Sparkfun Tears Apart Power Supplies

We love a good tear-down, and last week’s “Enginursday” at Sparkfun satisfied our desire to see the insides of AC-DC switching power supplies, accompanied by knowledgeable commentary. [MTaylor] walks us through how the basic circuit works and then points out why various other elaborations are made, and how corners are sometimes cut, in a few power supplies that he’s taken apart.

lishin_bottomshieldedWhat struck us in the comparison was that some of the power supplies were very minimal designs, while others had “features” that were obviously added after the fact. For instance, the Li Shin supply (about half-way down the page) has an extra circuit board tacked on to the bottom of the real circuit board to act as EM shielding.

Rather than declare this a dodgy hack, as we would have, [MTaylor] declares it to be “Good News!” because it means that they’ve probably run an emissions test, failed it, and then added this bit on to make it pass. This is of course in contrast to the other makers who’ve probably never even considered emissions testing. Sigh.

If you’re interested in seeing more inner bits of power bricks, Sparkfun forum reader [sgrace] passed along this field guide to various power supplies, which is also worth a look. And if you’re interested in building yourself the ultimate bench power supply, look no further than this Hackaday.io project by [The Big One].

Crack Open a USB Car Charger to make it a Variable DC-DC Converter

[Boolean90] hacked a cheap USB car charger into a variable power supply. His proof of concept is to use this as a variable-speed motor controller. The best part is that nothing is being abused, the regulator inside is still running within manufacturer’s spec.

While we’ve seen similar hacks before, [Boolean90]s video is pretty cool and provides a nice insight into the components used in these cheap devices. Rather than a linear regulator, which would dissipate too much heat the device uses a common jelybean MC34063A (PDF) switching DC-DC converter which costs about 10 cents on eBay (about two dollars for twenty, shipped). Here it’s used to step the car batteries 12 volts down to 5, but can also be used in step-up and inverting configurations.

Like all switching buck converters the MC34063A uses a PWM (pulse width modulated) signal to drive an inductor and capacitor, which effectively form an LC filter. By controlling the pulse width, the output voltage can be regulated. [Afrotechmods] has a great tutorial on the basic principle. The regulation is controlled by feedback resistors. [Boolean90] simply added a variable resistor to allow the output voltage to be controlled.

Neat hack [Boolean90]! Continue reading “Crack Open a USB Car Charger to make it a Variable DC-DC Converter”

DIY table saw cuts through anything, leaves no room for mistakes

Students in the BASTLI lab at the Swiss Federal Institute of Technology Zurich had been stuck using underpowered and unreliable saws for quite some time. The saws often got stuck while cutting through PCBs and were generally a drag to use. When group member [Mario Mauerer] came across a big and powerful brushless motor in his basement, he decided it was time to upgrade the lab’s cutting tools.

Along with fellow student [Lukas Schrittwieser] he built a test rig to see how powerful the motor really was, and satisfied with the results, the pair set off to build their own table saw. The enclosure was wrapped up pretty quickly, leaving the pair to source a power supply. Rather than purchase one, they built a 700w monster switching PSU to power their saw.

As you can see in the video below the saw chews through most things with the greatest of ease, but the students added a “boost button” to the saw just in case they need to run it at full tilt.

While we can’t exactly overlook the lack of finger and eye protection in their demonstration, it does look like a great little tool to have around.

Continue reading “DIY table saw cuts through anything, leaves no room for mistakes”