| Electronics > Beginners |
| MOT (microwave oven transformer) cooling. |
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| soldar:
You are trying to build a PSU that will supply up to 30 A at 13.8 V? Regulated? That sounds pretty easy and there are many designs out there. It is about 400 W which is not that much. But you'd be better off going with a specific design than trying to reuse components that are ill suited for the job. IMHO a SMPS is better suited for this end. In any case, a transformer or transformers followed by bridge rectifier and capacitor has a terrible wave form power factor which means everything will need to be oversized. I would go with a SMPS with power factor correction included. You will save bulk, heat, and probably cash. You can search for Texas Instruments Power Factor Correction Circuits as they have resources online. I guess I am getting older and lazier but I would not spend my time designing and building things which are very commonly sold commercially and can be bought for much less money than my time is worth. You can buy a PSU with those specs which will be better designed and put together than anything you can do with repurposed microwave oven transformers. |
| james_s:
It would be silly to try building a SMPS like that. You can get surplus hot-swap server PSUs for not much more than the cost of shipping. These are mostly 12V at 30-60A but many can be tweaked to increase the output voltage slightly. |
| langwadt:
--- Quote from: james_s on January 04, 2019, 04:55:12 pm ---It would be silly to try building a SMPS like that. You can get surplus hot-swap server PSUs for not much more than the cost of shipping. These are mostly 12V at 30-60A but many can be tweaked to increase the output voltage slightly. --- End quote --- or just get one of these in 12V or 15V (adjustable +/- ~15%) https://www.meanwell.com/Upload/PDF/LRS-350/LRS-350-SPEC.PDF $36.42 from Digikey |
| T3sl4co1l:
1a. Reduce input voltage to, probably 80-100V (use another transformer in buck configuration). Adjust secondary turns accordingly. 1b. Equivalently, add more primary turns (in the gap left from the magnetic shunts?) to the same end. These both reduce capacity, but mind that an MOT is only about 500VA in size, for a typical (cool running, good regulation) design. Don't be greedy about their ratings! The reduction in V/turn will save input (magnetizing) current, and mechanical noise, because the core is not saturating every half-cycle. 2. Sure, go ahead and bolt or clamp some heatsinks to it. Iron's not the greatest thermal conductor, but there's a lot of it. You'll need a lot of thermal goop to fill in the somewhat uneven laminated surface. If possible, stick a thermistor inside the winding so you can monitor wire temperature. Use high temp wire if possible, too. 3. Just forget about them. More effort than it's worth? A nice MeanWell switcher that size is only a few hundred bucks, and will perform very nicely indeed! Tim |
| davelectronic:
Thanks again all for your replys. It's the something for nothing, or next to nothing that's appealing. They are far from perfect or efficienct I know this. A first stage transformer sounds interesting idea.. I have had other projects from the past with bought toroidal transformers for. Yes I could purchase another transformer. I've lost count of the smps units I have modified over the years, from good quality ATX units to very powerful server psu's. It's just for the fun of it really. The MOT is never going to be fantastic, adding surface area creates bulk. Andding ballast creates weight, as does second transformers. First I will try heatsinking with thermal epoxy, see how that goes. |
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