12V power supply issues - Page 1
Forum section: electronics / beginners

author: ChrisGreece52
author_rank: Frequent Contributor
timestamp: April 08, 2021, 04:09:54 pm
content: Hello everyone!Good to have the blog back in operation!My question has to do with a power supply that I got from aliexpress as a cheap power supply for my 12V RGB LED strip.The power supply is noisy! When I have the power supply connected to the same breaker circuit like an old Dell monitor and a guitar amplifier weird things happen. (I would assume that in campus accommodation every room has a separate breaker)My main issue is with the monitor though! When I have the LED strip powered on red, green, or blue the monitor works.Things get weird when I power more than one of the colors. For example when I mix blue and red to get violet the screen functions at low brightness but the signal gets lost after a certain point.Another issue is that when I have the power supply connected and powered on (even with no load), I get a pretty significant humming noise out of my guitar amplifier.Is this just a noise issue? How are issues like that solved in power supplies and what causes them?

author: Jwillis
author_rank: Super Contributor
timestamp: April 08, 2021, 05:11:44 pm
content: Sounds like a typical cheap SMPS . They have minimal filtering because they are cheap. So they tend to be very noisy which propagates back into mains into other circuits . More noticeable on audio circuits . The more the load the noisier they get.

author: camila
author_rank: Contributor
timestamp: April 08, 2021, 06:32:06 pm
content: Better to update with the new SMPS. I believe there is the problem with your wiring also

author: ChrisGreece52
author_rank: Frequent Contributor
timestamp: April 08, 2021, 08:44:27 pm
content: Thank you for your replies!There is no question that the SMPS is cheap and noisy.The following question is more theoretical than practical though.Assuming my scenario with the cheap SMPS. What would need to be done in order to filter the switching harmonics?In addition, camila said about the wiring issue. What kind of problems could be caused by the wiring when having a noisy device connected?Thank you for your helpfull answers!

author: BrokenYugo
author_rank: Super Contributor
timestamp: April 09, 2021, 01:48:07 am
content: This the metal case industrial type supply, or the wall wart/inline type? Either way I'd be inclined to open it up (those welded plastic cases come right apart with light hammering) for science, see what's missing. These super cheap power supplies tend not to be very safe, if they can't be bothered to spend the money on the cheap parts for the rfi supression they likely cheaped out on the isolation in the transformer and whatnot.

author: radiolistener
author_rank: Super Contributor
timestamp: April 09, 2021, 02:43:32 am
content: Quote from: ChrisGreece52 on April 08, 2021, 08:44:27 pmwith cheap Chinese SMPS the better way is to put it into the garbage and buy a good one. Because attempt to fight with the noise will cost you much more than a new good PSU. Usually these cheap SMPS made from very cheap components and have very cheap design, which make fighting with noise very complicated and in most case almost impossible.In addition they are also unsafe.

author: tunk
author_rank: Super Contributor
timestamp: April 09, 2021, 09:56:27 am
content: Could you open it and post some photos?

author: HB9EVI
author_rank: Frequent Contributor
timestamp: April 09, 2021, 06:41:54 pm
content: sounds like the usual cheap garbage; it already happened to me that capacitors blew up when running such supplies at nominal load for a while.I'd recommend to go with e.g. Meanwell; I have several ones which do a fine job for a reasonable price

author: Jwillis
author_rank: Super Contributor
timestamp: April 11, 2021, 03:28:01 am
content: The medium range ones are not bad. They don't have near the filtering of a Meanwell but much better than the ultra cheap ones . I have a really cheap one and most of the components are not near adequate for the rated power . Even the out put inductor was replaced with jumpers. It works but I won't run it even 50% it's rated power. If someone wanted to they could replace the subpar components and add what was needed but by the time you do that you bought yourself a mid range supply. Just not worth the trouble unless you did it as a learning experience .The mid range ones I have never been pushed beyond 75% and don't exhibit any noticeable noise . The Mid range ones I have were probably 5 times the price as the ultra cheap one for the same rated power . Lesson learned . You get what you pay for regardless of it's origin.