Hardware SpecificationsInput Voltage: 110/220 VAC
Output Voltage: 0 - 30 V
Output Amperage: 0 - 3 A
Modes: Constant Voltage/Constant Current
Voltage Regulation: < 0.01% + 1 mV
Amperage Regulation: < 0.2% + 1 mA
Display Type: LED
Display Accuracy: +/- 2.5%
Size: 292 mm x 158 mm x 160 mm
Weight: 3.6 Kg
Power Supply and DemandIf you are going to do any sort of electronic work or experimentation, the first piece of real equipment you should get is a decent adjustable power supply. Unfortunately, for various reasons I was personally unable to follow this bit of advice and instead relied on one-off battery packs, hacked together wall-wart style DC adapters, and other unreliable and largely ineffectual means of powering my projects. There was a very dark period in which all of my projects had to run off of one brave little 9 volt battery.
Now that I am taking things more seriously, I decided it was time to upgrade this particular part of my workbench. Luckily, adjustable power supplies are the latest bit of electronics that Chinese factories have decided to churn out at ridiculously low prices. There's a very large market for these adjustable power supplies on eBay, where it turns out they are largely used for powering tattoo guns. The variable voltage gives an easy way for the operator to control speed, and some even come with foot pedals. The hacker in me wonders why the guns couldn't use some kind of solenoid fired off using pulse width modulation (PWM), which would give you full strokes at a selectable interval rather than having to change the rotational speed of a flywheel and attached needle, but that is research for another day. Most of these supplies are adjustable between 0 and 18 VDC, and go for an average price of $60 or so.
I was very fortunate to find the Mastech HY3003 selling for the suspiciously low price of $90 from an eBay seller specializing in tattoo equipment (qualitytattoosupplies). Seeing what they were going for on other auctions I was actually a bit nervous about buying it, and the fact that I couldn't find any reviews (or really, any legitimate information at all) certainly didn't help matters. But I figured it was worth a shot, and in any event I would document the device on DigiFAIL and maybe help others who were interesting in this particular supply.
ConstructionThe first thing I noticed about the HY3003 was that it wasn't nearly as large as I was worried it would be. Since I was hoping to leave this out on my bench all the time with my soldering station, I was a little concerned by how much space it would take up. Even though it is rather deep, it's not terribly wide and not so tall as to dominate over the workspace. It is however rather heavy, due to it's largely metal construction and monstrous internal transformer. In fact, aside from the case and transformer, there isn't a whole lot else going on in there. Just a circuit board for the LED display and a second board that is presumably used for managing the transformer output. Of course, this isn't too surprising for a linear power supply.
OperationThe usage of this power supply is rather straight forward. Both the current and voltage sides of the supply can be variably adjusted independently through both the Course and Fine adjustment knobs under each respective display. The Course adjustment allows you to make large and rapid adjustments, while the Fine knob let's you hone in right on the spot you want to hit. In addition, the HY3003 can be run in either a constant voltage or constant amperage mode. These modes are used when you want a load to be able to draw more power without increasing voltage to it, or vice versa. This is perfect for applications like lasers, where you want voltage to always remain the same but also allow the diode to draw more if necessary.
Beyond the 4 knobs, the most obvious feature on the front of the HY3003 is it's dual red LED displays. These displays not only have an awesome retro coolness about them, but are also very easy to see in low light conditions or from a distance, neither of which can be said about LCD or even analog displays. If there is any downside of these displays it's the margin of error. The spec sheet says the displays are accurate to within 2.5%, and while I haven't done any terribly scientific tests on the device, even with my multimeter I was able to see a slight deviation between the displayed and actual output voltage. Still, it's more than close enough for any work I am going to do.
PerformanceBeyond the small deviation from displayed voltage I noted with my multimeter, I also found that there is a noticeable ripple on the output when viewed on my oscilloscope. The fluctuation was slight, but clearly visible. To be fair, both of my oscilloscopes are nearly as old as I am, so I generally take their results with a grain of salt when dealing with anything under half a volt or so.
While using the HY3003, I have also noted that dialing in to a specific voltage seems considerably more difficult than it should be. The controls have a rather unpredictable "float" to them, so you need to fiddle around with them to get where you want to be. Again, for the type of work a hobbyist gets into, this won't be an issue.
VerdictFor $90, the HY3003 is an exceptional deal. It is more than adequate for working with things like microcontrollers, lasers, and consumer electronics. However, most sites and eBay sellers have the HY3003 listed for considerably higher than that, usually in the $150 neighborhood. If you are willing to spend that much money on a power supply, you may be better off kicking in a few more dollars and trying to pick up a second hand laboratory-grade power supply from eBay or Craigslist; where I have seen them going for as little as $200.
Considering the questionable background of this device, I will be keeping a rather close eye on it as I use it more and see if any problems develop. Any changes or problems that arise will be added to this page.