| Electronics > Projects, Designs, and Technical Stuff |
| Disapating 750W of MOSFET heat for under $100 |
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| Mr.B:
--- Quote from: Nerull on April 12, 2019, 01:52:13 am ---A Corsair H115 can barely keep up with a 210W 9900k. --- End quote --- Because Corsair would not, or could not, supply me with any specs I had to make an educated guess at what the H60 was capable of. Assuming it can be fitted to a reasonably grunty CPU, I figured it should be good for 200W. I am using Noctua PPC NF-F12 PPC-3000 fans. Up to 3000rpm - but bloody noisy at full speed. |
| digsys:
Having made and sold many high power linear power supplies, using FETs in linear mode, I can add the following - There is a LOT of good cautionary advice here ! Adding to them - 1/ DO NOT believe any of the datasheets. I had to destroy literally many dozens of FETs to make my own SOA curves. As posters note, even the linear specified FETs are estimates / or plain bogus. 2/ De-rating is VERY important, both Temp and Voltage (current) 3/ Use a independent sense / share drive for each FET. There are ICs that do just that. Hot-spotting is bad enough, and you don't want one FET taking off. 4/ Select a proper thermal paste ! not just the crappy standard one people use. Arctic silver is a good start. If you have to isolate each FET, there are MUCH better types available than the standard Silpad. This is very important. There is at least one thread here going over all of this stuff. There's more to add, but I have to run :-) .. bbl |
| T3sl4co1l:
--- Quote from: nAyPDJ on April 11, 2019, 05:49:12 pm --- --- Quote from: T3sl4co1l on April 11, 2019, 05:49:21 am ---The better solution is to use resistors, which are smaller and cheaper than heatsinks for the same wattage. --- End quote --- You'd think so, but the exact opposite is true. MOSFETs rated for 200W can be found for about $1, but chassis mount resistors rated to 80W cost around $5. --- End quote --- Fortunately I wasn't talking about transistors. ;) How much will the heatsink cost? $20 per 100W? How much time will it take to cut to length (if applicable), drill and tap holes, grease the parts and bolt them in? If you aren't having a Chinese worker do it en masse, the answer may be surprising. :D Now, the resistors need to be mounted too, but that can be with much simpler means, like clips and self-tapping screws, or entirely with CNC'd custom sheetmetal. If you're starting from an off-the-shelf box and cutting and drilling that, your labor costs will about wash out, and then other considerations may apply, like physical size. (Resistors run hotter, so they can dissipate more heat for the same volume of air moved. The air moves faster when it's hotter, too.) Don't forget the knock-on costs, either. Resistors probably need wiring. You may be able to arrange a PCB to do it -- but mind issues of temperature, thermal expansion and other mechanical tolerances, and the cost tradeoff for a relatively large PCB, or a multi-board design. Transistors need support components (at least a beefy source resistor; preferably an op-amp and support passives), and protection. Tim |
| nAyPDJ:
--- Quote from: thm_w on April 12, 2019, 01:05:14 am ---Evo212 slightly better at 0.17°C/W for $30: https://www.anandtech.com/show/10500/stock-cooler-roundup-intel-amd-vs-evo-212/6 Wonder how a corsair H60 or similar compares, probably better with a high power fan, but I can't seem to find any specs. --- End quote --- That's a list of stock coolers, which have a reputation for being crap. AnandTech also reviewed some aftermarket air coolers, with 0.18°C/W being fairly typical And they also reviewed some liquid coolers, and while the Corsair H60 isn't in the list, I'd expect it to be 0.08°C/W or so --- Quote from: EmmanuelFaure on April 11, 2019, 08:09:00 pm ---"Disapating 750W of MOSFET heat for under $100" The Rth of a common CPU cooler, costing about $20, is about 0.5°C/W. Let's say you want a max delta T = 50K (Between junction and air), this leads to 100W dissipated for $20, 750W for $150. That doesn't take into account all the custom hardware to mount your FETs, the assembly work, etc. For this range of dissipated power, there's no any heatsink cheaper per watt dissipated than CPU coolers, they're manufactured by millions. Any solution with industrial parts will cost more than that. --- End quote --- Your numbers are a little off here. The cooler I've ordered (and not yet received) advertises 0.18°C/W & cost me $16 each ("bulk" discount--I bought two). You can't super trust the ratings, but it's about as hefty as my Wraith cooler in my current computer, and that's 0.18°C/W, so it seems about right. This comes out to 0.01125°C/W$, which is more than half of 0.025°C/W$ |
| magic:
--- Quote from: Mr.B on April 12, 2019, 01:24:28 am ---The Corsair H60 is what I used in my design - see previous post. I could not find any specs on it, so contacted Corsair directly. Their response was that it was confidential information. What I interpreted was "We have no idea"... --- End quote --- And I interpret "it's confidential". These aren't audiophools, they must know how their design performs ;) I suppose it's a matter of - it depends on operating conditions and they don't want to publish a single number or a set of plots that Johny Overclocker wouldn't understand anyway - they don't want to be beaten by other vendors using crooked methodologies when the game gets reduced to Johny Overclocker comparing one number printed on the box (see also: PMPO) As is customary with computer hardware, you look for performance data in 3dr party reviews, which specify testing conditions and methodology. If your application is different than the reviewer's, you have to do the math yourself. |
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