Electronics > Projects, Designs, and Technical Stuff
Disapating 750W of MOSFET heat for under $100
mikeselectricstuff:
Might be worth looking at PC watercooling hardware
nAyPDJ:
--- Quote from: T3sl4co1l on April 11, 2019, 05:49:21 am ---I'm rather more concerned with heat sinking a D2PAK. What's that board made of? Is there solid copper inside it?
--- End quote ---
Nope, the plan was to mount the heatsink on top of the PCB, so that the heat is transferred through the plastic chassis. Unfortunately I did the math wrong before designing that board, and that package has too much thermal resistance.
However mounting TO-3Ps directly to the heatsink seems like it may work.
--- 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.
--- Quote from: grifftech on April 11, 2019, 03:55:30 pm ---aluminium pot https://www.amazon.com/dp/B001PZBEKE/ref=twister_B002KMJ8GI?_encoding=UTF8&psc=1
--- End quote ---
I've definitely considered a bucket full of oil :P
I guess that's my fallback. If I can get continuous power dissipation, that'd be great, but otherwise a big bucket full of oil would be fine for (I did the math!) about 45 minutes.
--- Quote from: magic on April 11, 2019, 06:28:56 am ---Realize that at hundreds of watts even case to sink resistance can become significant.
--- End quote ---
Absolutely. That design that I have in the OP was made before I realized that case-to-sink resistance existed. It marginally would work with 0°C/W case-to-sink, but fails completely with the actual ~.5°C/W.
--- Quote from: magic on April 11, 2019, 06:28:56 am ---You may consider GPU coolers too, some are designed to dissipate 200~300W or more.
--- End quote ---
This is what really bugs me about cooler manufactures: they do a crap job of actually providing specs for their products. They'll sometimes publish a power rating--meaningless, since they never publish the max temperature. However, they also *never* publish any kind of thermal resistance numbers.
--- Quote from: NANDBlog on April 11, 2019, 04:54:39 pm ---1.) use a FETs which are qualified for linear operation
--- End quote ---
I'm going to pick this one :). Both the mosfets which I listed are qualified for linear operation, my problem is efficiently removing the heat.
--- Quote from: NANDBlog on April 11, 2019, 04:54:39 pm ---3.) use a lot of FETs at low temperature (separate gate drive and feedback)
--- End quote ---
That gives me an idea... take a look at the attachment. 0.166°C∕W for the whole thing--but unfortunately I'd be a bit over-budget with 375x KIA Semicon KNH9120A costing $232.
PartialDischarge:
--- 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 ---
Like the W from a mosfet are the same as W from a resistor...
Some $1 resistors can also withstand hundreds of W, for a few ms.
OM222O:
if you don't need requirements for near zero resistance, just add a few power resistors in series to drop the voltage before mosfets, that way they have to do less work. for example 1ohm power resistors drop 1volt per amp. using 5 or 10 of them in series would allow you to easily drop about 100 watts with just a basic fan to keep them cool. their absolute value and temperature stability is also not important as they are kept outside of the current sensing circuit.
Mechatrommer:
--- Quote from: mikeselectricstuff on April 11, 2019, 05:30:33 pm ---Might be worth looking at PC watercooling hardware
--- End quote ---
his problem is to spread the heat on bigger surface. so i suspect he will need few watercool based anyway as cpu copper contact area is that small. few water based can multiply the cost.
--- Quote from: nAyPDJ on April 11, 2019, 03:58:25 am ---
--- Quote from: wraper on April 11, 2019, 03:31:41 am ---100W per mosfet in linear mode, good luck with that. Hot spots on the die guaranteed. Even if used as switchers, it would be highly questionable.
--- End quote ---
Sounds like the kind of knowledge only gained through experience :)
--- End quote ---
datasheet can looks charming until we learn about heat transfer rate. 400W of that size, and then there's pcb FR4 in between heatsink is not going to cut it anywhere close. you can burn mosfets (while the heatsink still cool) however many you like until the shop is empty. 100W on small package is tough. i saw youtube a while ago that turns mosfets into a nasty water heater in a jar.
Navigation
[0] Message Index
[#] Next page
[*] Previous page
Go to full version