Faulthy PSU? - Page 1
Forum section: electronics / beginners

author: anfang
author_rank: Regular Contributor
timestamp: January 02, 2017, 02:27:10 pm
content: Hi,I have purchased a brand new power-supply from a reputable seller here in the country. However, without load it produces an extremely annoying buzz when I select a specific voltage:https://sendvid.com/8g69q1v4Should I return this as faulty, or can it still be used ?

author: Zero999
author_rank: Super Contributor
timestamp: January 02, 2017, 02:41:32 pm
content: That sort of thing is common.How much did you pay for it?Have you looked at the output on an oscilloscope? Does it meet its ripple specification?

author: Kleinstein
author_rank: Super Contributor
timestamp: January 02, 2017, 02:45:31 pm
content: The sounds very much like a relay switching very fast. If this is done with a considerable load to the supply, it will relatively fast damage the relay contacts and maybe other parts. So this unit is broken and should be returned.Typically such supplies have a relays or two to switch between transformer taps, depending on the output voltage. Normally there is quite some hysteresis to prevent to fast switching. Here the hysteresis is missing or way to small - likely something like a missing resistor or solder joint / broken line.

author: anfang
author_rank: Regular Contributor
timestamp: January 02, 2017, 02:46:12 pm
content: edit: now confused as someone says its broken and other one perfectly fine.. hmmIt's this one for your info:http://www.velleman.eu/products/view/?country=be&lang=de&id=348800https://www.amazon.com/Velleman-PS1503SBU-Digital-Display-Backlight/dp/B000I3X7Z4I actually paid only $70 for it (66 euro's). Unfortunately I don't have an oscilloscope (yet), and not even the wires, so cannot test it under load.

author: Richard Head
author_rank: Frequent Contributor
timestamp: January 02, 2017, 02:51:10 pm
content: You would think that an extra 60 seconds spent on actually testing the unit after manufacture would be worthwhile for them. Apparently not.

author: Zero999
author_rank: Super Contributor
timestamp: January 02, 2017, 02:53:46 pm
content: Quote from: anfang on January 02, 2017, 02:46:12 pmBecause, in the absence of all the information, people make assumptions?I assumed it was a switched mode power supply, which often make noises when lightly loaded.QuoteGoing by that, it seems like it's a linear power supply, in which case it's quite likely Kleinstein is right: a relay is buzzing.

author: MK14
author_rank: Super Contributor
timestamp: January 02, 2017, 03:26:44 pm
content: Quote from: anfang on January 02, 2017, 02:27:10 pmYes, return it as faulty.I've seen the video, and definitely think it is faulty.If it is NOT faulty, then it is a VERY bad design, which does not have suitable hysteresis on the (presumably) relay switching voltages.

author: anfang
author_rank: Regular Contributor
timestamp: January 02, 2017, 03:48:37 pm
content: Quote from: Hero999 on January 02, 2017, 02:53:46 pmhi, I didn't mean any offense. due to lack of emotional communication through chat I might have stated my state of confusion in less than ideal way. Apologies if this was taken as offense.Thanks all! I'll return this supply.

author: Zero999
author_rank: Super Contributor
timestamp: January 03, 2017, 11:39:58 am
content: Quote from: anfang on January 02, 2017, 03:48:37 pmNo offence taken. I was just pointing out the fact that you'll often find people on online forums give differing responses. Sometimes it's because one person has overlooked something or has less experience than the others but it could also be that both answers are right.