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 new
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!
I 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.
I wonder what the conclusions would have been if the maker had not known the brands and the prices?
It 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.
Well 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, a
listed 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.
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