Is this normal? PSU unsteady



  • Today I recieved a brand new chinese 24v power supply.
    The first thing I did was to test the output voltage, but it fluctuates a bit.

    Is this normal? or should I ask for another one?

    https://www.youtube.com/watch?v=Zai0dftsl40&feature=youtu.be

    Thanks in advance.
    Martin



  • Is it fair to test Chinese stuff with other Chinese stuff? 😄 I'd run it under a load and see what you get, even if just a light load.



  • I'm currently thinking what to connect. I've some 24v fans but they won't draw much power.



  • Shouldn't take much. Just something to give it a load.



  • Indeed my good sir. I connected the Duet and in stand by mode the readings are stable.

    Thank you for the help.
    Case closed 😛



  • Don't be fooled by the measure: I think your multi-meter have a 0.2V resolution as many, and the voltage is just at the edge, so very small variations make the voltmeter switch +-0.2V… I don't think the power supply really change that much.



  • @fma:

    Don't be fooled by the measure: I think your multi-meter have a 0.2V resolution as many, and the voltage is just at the edge, so very small variations make the voltmeter switch +-0.2V… I don't think the power supply really change that much.

    I'm pretty sure that is stable with the load, it didn't fluctuate once. But yes, the resolution for measuring 24v is of ".0".
    So as soon as I arrive home, I will dial it down to 19 volts and use the 20v range. With that one, the resolution is of ".00".

    Either way, lets say the power supply didn't change much as you said.
    Will this be an issue? Is this a symptom of a bad power supply or it's normal?



  • The best way to check would be to use an oscilloscope. There is always a ripple, which should be given by the manufacturer. Usually, this ripple is fast, and you don't see it with a multimeter. As long as the period of the ripple is much higher than the thermal constant of heaters, I think it is not a problem.



  • Hello Frédéric, thanks for the explanation, but I don't have access to such tool.
    It was dialed down to 19.8v and it changes from 19.83v to 19.84 at much slower rates. It doesn't seems like a problem, but well I'm no expert here.

    https://www.youtube.com/watch?v=RD8l8qHkiro&feature=youtu.be

    Thanks for the help.



  • Again, you may be at 19.835V, so your multimeter oscillate between 19.83V and 19.84V. Also keep in mind that real voltage is maybe 20.12V, 18.83V, 19.52V or anything else, as your multimeter is probably not calibrated.


  • administrators

    Martin, It looks fine. If you have your printer setup so you can load it with the full heaters on (or an equivalent load) then check. You may see a small amount of voltage sag between full power and almost no load but that is not a generally a problem.



  • I know it's not a Meanwell PSU so I won't expect the same performance.
    Tested it under motor load and the oscilation is practically none. Yes…. with this cheap multimeter. It's not the best way but I can't afford an oscilloscope or a more professional calibrated multimeter.

    My concern was if I had to ask for a refund/return or to confirm the transaction.
    I've already did the last one.

    Thank you all for the help and have a nice weekend.
    I will for sure stay at home nerding with the CoreXY build 😛


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