Repairing and Improving Cheap Bench Power Supplies

Cheap benchtop power supplies are generally regarded as pieces of junk around these parts. They can measure well enough under perfect conditions, but when you use them a little bit, they fall over. There’s proof of this in hundreds of EEVblog posts, Amazon reviews, and stories from people who have actually owned these el-cheapo power supplies.

One of the guys who has had a difficult time with these power supplies is [Richard]. He picked up a MPJA 9616PS (or Circuit Specialists CSI3003SM) for a song. It quickly broke, and that means it’s time for a repair video. [Richard] is doing this one better – he has the 3A power supply, that sells for $55. With a stupidly simple modification, he upgraded this power supply to the 5A model that usually sells for $100.

The problem with [Richard]’s broken power supply were voltage and current adjustments knobs. This cheap power supply didn’t use rotary encoders – voltage and current were controlled by a pair of 1k and 10k pots. Replacing these parts cost about $5, and [Richard]’s power supply was back up on its feet.

After poking around inside this power supply, [Richard] noticed two blue trim pots. These trim pots were cranked all the way to the left, and by cranking them all the way to the right, the power supply could output 5 Amps. Yes, the 3A version of this power supply was almost identical to the 5A version, with the only difference being the price. It’s a good repair to a somewhat crappy but serviceable supply, but a great mod that puts a beefier power supply on [Richard]’s desk.

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What’s in a tool? A case for Made in USA.

A lot of people make the argument that you can’t go wrong buying a tool made in USA, Germany, Japan, Switzerland, etc. They swear that any Chinese tool will be garbage and it’s not worth purchasing them. Now, any discerning mind will say, “Wait a minute, why? China has a huge economy, experienced people, and the ability to use all the scary chemicals that make the best steel. Why would their tools be any better or worse than ours?” It’s a very valid argument. There are lots of Chinese tools that are the best in the world. Most of what we see in our stores are not. So what is the difference. Why does a country who can make the best tools not make the best tools? Surely it isn’t purely cost cutting. Is it cultural? The opinion I wish to put forth is that it’s a matter of design intent communication.

I’ve worked as an engineer in industry. The one common thread between a quality product and a bad product has always been this, ”Is the person who designed the product involved in making the product?” If the person or peoples who imbued the design intent into the original product are actively involved in and working towards the execution of that product, that product has a vastly greater chance of being good. Or in other words: outsourcing doesn’t produce a bad product because the new people making the product don’t care. It makes a bad product because the people who understand the intent behind the product are separated from its execution.

As you can see the export made crescent wrench is not made to the same tolerances as the previous wrench.
As you can see the export made crescent wrench is not made to the same tolerances as the previous wrench.

Let’s take the Crescent wrench as an example. Crescent wrenches used to be made in USA. In the past few years they have begun to make them in China. We can spot many visual differences right away. The new Crescent wrench has a different shape, the logo has changed and the stamping for the logo is dodgy, and worse, the tool just doesn’t operate as well as it used to. The jaws aren’t as hard and they wiggle more. What happened? How could Crescent mess up their flagship so badly. Surely they intended just to cut costs, not to reduce quality. This isn’t shameful in itself

What happened to the Crescent wrench is easily explained by anyone who has seen a product from design to execution before. A factory in the USA set out to make a good adjustable wrench. Hundreds of engineers and employees worked in a building to make a good wrench. When their machines didn’t work, they came up with solutions. When their quality was lacking, they implemented better processes. They had a list of trusted suppliers. They could guarantee that the materials that came in would be imbued with their vision and intent when the product came out. The intent and will of all those people built up in one place over time.

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The Unreasonable Effectiveness of Adhesive Tape

No doubt many of you have spent a happy Christmas tearing away layers of wrapping paper to expose some new gadget. But did you stop to spare a thought for the “sticky-back plastic” holding your precious gift paper together?

There are a crazy number of adhesive tapes available, and in this article I’d like to discuss a few of the ones I’ve found useful in my lab, and their sometimes surprising applications. I’d be interested in your own favorite tapes and adhesives too, so please comment below!

But first, I’d like to start with the tapes that I don’t use. Normal cellulose tape, while useful outside the lab, is less than ideally suited to most lab applications. The same goes for vinyl-based insulating tapes, which I find have a tendency to fall off leaving a messy sticky residue. When insulation is necessary, heatshrink seems to serve better.

The one tape I have in my lab which is similar to common cellulose tape however is Scotch Magic Tape. Scotch Magic tape, made from a cellulose acetate, and has a number of surprising properties. It’s often favored because of it’s matte finish. It can easily be written on and when taped to paper appears completely transparent. It’s also easy to tear/shape and remove. But for my purposes I’m more interested in it’s scientific applications.

Here’s a neat trick you can try at home. Take a roll of tape (I’ve tried this with Scotch Magic tape but other tapes may work too) to a dark room. Now start unrolling the tape and look at interface where the tape leaves the rest of the roll. You should see a dim blue illumination. The effect is quite striking and rather surprising. It’s called triboluminescence and has been observed since the 1950s in tapes and far earlier in other materials (even sugar when scraped in a dark room will apparently illuminate). The mechanism, however, is poorly understood.

It was perhaps this strange effect that led researchers to try unrolling tape in a vacuum. In 1953 a group of Russian researchers attempted this and bizarrely enough, were able to generate X-rays. Their results were unfortunately forgotten for many years, but were replicated in 2008 and even used to X-ray a researcher’s finger! As usual Ben Krasnow has an awesome video on the topic:

In my lab however I mostly use Scotch tape to remove surface layers. In certain experiments it’s valuable to have an atomically flat surface. Both Mica and HOPG (a kind of graphite) are composed of atomically flat layers. Scotch tape can be used to remove the upper layers leaving a clean flat surface for experimentation.

The mechanical exfoliation of Graphene

Researchers have also modified this technique to produce graphene. Graphene is composed of single carbon layers and has a number of amazing properties, highly conductive, incredibly strong, and transparent. For years producing small quantities of graphene provided difficult. But in 2004 a simple method was developed at the University of Manchester using nothing but bulk ordered graphite (HOPG) and a little Scotch tape. When repeatedly pressed between the Scotch tape, the Graphite layers can be separated until eventually only a signal layer of graphene remains.

Using Kapton to maskout traces via Dangerous Prototypes



The other non-conductive tape I use regularly in my lab is of course Kapton tape. While Kapton is a Dupoint brand name, it’s basically a polyimide film tape which is thermally stable up to 400 degrees C. This makes it ideal for work holding in electronics (or masking out pins) when soldering. You can also use it for insulating (though it’s inadvisable for production applications). Typically polyimide tape is available under a number of dubious synonyms (one example is Kaptan) from a variety of Chinese suppliers at low cost.


Carbon tape is conductive in all axes. This means it you can create a electrical connection by simply taping to your devices. It’s resistance however is somewhat high. I’ve most commonly come across this when using electron microscopes. Carbon tape is used both to keep a sample in place and create an electrical connection between the sample and the sample mount.

Carbon tape, applied to a SEM mount.

Other conducting tapes are available with lower resistance, creating a electrical connection without soldering is valuable in a number of situations. Particularly when heat might damage the device. One example of this is piezoelectric materials. Not only does solder often bond poorly to ceramic materials, but it may also depole the material removing its piezoelectric properties. I tend to use conductive epoxies in these situations, but conductive tapes appear to be an attractive option.

Aluminum tape is commonly used for (heat) insulation in homes. It’s therefore very cheap and easily available. As well as conducting heat aluminum tape of course also conducts electricity. Around the lab this can be pretty handy. While the adhesive is not conductive, making it less attractive for connection parts, I’ve found aluminum tape great of sealing up holes in shielded enclosures. It also makes a great accompaniment to aluminum foil which is used to provide ad-hoc shielding in many scientific environments. Copper tape is also easily obtained, though slightly more expensive.

Z tape under a microscope

A much less common, but far cooler conductive tape is so called Z tape. This tape is composed of regular double-sided tape impregnated with spaced conductors. The result is a tape that conducts in only one direction (from the top to the bottom). This makes it similar in structure to a zebra strip, commonly used to connect LCDs. Z tape is unfortunately pretty expensive, a short 100mm strip can cost 5 dollars. What exactly 3M had in mind when creating Z tape is unclear. But it can be used for repairing FPC connectors on LCDs or in other situations where soldering is impractical.

One of the more awesome applications is Jie and Bunnie’s circuit sticker project. The kits are designed to allow kids to assemble circuits simply by sticking components together. Z tape is ideal for this, as it allows multiple connections to be made using the same piece to tape.

I couldn’t write an article on tape without mentioning the somewhat apocryphal “Invisible Electrostatic Wall” incident. A report at the 17th Annual EOS/ESD Symposium describes a “force field” like wall that appeared during the production of polypropylene film. While the story seems slightly dubious, it reminds us of the surprising applications and utility of tapes.

Next time you’re sending off a package or ripping open a package, spare a thought for the humble tape that holds it together.

Clamps, Cauls, And The Mother Of Invention

If there’s one thing you need in a woodshop, it’s more clamps. There are bar clamps, pipe clamps, spring clamps, and trigger clamps, but for one task in the workshop, no clamp does the job just right. Gluing up panels – a few wide pieces of wood joined on edge – either requires more clamps than you have or cauls, devices that press down on the boards vertically while the clamps press the board together horizontally.

[Andrew Klein] has just invented a new type of clamp for this task, proving once again that not all problems are solved, and there’s still some places where an invention can pop out of mid-air.

The new clamps are a modification to traditional bar clamps that allow for two clamps to interlock. On each of the ‘working’ ends of the clamps, there are two adjustment handles. The first screws the clamp horizontally, just like any bar or pipe clamp. The second adjustment handle moves a bearing up and down. When this bearing meshes with a riser on the mating end of another clamp, the two clamps are pressed together vertically.

The new clamps are effectively clamps and cauls, able to push material together from side to side and top to bottom. The new clamps work, too. In the video below, you can see [Andrew] gluing up a panel. When the vertical adjustment wheel is loosened, the boards come apart vertically. When the vertical adjustment wheel is tightened, the boards are perfectly in line with each other, both edge to edge and face to face.

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Matthias Builds A Belt Sander

[Matthias Wandel] is the preeminent YouTube woodworker, with dozens of machines constructed from wooden gears, amazing machines that produce perfect mortise and tenons, and home-built table saws and jointers. Actually building something instead of buying it is a hallmark of [Matthias]’ channel, and he’s at it again, building his own woodworking machines. This time it’s a 1″ wide belt sander. Of course anyone can go out and simply buy one of these sanders for under $100, but what’s the point in that when you can build one out of plywood and a motor you picked out of the trash?

The design of this belt sander – just like the commercial version he’s improving upon – uses three wheels to guide the 42″ long strip of sandpaper around its course. [Matthias] is using rollerblade wheels for the front wheels. Rollerblade wheels aren’t the best shape for bearings, this can be fixed by using a table saw as a lathe. Yes, [Matthias] lathes with a table saw. He’s just that good.

The rest of the frame was carefully constructed out of plywood and powered by a 1/3 horsepower furnace fan motor pulled from the trash. There are a few interesting features that make this belt sander exceptionally useful: a rounded platen behind the belt makes sanding interior corners very easy, and is something that isn’t usually found on commercial belt sanders.

You can check out [Matthias]’ video below.

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Measuring Capacitors Over Their Working Voltage

Ceramic capacitors are small, they don’t leak, they’re convenient, but they are downright strange. Certain types of caps will lose their capacitance depending on the voltage they’re operating at. If you’re using ceramic caps for filters, DC to DC power supplies, bypass caps, or anything where you need an exact capacitance in a circuit, this can be a problem.

[Mathieu] has come up with a tool that’s able to measure the capacitance of a cap over its entire working range. He’s calling it the OpenCVMeter, and although the name might be slightly confusing, the functionality is not. This little box will measure the capacitance of a part over a voltage range from 1.3 to 15.5V.

By attaching the SMD tweezers or test clips to a capacitor, the OpenCVMeter ramps up the voltage and measures the capacitance of the part through the test cycle. This data is then dumped to a Chrome app – a surprisingly popular platform for test equipment apps – and a determination of the cap’s ability will to work in a circuit is displayed on the screen

If you’ve ever tooled around with antique electronic equipment, you’ll know the first thing to go bad in any piece of equipment are caps. Either caps had extremely loose manufacturing tolerances back in the day or the values really were that critical, but a dodgy cap can bring down everything from tube amps to computers. It’s a very neat tool, and something that doesn’t really exist in a single dedicated device.

A Handheld CNC Router

Over the last few years, the state of the art in handheld routers has been tucked away in the back of our minds. It was at SIGGRAPH in 2012 and we caught up to it at Makerfair last year. Now, it’s getting ready for production.

Originally called Taktia, the Shaper router looks a lot like a normal, handheld router. This router is smart, though, with the ability to look at a work piece marked with a tape designed for computer vision and slightly reposition the cutter in response to how the user is moving it. A simple description doesn’t do this tool justice, so check out the video the Shaper team recently uploaded.

With the user moving the Shaper router over a work piece and motors moving the cutter head, this tool is able to make precision cuts – wooden gears and outlines of the United States – quickly, easily, and accurately. Cutting any shape is as easy as loading a file into Shaper, calling that file up on a touch screen display, and turning on the cutter. Move the router around the table, and the Shaper takes care of the rest.

Accuracy, at least in earlier versions, is said to be on the order of a hundredth of an inch. That’s good enough for wood, like this very interesting bit of joinery that would be pretty hard with traditional tools. Video below.

Thanks [martin] for the tip.

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