Are cheap Ebay switch-mode Power Supply Units any good? - Page 1
Forum section: electronics / general

author: loneoceans
author_rank: Contributor
timestamp: January 19, 2015, 07:59:44 pm
content: Hi,I was working on a project recently that required a 24V power supply. I found some really cheap ones on eBay selling for a few dollars shipped from China. This made me wonder - are they any good?I wanted to answer the question myself, so I did a comparison and teardown between a brand-name $85 retail made-in-Japan Cosel power supply vs. the cheap $8 Chinese one. Some of my friends also expressed interest in knowing what was inside these common power supplies, so I made a video. You can see it here. It's my 2nd teardown video so would appreciate comments on how I can improve:To summarize - yes there is a big difference between the internal and external construction. However, most surprisingly was that the output rippleseemsto be better for the Chinese power supply!However, there are loads of other things I didn't / cannot test, such as transient response, overload protection, safety, long-term reliability, precision, isolation, etc... and keep in mind that this is only at a single test point, and its performance will change with varying loads, so I am aware of the limitations of my test but I hope it serves as a quick example.So while the chinese supply does indeed work, I would still very much prefer to use a brand-name power supply.See higher resolution photos here:www.flickr.com/loneoceans/Finally, I recently did a teardown of anadjustable bench SMPSover here as well:https://www.eevblog.com/forum/reviews/teardown-review-tekpower-tp3010e-switching-bench-power-supply/which I think makes for an educational comparison, such as the differences in SMPS topology.What do you all think?By popular demand, review of a reasonably priced brand-name $18 Delta Supply-

author: dannyf
author_rank: Super Contributor
timestamp: January 19, 2015, 10:22:17 pm
content: Nice work. Keep it up.

author: mariush
author_rank: Super Contributor
timestamp: January 19, 2015, 11:36:04 pm
content: I kinda disagree with you when you say that Japanese psu has a much nicer "construction".Yes, one one hand it has better input filtering and uses more brand name parts and I like how they added ferrite beads but on the other hand ... it just seems over engineered.The pcb sucks (it's not quite high quality fr4, not much higher quality than the cheap 8$ psu pcb), they did some weird cutouts and had to resort to metal bars just to be able to connect the diodes and mosfet to case using some metal clips. For 2 amps of current, there was plenty of pcb space to go with some large traces.. or just make pcb with some thicker copper. Oh... and for so much money I would have expected removable/replaceable fuse.

author: loneoceans
author_rank: Contributor
timestamp: January 20, 2015, 12:59:23 am
content: Quote from: mariush on January 19, 2015, 11:36:04 pmYou make some interesting comments, so here are my thoughts.I don't actually think it's 'over-engineered' considering that I think it actually does have a 3 year warranty (IIRC), complies with a lot of standards including leakage current, conducted noise, harmonic attenuation, etc (too long to discuss in the video and I'm probably not qualified to discuss about them in much detail), along with proper documentation, high MTBF (489,000hrs) etc. It's expensive not only because of the materials, but also because of all the standards (EMC, Safety, etc) tests and certification they had to pay to go through for this, plus the extra parts they come as accessories such as mounting options. It is important to see that power supplies like these are also used in systems, where multiple of them might be used in a rack and paralleled or series-ed together. I assure you that there are a lot more power supplies out that with far far greater complexity, some even having an ARM core on board!I also assure you that the Cosel board is in fact, as far as I can tell, a good quality single sided fiberglass material, and significantly higher quality than the paperboard material used in all cheap supplies. These are commonly known as CEM-X (usually CEM1 - composite epoxy material), and the cheaper variants use some sort of paper fiber laminate with maybe one or two glass layers. They are also bad for plated through-hole boards, which is why they are commonly used in cheap single-sided PCBs only.It seems that with a bit more routing thought it might be possible for them to route a PCB with a 2A trace, but I'm quite sure they used a very similar or identical PCB for different voltage PSUs, which would need the higher current. For example, Cosel makes a 5V 50W version of the power supply in the same case, so if they used similar components, the bus bar would need to handle 10A. Also keep in mind that the high switching frequency reduces the effective cross-section of the conductor due to the skin effect, and it starts to get significant in the 100s of kHz. Thick copper PCB may not be cost effective as well, given that they do have a fair amount of SMD components on board, which would not only make the surface finish slightly poorer (in general depending on the PCB finish), but also be a bit of a waste since the rest of the board doesn't need to handle the high current.Hope this makes sense

author: loneoceans
author_rank: Contributor
timestamp: January 20, 2015, 07:14:02 pm
content: Quote from: mojo-chan on January 20, 2015, 11:02:27 amThat's right. The Cosel datasheets are very comprehensive as well so I encourage people to go check them out.Since I stilldoneed supplies like these, I'll be checking out a few Delta PSUs soon. While I did get the Cosel for about $20 on ebay, I probably won't have luck finding too many of these. The low-end Delta ones go for about $20 new, so I'll compare them to see how a brand-name low-cost one compares with these two. I'd expect something in the middle of the spectrum but I hope to find a few surprises inside

author: rickselectricalprojects
author_rank: Regular Contributor
timestamp: January 20, 2015, 11:40:06 pm
content: I mainly use three power supplies. One is a computer power supply and the other two are cheap ebay switching power supplies. I have a 12v 8.4a power supply and when i put a high load on it is actually quite stable unlike my computer psu. although it does get very warm (not burning but still not good for the caps) but my guess is that because the heatsinks are on the case. The second one is a 24v 15a 360w psu which i use to power my induction heater and its usually putting out 10 amps or more for a very long time (about 10-12 hours a day) and its very stable. i only payed $35 for it and for the price its a great deal. It has a built in fan which has a mind of its own because some times it swiches on and off every 5 seconds.In summary, there not perfect but they do the job and they are very good value for the price.(Also loved the video! Keep up the good work!)

author: nanofrog
author_rank: Super Contributor
timestamp: January 21, 2015, 08:53:22 am
content: FWIW, the brown PCB material is usually referred to asphenolic paper, and it is the cheapest stuff you can get.

author: coppice
author_rank: Super Contributor
timestamp: January 21, 2015, 09:23:44 am
content: Quote from: nanofrog on January 21, 2015, 08:53:22 amIts also known as SRBP (synthetic resin bonded paper) and FR2.

author: coppice
author_rank: Super Contributor
timestamp: January 21, 2015, 09:33:59 am
content: Quote from: loneoceans on January 20, 2015, 12:59:23 amThat's not quite right. You said CEM-X, so you are referring to the range of materials, and not just CEM1. CEM1 is not suitable for PTH, but in Japan CEM3 is widely used for 2 sided PTH boards. I am not clear why you don't see it much outside Japanese products. Its cheaper than FR4, and seems to be a fully satisfactory alternative.

author: nanofrog
author_rank: Super Contributor
timestamp: January 21, 2015, 09:48:43 am
content: Quote from: coppice on January 21, 2015, 09:23:44 amYep, and there's also FR1.

author: kripton2035
author_rank: Super Contributor
timestamp: January 21, 2015, 09:52:26 am
content: is there another supply between $8 and $85 that would be a good compromise ?

author: loneoceans
author_rank: Contributor
timestamp: January 21, 2015, 07:54:45 pm
content: Quote from: kripton2035 on January 21, 2015, 09:52:26 amYes I'm interested to find out as well so I'll be reviewing a mid-range $20 Delta unit or similar when I get my hands on them.Also, thanks to everyone for pointing out the different PCB / fiberglass materials! I think there is a bit of confusion for most people including myself, but my personal preference for sure is FR4

author: loneoceans
author_rank: Contributor
timestamp: February 01, 2015, 07:49:31 pm
content: Quote from: kripton2035 on January 21, 2015, 09:52:26 amThere sure is!I made a new video reviewing a$18 Delta power supply unit(yes the company that makes computer fans!). Delta is in fact one of the largest SMPS manufacturer on the planet! I chose this unit because it was one of the more affordable supplies listed on Mouser.Check it out here:After playing with it a bit more extensively, I think I'll be using more Delta supplies in the future. I haven't had a failure with any of my eBay power supplies yet, but I think I'll swap them out for Delta units for more confidence and known reliability

author: HighVoltage
author_rank: Super Contributor
timestamp: February 01, 2015, 11:07:08 pm
content: Thanks for the great review.I had a project last December and needed two 12V / 8A PSU's for two different projects and came across the low cost china one.One Project got a good quality LAMBDA PSU and the other got the China one installed.Both projects are working great at the customer now and I really could not detect any difference.I guess, only longevity will tell if it is worth to buy the low cost oneBut even then, we have to wonder how it is possible to sell such PSU for $8 with free shipping

author: Paul Moir
author_rank: Frequent Contributor
timestamp: February 02, 2015, 05:39:41 am
content: I've been surprised by how inexpensive the TDK-Lamda supplies are. A 2A DIN rail 24v is only $50 and an open frame one is something like $25. I only glanced inside one though and saw some Nippon Chemicons, and didn't look further.Thanks for the great videos loneoceans!

author: nanofrog
author_rank: Super Contributor
timestamp: February 02, 2015, 10:45:30 am
content: Quote from: loneoceans on February 01, 2015, 07:49:31 pmFWIW, I noticed there was a woven pattern on the non-copper side of the PCB in the Delta supply, so I'd venture to say it's actually made of FR4 rather than phenolic.Also looking at a datasheet, it's rated at 1M hrs MTBF, and caps at 10 years (50% duty cycle @ 40C), so should be rather reliable.Quote from: Paul Moir on February 02, 2015, 05:39:41 amAlso good supplies IMHO.

author: nowlan
author_rank: Frequent Contributor
timestamp: February 06, 2015, 12:53:54 pm
content: What about meanwell? surely inside your 20-85$ bracket.I was under the impression everyone was cloning theirs.

author: gocemk
author_rank: Regular Contributor
timestamp: February 06, 2015, 01:11:33 pm
content: Quote from: nowlan on February 06, 2015, 12:53:54 pmRecently we had a very unpleasant experience with 12V/5A Meanwell power supplies (DIN rail mount). Four of them died within 2 months (there were total 10). The only load they were driving was an IP camera which drew max 0.3A. Maybe it was dodgy batch or something......

author: N8AUM
author_rank: Regular Contributor
timestamp: February 25, 2015, 03:58:47 am
content: Thank you for the very informative comparison and the video.Can you grab a portable radio and get close to the supply to see how much garbage they radiate or just scope probe with ground wire connected to to probe tip ?I just purchased a cheap 30 amp for $20 usd for my radio, works fine but I need to add more CM filtering.

author: JohnnyBerg
author_rank: Frequent Contributor
timestamp: February 25, 2015, 08:30:45 am
content: Nice review!What I am missing is the part about PFC (Power Factor Correction).I would not expect to have the cheap Chinese PSU to have PFC, but the expensive should have!Also a bit disapointed that the expensive PSU does not have synchronous rectification.The expensive PSU has a 20x5mm fuse soldered on the board. Pff ..

author: PeterHouse
author_rank: Contributor
timestamp: February 25, 2015, 07:10:08 pm
content: The large 200v 680uF capacitor seems to be seriously underrated in terms of voltage. With Full wave rectification I would expect roughly 185v DC with 120 in and 370v DC with 240 in. At the same time, I find it hard to believe this is the case. Am I missing something?

author: dom0
author_rank: Super Contributor
timestamp: February 26, 2015, 11:38:24 am
content: Didn't watch the video, but if it has active PFC it might be a buck/boost PFC with, say, 150 V output voltage. But that would be rather unusual I think (since you can just use a boost PFC as well with a higher output voltage, saving parts)

author: JohnnyBerg
author_rank: Frequent Contributor
timestamp: February 26, 2015, 12:12:42 pm
content: Quote from: dom0 on February 26, 2015, 11:38:24 amNope, it has not.Generally speaking, most reviews I watch are often biased in the advantage of the more expensive or big name device. Chinese and cheap is mostly crap. Headers like "Are cheap Ebay switch-mode Power Supply Units any good?" or "Why UNI-T multimeters suck" are pretentious and not objective.I wonder what the conclusions would have been if the maker had not known the brands and the prices?IMHO the $80 PSU does not give value for money. No PFC, the soldered glass fuse, no synchronous rectification. I would expect those things in a $80 / 50Watt PSU.A more critical approach for the "big" brands would be appreciated!

author: dom0
author_rank: Super Contributor
timestamp: February 26, 2015, 12:41:22 pm
content: Then I suppose it only works at 110 V...

author: JohnnyBerg
author_rank: Frequent Contributor
timestamp: February 26, 2015, 02:52:08 pm
content: Quote from: mojo-chan on February 26, 2015, 02:20:54 pmAnd how is the $80 more durable the the $8 one? Better thermal design? The fancy ferrite bread around the legs of some components? Or is it th $0.001 20x5mm glass fuse that is soldered on the PCB, so it can't get loose in its holder?The video does not mention any of these things. Neither where there any measurements on temperature, or on their effectiveness.QuoteBoth's PSU will never pass a test to use them as a medical device. The isolation of both transformers isn't good enough. For medical devices you want separate chambers.Quotedoes that mean that it is any good? I don't think so.

author: dannyf
author_rank: Super Contributor
timestamp: February 26, 2015, 03:06:43 pm
content: QuoteIt would be hilarious and highly revealing, both about the projects being reviewed and the reviewers doing the reviews. That's why you will never see it done.Most of the product reviews you see are predictable: the expensive ones are always the better ones, the brand name ones are the better ones, ....Such reviews tell far more about the reviewers than the products being reviewed.It is in that way I find this particular review (of switching mode power supply) highly interesting and refreshing - it recognizes the shortcomings of the cheaper unit but tries to put such shortcomings in perspective vs. the more expensive unit. That kind of information is highly valuable to a potential user of those units.

author: JohnnyBerg
author_rank: Frequent Contributor
timestamp: February 26, 2015, 03:19:47 pm
content: Quote from: dannyf on February 26, 2015, 03:06:43 pmQuoteI agree.Except for the last 45 second of the video. The maker concludes that the more expensive unit will last much longer the the cheap one. No proof of that, of couse.

author: Ice-Tea
author_rank: Super Contributor
timestamp: February 26, 2015, 04:01:02 pm
content: Don't have audio here so can't do much with the video, but it would seem to me the Cosel has PFC, no? If not, it would seem there's a bit much magnetics on the board...EDIT: hmmm, checked the datasheet of the controller. No PFC. Odd... I suppose it's a flyback + buck for additional accuracy or some such then?

author: JohnnyBerg
author_rank: Frequent Contributor
timestamp: February 26, 2015, 04:11:34 pm
content: Quote from: Ice-Tea on February 26, 2015, 04:01:02 pmAs there is only 1 power mosfet, I asume it is a flyback converter.IMHO the real deal would be be a PFC boost converter to 380V line, and the some kind of half bridge.Would have love to see the more expensive PSU on 90V in with max output power. Currents though are highest then.

author: dom0
author_rank: Super Contributor
timestamp: February 26, 2015, 04:14:38 pm
content: The two inductors and black caps in the image on the lower left edge of board is likely the input filter. PCB spark gaps over the inductors suggest that, too. Also the splitted resistors across the two traces there indicate this.

author: Ice-Tea
author_rank: Super Contributor
timestamp: February 26, 2015, 04:46:28 pm
content: Quote from: JohnnyBerg on February 26, 2015, 04:11:34 pmI already modified my original post as I checked the controller and it seems only flyback controller. But thereare two power FETs, hence my suggestion it is perhaps a flyback + buck.

author: JohnnyBerg
author_rank: Frequent Contributor
timestamp: February 26, 2015, 04:48:32 pm
content: Quote from: mojo-chan on February 26, 2015, 04:24:16 pmWhy not?Labor in China is cheap, and the plants I visited all had large climate controlled test chambers for burn in.QuoteDoes the $80 PSU manufacturer release all the test data?You are making a lot of statements and assumptions, without any proof.Perhaps you should pay a visit to Shenzhen. It will broaden your horizonsnote: I am not saying that everything that comes from China is good. There is a lot of crap coming from there. What I am saying that every product should be reviewed on it merites, and unbiased.

author: JohnnyBerg
author_rank: Frequent Contributor
timestamp: February 26, 2015, 04:52:28 pm
content: Quote from: Ice-Tea on February 26, 2015, 04:46:28 pmI need new eyes, as I only see 1 mosfet? The other TO-220-isch device are 2 diodes with common cathode?

author: Ice-Tea
author_rank: Super Contributor
timestamp: February 26, 2015, 05:00:11 pm
content: Quote from: JohnnyBerg on February 26, 2015, 04:52:28 pmApparently. I just assumed

author: SeanB
author_rank: Super Contributor
timestamp: February 26, 2015, 06:14:35 pm
content: There is active PFC in there, the choke next to the mains capacitor and the little silver heatsinked device next to the white power resistors along with the 3 diodes say that. Then the main TO247 switching mosfet and the power transformer, then the output diode at the bottom. LC filter on the output is also a nice thing they added, reducing ripple a lot.

author: Ice-Tea
author_rank: Super Contributor
timestamp: February 26, 2015, 06:28:27 pm
content: That's what I thought at first, but the controller does not seem to be a PFC controller?

author: SeanB
author_rank: Super Contributor
timestamp: February 26, 2015, 07:34:14 pm
content: You do get single chip PFC regulators, and there must be somebody putting the PFC and controller into a single package somewhere for this use. 5 pin TO220 package has enough pins (barely) for this to fit, especially at low power levels where you will likely be seeing active PFC as a retrofit to a supply design.

author: Ice-Tea
author_rank: Super Contributor
timestamp: February 26, 2015, 08:38:04 pm
content: You can find the controller on the bottom. Does not seem to be PFC....

author: JohnnyBerg
author_rank: Frequent Contributor
timestamp: February 26, 2015, 08:46:49 pm
content: Controller is aM51995

author: loneoceans
author_rank: Contributor
timestamp: February 26, 2015, 11:43:36 pm
content: Wow I have no idea this thread became so popular!As mentioned, the goal for this video was simply motivated by the fact that I was needing a reliable 24V power supply for my projects, and I happened to score a $80 supply on ebay for really cheap 2nd hand, so I was very curious as to why it was so expensive, and the differences between the cheap ebay supplies which I have been using for some time. I don't claim to be an expert in PSU design, but I do have some background in electrical engineering, and thought I'd make a video since others might be interested.For the record, I also agree that $80 is really a bit too pricey for a power supply, and I have decided to use the more reasonable $20 Delta or TDK Lambda supplies for my projects (I made a follow up video for the Delta supply) because they represent much greater value. Also to try to set this straight, I think I'll do a second investigation on the many points you guys bring up, and hopefully we'll all learn something newQuote from: JohnnyBerg on February 26, 2015, 12:12:42 pmI think I did make it clear that the Cosel did seem to have poorer ripple, which really surprised me. I also never intended to think that the cheap supply was 'mostly crap'. However upon opening them up, many things already raised red flags, like cheap capacitors (which I know for a fact do fail), dodgy soldered components (did I mention, in another similar $8 eBay supply, I had to open it up and re-solder the adjust pot because the solder joint was loose?), and the fact that it lacks significantly fewer components, probably means that they had to cut some corners. I'm not saying that it will, but as a customer, who wants some confidence that this supply won't suddenly fail and bring my expensive project down with it, having confidence (and warranty) in a product does mean something.I would like to invite you to also check out the Delta power supply comparison, where you can see that the topology is very similar, but the Delta does everything better with more attention to detail, and most importantly, using known high quality components AND publishing detailed details on thermal and electrical performance. Also, the Cosel is a forward converter topology for sure, and I just checked the product guide overview and it says it does use a forward converter topology so that settles it.Quote from: dannyf on February 26, 2015, 03:06:43 pmWell in a field like this you almost always get what you pay for, especially in the PSU market where competition is quite fierce and prices are already pretty low. I eventually picked the Delta supply as my supply of choice, after concluding that the ebay supply was a bit too dodgy for my liking, and that the Cosel was far too expensive and with somehow poor ripple performance.Finally, the point on Power Factor Correction - just a quick note and I hope to spend some time to investigate more.I noticed the Cosel supply does have, in-fact, alisted PFC of 0.95(http://www.cosel.co.jp/en/products/pdf/SFE_PAA.pdf), which is very high, and it seems to me that there must be some sort of PFC going on at least (their 100W models and higher have a PFC of 0.99). If you look at the Ebay supply, the bridge rectifier is connected directly to the bus cap, so the PFC will be pretty low for that. If you look at the Delta or TDK Lambda $20ish supplies, they don't list the PFC, but simply say that they have PFC to "EN 61000-3-2 standards", but the EN 61000-3-2 standard does not apply to supplies <75W. In the Delta supply also connects the bridge rectifier directly to the bus cap and there is nothing in front of it besides the standard coke and x / y caps, and I would expect this to have a PFC of more around 0.55 to 0.75 depending if there is passive PFC or not.This leads me to suspect that the Cosel is indeed doing some sort of active power supply correction - it does look like this was the part which I missed out, and the supply might be doing it perhaps with the extra TO220 package (it's labeled as TR, so it seems to be some transistor) and the extra inductor/transformer and diodes I see on the board (maybe a buck boost or something). So I think I'll give this another go and see if I can answer the questions, and maybe trace the circuit.This will also help explain why the 200V bus cap is a 200V cap. Then it follows that Cosel can easily use the same supply layout, tweak the voltage references and output power to make this essentially the same for their other higher power PSU lines like the 75 or 100W ones, all using the same case and same PCB, and not worry about EN 61000-3-2 PFC standards.

author: jaxbird
author_rank: Frequent Contributor
timestamp: February 27, 2015, 08:11:36 am
content: Good work, you should consider building an electronic load for testing.Have a look at this simple but well designed project by Jay_Diddy_B using very common and cheap components:https://www.eevblog.com/forum/projects/dynamic-electronic-load-project/