diy solar

diy solar

DIY Inverter

Any reason we couldn't fabricate a planar transformer from sheets of copper mounted to pins soldered to a PCB? Not a good solution for production, but DIY friendly for making one-offs.

I could see using a CNC router to machine traces into a copper sheet. Or if the traces are big enough, just freehand it.
 
You can make a spiral with a cylinder and a string. As you wind it around the central cylinder, the router gets closer and closer to the center of the spiral.


Use Kapton tape as an insulator between windings. Laminate the winding between two pieces of FR4 with high temperature epoxy. The PCBs would provide the connection points to the coils.

 
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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.

You can make a spiral with a cylinder and a string. As you wind it around the central cylinder, the router gets closer and closer to the center of the spiral.


Use Kapton tape as an insulator between windings. Laminate the winding between two pieces of FR4 with high temperature epoxy. The PCBs would provide the connection points to the coils.

Yes. There are planar transformers made of stamped copper rather then pcb. The primary could be one or two turns.
 

Small footprint to get to 5kW. I would think it would be fairly straightforward to create some copper windings. Maybe even laser cut.
Could you share what what a winding would look like?

Here I am talking about winding a string around a pencil tied to a zip router, and he is talking about laser cutting copper.

I think we have vastly different ideas of what DIY means.
 
Hi Roswell Bob
Is it possible to make an inverter that runs on 24 volt dc and for only say, 50 or 100 watts 120 AC?
 
I don't know exactly what a zip router is. They are used on sheetrock I think? If it will cut copper then it will probably will work. I suppose copper would be a 1mm or so thick. Something like the picture could probably be hacked out with a pair of tin snips. If frequency is reasonably high it would not require a lot of turns. One turn primary would probably work at 48v. Larger core and higher frequency I would guess. By interleaving the primary and secondary windings some nice things happen too. A CNC machine could be programmed to do the cutting. Laser cutting copper is becoming fairly common these days. I recall reading $20-$40 an hour. I suppose that is machine time, but no idea really. I spoke to a ME today and he thought hydro cutting might be a possibility too. He also mentioned using stacks of double sided boards. He said you could buy them at a very good price using 4oz copper and plate them up to whatever you need. That is DIY enough for me. I just worked on a transformer that was near 200A. My client used boards from China. I'll ask what he paid for them. The alternative to a planar core would most likely require using copper foil. That is a cluster bomb to work with. Their is another possibility. That would be looking at off the shelf or more likely production overruns. Customer cancels an order for some reason and vendor is sitting on a pile of scrap that he would unload for pennys.
 
Any reason we couldn't fabricate a planar transformer from sheets of copper mounted to pins soldered to a PCB? Not a good solution for production, but DIY friendly for making one-offs.

I could see using a CNC router to machine traces into a copper sheet. Or if the traces are big enough, just freehand it.
Yes. this is one of the construction methods. Sheets of copper are often used. They can be cut like paper dolls and folded back on each other to get more turns. Copper could also be used as bus bars plugged into the pc board. Instead of using 16oz copper to do a power board - use bus bars to get the current where you need it.
 
Yes. this is one of the construction methods. Sheets of copper are often used. They can be cut like paper dolls and folded back on each other to get more turns. Copper could also be used as bus bars plugged into the pc board. Instead of using 16oz copper to do a power board - use bus bars to get the current where you need it.
I like the idea of folding sheets and then cutting them to turns.

What kind of core material do you use?
 
I haven't done a lot of magnetics designs these days. I pick a platform and see if I can get parts from distributor or amazon :) If I was going to do a full bridge 48v primary to 4x48v secondary I would pick 500kHz or 1MHz as a starting point. Then the fun begins. You design the copper (paying some attention to skin effect) and iterate into a core size. The major factor in the core is the window or actually the core window area. Can you fit the copper into the core is the question. A 1 turn primary would be my choice. Probably 2 turns on the secondary and use a voltage doubler rectifier. You calculate the core losses based on your flux density and frequency and material. That's when you look at the material. TDK, Magnetics. Phillips and everybody else have their own recipes. Every few years they push a new material that is way way better than the last material which was way way better than the time before. Then you can trade off frequency for mosfet losses and core losses. That's how I goes with everybody I guess. When I was doing a lot of design I would write Mathcad files and just plug the numbers in. Wish i kept all of the Mathcad and LT Spice programs I wrote.
 
Why using planar for that?

Usually you use it for two reasons: low profile and cost savings. Here we don't need the low profile advantage, and cost savings would be very small (actually it'll probably cost more here...) for a DIY inverter. So I don't see why you would use that solution since it has more inconvenients than advantages for our use case.
 
Why using planar for that?

Usually you use it for two reasons: low profile and cost savings. Here we don't need the low profile advantage, and cost savings would be very small (actually it'll probably cost more here...) for a DIY inverter. So I don't see why you would use that solution since it has more inconvenients than advantages for our use case.
 
Ok. I picked because it could be easier to put together more repeatable, a good power density and can be stuck to a heatsink. I do like the low profile tho. I suppose coax design would be another choice. What would you consider a better platform? This is kicking tire stage so all directions are on the table.
 
Classic toroidal core, not too high in frequency to limit switching losses (something around 100-200 kHz seems a good compromise), and Litz wire to limit copper losses ;)

Also, massively // topology with small transformers and only one MOSFET bridge per transformer (like having 20x 100 W inverters instead of 1 or 2 big one). That should allow for better efficiency, higher reliability, and easier design (current sharing becomes less critical).
 
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