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Disapating 750W of MOSFET heat for under $100
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Mechatrommer:
it should be around 120W ballpark official figure they knew that already. but with slight mod and working at higher than rated temp, i guess it can be made 200 - 400W, at limited time interval if not continuous, water is a great specific energy container. https://www.ebay.com/itm/ID-COOLING-ICEKIMO-7V-120W-Pure-White-AIO-Water-Cooler-CPU-Radiator-Cooling-Fan/113695211003?hash=item1a78c33dfb:g:QvUAAOSwLvxbq0mc
nAyPDJ:

--- Quote from: T3sl4co1l on April 12, 2019, 04:23:39 am ---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

--- End quote ---

Plan is to use commercially available CPU cooling gear for the majority, which can be obtained at about 0.01125°C/W$ from china.

If this goes anywhere (big "if" here!), I'd expect this to go a little lower@100s. At that point, I'd expect it to few a couple extra dollars ea. to have a childadult worker fabricate the mounting brackets (Mr.B's clever design means that the heatsinking can be symmetrical & the clamps can be just tapped metal plates).

However, your point is taken, thank you.


--- Quote from: digsys on April 12, 2019, 02:52:00 am ---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 -

--- End quote ---

Thanks for the advice! It's great hearing from someone who has done this before.


--- Quote from: digsys on April 12, 2019, 02:52:00 am ---There is at least one thread here going over all of this stuff.

--- End quote ---

I think this is it, I'll just link it here for anyone following along: Programmable Electronic Load, 0-5A.

The discussion is mostly centered upon making it high precision, but OP is also working on (and having difficulty) paralleling the mosfets. I might steal some parts of his control design so that I can focus on the heat dissipation for now :)


--- Quote from: max_torque on April 11, 2019, 07:13:56 pm ---The advantage that dropping power across a dumb resistor is of course the fact that the resistor, being a dumb passive element, can run at very elevated temperatures without failure. 

For example, here is a 50 watt "resistor" that operates at something like 2,500 degrees centigrade

--- End quote ---

I really like the idea of dissipating my heat using exposed 500°C wires, but while the electrical design is more straightforward, the mechanical design is quite tricky. Roughly 300cm of 22AWG nichrome wire is needed to get 10ohm.

- the wire needs to be mounted on something non-conductive & conveniently shaped. An 80mm ceramic square would be perfect, but it needs to be fabricated & I can't even find prices for ceramic 3-d printing.
- the copper wires need to be bonded to the nichrome in a way that doesn't fail at high temperature. A bolt & nut would work, but then where would the bolt and nut be mounted?

Light bulbs wouldn't work since their resistance goes from ~16ohms cold, to hundreds of ohms hot. I haven't done the math exactly, but I figure I'd need hundreds of bulbs as an order-of-magnitude approximation.
digsys:
This post shows a method I use to have several FETs track almost perfectly. 2x is shown, but easy to add more.
https://www.eevblog.com/forum/beginners/linear-psu-with-modern-components-will-it-matter/msg2041252/#msg2041252

Added: Also discussion here -
https://www.eevblog.com/forum/beginners/linear-mode-operation-and-mosfet-fbsoa-question/msg1235696/#msg1235696
Maybe not specific to your question, but helpful info

Added: more discussion of issues
https://www.eevblog.com/forum/beginners/question-on-mosfet-in-linear-mode-does-_hot-spotting_-a-serious-problem/msg99612/#msg99612
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