Silencing a Chinese pre made PSU - Page 1
Forum section: electronics / rf-microwave

author: thickpeter
author_rank: Newbie
timestamp: November 10, 2018, 07:37:00 am
content: I keep seeing these power supply units from China. The pre made ones advertising 12 volts and 2 to 50 amps. they come pre made and inside an aluminium case.I also see a lot of people saying they are RF noisey. Is there a way to work out where that noise comes from and a way to cancel it out or to lower it or control it.why are they noisey and compared to other PSU are they any goodhttps://www.ebay.co.uk/p/12-Volt-DC-Power-Supply-Enclosed-Switch-Mode-12v-8-5a-100w/1812710234?iid=221233365175

author: ogden
author_rank: Super Contributor
timestamp: November 10, 2018, 09:38:33 am
content: Why most (but not all) low cost "made in China" supplies are noisy? - Because they are cost-optimized down to last possible component and EMC test.Silencing crap supply definitely is not worth it. You can try to add filters on input & output, but could be so that filters and RF-tight enclosure cost you more than genuine Meanwell or similar supply. When shopping for supply that is not noisy, make sure it has declaration of conformity (sample):https://www.meanwell.com/Upload/PDF/LPS-75/LPS-75-CE-DEC.PDF

author: dzseki
author_rank: Frequent Contributor
timestamp: November 10, 2018, 11:37:29 am
content: Switching components make RF noise. You'd need to dampen the ringing of them by means of adding snubbing networks and such. You'd need some some special information for such work, like leakage inductance of the transformer(s) etc. Sometimes even the physical arrangement of the parts contribute to the noise, It may be a fun project, but most likely not a profitable one, compared to the availablity/price of a decent PSU. Especially because this isn't even a special PSU.

author: German_EE
author_rank: Super Contributor
timestamp: November 10, 2018, 05:43:08 pm
content: 1) Grounded metal case with as few openings as possible. If you really need a fan vent then fit wire mesh over the hole2) Decent mains filter on the input with a solid ground connection.3) When wiring the filter to the PSU input wind a couple of turns through a ferrite ring.4) Case of the switched mode PSU electrically bonded to the outer metal case at multiple points.5) High current inductors in series with both the positive AND negative outputs.6) 100uF low ESR capacitors either side of each inductor from positive to negative forming a balanced Pi filter7) 100nF capacitors in parallel with each 100uF100nF capacitors across the output terminals and to chassis on each pole.9) Output cable has two turns through a ferrite ring.Yes, I am serious about RFI from Chinese power supplies

author: coppercone2
author_rank: Super Contributor
timestamp: November 10, 2018, 09:43:56 pm
content: an upgrade to your metal mesh would be to use a RF honeycomb structure. Basically a bunch of waveguides made of thin sheet metal that channel air flow.

author: cdev
author_rank: Super Contributor
timestamp: November 11, 2018, 02:05:55 am
content: This is a good resource on quieting RFI at 144 MHz for weak signal work from a real expert on the subject.http://www.sm5bsz.com/linuxdsp/hware/quietpc.htm

author: james_s
author_rank: Super Contributor
timestamp: November 11, 2018, 02:17:06 am
content: Why even bother when you can get something like this for less?https://www.ebay.co.uk/itm/Dell-PowerEdge-2800-Server-Power-Supply-0D3014-D3014-930Watts-Hot-Swap-PSU/332416221833There are loads of different models of similar PSUs. They typically produce 12V at 30-60A or more depending on the type. Additionally they have load sharing pins so you can connect multiples in parallel if you need even more power. Along with lots of other guys, I use server PSUs to power the chargers for my electric RC airplanes, they're rock solid reliable, well designed, and available for peanuts as they are orphaned when obsolete servers get decommissioned.

author: Wolfgang
author_rank: Super Contributor
timestamp: November 11, 2018, 10:26:36 pm
content: Quote from: cdev on November 11, 2018, 02:05:55 amIts incredible how much effort is necessary to get a switch PSU quiet. For the effort involved, you can probably buy a better engineered, more quiet switching PSU from a renowned manufacturer. I you need absolute quietness, you probably have to go for a linear PSU. These are only electrically quiet. The fan noise at your power levels is not

author: coppercone2
author_rank: Super Contributor
timestamp: November 12, 2018, 01:40:33 am
content: if your gonna go for that many watts from a linear supply you can put the motor else where and use a duct lol

author: Wolfgang
author_rank: Super Contributor
timestamp: November 12, 2018, 01:49:53 am
content: ... or water cooling.

author: CJay
author_rank: Super Contributor
timestamp: November 12, 2018, 09:56:41 am
content: I wondered about the noise level from the Meanwell supplies as I spotted one being used by Pete Juliano in a video, he reckons they are well behaved.

author: ogden
author_rank: Super Contributor
timestamp: November 12, 2018, 01:34:05 pm
content: Quote from: CJay on November 12, 2018, 09:56:41 amGenuine Meanwell supplies comply to EMC standards (sample), so they shall be OK in this regard. Also it shall be noted that there are no "silent" supplies, they all have some noise. Question is - how much noise is too much.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: November 12, 2018, 01:43:02 pm
content: The dirty secret of almost all PSUs is that they are typically tested at full load, with a resistive load. It is possible that they get noiser if teh load itself is noisy, or possibly if the load is different, though that's probably fairly rare.A good PSU will have plenty of margin in its EMC performance to deal with this.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 12, 2018, 01:55:23 pm
content: Quote from: mikeselectricstuff on November 12, 2018, 01:43:02 pmAnd the load is literally just that, a resistor sitting there. So it radiates little, and common mode noise contributes nothing to conducted emissions. So you may need more filtering if you actually do anything with the output.Small modules are a bigger offender here -- I recall a <= 5W module by XP Power that is quite noisy, despite claiming compliance. There's no EMI filter in it, as far as I know -- it's too small to have one anyway.As you go up in quality, you go up in EMI performance too. MeanWell medical grade modules are very nice.Tim

author: CJay
author_rank: Super Contributor
timestamp: November 12, 2018, 02:10:51 pm
content: Quote from: ogden on November 12, 2018, 01:34:05 pmDefinitely always some noise, I don't think it's possible to regulate voltage without creating noise (have seen 78xx regulators that drowned out FM broadcast) but as I say, the Meanwell ones are reputedly quite good.As Mike says, there are flaws in the testing methodology and I'm no expert on exploiting those but some just completely ignore the regulations and take a chance that nobody will bother checking.

author: cdev
author_rank: Super Contributor
timestamp: November 12, 2018, 02:30:50 pm
content: Making one's own dedicated AC line filter with toroids or other magnetics and beefier caps is a good idea if you really want to cut down RFI riding in or going out on a power lines. With DC lines and control cables you can use Leif Asbrink's approach, using feed through caps with integrated RFI filtering when its possible. Having wires bypassed when they exit the power supply or go through a case transition seems like the most logical straightforward approach. And of course, look a power supply over and see if they left out any parts that should be there, for cost reasons. If there are empty footprints for caps, it often may make sense to add the omitted part back in, taking care to use one thats appropriately rated.

author: thickpeter
author_rank: Newbie
timestamp: November 16, 2018, 06:40:30 am
content: cheers, for those tips.i can use them to rework a power supply unit i have to reduce the noise as far as i am reasonably practicable to do.some great ideas there and also i can use those points to judge a newer power supply i want to buy, so see how noisey it is as well

author: cdev
author_rank: Super Contributor
timestamp: November 16, 2018, 02:37:43 pm
content: A super cheap "rtlsdr" modified for 'direct sampling' mode can be super useful for finding RFI sources when paired with a probe of some kind.Using it you could improve your case and power supply decoupling. Get the cheapest one you can find, except the really small one. If you can afford one pre-modified for direct sampling that would be easiest. Their response in DS mode goes down into the MF range and below. Thats where a lot of the switching noise originates.Look at the probes used with high end equipment and try to make your own version. A tiny loop can work really well. Actually its best to have multiple probes for different frequencies. I just make them as needed from a bit of coax and a BNC or SMA connector.

author: ConKbot
author_rank: Super Contributor
timestamp: November 16, 2018, 04:54:55 pm
content: Quote from: CJay on November 12, 2018, 02:10:51 pmParalleled ones? I've seen ones paralleled with 0.1 ohm ballast resistors still manage to sing at ~70MHz with enough amplitude to make HC and ALS logic ICs with local decoupling glitch out pretty badly.

author: coppercone2
author_rank: Super Contributor
timestamp: November 17, 2018, 03:51:20 pm
content: has anyone compared meanwell and lambda supplies to see which ones are better?I have a hunch based on some older stuff if you are getting older equipment then lambda might be a better choice, but I don't know what the status is with recent equipment.All I found is this:https://www.eevblog.com/forum/projects/rs-pro-vs-mean-well-vs-tdk-lambda-embedded-switching-supplies/

author: mrf245
author_rank: Regular Contributor
timestamp: November 20, 2018, 05:41:01 am
content: I suggest you to buy a second-hand server power supply module, some one can output 12V with 30A or more, very good quality.There are lots of obscure manufacturer here, made switch PSU which are no EMC filter, or use very cheap component----just cheap.

author: DonRon
author_rank: Regular Contributor
timestamp: November 20, 2018, 08:29:27 pm
content: A german ham published a good description how to lower emission of those chinese switch psu. Even if it's in German language it might help you.www.dg0sa.de/snt.pdfRegards,Ronald

author: cdev
author_rank: Super Contributor
timestamp: November 21, 2018, 12:59:15 am
content: Although the PDF is too large for Google Translate the pictures tell most of the story, and it should be possible to work ones way through the PDF translating it page by page by hand. Definitely worthwhile downloading.

author: thickpeter
author_rank: Newbie
timestamp: November 22, 2018, 01:24:56 pm
content: cheers i will work my way through it at the weekend. looking for design ideas and practical aspects to power supply design

author: rhb
author_rank: Super Contributor
timestamp: November 22, 2018, 02:13:12 pm
content: A small loop of copper wire from ground ring to tip makes very good H field sensor. Wind spring coils at the ends of the loop. But don't use a probe for the winding forms.A probe with no ground lead makes a good E field sensor. I was quite amazed. But I noticed that the tips were replaceable and unscrewed the top. Did not pick up anything even next to a power cord.I tested both by holding them close to an instrument power cord. The 60 Hz E field was very easily detected but I could detect no H field.I use what in the US is called "hardware cloth". It's coarse metal screen that has been galvanized by dipping in molten zinc. I put 1/8" over the computer PSU fan openings ,etc. It's cheap and very effective.I had a huge problem with the LED 4 ft fluorescent lamp replacements, but a $3 eBay Chinese EMI filter cleaned that up beautifully. So I now keep a supply of those along with various ferrite clamp on and toroidal cores.I'm currently trying to track down an EMI source which is not in my work area unless it's the scope itself. So I'm about to make a large, multiturn loop antenna for my scope probe to help me with direction finding. Even with everything else unpowered I still had noise. Though I should have unplugged the UPS's in hindsight.

author: cdev
author_rank: Super Contributor
timestamp: November 22, 2018, 08:03:54 pm
content: That German article has a photo of a clamp on probe for use on wires, for evaluating (often common mode) signals riding on wires. I would love to get some larger magnetics of various kinds that could be used to make clamp on probes.I've seen clothespins used to make flexible, nice clamp on probes in various sizes.Have you see Leif Asbrink's (the author of Linrad) YouTube series on making probes for EMI detection? I think they are just entitled "Probes".rhb, by EMI filter, do you mean a line filter? If so I wouldn't mind knowing where you got them.I also have a lot of split bead ferrites. I put them on all the electronic equipment that I have, pretty much.I'm always buying more of them.They help a lot. it seems one almost can't have too many on things.

author: rhb
author_rank: Super Contributor
timestamp: November 22, 2018, 08:58:45 pm
content: I don't recall the seller, but I bought a bunch of these:https://www.ebay.com/itm/Solder-Lug-Terminal-6A-115-250VAC-Power-Line-EMI-Filter/182696788083I've swept them from 300 KHz to 3 GHz with an 8560A w/ TG. They are not as good at the low frequency end as a Corcom. But nothing to complain about for the price. And they have the advantage of being quite small which the Corcoms I have are not. I'd never have been able to fit any Corcom I have in the light fixture. Even these were a tight fit.I'm just recovering from reorganizing my work space, but at some point I plan to remove everything and shield the entire room, apply a 1/4" gypsum board overlay and repaint white instead of beige. So color me *very* serious about EMI.