've done a bunch of the ZVS full-bridge designs that have worked well. I am thinking a resonant push-pull where they could be interleaved. I have not done a LLC full-bridge so that might be worth looking at.

There is a paper that describes getting ZVS bridge to switch at low outputs. Basically you put a pair of caps in series on the bus. Connect inductor from center point to passive pole leg. I have used scheme on audio modulator with good results. I will look for paper.
 

Roswell Bob

Solar Enthusiast
Some random thoughts:
Biggest pain in the butt for DIY SMPS projects are always the transformers/magnetics.
Probably best way to go is the same as the chinese hf inverters: several smaller transformers in parallel-series confiquration.
You avoid the need for exotic core sizes, no need to try to source and wind with copper foil, less hassle with proximity losses on windings etc etc.

DC-DC topology?
push-pull is the "classic" choice but bit prone to go up in flames and you have to deal with hard switching and body diodes.
2-transistor forward: hard switching but IMO most bulletproof topology. At 2kW power level I'd probably opt for interleaved 2-phase solution.
ZVS full-bridge: hard to archieve soft switching at low loads
LLC full-bridge: ?
Joao Pedro Beirante and Beatriz Vieira Borges—A New Full Bridge
Zero Voltage Switched Phase Shifted dc to dc Converter with Enlarged Duty
Cycle and ZVS Range Project PraxisXXI/98/P/EEI/12026/1998.
 

MattiFin

Solar Enthusiast
Good comments. Yes, the magnetics are the difficulty. We've been doing planar designs for a few years now and that takes a lot of the grief out of winding. We're in the middle of a 2.8kW design now. I think transformer is 16oz copper. I've done a bunch of the ZVS full-bridge designs that have worked well. I am thinking a resonant push-pull where they could be interleaved. I have not done a LLC full-bridge so that might be worth looking at.

There is a paper that describes getting ZVS bridge to switch at low outputs. Basically you put a pair of caps in series on the bus. Connect inductor from center point to passive pole leg. I have used scheme on audio modulator with good results. I will look for paper.
Planar magnetics would be nice but probably another factor of 10 harder to source/make for DIY project.
Or is there nowadays cheapo chinese shop where you could order prototype quantities of planar transformers cheaply?

Cheap asian pcb manufacturers for example have been game changer in DIY electronic projects. 8 usd for 5 pcs 4-layer boards is damn cheap!
 

Cal

Solar Addict
We've been doing planar designs for a few years now and that takes a lot of the grief out of winding. We're in the middle of a 2.8kW design now. I think transformer is 16oz copper.
That's cool! Just about 30 years ago I was doing some dc/dc planar designs. That was cutting edge at the time.

Edit: One of my first planer transformer and inductor test boards.

P1001617R.jpg
 
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Roswell Bob

Solar Enthusiast
Planar magnetics would be nice but probably another factor of 10 harder to source/make for DIY project.
Or is there nowadays cheapo chinese shop where you could order prototype quantities of planar transformers cheaply?

Cheap asian pcb manufacturers for example have been game changer in DIY electronic projects. 8 usd for 5 pcs 4-layer boards is damn cheap!
Not hard to source/make. Just use the cheap asian pc boards and slap a planar core on them and away you go. So easy to do compared to winding and tape and winding and tape..... Each transformer is just like the other one. You can even make a complete set - transformer and a pair of inductors on one board.
 

MattiFin

Solar Enthusiast
Not hard to source/make. Just use the cheap asian pc boards and slap a planar core on them and away you go. So easy to do compared to winding and tape and winding and tape..... Each transformer is just like the other one. You can even make a complete set - transformer and a pair of inductors on one board.
Once you need more than 4 layers and 1oz copper the 8 usd Cheap boards becomes 1000 usd "cheap" :(
At minimum we would need some sort of group buy. 12-layer 6oz board from pcbway.com is 1002 usd for 5 pcs and 2370 usd for 100pcs.

Maybe could use for some low-power project where 4-layer 1 oz board would be ok.
 
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