Are cheap Ebay switch-mode Power Supply Units any good?

[loneoceans]

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 ripple seems to 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 an adjustable bench SMPS over 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?

[Update]

By popular demand, review of a reasonably priced brand-name $18 Delta Supply -

[dannyf]

Nice work. Keep it up.

[mariush]

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.

[loneoceans]

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.

You 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

[loneoceans]

Nice work, thanks for your effort. I'm in the market for a PSU so this came at just the right time.

I agree about the design, it's done that way for a reason. Japanese boards can seem a bit odd at first because they don't use the same design conventions as western boards, but you can be sure it meets all the standards and probably exceeds them by some margin. Cosel parts are used in a lot of test equipment and other sensitive devices. The higher ripple level will be a trade off to make other parameters better, and most importantly it will be reliable and well documented. If it says the transient response is X in the datasheet you can be sure that it really is. If the $8 model even gives you that data you had better check it for yourself, and check that it stays in spec over time, and that it doesn't vary between samples etc.

Cosel PSUs are used in arcade hardware sometimes, which is what I want one for. Harsh environment, full of dust and smoke, high ambient temperatures, high vibration levels and long hours of uninterrupted operation.

That's right. The Cosel datasheets are very comprehensive as well so I encourage people to go check them out.

Since I still do need 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

[rickselectricalprojects]

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!)

[nanofrog]

FWIW, the brown PCB material is usually referred to as phenolic paper, and it is the cheapest stuff you can get.

[coppice]

FWIW, the brown PCB material is usually referred to as phenolic paper, and it is the cheapest stuff you can get.

Its also known as SRBP (synthetic resin bonded paper) and FR2.

[coppice]

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.

That'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.

[nanofrog]

FWIW, the brown PCB material is usually referred to as phenolic paper, and it is the cheapest stuff you can get.

Its also known as SRBP (synthetic resin bonded paper) and FR2.

Yep, and there's also FR1.

[kripton2035]

is there another supply between $8 and $85 that would be a good compromise ?

[loneoceans]

is there another supply between $8 and $85 that would be a good compromise ?

Yes 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

[loneoceans]

is there another supply between $8 and $85 that would be a good compromise ?

There 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

[HighVoltage]

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 one

But even then, we have to wonder how it is possible to sell such PSU for $8 with free shipping

[Paul Moir]

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! 

[nanofrog]

Delta is in fact one of the largest SMPS manufacturer on the planet!

After playing with it a bit more extensively, I think I'll be using more Delta supplies in the future.

FWIW, 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.

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.

Also good supplies IMHO.

[nowlan]

What about meanwell? surely inside your 20-85$ bracket.
I was under the impression everyone was cloning theirs.

[gocemk]

What about meanwell? surely inside your 20-85$ bracket.
I was under the impression everyone was cloning theirs.

Recently 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......

[N8AUM]

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.
 

[JohnnyBerg]

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 ..

[PeterHouse]

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?

[dom0]

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)

[JohnnyBerg]

Didn't watch the video, but if it has active PFC it might be a buck/boost PFC with, say, 150 V output voltage.

Nope, 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!

[dom0]

Then I suppose it only works at 110 V...

[JohnnyBerg]

It's a robust, long life PSU that meets the datasheet specs for years of constant operation. It sacrifices complexity and features like PFC for durability.

And 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.

If you are building a medical device or some expensive lab equipment you probably care more about that than PFC and synchronous rectification.

Both'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.

Expensive lab equipment

does that mean that it is any good? I don't think so.