Power Supplies Without Transformers

For one-off projects or prototyping, it’s not too hard to find a wall wart or power supply to send a few joules of energy from the wall outlet to your circuit. Most of these power supplies use a transformer to step down the voltage to a more usable level and also to provide some galvanic isolation to the low voltage circuit. But for circuits where weight, volume, or cost are a major concern, a transformer may be omitted in the circuit design in favor of some sort of transformerless power supply.

While power supplies with this design do have many advantages, some care needs to be taken with regard to safety. The guide outlines four designs of increasing complexity which first puts out a basic transformerless power supply, using a series capacitor to limit current. To bring the voltage to an acceptable level, a recognizable bridge rectifier is paired with a capacitor as well as a zener diode. The second circuit presented adds voltage stabilization using a transistor and 78XX regulator. From there, zero-crossing detection is added to limit inrush surge currents, and the final design uses the venerable 555 timer to build a switching power supply.

Although it is noted several times throughout the guide, we’ll still point out here that transformerless designs like these introduce several safety issues since a mistake or fault can lead to the circuit being exposed to the mains voltage. However, with proper care and design it’s possible to make use of these designs to build more effective power supplies that can be safe to use for powering whatever circuit might energy but might not require the cost or weight of a transformer. For more on the theory of these interesting circuits and a few examples of where they are often found, check out the shocking truth about transformerless power supplies.

Thanks to [Stephen] for the tip!

Motorcycle Regulator By Popular Demand

A few weeks ago we posted a build of an avid motorcycle enthusiast named [fvfilippetti] who created a voltage regulator essentially from the ground up. While this was a popular build, the regulator only works for a small subset of motorcycles. This had a large number of readers clamoring for a more common three-phase regulator as well. Normally we wouldn’t expect someone to drop everything they’re doing and start working on a brand new project based on the comments here, but that’s exactly what he’s done.

It’s important to note that the solutions he has developed are currently only in the simulation phase, but they show promise in SPICE models. There are actually two schematics available for those who would like to continue his open-source project. Compared to shunt-type regulators, these have some advantages. Besides being open-source, they do not load the engine when the battery is fully charged, which improves efficiency. The only downside is that they have have added complexity as they can’t open this circuit except under specific situations, which requires a specific type of switch.

All in all, this is an excellent step on the way to a true prototype and eventual replacement of the often lackluster regulators found on motorcycles from Aprilia to Zero. We hope to see it further developed for all of the motorcycle riders out there who have been sidelined by this seemingly simple part. And if you missed it the first time around, here is the working regulator for his Bajaj NS200.

Motorcycle Voltage Regulator Uses MOSFETs

For how common motorcycles are, the designs and parts used in them tend to vary much more wildly than in cars and trucks. Sometimes this is to the rider’s advantage, like Honda experimenting with airbags or automatic transmissions. Sometimes it’s a little more questionable, like certain American brands holding on to pushrod engine designs from the ’40s. And sometimes it’s just annoying, like the use of cheap voltage regulators that fail often and perform poorly. [fvfilippetti] was tired of dealing with this on his motorcycle, so he built a custom voltage regulator using MOSFETs instead.

Unlike a modern car alternator, which can generate usable voltage even at idle, smaller or older motorcycle alternators often can’t. Instead they rely on a simpler but less reliable regulator that is typically no more than a series of diodes, but which can only deliver energy to the electrical system while the motor is running at higher speeds. Hoping to improve on this design, [fvfilippetti] designed a switched regulator from scratch out of MOSFETs with some interesting design considerations. It is capable of taking an input voltage between 20V and 250V, and improves the ability of the motorcycle to use modern, higher-power lights and to charge devices like phones as well.

In the video below, an LED was added in the circuit to give a visual indication that the regulator is operating properly. It’s certainly a welcome build for anyone who has ever dealt with rectifier- or diode-style regulators on older bikes before. Vehicle alternators are interesting beasts in their own right, too, and they can be used for much more than running your motorcycle’s electrical system.

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Seeing Inside A Gas Regulator

We’re surrounded by interesting engineering, but some of it is sealed inside a housing, away from easy inspection. A case in point; the humble gas regulator. It’s in equipment all around us, from a propane grill to welding gear. It’s a sealed unit — have you ever seen the inside, to know how it really works? Well thanks to [FarmCraft101], we get to do just that, in the video after the break.

To let the cat out of the bag, it’s essentially a hydraulic lever. A large diaphragm is pressurized by the low pressure side of the regulator, and is held back by a spring. When the pressure compared to ambient atmosphere is high enough to overcome the spring tension, the lever is tilted, closing the high pressure valve. Hence, pressure is determined by spring strength. We also get a look at how the system can fail — in this case it seemed to be some grit interfering with the valve. We find hidden engineering to be supremely satisfying, particularly when we get to understand it so clearly as we do here. Enjoy!

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The Fix Is In: Hubble’s Troubles Appear Over For Now

Good news this morning from low Earth orbit, where the Hubble Space Telescope is back online after a long and worrisome month of inactivity following a glitch with the observatory’s payload computer.

We recently covered the Hubble payload computer in some depth; at the time, NASA was still very much in the diagnosis phase of the recovery, and had yet to determine a root cause. But the investigation was pointing to one of two possible culprits: the Command Unit/Science Data Formatter (CU/SDF), the module that interfaces the various science instruments, or the Power Control Unit (PCU), which provides regulated power for everything in the payload computer, more verbosely known as the SI C&DH, or Scientific Instrument Command and Data Handling Unit.

In the two weeks since that report, NASA made slow but steady progress, methodically testing every aspect of the SI C&DH. It wasn’t until just two days ago, on July 14, that NASA made a solid determination on root cause: the Power Control Unit, or more specifically, the power supply protection circuit on the PCU’s 5-volt rail. The circuit is designed to monitor the rail for undervoltage or overvoltage conditions, and to order the SI C&DH to shut down if the voltage is out of spec. It’s not entirely clear whether the PCU is actually putting out something other than 5 volts, or if the protection circuit has perhaps degraded since the entire SI C&DH was replaced in the last service mission in 2009. But either way, the fix is the same: switch to the backup PCU, a step that was carefully planned out and executed on July 15th.

To their credit, the agency took pains that everyone involved would be free from any sense of pressure to rush a fix — the 30-year-old spacecraft was stable, its instruments were all safely shut down, and so the imperative was to fix the problem without causing any collateral damage, or taking a step that couldn’t be undone. And further kudos go to NASA for transparency — the web page detailing their efforts to save Hubble reads almost like a build log on one of our projects.

There’s still quite a bit of work to be done to get Hubble back into business — the science instruments have to be woken up and checked out, for instance — but if all goes well, we should see science data start flowing back from the space telescope soon. It’s a relief that NASA was able to pull this fix off, but the fact that Hubble is down to its last backup is a reminder Hubble’s days are numbered, and that the best way to honor the feats of engineering derring-do that saved Hubble this time and many times before is to keep doing great science for as long as possible.

See The Fabulous Workmanship In This Smart Pressure Regulator

For many projects that require control of air pressure, the usual option is to hook up a pump, maybe with a motor controller to turn it on and off, and work with that. If one’s requirements can’t be filled by that level of equipment and control, then it’s time to look at commercial regulators. [Craig Watson] did exactly that, but found the results as disappointing as they were expensive. He found that commercial offerings — especially at low pressures — tended to leak air, occasionally reported incorrect pressures, and in general just weren’t very precise. Out of a sense of necessity he set out to design his own electronically controlled, closed-loop pressure regulator. The metal block is a custom manifold with valve hardware mounted onto it, and the PCB mounted on top holds the control system. The project logs have some great pictures and details of the prototyping and fabrication process.

This project was the result of [Craig]’s work on a microfluidics control system, conceived because he discovered that much of the equipment involved in these useful systems is prohibitively expensive for small labs or individuals. In the course of developing the electronic pressure regulator, he realized it could have applications beyond microfluidics control, and created it as a modular device that can easily be integrated into other systems and handle either positive or negative pressure. It’s especially well-suited for anything with low air requirements and a limited supply, but with a need for precise control.

Fail Of The Week: Never Trust A Regulator Module

[Ryan Wamsley] has spent a lot of time over the past few months working on a new project, the Ultimate LoRa backplane. This is as its name suggests designed for LoRa wireless gateways, and packs in all the features he’d like to see in a LoRa expansion for the Nano Pi Duo.

His design features a three-terminal regulator, and in the quest for a bit more power efficiency he did what no doubt many of you will have done, and gave one of those little switching regulator modules in a three-terminal footprint a go. As part of his testing he inadvertently touched the regulator, and was instantly rewarded with a puff of smoke from his Nano Pi Duo. As it turned out, the regulator was susceptible to electrical noise, and had a fault condition in which its input voltage was routed directly to its output. As a result, a component in the single board computer received way more than its fair share, and burned out.

If there is a moral to be extracted from this story, it is to never fully trust a cheap drop-in module to behave exactly as its manufacturer claims. [Ryan]’s LoRa board lives to fight another day, but the smoke could so easily have come from more components.

So that’s the Fail of The Week part of this write-up complete, but it would be incomplete without the corresponding massive win that is [Ryan]’s LoRa board itself. Make sure to take a look at it, it’s a design into which a lot of attention to detail has been put.