Absolute Power

We recently noticed a very cool-looking series of power supply modules on a few of the Chinese deal web sites. Depending on the model, they provide a digitally-controlled voltage with metering. You need to provide at least a volt or so over the maximum desired output voltage. You can see a video from [iforce2d] below. The module in the video is rated for 5A at 50V maximum, but there are other sizes available. For those interested in graphs and numbers [lgyte] did a lot of characterization of these modules.

There was a time when importing goods from far away places was somewhat of an art. Finding suppliers, working out payment, shipping, and customs meant you had to know what you were doing. Today, you just surf the web, find what you want, pay with PayPal, and stuff shows up on your doorstep from all four corners of the globe.

There is one problem, though. We see a lot of cool stuff from China and some of it is excellent, especially for the price. Frankly, though, some of it is junk. It is hard to tell which is which. What’s more is even though in theory you might be able to return something, usually the freight charges make that impractical. So when you get a dud, you are likely to just eat it and chalk it up to experience. So the question is: how good (or bad) or these power supply modules?

The video is a good way to see what you are getting. Certainly, you get a better idea of the size of the module. However, what’s it look like electrically? The testing from [lgyte] is very comprehensive and not only includes graphs of key parameters but also IR photos of the circuit board to identify hot spots. There’s also a longer video about a similar module from [neutronstorm], below.

For the low price, the features of these supplies look good. You can set the supply to shut down when you exceed a voltage, current, or power limit. The DPS series modules have a slightly improved user interface compared to the DP series.

We’ve seen digital power supplies before (including some nicely packaged ones), of course. However, these are cheap, look good, and would be dead simple to use. A transformer, bridge rectifier, and filter capacitors on the input of one of these and you are set. For many applications, an old 18.5V laptop power brick would be a great way to feed one of these.

42 thoughts on “Absolute Power

  1. I bought one of these for a cheap bench supply. Piggy-backed it on a 48V old laptop supply, printed a quick enclosure with room for banana lead sockets and BAM – my new favorite adjustable PS. I think I spend about $20 for the module, and maybe a quarter for the filament required. Super happy, works great, no negatives that I can think of.

  2. “So when you get a dud, you are likely to just eat it and chalk it up to experience?” With stuff from China you pays your money and you takes your chances, and you do it heads up. Sometimes you win – sometimes you lose. That’s just the way the game is played now.

    1. Exactly, “you pay your money and take your chances”. If you want a warranty you will have to pay for it. However so far the folks in China seem to be hitting one home run after the other for me. Or maybe I am just lucky. Good old AliExpress, the only bad thing is the wait.

      1. My son and his partners design and build small-runs of bespoke industrial controls. They source from China because the cost is low, but they know what they get will either be fine, or need to reworked in-house before they can use it, or be garbage. If it’s the latter, that’s just the way it goes and they look elsewhere. But in the long run it is worth the risk to try China first.

  3. I picked up one of the 50V/5A under the DROC brand-name on Amazon and so far it’s worked perfectly. Much less voltage/current spike then my entry level linear bench power supply, much lighter/quieter, and much more compact/efficient. Though the membrane buttons will surely fail far sooner under regular use.

    Probably a bit more expensive on Amazon then other sources, but you can return it.

  4. there was one model with 0 – 120vdc at 10amp i was wanting so badly, but it is very hard to find, and mostly out of stock. On Ebay you have : ZXY-6020S DC-DC 1200W Constant Voltage & Current Regulated Power Supply … not to expensive … my friend have one and it works very well.

  5. “There was a time when importing goods from far away places was somewhat of an art. Finding suppliers, working out payment, shipping, and customs meant you had to know what you were doing. Today, you just surf the web, find what you want, pay with PayPal, and stuff shows up on your doorstep from all four corners of the globe.”

    My pony still hasn’t arrived. :-)

  6. I see an STM32 and clearly marked RX and TX pins. I wonder if the supply parameters can be controlled with a PC or microcontroller. If so, it could make this a nice multi-purpose device for charging a variety of battery chemistries or for use in automated equipment testing when it isn’t tasked with general purpose bench supply duty.

    1. That was exactly what I was wondering, driving small pumps, fans, heaters and coolers etc. It would add so much value to the unit because there are a lot of smaller scale applications where 750W is sufficient power.

    2. So, could anyone who has it try to get something from that serial port and get the info back to us? Thanks.
      I, as many others, would insta-buy it and put a serial bridge using an ESP8266.

  7. I’d be interested in seeing the noise on the output… if it’s quiet, it seems as if it could be quite valuable. If it’s a chopper without sufficient filtering it’s going to be a mess. I scanned through both videos and didn’t see any measurement/discussion of this, but the length of the videos make them unsuitable for a full 1x viewing pass. Anyone who’s watched the videos fully see any measurement/discussion of output noise? Anyone have a few of these and a scope to do noise measurements with?

    1. The noise on mine was around 100mV peak, but a simple L-C filter knocked it down to less than 1mV, which I am now very happy with. I can draw 28V at 2A with only 1mV of noise, which is impressive for a switching supply.

    2. from the linked review
      There is some noise in the output, below is the values I measured:
      Noise at 12V 1A (Vin 40V) is 10mV rms and 62mVpp
      Noise at 12V 5A (Vin 40V) is 14mV rms and 148mVpp
      Noise at 12V 14A (Vin 20V) is 65mV rms and 300mVpp
      Noise at 12V 14A (Vin 40V) is 30mV rms and 310mVpp
      Noise at 12V 14A (Vin 60V) is 65mV rms and 420mVpp
      Noise at 10V 10A constant current (Vin 40V) is 32mV rms and 255mVpp

  8. The graphic screen is unreadable. Low def windows style BS with fake shadows and imitation glare. There is an more efficent way to display info in a small area. The numbing matrix of zeros to read a value each time, no thanks. Leading zero suppression! It’s rather noisy of course.
    Things from China like fancy machined flashlights without switching regulated led drivers (resistors) and 4.4 volt directly connected chargers to 18650 lithium cells are the norm. I have found several lately.

  9. I have one of these. and so far it’s been great, but there’s two things I’m not a fan of:
    It’s not RoHS compliant, and the firmware does not take full advantage of the potential of the hardware. I’m pretty sure they could easily do MPPT charging if the firmware allowed,

  10. The “U-IN” label on the display is probably for “Unregulated-Input” (such as from an unregulated analog power supply with voltage inversely dependent on load current (like cheap unregulated wall-wart power supplies from the pre-microUSB powercube days).

    1. Ahh… I see that the IEEE and American standards voltage is described by “V” letter. So European AC mains would be U = 220V, which in US we still write our mains voltage as V = 110V (though E seems to have lost favor for voltage).

  11. I have one of the 5005 (50v 5A) model. I was impressed with the accuracy of the voltage and current reading it displays. I’m using it with a lithium battery pack as truly portable variable power source. There are some features that I wish it had:

    1. Shutdown the load when input voltage is below some certain threshold so that I don’t over discharge the lithium pack
    2. Counting how much capacity it’s been used or supplied.

    Maybe we need to reverse engineer and write a new firmware for these.

    1. I think you can build one with an Arduino putting out PWM signal that drives a TRIAC and a diode bridge connecting to a DC motor. Remember to have some opto coupler between your TRIAC and your Arduino.

      1. Hi Galane.
        Are you from a 110Vac county or from a 230Vac one?

        Using a TRIAC (to switch ac), put it through some rectum fire (Turd into DC) and use that to feed a DC motor can work. Add a moc3040 (or equivalent, but WITHOUT zero crossing detection) for isolation, or use a pre-built solid state relay (Again: Without zero crossing detection).
        You can not use a regular pwm output of a uC to contol this though.
        You will need phase angle controll, just as with a regular triac based light dimmer.

    2. I have one of these to control my 110VDC 350W Mini Mill motor.
      http://www.kbelectronics.com/kbsearch/descriptions/popup_kbic_120.htm

      I’ve read about them being used to run treadmill motors as well with the proper “Horsepower Resistor” installed. They can be run in the “voltage following” mode, which, if I remember correctly, will let you apply anywhere between 0V to 7V DC corresponding to 0% to 100% speed. They are also capable of using a potentiometer for speed control (how I use mine). It might be possible to simultaneously use voltage following and a potentiometer for speed control somehow.

      My 30 seconds of thinking about a solution would be to use an Arduino (for ease/speed of development) with an R-2R resistor ladder DAC to the voltage following input on the motor controller. Put a potentiometer on the Arduino for speed control. Add the ability to select PC/potentiometer as the speed input. Use the Arduino’s USB-to-serial interface to control the speed with a PC. Using a 5V Arduino would only give you 0V to 5V of output on the R-2R resistor ladder DAC. That’s roughly 75% of full scale assuming my previously stated 7V figure is correct. I don’t know your exact specs/requirements. It shouldn’t be that hard to bump up 5V to 7V with an opamp or simple transistor amplifier circuit.

      This entire solution isn’t necessarily ideal, but I think it could be implemented inexpensively. I would guess under $100 for a used motor controller, an Arduino, and the other miscellaneous bits you’d need.

  12. I’m looking for a small PSU for microcontrollers and small electronic projects.
    I think USB powered (there are 10W USB chargers) should be ok.
    I don’t know if the 10W limit would leave out retro-computing projects, because I don’t know how much power does a ZX spectrum or a C64 need, but being able to power such old small computers would be great!

    I would also like it to do 5V and 3,3V at the same time.
    Maybe have one of the outputs fixed and the other one variable.

    Has anybody seen something like that? If not, where should I look to do-it-myself?

    1. LM2596S buck converter
      http://www.aliexpress.com/item/32272430344/32272430344.html
      XL6009 boost converter
      http://www.aliexpress.com/item/32340934616/32340934616.html
      Those are two popular converters available on Aliexpress for under a US Dollar apiece. The only have a single variable output each. The buck converter is also available in constant current, with three potentiometers.
      For low power usage like microcontrollers, these are probably fine but would get extremely hot, if not fail, at the ‘rated’ specs.
      You could use the 5v from your USB supply direct for the 5v portion, and then the buck for the 3v. The usb could be obtained from a mains to usb adaptor, or a usb power bank for portability.
      There are also versions with LCD voltage and current readouts, but they cost more.

  13. If it has constant current down to short circuit conditions (i.e. 5A @ <0.01v) and it doesn't cut off into some "safety" mode then I'm sold.

    Have two PSUs at work and one at home. one out of three as soon as the current is reached trips a relay and beeps at me. No good for various battery charging.
    This device (with some modding) will make good replacements as the only useful PSUs for battery charging go to 2.5A max and need fan cooling for extended use (both of them).

    1. You bring up an important point and one I hadn’t considered yet. I researched it a little and if you follow the first link under the “Measurements” heading of [lgyte]’s link from the article, he mentions shorting the output and performing a voltage sweep. It looks like it doesn’t cut out at it’s rated limit of 15A. I do recall reading somewhere, though, it does have hard thermal cutoffs. Don’t hold me to that. I personally feel that any good bench supply should hit limits gracefully and not kick out.

    2. Watch out when using these for battery charging. I have two as bench supplies and found that I must be sure to disconnect the battery before killing bench power or the battery will feed back to the supply. I ended up putting together a special charging clip with a diode and adjust charge voltage accordingly.

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