SMPS issue? - Page 1
Forum section: electronics / beginners

author: _ar_
author_rank: Contributor
timestamp: July 10, 2018, 04:28:14 pm
content: Hi,I have a Meanwell RT-50B SMPS which I have wired up a couple of days ago, correctly, to my best knowledge. However, I noticed something strange, but I'm a noob so what do I know: there's connectivity between the PSU's +12v, COM and +5v lines. Is this normal for these supplies? Checked an ATX v1.0 supply and there's no such thing. The wired up PSU also does not work.Thanks for your response!

author: _ar_
author_rank: Contributor
timestamp: July 10, 2018, 04:29:03 pm
content: BTW, I have checked all my wiring and there're no shorts.

author: X
author_rank: Regular Contributor
timestamp: July 10, 2018, 04:32:52 pm
content: What do you mean by "there's connectivity between the PSU's +12v, COM and 5v lines?" As in continuity (ie. zero resistance between these lines)?Most likely the PSU is setup like this at the output:0V ---- +5V ---- +12V

author: _ar_
author_rank: Contributor
timestamp: July 10, 2018, 04:41:56 pm
content: Yup, meant to write 'continuity', sorry for that. So yeah, theres continuity between the +12v and +5v terminals as well. But then it can happen and be perfectly normal, depends on the PSU's design, if I understand you right. Thanks for your answer. I need to do some more fault finding then.

author: X
author_rank: Regular Contributor
timestamp: July 10, 2018, 04:57:22 pm
content: You're saying continuity between 0V+12V, 0V+5V, and 5V+12V? Zero ohms between these rails doesn't sound right. Do you actually get any voltage out of them with a load across?What sort of multimeter do you have? I have encountered cheap Chinese ones that will beep if the continuity tester is connected to some circuits even though there's several hundred ohms in between the probes, or if there is some kind of arbitrary exotic circuit connected.

author: wraper
author_rank: Unknown
timestamp: July 10, 2018, 05:10:53 pm
content: Just disconnect the load and measure the voltage. Saying continuity is meaningless, what resistance there is particularly? There should be some dummy load inside the PSU.QuoteCheck the issues with your load, what it is to begin with?

author: _ar_
author_rank: Contributor
timestamp: July 10, 2018, 05:19:12 pm
content: No, I'm saying that my meter (a BM235) in beep continuity mode beeps continuously when I connect either of those 3 terminals on the PSU. The resistance is not 0 Ohm, I measure 79, 300 and 337 Ohms.AFAIK it needs no load to produce its output and I did not measure it (nor would I connect my load to it) because when I plug this in to my power strip there's a crackling/sizzling noise coming of from the power strip's switch and the led inside the switch seem to have died as well. Maybe it's not the wiring but the wires? ...

author: wraper
author_rank: Unknown
timestamp: July 10, 2018, 05:31:49 pm
content: Quote from: _ar_ on July 10, 2018, 05:19:12 pmThen why you didn't replace the faulty power strip?

author: wraper
author_rank: Unknown
timestamp: July 10, 2018, 05:36:52 pm
content: Didn't you have a thought it's not the bulb what died but switch is dead and there is no voltage in the sockets?

author: _ar_
author_rank: Contributor
timestamp: July 10, 2018, 05:49:13 pm
content: The power strip was working seconds before I tested the PSU. I just did not go on with testing the output because of the clearly audible crackling/sizzling sound (like when one fries an egg) coming from the direction of the switch/PSU connector. ... BTW, just checked, the power strip is still working and the led is working as well. It's just it gave off that sound and the LED went dark when the PSU was plugged in.

author: _ar_
author_rank: Contributor
timestamp: July 10, 2018, 06:01:34 pm
content: To give a little bit more context, I'm replacing the internals of an old Amiga power supply with the Meanwell. I kept all the old/original AC and output side cables/connectors. The PSU arrived with the PCB broken into two halves, so I do not know what issues it originally had. That's why I'm thinking maybe there's a problem with the old UK AC connector which I'm using with a known good EU converter? Just shooting in the dark here...

author: wraper
author_rank: Unknown
timestamp: July 10, 2018, 06:03:52 pm
content: Quote from: _ar_ on July 10, 2018, 05:49:13 pmThat means there is a very very bad contact in the switch. Good good enough to provide a tiny current for the neon bulb. But not to any real load like PSU. Multimeter also does not add any significant load, so you may measure the voltage. Plug in any appliance you have into the power strip and see yourself that it's dead.

author: _ar_
author_rank: Contributor
timestamp: July 10, 2018, 06:11:35 pm
content: Did, it could power a hair dryer just fine. Anyway, I'm thinking wiring up only the AC side and see if those noises go away. If not maybe get rid of the old AC cable and try a new one? Replace the fuse in the UK plug maybe. Also check the output on the PSU terminals without the output wires screwed in.

author: _ar_
author_rank: Contributor
timestamp: July 10, 2018, 08:16:49 pm
content: Wired up only the AC side. The power strip light is ok now and the PSU gives out a high pitch noise. Will rebuild the whole thing step by step and see how it goes. Thanks for everyone for the input!

author: _ar_
author_rank: Contributor
timestamp: July 12, 2018, 03:39:47 am
content: Put the whole thing back together one by one and now it's working perfectly. No crackling noises and the output is spot on. The only thing I done differently is that the output wires are not tucked under and not touching the Meanwell's shield. Anyway, thanks again guys for your inputs/ideas!