What do you think of this big 10lb heatsink ?? - Page 1
Forum section: electronics / projects

author: MathWizard
author_rank: Super Contributor
timestamp: August 25, 2025, 02:54:34 pm
content: I'm designing an electronic load, and I was testing with some small heatsinks I salvaged, for cheap IRFZ44N's. But now I got some real IRFP250N's in TO-247, so I started looking for proper heatsinks. I found some nice 200W, 0.5kg ones for stereo IC's in China, but then I found this one in Canada. It's ~10lb (4.6kg), and about 220x160x120mm, 15mm base, and I guess ~2mm fins, of which it looks like there's 34.So according to this online calculator, I'm guessing 200W should be easy in open air, if say the thermal resistance was as bad as 0.2C/W. The online calculator starts around 0.11C/W with a bit of forced air. If it was as good as it says with full fans, then I could do 400W total from 8FET's and keep the junction temps ~100C.I have lots of 120mm or 140mm ArcticCooler2 12V computer fans.What do you folks think ?https://radianheatsinks.com/heatsink-calculator/

author: Simmed
author_rank: Frequent Contributor
timestamp: August 25, 2025, 03:40:32 pm
content: have you chosen a fan/fans ?have you decided how to house it ?because the fin is so long and very narrowyou need to engineer how the air will enter / exitotherwise some surface area is wasted16cm wideyou could put 2 x 8cm fan exactly across itso many variables to play with

author: Benta
author_rank: Super Contributor
timestamp: August 25, 2025, 08:40:53 pm
content: What I think? Damned cool!If you mount it so the fins are vertical, I doubt that you'll need fans at all. The chimney effect will take care of air flow.The main problem will be the thermal interface between your power devices and the heat sink.Good find!

author: TimFox
author_rank: Super Contributor
timestamp: August 25, 2025, 08:56:06 pm
content: Before mounting your semiconductors, you can do a test (with or without fans, in different orientations) by bolting an aluminum-cased power resistor (with thermal compound) to the heat sink and measuring the temperature rise (at the location where you intend to mount the semiconductors) as a function of DC or AC power in the resistor.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: August 25, 2025, 10:39:07 pm
content: Quote from: MathWizard on August 25, 2025, 02:54:34 pmHehe yes, there is some appeal toreal thermal mass.My personal preference is for tunnel type designs, but they do not come at 4.6kg !Below is one rare tunnel I book-marked in Alihttps://www.aliexpress.com/item/1005005786861131.html,has solid webs and suits a push and pull fan tunnel, and can come to 400mm long.Ali also have a 98 x 93mm high-power fan aluminum heat sink, but listings seem to be all 130mm long, nothing larger. I guess you could simply stack them?https://www.aliexpress.com/item/1005006161787302.htmlI did find this one, for 'price no object' projects- you can get them up to 300x108x300mm but they are not well fan suited. No mention of weight ?https://www.aliexpress.com/item/1005008223947077.html

author: Benta
author_rank: Super Contributor
timestamp: August 25, 2025, 11:21:01 pm
content: What's really nice about MathWizard's heatsink is, that it's been machined/planed on the "thermal interface" side.The standard extrusions do not have such a nice surface.Clearly a top-notch part. I'm envious.

author: MathWizard
author_rank: Super Contributor
timestamp: August 26, 2025, 08:01:03 am
content: Yeah I was worried maybe the fins are too tight or something. The total cost (a lot of it is shipping) is about 3x what the 200W ones are.For thermal paste I have some good 13W/m*K CPU stuff, and jar of 4W/m*K stuff on the way too, for general use.I need to listen to some physics lectures on heat flow, and then maybe try some simulator besides LTSpice, for heatflow. I'll plan and measure and mark everything before I go drilling any new holes and make it ugly.I'll have to make some kind of base for it to sit on and not move, even just a wooden box frame with a handle would be nice. But for now I'm not trying to make anything too permanent. Some cardboard can any do any airflow control. I've made the Rsense board already, so it's only to put the TO-247's on a protoboard, and mount them. But I already have another small 2FET Eload built that I can test with. There's lots of stuff I'm still designing for the control circuits.But I'll probably want to use the heatsink for other stuff too, and maybe the same FET's too. Like the homemade PSU I made, it uses a stereo transformer, that I also use for a Curve Tracer project that's almost done. I just swap the box that sits on the old stereo chassis and hookup the rails.But either way the only high power thing I'll want to do, is test some computer PSU's, (I have a junk box of repaired and untrustworthy ones, nothing really important tho).Besides that, I might want to test some higher voltage parts, like transformers, or rectifier outputs, so that's another reason I upgraded the FETs to IRFP250. At some point I might go with 300V max like the Array Eload I'm modding.But so far in LTSpice, I've had a harder time getting the Eload stable w/ the IRFP250 vs IRFZ44. With the latter, it seemed I didn't need feedback caps on each FET driver op-amp, just 1 main 1 in the loop would do. And now I want to try more composite amplifier setups too, all that's new to me. I know I'm going to enjoy deriving some of those equations.

author: 5U4GB
author_rank: Super Contributor
timestamp: August 26, 2025, 09:25:04 am
content: Quote from: Benta on August 25, 2025, 08:40:53 pmNever underestimate the effect of even the smallest amount of forced-air movement vs. no (or at least convection-only) movement. Many years ago I did some tests on a crappy heatsink that wasn't cutting it and just a gutless 40mm 5V fan made all the difference. Wish I'd kept the data for it since it was such an eye-opener.If you really want to do it properly, see if you can find someone selling aZalman Reserator v1somewhere.

author: MathWizard
author_rank: Super Contributor
timestamp: August 26, 2025, 11:16:18 am
content: I saw a bunch of Peliter coolers, that looks interesting. I was also looking at getting a bunch of CPU coolers.It also kills me that everyday, all kinds of heatsinks and everything else gets dropped off at the dump, and sent off to be scrapped.I have a broken 200-300W GPU, it's heatsink/cooler is good for that, but sure gets loud. I was also thinking of buying some older GPU's, just for the coolers.

author: 5U4GB
author_rank: Super Contributor
timestamp: August 26, 2025, 11:36:14 am
content: The problem with Peltiers is that they just move the heat from one place to another while adding a little more in the process. So you still need to dissipate it somewhere afterwards.Incidentally, Peltiers are great for making small-scale dehumidifiers, you use the Peltier in place of the usual compressor. I'm using some in electronics cabinets in case moisture gets in.

author: Conrad Hoffman
author_rank: Super Contributor
timestamp: August 26, 2025, 12:25:50 pm
content: The trick with peltiers and humidity is keeping the water out of the peltier! Over time it makes a mess of things. As far as heat sinks, I could be wrong, but I remember that closely spaced fins require forced air as they don't convect well. You always want to blow air into/at the fins, not draw it with the sink on the suction side of the fan. Thermal mass has no great benefit in itself; you just need enough material to get the heat out of the devices and into the fins. Surface area is king. Sometimes copper spreaders are useful. I won't call expensive high conductivity compounds a scam, but application and getting the layer as thin as possible is the most important thing. Even the best compounds are many times worse than the metals we're trying to thermally connect, so the layer has to be thin. Flat machined surfaces beat unfinished extrusions.

author: MathWizard
author_rank: Super Contributor
timestamp: August 26, 2025, 04:55:09 pm
content: Now what about the screw that goes through the package, and into the heatsink, I've not seen any models mention them, and I never thought of it till now. I can find the data for common steel and maybe do some basic calculations on a cylinderI'm not sure how good/bad my fans will be for this, but at least they are brandname with a datasheet. I'm just watching some more EE video's on heat transfer.IDK much about Ferrite beads or if I'll need them for this or not, it's mainly a DC E-load, but it does ok with AC signals in LTSpice, and can be turned into an oscillator pretty easily too, if not compensated enough.Depending on the voltages I want to test tho, I probably should isolate the heatsink from the voltage, especially if I'm not making a full case anytime soon. I'll have to check the thermals for those options too. I don't want to spend another 8x$15 for thermal pads or anything tho, that would be way more than the FETs themselves.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: August 26, 2025, 08:05:26 pm
content: Quote from: MathWizard on August 26, 2025, 04:55:09 pmThe best mounting is a clip or clamp. Screws apply a skewed force.I saw one design run a copper u channel over all the TO247’s but the copper was just for visual effect and bragging rights, Al u channel would work just fine.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: August 26, 2025, 11:50:11 pm
content: Quote from: MathWizard on August 25, 2025, 02:54:34 pmI've seen such fans mounted straight above the fins, rather than at one end. With such tall one-sided fins, it could be worth testing ?https://www.aliexpress.com/item/1005009194912569.htmlOthers have me more scratching my head, here the air turns a lot of cornershttps://www.aliexpress.com/item/4000415472825.htmlThis approach at least allows you to baffle off the exit airhttps://www.aliexpress.com/item/1005003634031903.html

author: d-el
author_rank: Regular Contributor
timestamp: August 27, 2025, 12:52:00 am
content: I like this type of radiators:It is convenient to design a purge with individual fans, the solution is easily scalable.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: August 27, 2025, 01:06:08 am
content: Quote from: d-el on August 27, 2025, 12:52:00 amYes, tunnel cooling is well suited to fans, but many have strange fin designs.The tunnel example you give, has empty space for 'lazy air' to flow into, and do no cooling at all.Very close to the fan would be ok, but it would be less suitable for a long tunnel.It is also common to see quite skinny corners, for not-great thermal travel around the corners.In typical use one or two sides have power devices, the unused planes are less efficient use of metal.This one has interleaved fins, designed to cool 2 sides best and has no sneak space for air.and this one is a large single piece - seems to only come in 500mm lengths for serious cooling projects.

author: d-el
author_rank: Regular Contributor
timestamp: August 27, 2025, 11:28:43 am
content: Quote from: PCB.Wiz on August 27, 2025, 01:06:08 amTurbulence will do its job.Quote from: PCB.Wiz on August 27, 2025, 01:06:08 amThis type of radiators is used in the Japanese powerful load Kikusui PLZ1003W (and others from this series). In general, I like their design. I recommend considering their solution.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: August 28, 2025, 11:05:15 am
content: I don't agree with Benta of not using fans at all.Even with a little bit of forced air movement, the efficacy of a heatsink doubles or tripples. And with a lot of forced air flow it is reduced further, but not by much. But you've used an calculator and that probably gave similar results as I wrote.