Multiple SMPS with same fault (clicking caps) - design flaw or deterioration? - Page 1
Forum section: electronics / repair

author: dalius98
author_rank: Newbie
timestamp: July 25, 2021, 03:09:26 pm
content: About 4 years ago, I've received ~15 XPPower JPS350PS24 power supplies from a closing down shop. I've used one for a project and paid no mind to the clicking noise - it's been working fine ever since. Recently, it was brought to my attention that clicking noise might signal a power supply going "bad" and I started checking the other 14 I had in storage - all of them have the same clicking/arcing sound...The sound comes from the (LC?) filter right after the rectifier. I know it's not the nearby relay, as I hear it click upon startup and the noise is gone with the two (red) capacitors removed. I do not have an ESR meter, so I tried replacing them with unused (though similarly aged) (blue) capacitors of equal value - the clicking noise came back. I've heard some supplies might click when unloaded, but a 60W load did not alter the clicking at all. The output voltage is stable, with and without the load.If the cause is old capacitors, could it happen to all PSUs this equally? Could it be a design flaw (though the manufacturer seems at least of decent quality - based in Taiwan, offering PSUs to medical industry...)? Could it be caused by improperly configured (unused) remote sense, remote on/off or whatever else technology? Could it be no fault at all?I'm keen on using these in a few projects, so I'll buy some new capacitors to test, and will try to reverse engineer it a bit more, but I am hoping someone could tell what the issue is just from these symptoms...

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 25, 2021, 03:13:58 pm
content: Clicking how, like, erratically? Periodically or what?Tim

author: dalius98
author_rank: Newbie
timestamp: July 25, 2021, 03:36:10 pm
content: Now that I think about it, "clicking" might not accurately describe the noise... It's consistent, close to mains frequency buzzing. This probably completely changes my question, sorryEdit: wow, "buzzing" returns so much more results, I wonder why I was so fixated on the clicking thing...Edit no. 2: I take that back. While the one PSU that was used for 4 years has this frequent buzzing, the others in storage have a much lower frequency upon startup, much closer to clicking. I've attached a second attachment with the clicking issue. You can hear me turning on the power, relay click, and something struggling to startIt was clicking for much longer upon first start, but by the time I got out the recorder I got this result... I'd guess the one that's constantly being used has the capacitors at a higher temperature, and skipping the startup clicking?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 25, 2021, 04:11:32 pm
content: The buzzing is probably due to electrostriction of the dielectric, i.e. the capacitor is physically expanding (straining) due to applied voltage. I'm not sure why it's impulsive (hence the maybe perceptibly rapid-fire-pulses sound), maybe something to do with the dielectric popping into position due to voids in the construction, or something about the material.There's also some noise due to the magnetics (the analogous magnetostriction effect), usually moreso than the capacitors, but apparently not so much in this case. Give or take if the PFC even behaves with those caps removed (eh, it probably still does, there's still the gray caps further upstream of the rectifier).The startup sound is less frequent, sounds like it's having a couple of startup attempts before kicking on fully. This is normal behavior, or if not intended then at least not bad behavior. Supplies are usually made with a "hiccup" characteristic, implemented by powering it by itself -- if the output is overloaded (which is the case, momentarily, during startup as the big capacitors all charge up), the controller doesn't get enough power to keep running so it goes into shutdown, and waits for a new cycle to begin (timed by the large value bleeder resistor from the mains DC bus).The sound may also change with a load applied versus idling. If it's just idling, I'd expect the sound to be more of a variable whine, due to the output being switched on only every once in a while to keep its voltage up. The sound being from magnetics (or a few likely ceramic caps in the path). But eh, apparently you have noisy film caps this time!Tim

author: dalius98
author_rank: Newbie
timestamp: July 25, 2021, 06:36:03 pm
content: Thank you T3sl4co1l for your valuable input.I've confirmed that the characteristic of the buzzing changes depending on the load. Do you think it is caused by the capacitors being low quality or by the design of the PFC circuitry itself?Or is it likely for these capacitors to deteriorate to the point of buzzing in all power supplies at roughly the same time? I'd lean towards them being low quality and buzzing from the start, but then again, even replacement caps (perhaps of questionable quality) made the sound...Since I'd prefer the power supply to be quiet I'll see if my digital wattmeter can measure power factor (and if not I'll have to do it manually) and see how much of an impact removing the offending capacitors makes. At the very least I now know the PSU is not on the point of exploding.

author: Per Hansson
author_rank: Unknown
timestamp: July 25, 2021, 07:44:43 pm
content: Are you sure it is not the common mode choke between the capacitors that makes the noise?(Yes, I know you said removing the capacitors removes the noise but it also drastically changes the circuit).

author: dalius98
author_rank: Newbie
timestamp: July 25, 2021, 08:32:43 pm
content: can't tell if it's 100% the capacitors fault... I am basing it on the fact that removing them "removed" the noise as well, and also when I soldered the blue replacement capacitors I did so on the back of the PCB - thus providing greater sound separation between caps and the rest of the components. At the time I was convinced it was the caps, but I did it by ear (no stethoscope) so I can't be 100% sure. And based on the fact I misremembered the tone/frequency of the noise, I can't be even 50% sure when it comes to my ears...I'll see if I have a replacement inductor and experiment a bit tomorrow. Anyways, it's not vibration noise, as holding down either of the components (with a plastic pick of course) did not improve the situation.Edit: It's definitely the two red film capacitors making the noise.Edit 2: So after the newest finding, I think I should add that I found the source of noise by soldering the caps on the back side of the PCB and covering one or the other side to see where the sound is loudest. Performed at idle.

author: dalius98
author_rank: Newbie
timestamp: July 27, 2021, 06:20:57 pm
content: So I did a few brute force experiments, measuring current and power factor with a cheap power meter. I knew it is not accurate, but I expected at least to be able to use the data for comparison... But with results like these, I'm not so sure anymore... The distorted waweform might be too much for this poor meter to handle.I tried a stock power supply, and a supply with the two "offending" capacitors removed - here's the results:Stock|Caps Removed|Current, ACos F.|Current, ACos F.|0.1340.35|0.070.6|Idle-0.5|-0.85|Motor0.50.87|0.440.71|LEDs @ 100%0.250.4|0.170.71|LEDs @ ~50%What I've observed:With capacitors removed and no load, power supply is dead silent and wastes less power.But with a bigger load, the nearby choke starts buzzing and heats up (not the case with the caps present). I guess it's to be expected when removing half of the filterAdditionally, it seems like the stock PFC does not play well with PWM dimmed LEDs. Could this + bad idle performance signal at PFC circuitry malfunction?Unless I'll get told otherwise, the next step will be replacing caps with known good (new) ones, but I don't expect film caps simply went bad, unless they were poor quality from the start...

author: Mario87
author_rank: Frequent Contributor
timestamp: July 28, 2021, 07:18:23 am
content: 98-99% sure it's to do with the switching frequency of the power supply more than than anything, better components may reduce it, but won't eliminate it. If you google "coil whine" you will hear lots of people complain about this. Even a teardown video of the PlayStation 5 PSU to find the "coil whine" and it ended up being a capacitor similar to yours.Essentially a non-issue. A mix of component quality (some may be made better than others, even from the same batch) and the design itself. The video of the PlayStation 5 teardown and search for "coil whine" below....