REVIEW Cheap chinese PSU - 24v 5A

OK so this is a crowd funded review

I guess the point of this is to get some feedback on the quality (or lack thereof) of the PSU from our electronics Guru's on the forum.


I've added a YouTube video at the end of this post which prompted me to choose this PSU. The guy runs a couple of electrical tests on a (very !!) similar PSU and uses a scope etc, stuff which is way beyond my 'scope'

You guys may or may not agree with his opinions, that's what the point of this post is I guess - to confirm or deny his opinions, to suggest whether his review scales to suit the more powerful version I've bought, and to provide a guide for others who may or may not be considering buying one of these cheap PSU's.


THIS IS THE ACTUAL EBAY LISTING FOR THIS PSU. The price was AU $17.89 delivered, by standard post. Delivery took a couple of weeks.


I'm going to start with some images, the images of my new supercheap 24v 5A PSU.
This PSU is intended to run the Class D Amp in my AIO PC CASE build.










Given that I know nothing, the images of what I've bought, added to the youtube video below, are all I can offer.
All input gratefully accepted. I'm happy to examine the unit to provide any details which aren't clearly visible in the pix.

 

Every time I buy a cheap SMPS, I open it up and pull out the board. I have received some absolute shockers that would have at least blown up, or worst case made the case live.

Main quality issue I've seen is through-hole components not pushed down flush on the board (i.e several cm up in the air) and then either bending and contacting other parts, or being affected by shock/vibration and tearing the copper off the underside of the board. Sometimes I'll get out the soldering iron and reseat some of the heavier/taller components.

That board looks near immaculate compare to some of the disasters I've seen.

 

Yeah I found nothing too obviously scary. Keep in mind though that I am a rank amateur at this stuff and probably should be getting a sparky to wire it up

The plates which hold the black things to the body (in the images above, a single black thing on the far side and a pair on the left) came uncomfortably close to the pins which belonged to them. I'm sorry, I don't know what they are, they are just 'black things' but they are clearly intending to use the body as a heatsink. I was able, when I put the board back into the case, to put some slight bends in the pins to give a tiny bit of extra clearance, whilst still getting the whole thing solidly against the body for heat dissipation. I've probably improved clearance from <1mm to >3mm, I feel more comfortable with that,

Once I'd reassembled it, it was time to add a power cable. I've simply split the inner wires from each cable into two, soldered them to created a Y shape, covered most of the exposed wire with heatshrink, and inserted them into their appropriate places. After tightening them solidly and checking carefully that nothing was loose and every wire had proper clearance from the other wires, I added a bunch of Sikaflex 227 for some extra insulation over the bitey bits.

I installed a standard low profile side entry plug on the other end of the cable.

Can't be too careful, can I?



The connections have a plastic cover, but although I am sure it would help a bit, I like to make sure with 240v power that its as safe as I can make it, hence the Sika for some added protection.



I only have a cheap Jaycar multimeter, but I thought I'd test the output voltage (no load) with it. The 2 left connectors are labeled as -v and the 2 right connectors are labelled as +v. With my cheap multimeter, any combination of -v and +v came up as 24.5v. Hopefully that's a good sign The body is not live, also a good thing

Time for a grandpa nap now, but I'll attempt hooking the little class D amp up to it later on and see if anything explodes.

 

Personally I also like adding a link wire between mains earth and DC negative. This will help trip your home's RCD if there is an isolation fault that puts high voltages onto the DC rail. It might also help with noise suppression on the amplifier too.

That said, there's always the possibility of an audio ground loop so your mileage may vary.

 

I'll do that. Safety is always a good thing

So just a simple bridge between the green wire and the -v on the output?

 

Yep that's it. I usually just use a small length of wire with fork terminals at both ends, and slip one under the green terminal.

Edit: If you have a 3D printer, it's not too hard to design a rectangular cap that slides over the end of the PSU and protects all of the terminals. You can even mount IEC mains sockets into the cap. I designed my own but there is a good public example here: https://www.thingiverse.com/thing:753888

 

I don't have a 3D printer unfortunately. I haven't added the extra wire as you've suggested just yet, but I have wired the amp up to it. Got some bizarre behaviour which happens to be identical to the problem I was having with a 12v 3A brick I initially tried running the amp from. I plan on remaking my source cable, as a first port of call, and then I'll probably have to look at a problem with the amp, or even replace the amp since I don't have the skillz to find a fault in it. These little class D amps are a dime a dozen, its just annoying.

 

Nasty, saturating the drivers with a square wave. They will overhead and die in no time.

I wouldn't think noise or a ground loop would do that.

 

Any thoughts as to what might?

Also, like the pix above, any idea what the white plug is officially called? I'd like to google something like '3.5" stereo jack to *whatever that white plug is called* cable' is called, but nothing I can think of comes up with an answer.

I might have to wander up to Jaycar with it and see if I can buy individual bits to suit. I'd prefer a cleaner bodgy than the one I'm using, where the metal sheathing from the 3.5" becomes one of the wires to connect with what I hope should be the speaker common on the white plug. I'm assuming the sheathing is the speaker common??

 

it's poorly designed, built poorly, using cheap crap components, and they even save more cents by exclude anything that's not 100% essential. I wouldn't trust it.

going from the pics, so I may have missed something...
- no thermal protection
- no polyfuse
- non-replaceable glass fuse (not rated for 240v), should be a ceramic fuse, and ideally replaceable.
- bridge rectifier replaced with 4 diodes
- no filter caps on output (missing spaces for them) - could be your source of noise
- lack of safety clearance between HV and LV sides
- can't see the ratings on the electros, but they're probably not rated for proper temperature range (so they'll dry out and die 3 seconds outside of warranty, if not much before).

 

Cool, thanks for the input. Is there anything I can do to redeem it? Replace a few of the components for something better? Or is it a lost cause in your opinion?

Obviously I can't do a lot about the basic design, but I'm sure I could do things like replace the glass fuse with a ceramic one, stuff like that?

The noise was also there on the 12v 3A power brick I initially tested the amp with, so I am assuming at least that issue is either my dodgy source cable or a fault with the amp.

Lolz @ warranty, $17.89 posted, sourced from China but posted from Australia, it arrived too quickly to come from China.

I am tempted to do as I've done before and use a car amp powered by a computer PSU, but the tiny amp appeals to me and computer PSU's don't supply the 24v the little class D amp needs for maximum ear pain. It's all part of the journey

 

Lost cause, you couldn't fix it. and certainly not even for close for the expense of a good one outright.

~double what you paid, and this one won't kill you or burn down your house.
https://www.jaycar.com.au/mean-well-72w-12v-6a-power-supply/p/MP3287
and jaycar isn't even cheap.

and fyi, you're obviously not a sparky so you shouldn't be playing with 240 wiring at all.
you can buy nice plug packs all properly insulated and no 240 wiring to do, for similar $.


as for your noise, I didn't listen to the video before, I was expecting a nice 50hz hum, that is not 50hz hum. that is something wrong with the input stage (or whatever you are sending it).
don't run your speaker like that, as already covered, that'll quickly burn out the voice coil on the speaker.

 

Yeah, its more the 'project' part of it that would make me consider fixing it, but I know my limits. If it was just a matter of desoldering and replacing a fuse, or replacing a couple of caps or diodes, I'd have a go, but more than that I probably wouldn't attempt.

I've had some limited training in 240v, but I'm not kidding myself about how much I know.

I used to do repairs and maintenance on an aboriginal community and the local council sparky taught me enough to safely replace fan controllers, fans, light switches, light battens, power points and the like, but as he often pointed out to me and I've always been very conscious of.. a little knowledge can be far more dangerous than none at all.

I will at some point replace this PSU based on your advice, but it's the wrong time of the month for me so that will have to wait.

In the meantime it will have to do, just to diagnose the issue I'm having with that obvious problem in the video.. or I might even just go back to the 12v power brick since that would be safer I guess. In the long term I want to use 24v 5A though, for extra grunt, and within the quoted specs for the amp.

I will try to do something more pro with my source lead as a first port of call, if it's not that then it has to be an issue with the amp.

Since those amps are cheap as chips, I have no problem ordering another.. or even a couple maybe, just in case. In fact, although its a chinese amp it arrived days after I bought it.. perversely it was posted from Mordialliac, which is one suburb over from where I live!! If its the amp, I'll just contact the ebay seller and arrange to go to his house and swap it for another

I could buy a better amp of course, but the incredibly compact size of those cheap little class D amps appeals to me. It's only for the speakers, which I rarely use anyway, which I'm sourcing from the onboard sound on my X470 Taichi.

Source is good enough quality, no need for any audiophile stuff there as I only use the speakers on the rare occasions Eva wants to listen to the same video or music I am listening to. I have a half decent Xonar Essence STX sound card and Sennheiser headphones which I use most of the time.

 

Idiot that I am, I just realised I don't have to remake my source cable to see if its the issue. All I have to do is remove it and see if the sound continues with no source

I did. It does.

I've emailed the ebay seller I bought the amp from, who conveniently according to the address on the package it arrived in lives about 2km away Hopefully I can simply go to their house and exchange the old for new. Awaiting a response now.

 

I'm pretty sure I saw a couple bits of smoke in the video...

I've seen similar of that PSU brought to me at work. In both cases the diodes used on bridge rectifier had blown OC, and was outputting undervoltage/partial output.

 

I find this all the time in many things not just cheap e-bay gear

I would also be adding C21 & C22

 

meanwell make some great SMPS.
We use quite a few of their 24VDC versions though these days reduced to 1.1A, 2.5A & 6.5A

 

You shouldnt be playing with 220v unless you know what you are doing.

 

I've given up on this PSU for one basic but important reason. When inactive, it transmits a low hum to the speakers. I've substituted it with a 12v 2A wall wart, so far less power, but it still provides a more than satisfactory amount of grunt from the little 3116 D2 amp. Removing the PSU removed the hum, so I am pretty confident that the amp is the cause. I've binned it now.

 

Or a MOV/TVS diode

The input pi filter is incomplete (should have a second X cap). I also love the do-nothing voltage selector switch.