EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: exampler on February 07, 2021, 05:56:32 am
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Hi All,
Just been getting into electronics myself and invested in my first oscilloscope OWON SDS1102 and a cheap QW-MS3010D DC power supply. Naturally the first thing I did was test the output on the power supply and noticed a massive peak to peak (upwards of 2V peak to peak noise at 12V and at 5V), I am aware that switching power supplies are noisy but I figured there's no way that this type of deviation is a fit for purposes product?
I've attached some screenshots of my oscilloscope, here's what I think I understand interpreting the data:
- Peaks appear periodically at about 60kHz (I cannot find the switching frequency for this supply but I presume this is it).
- According to FFT though, the largest peaks are actually occurring at more like 1.35MHz (somewhat at odds with the above but ok). Worth noting that further checks showed a more consistent spread of noise.
- Getting massive voltage spikes on a DC power pack also which don't seem to show up as a periodic signal on FFT.
Points to note:
- Power Supply negative is not connected to ground but doing so produces no change. I was cautious here thanks to Dave.
- A DC battery with a similar probing and wiring setup (breadboard) produces no noise.
- A cheap 12V isolated DC supply for an external hard drive is producing peaks also, with massive spikes which are not really registering at all on the FFT. Images of readouts also given.
- I placed a 24VAC transformer of the input and measured. Perfect sine wave as expected.
Questions:
1. Based on my read of the data I was about to ask for a refund on the power supply... Is my DC power supply QW-MS3010D just a really bad switching power supply or is something afoot? What should I look into next based on attached information?
2. From the online videos I've seen people measuring DC never seem to have this type of issue, this goes to question 1, is there something else afoot and if not is this just because they are using better units?
3. My probing method wasn't best practice but with this level of noise I figured something else was afoot, how likely is my probing method the problem here?
4. With the level of peaking I'm seeing even in my DC power pack (images also attached). Should I be concerned about all my connected devices having to deal with constant spiking or is such just typically assumed to happen and catered for in the device design (Band filters, decoupling caps etc...)?
5. The ultimate question... as Dave would say... Have I come a gutser or has my DC supply?
Any thoughts would be appreciated. I'm sure its just a newbie question. :)