The Surface Area to Volume Ratio or Why Elephants Have Big Ears

There are very few things that are so far reaching across many different disciplines, ranging from biology to engineering, as is the relation of the surface area to the volume of a body. This is not a law, as Newton’s second one, or a theory as Darwin’s evolution theory. But it has consequences in a diverse set of situations. It explains why cells are the size they are, why some animals have a strange morphology, why flour explodes while wheat grains don’t and many other phenomena that we will explore in this article.

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Pi Keeps Cool at 1.5 GHz

Hackers have a long history of overclocking CPUs ranging from desktop computers to Arduinos. [Jacken] wanted a little more oomph for his Pi Zero-Raspberry Pi-based media center, so he naturally wanted to boost the clock frequency. Like most overclocking though, the biggest limit is how much heat you can dump off the chip.

[Jacken] removed the normal heat sink and built a new one out of inexpensive copper shim, thermal compound, and super glue. The result isn’t very pretty, but it does let him run the Zero Pi at 1.5 GHz reliably. The heat sink is very low profile and doesn’t interfere with plugging other things into the board. Naturally, your results may vary on clock frequency and stability.

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Old Heatsink Lets Ham Push Duty Cycle for Digital Modes

Listen to the amateur radio bands long enough, and you’ll likely come to the conclusion that hams never stop talking. Of course it only seems that way, and the duty cycle for a transmitter operating in one of the voice modes is likely to be pretty low. But digital modes can up the duty cycle and really stress the finals on a rig, so this field-expedient heat sink for a ham transceiver is a handy trick to keep in mind.

This hacklet comes by way of [Kevin Loughin (KB9RLW)], who is trying to use his “shack-in-a-box” Yaesu FT-817 for digital modes like PSK31. Digital modes essentially turn the transceiver into a low-baud modem and thus messages can take a long time to send. This poses a problem for the 5-watt FT-817, which was designed for portable operations and doesn’t have the cooling fans and heavy heatsinks that a big base station rig does. [Kevin] found that an old 486 CPU heatsink clamped to a lug on the rear panel added enough thermal mass to keep the finals much cooler, even with a four-minute dead key into a dummy load at the radio’s full 5-watt output.

You may scoff at the simplicity of this solution, and we’ll concede that it’s far from an epic hack. But sometimes it’s the simple fixes that it pays to keep in mind. However, if your project needs a little less seat-of-the-pants and a little more engineering, be sure to check out [Bil Herd]’s primer on thermal management.
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Penny and Paper Clip Heat Sinks

A bunch of audio heads over at the Head-Fi forum were discussing handy and quick heat sinking methods, leading to much speculation and conjecture. This finally prompted [tangentsoft] to take matters in his own hands and run some tests on DIY Heat Sinks.

The question that sparked this debate was if a paper clip is a good enough heat sink to be used for a TO220 package. Some folks suggested copper pennies (old ones minted 1981 and earlier – the new ones are zinc with copper plating and won’t help much). [tangentsoft] built a jig to test six LM317 regulators in constant current mode set to 0.125A and 2w dissipation. The six configurations were a paper clip, a single penny bolted to the regulator, a regular Aavid TO220 heat sink, a set of 4 pennies bolted, a single penny epoxy glued and finally a single penny soldered directly to the regulator.

The results were pretty interesting. The paper clip scored better than any of the single pennies! The quad-penny and the Aavid heat sink fared above all the other configurations, and almost at par with each other. [tangentsoft] posts his review of each configurations performance and also provides details of his test method, in case someone else wants to replicate his tests to corroborate the results. He tested each configuration independently for one hour, gathering just over 10000 readings for each setup. Other nearby heat sources were turned off, and he placed strategic barriers around the test circuit to isolate it from the effects of other cooling / heating sources. He even removed himself from the test area and monitored his data logging remotely from another room. When he noticed a couple of suspect deviations, he restarted the test.

[tangentsoft] put all the data through Mathematica and plotted his results for analysis, available at this link [pdf, 2.8MB]. So the next time you want to heat sink a regulator for cheap, just hunt for Clippy in your box of office supplies. Do remember that these methods will work for only a couple of watts dissipation. If you would like to cast and build your own heat sinks out of aluminum, check out this post about DIY Aluminum heat sink casting. And if you need help calculating heat sink parameters, jump to 12:00 minutes in this video from [Dave]’s EEVBlog episode on Dummy loads and heat sinks.

Thanks to [Greg] for sending in this tip.

Reflowing an Entire MacBook Pro

[Sterling]’s MacBook Pro has a propensity to heat up at times. Some of this overheating is due to to what he uses his Mac for – gaming and making music. A larger part of this overheating is that this laptop is a consumer electronics device – it’s going to die sooner or later. One day in March, this laptop bit the bullet, and that’s where this story gets interesting.

Before the MacBook died, [Sterling] was logging temps between 80 and 90ºC, with a maximum of 102º. The simple fixes, compressed air, a laptop stand, and running the fans full blast all the time didn’t help. When the laptop died, [Sterling] was pretty sure some solder joints came loose. Sending the logic board off to a place that specializes in reflowing would take weeks. A more drastic plan of attack was necessary.

[Sterling] disconnected all the wires, connectors, and heat sinks and preheated his oven to 340º F. The logic board was placed on a cookie tray and stuffed into the oven for seven long minutes. Thermal paste was reapplied, heat sinks reinstalled, connectors connected, and the machine booted. It worked great for about eight months with temperatures averaging around 60 or 70º C.

Two weeks ago, the laptop died again. This time it was reflowed with a heat gun and ran for about an hour. The third attempt was the cookie sheet again, only this time [Sterling] added something. Speed holes. Or vents, or whatever else you want to call them.

Now there’s a noticeably increased airflow in the Mac, much better than before. Average temps are back down to 40 or 50º C, lower than they were with just a reflow. The jury is still out if this new addition can go the distance, but with any luck, this mod might make it through 2015.

Thanks [Doug] for the tip.

Silent HTPC build is an art piece for the livingroom

silent-htpc-build

This sexy beast is [DeFex’s] new silent home theater PC. To give you an idea of scale, that motherboard is a Mini ITX form factor. Mounted below it is the solid state drive which is an SLC version chosen because they tend to last longer than the MLC variety. This distinction comes with a price tag that is $100 more expensive.

But we digress. It’s the custom case that really caught our eye with this build. The frame is made of a huge aluminum heat sink. It measures about 7″ by 10″ and sets the final foot print for the computer. An aluminum puck was added to transmit heat from the processor to the heat sink. Holes were drilled and tapped into the heat sink to accept the brass stand offs which hold the motherboard in place.

The near side of the case is a sheet of acrylic. It connects to the rest of the case using 3D printed brackets at each corner. There is an additional bracket on the bottom to hold the hard drive in place. The sides of the case are filled in with bicycle spokes which also find a home in the corner brackets. Now the hard part will be figuring out which orientation looks the best for displaying his fine craftsmanship.

[via Reddit]

Fixing a first generation GuruPlug’s cooling problems

[Doragasu] had been using a hacked Xbox as his file server but upgraded to a single board Linux device when the GuruPlug was released. Unfortunately the first run of these devices had an overheating issue, which resulted in reboots even at moderate CPU load. The design was changed from a passively cooled heat sink to an internal fan, but that didn’t really help those who already had one of the early models. Above is [Doragasu’s] method of cooling down the overheating computer.

The original sink — which was really just a fin-less metal plate — was removed and replaced with a proper heat sink. This makes contact with the ARM, RAM, and Ethernet chips. They were all coated with thermal compound before installation and a silent fan was added to help whisk away the heat. This still fits inside of the original case, but to make way he did remove the original power source and cut a hole to allow for air movement.

The post also details an external LCD screen used to display system information. It’s along the same lines as this USB LCD screen project which inspired him to send us a link to the project.