Cheap 30V/10A Switchmode Bench PSU - Page 1
Forum section: electronics / testgear

author: jaxbird
author_rank: Frequent Contributor
timestamp: June 21, 2019, 07:28:11 pm
content: I think it's worth the $40-$50 including shipping despite the noise issues, agree or disagree?

author: nctnico
author_rank: Super Contributor
timestamp: June 21, 2019, 08:39:06 pm
content: Disagree. I have this PSU since a couple of years but never used it. It probably won't work up to 300W (or at least have a serious amount of ripple). There is a long thread about the 150W version.https://www.eevblog.com/forum/testgear/cheap-variable-switching-power-supply/I'm using the 150W version to power non-critical loads. The 300W one I have still needs the changes to improve safety and reduce the output noise.

author: ArthurDent
author_rank: Super Contributor
timestamp: June 22, 2019, 05:18:18 pm
content: I have one of these 30V/10A supplies and for the money it is a pretty good deal. I do have some high end HP and GW Instek lab grade supplies but this is a simple cheap supply that is at least a couple of steps up from a modified salvaged supply out of a PC.A couple of minor problems I found is that I use some test leads that have double and triple banana plugs and the banana jacks on the supply seemed to be almost a random spacing and I had to remove them and 'move' the holes so my standard plugs would work. You can see the moved holes in the photo below. If you use single plugs this isn't a problem. The second problem is that the output voltage seems to drift a few tenths if the supply has been left on for some time. This generally isn't a big problem but I find it annoying. I may be spoiled by the really good supplies drifting a couple of millivolts max as they warm up.

author: jaxbird
author_rank: Frequent Contributor
timestamp: July 03, 2019, 11:22:57 pm
content: Quote from: nctnico on June 21, 2019, 08:39:06 pmI had it running with ~240W load for around 10 mins during my review without detecting any issues. I am confident will supply the full 300W load continuously without any issues.However this is cheap Chinese electronics and quality control is not a thing, so one person might have a good experience while someone else will have a bad experience.

author: nctnico
author_rank: Super Contributor
timestamp: July 04, 2019, 11:42:58 pm
content: Quote from: jaxbird on July 03, 2019, 11:22:57 pmLook carefully at the output voltage. The unit with half the power rating already showed 100Hz in the output under heavy loads.

author: jaxbird
author_rank: Frequent Contributor
timestamp: July 06, 2019, 11:07:24 am
content: QuoteNot sure I understand, I had it running at 32V and 7.5A output into a large resistive load with a multimeter attached to confirm the output voltage.It's in the video if you want to see the details.

author: jaxbird
author_rank: Frequent Contributor
timestamp: July 06, 2019, 11:38:00 am
content: Quote from: ArthurDent on June 22, 2019, 05:18:18 pmYeah, I agree, it's certainly not a precision power supply and it's annoying they can't get the spacing right. I guess in my case I see it more as an additional power supply with a bit of extra grunt when you need it and for that I think it's well worth the money. Using an ATX power supply is likely causing a lot of people a lot of tears, it sucks when you short your board with 40A of current and no limit

author: coromonadalix
author_rank: Super Contributor
timestamp: July 06, 2019, 12:12:45 pm
content: As a small follow up, i had a mastech dual 30v 10 amp per rail, one rail failed miserably at outputting a mere 25 watt, bad solders on the board made it instable and pooof, even with the schematics, i cant find the #^#% trouble, changed all power mosfets even the most expensive and rarest one, many precision resistors, nadaEnded up in the scraps, costed lots of $$$Bought Kepco psu and Kikusui psu's, they are waayyyyyyyyy better than the " what you call cheap psu's "Been there and trying to save money on or for sometimes expensive(s) projects is enough. You must know what you buy and will use. Before use you have to dismantle them and check everything (solders / wirings etc ...) to be sure it wont fail due to poor designs considerations vs the price.The price says it all

author: jaxbird
author_rank: Frequent Contributor
timestamp: July 06, 2019, 12:21:14 pm
content: QuoteSurely you are overgeneralizing a bit hereOr do you mean that all cheap equipment is bad?

author: jaxbird
author_rank: Frequent Contributor
timestamp: July 06, 2019, 01:59:50 pm
content: QuoteWait... I'm struggling to understand your post, you say it's a follow up, but I don't see any previous post in this thread from you? and the equipment you are referring to got absolutely no relation to the equipment being discussed here.Did you perhaps post in the wrong thread?

author: nctnico
author_rank: Super Contributor
timestamp: July 06, 2019, 04:30:46 pm
content: Quote from: jaxbird on July 06, 2019, 11:07:24 amYou won't see the 100Hz on a DMM. You need an oscilloscope for that. This is a measurement I did on the 150W version:It shows 500mV peak-peak output ripple.

author: jaxbird
author_rank: Frequent Contributor
timestamp: July 06, 2019, 05:23:43 pm
content: QuoteSure, if you actually watched my review you'd see I have a scope hooked up to the output during the whole review, so I still don't understand your claim it will not work with 300W load when I tested it for 10 minutes with a 240W load?

author: nctnico
author_rank: Super Contributor
timestamp: July 06, 2019, 05:53:42 pm
content: I hate to go through video reviews because they are way too long winded to find something specific. I can't find where you measured the 100Hz ripple. Just test at full load and look at the output using AC coupling and set the sensitivity to 100mV/div or so and the timebase to 5ms/div.

author: jaxbird
author_rank: Frequent Contributor
timestamp: July 06, 2019, 06:19:50 pm
content: Quote from: nctnico on July 06, 2019, 05:53:42 pmYou are moving goal posts now and I can't just let it slide as it was your reply to my original review post disagreeing with my conclusion that it would still be worth $50 despite the noise issues, by saying "disagree, it probably won't work up to 300W"So all along it seems you are talking about a different power supply and you cannot be bothered to actually watch the review?How are we to take you seriously after this?

author: nctnico
author_rank: Super Contributor
timestamp: July 06, 2019, 06:52:09 pm
content: Instead of an ad hominem attack you could have simply re-tested the PSU. But I just did that for you. The blue math trace shows the 100Hz ripple (after a 1kHz filter because the noise the PSU pushes into the probe swamps the ripple completely).15V @10A30V @10AAs you can see there is a significant ripple at full load (it is likely the ripple is attenuated somewhat by the math filtering; I have not check the filter characteristic).Looking at the inside the 300W version is a beefed up version of the 150W model. The only difference seems to be bigger primary capacitors and some extra heatsinks.

author: jaxbird
author_rank: Frequent Contributor
timestamp: July 06, 2019, 07:04:42 pm
content: QuoteWhat are you talking about? please show where I used any adhominem, I'd say your accusation of adhominem is the most adhominem we've had in this discussion. So I'd appreciate an apology for that.How are your vague scope captures going to change anything you already said?

author: CDaniel
author_rank: Frequent Contributor
timestamp: July 06, 2019, 07:16:24 pm
content: For 50$ if you are a practical guy you could add an output LC filter to reduce that noise ... anyway I bet all the electrolytics are crappy and should be replaced .But you could have a nice power supply if you know what to do .

author: NoisyBoy
author_rank: Frequent Contributor
timestamp: July 07, 2019, 03:30:51 pm
content: Hey guys, let's keep some peace here. I believe all nctnico did was providing some data on the noise issue that was described in the original post, so all of us can decide quantitatively whether it would meet our need.Personally, I avoid cheap power supplies, especially the higher power models. I am more concerned about safety and fire hazard due to the lack of safety certification.

author: wraper
author_rank: Unknown
timestamp: July 07, 2019, 03:59:32 pm
content: Quote from: jaxbird on July 06, 2019, 07:04:42 pm100Hz ripple on output means there is very high 100Hz ripple on primary side caps and feedback cannot compensate for that. Which means that PSU cannot deal with such load properly and is very likely close to failing. Especially if operating for prolonged time under such conditions.

author: J-R
author_rank: Super Contributor
timestamp: July 08, 2019, 09:15:50 am
content: I appreciate someone taking the time to do a video of a product. I'll admit I didn't watch all of it. I personally would prefer a 5 minute, heavily edited version covering all the bases and then another 30 minute or longer video for anyone who wants a closer look.The ripple/noise at 10A seems like a reasonable compromise at this price point. Many loads probably won't care. Seems like a good option for a hobbyist on a tight budget who has no supply at all.The multi-turn voltage pot is nice compared to coarse/fine or other obnoxious methods. Not having it on the current is probably fine since for basic tasks you're just limiting current for safety.Comparing this review to the 2015 one, the only question I didn't easily find the answer to was whether the chassis was grounded now?

author: nctnico
author_rank: Super Contributor
timestamp: July 08, 2019, 12:53:06 pm
content: One thing to be aware of is that this supply isn't very useful if you want to use an oscilloscope to measure small signals in a circuit. The noise from the PSU will swamp whatever signal you measure in your circuit. All in all these power supplies are great as a glorified high power wall-wart (with adjustable voltage and current limit) but less suitable as a bench power supply to develop circuits.

author: radiolistener
author_rank: Super Contributor
timestamp: July 08, 2019, 11:02:27 pm
content: Quote from: nctnico on July 06, 2019, 06:52:09 pmThanks for measurement. Previously I planned to buy this PSU for high power purposes, the only thing that I worried about is noise level. Now I see it has just terrible noise. So, I'm happy that I didn't spend money on that crap.

author: MyHeadHz
author_rank: Regular Contributor
timestamp: July 08, 2019, 11:33:53 pm
content: Is that sort of noise only in low-end power supplies like this, or is it common in switchmode bench-style power supplies in general? Are transformer-based designs better in the noise department?

author: nctnico
author_rank: Super Contributor
timestamp: July 08, 2019, 11:43:35 pm
content: The PSU this thread is about is very bad when it comes to noise. Switching power supplies from A-brands are much better but not perfect.In this posting I compared a switching HP power supply (6024A) and a linear power supply (Keysight E36313A):https://www.eevblog.com/forum/testgear/e36300-series-programmable-dc-power-supplies-(e36311a-e36312a-e36313a)/msg1259142/#msg1259142

author: tautech
author_rank: Super Contributor
timestamp: July 08, 2019, 11:49:57 pm
content: Quote from: MyHeadHz on July 08, 2019, 11:33:53 pmGenerally much better but some are still better than others.The new Siglent SPD1000X single channel PSU's are so noise free it's very hard to even measure it, believe me I've tried.Better than 350uV for ripple and noise is waaaay down there.

author: Kosmic
author_rank: Super Contributor
timestamp: July 09, 2019, 12:44:24 am
content: Quote from: tautech on July 08, 2019, 11:49:57 pmYou mean, 350uV RMS or 3mV peak to peak3mV is ok. Most of my lambda PSUs are doing 1mV peak to peak. Back in the days lambda were selling some PSU with 500uV peak to peak. That's really low noise.Edit: I actually got something better. Just realised that my really old Power Designs 2005a is rated at 100uV peak to peak.

author: tautech
author_rank: Super Contributor
timestamp: July 09, 2019, 01:00:58 am
content: Quote from: Kosmic on July 09, 2019, 12:44:24 amCheck the SPD1000X datasheet for yourself.https://www.siglentamerica.com/download/6293/Some checks I did on the 16V 8A model:https://www.eevblog.com/forum/testgear/new-spd1168x-siglent-psu/msg1680749/#msg1680749

author: Kosmic
author_rank: Super Contributor
timestamp: July 09, 2019, 01:07:04 am
content: 3mVpp == 3mV peak to peakI'm not saying 3mVpp is bad. It's fine, pretty standard really.

author: radiolistener
author_rank: Super Contributor
timestamp: July 10, 2019, 04:03:02 am
content: Quote from: tautech on July 08, 2019, 11:49:57 pmIf it has noise with so high amplitude, this is bad.With 1 A load it will be 350 mW noise power (-4.5 dBm).All depends on what kind of ripple it produces.If it's high frequency pulses, this is very bad result.If it's 50 Hz sine, then this is excellent result.The good test for power supply noise is to power short wave transceiver from this power supply and to listen if there some noticeable noise from power supply are present.

author: tautech
author_rank: Super Contributor
timestamp: July 10, 2019, 06:01:12 am
content: Quote from: radiolistener on July 10, 2019, 04:03:02 amYes well if you'd checked the link supplied above you would have seen this 500uV/div ripple/noise measurement on a 5A 12V load on the 16V 8A SPD1168X PSU.We're 50 Hz mains so if you can see 100 Hz ripple you're a better man than I.However there is some HF noise that's not consistent over various settings and loads that I put down to the 10 LED downlights and their supplies in the room that the PSU was tested in.

author: radiolistener
author_rank: Super Contributor
timestamp: July 10, 2019, 12:33:44 pm
content: Quote from: tautech on July 10, 2019, 06:01:12 amNoises needs to be tested with spectrum analyzer, where all noise issues will be quite visible with no need for extra abilityHere is example.50 Hz component with -45 dBm and 100 Hz component with -75 dBm level. All harmonics also pretty visible.But I'm afraid, in such test, switching power supply will unconditionally surrender against linear power supply.