buying a basic dc power supply unit - Page 1
Forum section: electronics / testgear

author: rorymax
author_rank: Contributor
timestamp: November 18, 2021, 07:14:03 pm
content: Hi Folks,This rank amateur is considering this for a starter into PSU's.Can I have any of your thoughts on whether I am wasting my money or not please.Much appreciated for any replieshttps://www.amazon.co.uk/gp/product/B07R2KHPTH/ref=ox_sc_act_image_2?smid=A1Y0G7ZSK431JL&psc=1

author: dorkshoei
author_rank: Frequent Contributor
timestamp: November 18, 2021, 10:24:30 pm
content: If I look at that Amazon.uk link it says not available but I see the same item on AliExpress for US$90 + shipping.When I was in your position I got a used HP E3610A from a fellow inmate here. I just checked and I paid US$50+shipping for it (in 2016). There are several different supplies in the E36xx series with varying outputs (*1). If it breaks they can be fixed and people here can help you fix it. Unlikely with a Chinese supply, you'll be lucky to get schematics.I try to buy used not new as it's better for the planet.1:http://www.rainer-foertig.de/td/E36xxA%20TD.pdf

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: November 19, 2021, 12:17:21 am
content: I assume you are going to be working on low voltage low watt transistor applications.I would look into a used triple supply. These have two adjustable supplies and one dedicated 5 volt supply. You can have a negative voltage and a positive voltage for circuits that use both voltages.If you are going to supply power to a transceiver (CB or HAM equipment) You need a higher wattage supply.(usually only for Transmit though)The cheap new supplies frequently have all sorts of RF noise since they are switching supplies and run on high frequency themselves. Even though they are NEW there appear to be lots of failures apparent by reading the Repair section here.I would get an older supply, the heavier the better and a brand name like HP. Do not be scared by analog meters, you have to check the output with a good voltmeter anyway. DIgital panel meters are not always accurate.You could try a local Hamfest or look at the local Ham club's website, they have Buy/Sell sections.At least that is the case here in the country formerly known as the USA.Look at the Buy/Sell section here also.dorkshoei's comments are quite validAlso, if you buy a decent used unit, you can probably sell it at the same price if you upgrade later.

author: Brumby
author_rank: Unknown
timestamp: November 19, 2021, 12:30:00 am
content: As a "rank amateur" buying second hand might be a risk best avoided until you've got some experience under your belt. That said, you can score some older kit that is perfectly functional.The style of supply you have shown is typical of what a lot of people have acquired and it will likely be with you for many years to come - even when you get another supply (or two, or three, or ......). The voltage and current range indicated will be very useful.There is a lot of gear coming out of China and while you can sometimes get some shoddy construction, things are mostly OK. One recommendation - which is the catch-cry of the EEVblog - is "Don't turn it on, take it apart!". This is simply removing the cover to see if there are any construction issues that would be best addressedbeforebeing put into service. Typical remedies might be to touch up a poor solder joint, dress some cabling or secure an earth connection properly. If you like ... should you get one, open it up, take some photos and present them here for opinion.

author: beanflying
author_rank: Super Contributor
timestamp: November 19, 2021, 12:34:14 am
content: There is a few threads on the forum with similar units with Brand X on the outside. I did buy a 120V 3A one for use on a hotwire cutter but I did run some load tests on it and it looked 'ok' for noise and ripple.Have a look at this thread for a start for some photos of this sort of unithttps://www.eevblog.com/forum/testgear/kungber-bench-ps-tear-down-images-as-requested/Personally I would go looking for a Linear supply as mentioned above. So HP Agilent etc. It gets old really fast if you get a transient spike or noise that fries your electronics. You should also maybe consider saving a bit more for a dual channel supply.

author: Brumby
author_rank: Unknown
timestamp: November 19, 2021, 01:00:24 am
content: Quote from: Wallace Gasiewicz on November 19, 2021, 12:17:21 amA triple supply is a common choice, since it does provide more power options. Getting a single channel supply now doesn't stop you from getting a triple supply later - but if your budget can cope with the higher cost, then it is a good option.If you come across something used, ask about it here and there will, no doubt, be one or more members who can tell you about it. Also, if there is a problem and you have some basic skills, they may be able to step you through a repair.QuoteIf you will be working on RF projects, then this will be an issue - but someone just stepping into the electronics playground might not travel that path just yet.QuoteI've not checked that section, so I can't comment.QuoteIf it can be confirmed as functional, then not an unreasonable direction.QuoteOK if local, otherwise shipping cost could be a killer.QuoteYeah ... I like HP too.QuoteFor many applications, whether a voltage is 11.7 or 12.2 won't affect circuit operation, so analogue meters are often adequate. If you do need precision, then always check with an external meter.QuoteIf you have them.QuoteOften worth the effort. I check it regularly, but there is rarely anything that is economical for Aussies.QuoteIF you sell it. From my experience, interest in selling a supply usually comes when you have at least 5 or 6.

author: Brumby
author_rank: Unknown
timestamp: November 19, 2021, 01:05:43 am
content: Quote from: beanflying on November 19, 2021, 12:34:14 amWhile the name brands are better known for taming such nasties, this is a consideration for ANY supply. There is less risk with linear as compared to switching, but you still need to be aware.Also be aware that some of the things you hang off a well-tamed supply can create their own problems ... but that is another discussion.

author: dorkshoei
author_rank: Frequent Contributor
timestamp: November 19, 2021, 01:09:45 am
content: Quote from: Brumby on November 19, 2021, 01:00:24 amGolden rule of buying anything is make sure you know how to test it and do so before the return window expires. As a beginner this can be hard(er). Stick to buying from somewhere where seller is responsible for paying for any return if the item is faulty (so Amazon, eBay "used" etc).

author: AVGresponding
author_rank: Super Contributor
timestamp: November 19, 2021, 06:31:30 am
content: Since you're in the UK, you should find it relatively easy to pick up a used Thandar/TTi (sometimes rebranded to RS or Farnell) for relatively little money.Avoid the cheap and flashy new stuff, it's invariably a poorly made, poorly regulated SMPS. Yes, this is personal experience speaking, I'm not just regurgitating someone else's tired old tropes.They appear regularly on ebay and can usually be had for a similar price to a new cheapie, but will bewaymore reliable/fixable/usable/flexible.

author: rorymax
author_rank: Contributor
timestamp: November 20, 2021, 11:48:26 am
content: Thank you everyone, the comments are really helpful, I shall consider options a little further before making a decision.I ike the suggestions of buying a second hand unit of higher quality, my main problem is my lack of knowledge in as far as whether the device is in good working order.I cannot think of anywhere remotely local where I could view any second hand products, I would be relying on trust more likely for an ebay\gumtree type sale offering.Thanks again for all the very useful replies.R.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: November 20, 2021, 02:26:35 pm
content: Lets not be so judgmentalQuoteI only have 6 supplies and have sold at least two and thrown away two. OK maybe I forgotten some....There is a UK guy selling some stuff on this blog. There appears to be a PS. One that I have not used. A Rigol Triple.https://www.eevblog.com/forum/buysellwanted/fs-electronicsrf-lab-clear-out-(keysight-tek-rs-rigol-)-reasonable-offers/msg3710440/#msg3710440

author: AVGresponding
author_rank: Super Contributor
timestamp: November 20, 2021, 03:33:18 pm
content: Quote from: Wallace Gasiewicz on November 20, 2021, 02:26:35 pmIf you read to the end of that thread you'll see there may be an issue with the reliability of that vendor.If you buy on ebay, at least you have some protection if it is listed as "used" but doesn't work/work properly/fully.EDIT: Personally I wouldn't buy anything from anyone on here unless they have a respectable post-count, which at least would give some indication that they are not some fly-by-night or scammer.

author: rorymax
author_rank: Contributor
timestamp: November 20, 2021, 04:58:51 pm
content: Very valid observation AVGresponding, thank you, I would not discount purchasing from a long term valued poster on this forum.Your comment is valued and appreciated,

author: dorkshoei
author_rank: Frequent Contributor
timestamp: November 22, 2021, 03:32:45 am
content: There are plenty of folks here who can help you verify a supply.In the absence of a digital load tester you can use appropriately valued power resistors.Keep an eye on eBay.UK for something "used"Remember you're trying to learn which means being open to asking for help and also making mistakes.

author: Fungus
author_rank: Super Contributor
timestamp: November 22, 2021, 04:32:52 am
content: Quote from: rorymax on November 18, 2021, 07:14:03 pmIgnore the curmudgeons here, it's definitely not a waste of money.A power supply like that allows you do experiments like "how bright is this LED at X mA", "what does this motor do at Y volts", "let me power this unknown thing on gradually"...etc.That's valuable.Get one of those and a couple of $10 switching supplies (eg. 5V, 12V) on your bench and you can do an awful lot.When/if you outgrow it you'll know a lot more about power supplies and what your needs are,thenyou can start looking for something more fancy.

author: dorkshoei
author_rank: Frequent Contributor
timestamp: November 22, 2021, 05:04:33 am
content: Quote from: Fungus on November 22, 2021, 04:32:52 amDid you skip socialization 101?

author: beanflying
author_rank: Super Contributor
timestamp: November 22, 2021, 05:57:03 am
content: Quote from: dorkshoei on November 22, 2021, 05:04:33 amIts all about yelling the loudest while beating his chest with the opposing view to other posters regardless of the topic or contentNo one said don't buy it or that it is a disaster but hey as a newbie consider looking at some alternate ways to spend a similar level and look forward a bit at what you might need next. I would call EVERYTHING above even Fungus's ACTUALLY constructive part useful options to consider.Quote from: rorymax on November 18, 2021, 07:14:03 pm

author: Fungus
author_rank: Super Contributor
timestamp: November 22, 2021, 06:04:19 am
content: Quote from: dorkshoei on November 22, 2021, 05:04:33 amThe original question was: "Can I have any of your thoughts on whether I am wasting my money or not please?"A lot of the replies above seemed to imply that anything less than a linear, triple output supply is a waste of time and money.

author: beanflying
author_rank: Super Contributor
timestamp: November 22, 2021, 06:11:15 am
content: Then READ what was written before writing off ALL the replies you rude twerp!

author: Fungus
author_rank: Super Contributor
timestamp: November 22, 2021, 06:45:27 am
content: Quote from: beanflying on November 22, 2021, 06:11:15 amOK, let's read whatyouwrote:Quote from: Wallace Gasiewicz on November 19, 2021, 12:17:21 amThat's amassiveassumption, right there.Why notaskwhat it would be used for?Quote from: beanflying on November 22, 2021, 06:11:15 amSeems to be an awful lot more assumptions there, all based onyoudo with power supplies.Maybe it's not going to be used like that at all, maybe it's going to be used with Arduinos and LED displays.Now let's look at what I write that offended everybody so:Quote from: Fungus on November 22, 2021, 04:32:52 amI gave usage scenarios and tried to give the idea that a power supply's most important function isn't really to supply voltage, it's to gave you information and feedback about the load.Was that so terrible?Quote from: beanflying on November 22, 2021, 06:11:15 amI did, I read them. When I said"A lot of the replies above seemed to imply that anything less than a linear, triple output supply is a waste of time and money"I was referring directly to posts like yours. Nobody mentioned tranceivers(sic) or negative supplies. The OP was looking at a simple, basic power supply and you're here upselling based on zero information.PS: I may have skipped socialization 101 but I have never, ever, called anybody any names here.

author: beanflying
author_rank: Super Contributor
timestamp: November 22, 2021, 07:13:56 am
content: YOU TOLD the OP to universally "Ignore the curmudgeons here" so you made a sweeping STATEMENT you rude twerp! As you don't want to not apologize for that to bad Junior!Learn some manners!

author: Fungus
author_rank: Super Contributor
timestamp: November 22, 2021, 07:38:15 am
content: One of the replies actually said: "I would get an older supply, the heavier the better..."Quote from: beanflying on November 22, 2021, 07:13:56 amIt's true, I did.I hope Brumby didn't feel like I was including him, I apologize in advance if he got that impression.

author: Fungus
author_rank: Super Contributor
timestamp: November 22, 2021, 08:26:15 am
content: How about we reboot this thread by asking what sort of things the OP wants to use his power supply for and what sort of electronics he works on?

author: beanflying
author_rank: Super Contributor
timestamp: November 22, 2021, 08:28:16 am
content: How about you apologize for your sledge of the posters (and not what was written by them) instead of multiple posts of waffle to cover being a rude twerp!

author: nctnico
author_rank: Super Contributor
timestamp: November 22, 2021, 10:33:41 am
content: Quote from: Fungus on November 22, 2021, 06:04:19 amThat is definitely true for the linear part. Switching PSUs are likely to become useless pretty quick if you want to measure something on a circuit. Even the higher quality ones from HP (which do have a decent amount of filtering) are not without their noise issues. On the other hand the older/used PSUs have a tendency to have inaccurate meters and/or loud fans so that is not ideal either. In my experience a PSU which shows only 1 decimal digit for voltage and current is not good enough because you never really know which voltage it is at when needing single digit voltages. And buying new doesn't have to break the bank. It seems that the Korad KD3005D ticks all the boxes (linear regulation, high resolution meters and low cost).

author: Fungus
author_rank: Super Contributor
timestamp: November 22, 2021, 04:08:54 pm
content: Quote from: nctnico on November 22, 2021, 10:33:41 amThemanual for that power supplyfor the switching PSU says maximum 10mV of ripple.I'll leave it to the world to decide if 10mV of ripple makes it "useless".Quote from: nctnico on November 22, 2021, 10:33:41 amOK, the price difference isn't much so I'll give you that...

author: nctnico
author_rank: Super Contributor
timestamp: November 22, 2021, 04:37:08 pm
content: Quote from: Fungus on November 22, 2021, 04:08:54 pmIt is not the ripple that is the prolem but the inherent HF noise of the switching PSU core that is being pushed into the load and ground leads.I wrote it before and I'll write it again: a switching PSU is great to use as an adjustable wall-wart / lump in chord PSU to power finished project / finished products OR when you need a lot of power (>100W).

author: TheBay
author_rank: Unknown
timestamp: November 22, 2021, 07:03:41 pm
content: At this stage don't worry about how many outputs it has etc, just grab a cheap linear PSU like a Korad (Or under it's many different badges such as Tenma) The one you linked to on Amazon has the wrong description, afaik the UTP1306S is a SMPSU not a linear PSU.I have at least 6 linear power supplies in the workshop and lots of SMPSU's, some are single some are multiple outputs. And I still want more.My first bench PSU back in the late 80's was a project and just had adjustable voltage it is absolutely mindblowing what you can buy for very little money these days.You can always buy a PSU with more outputs later on or more power supplies, so do not stress about that at this stage. This one you buy now will always come in handy.The smallest of mine is a Tenma badged Korad single output linear PSU and I find that extremely handy to use away from the bench and in other rooms when I need to power something up, or even take in the car with me.

author: tunk
author_rank: Super Contributor
timestamp: November 22, 2021, 10:29:31 pm
content: In addition to this, you could also get a LM317 kit from ebay, aliexpress etc.Both as an learning exercise and as a second simple PSU (you will also needa transformer and a voltmeter).Edit: You'll probably need a (larger) heatsink as well.

author: Fungus
author_rank: Super Contributor
timestamp: November 24, 2021, 02:03:49 pm
content: Quote from: nctnico on November 22, 2021, 10:33:41 amThere seem to be some serious criticisms of that Korad supply here:https://www.eevblog.com/forum/testgear/korad-kd3005d-bench-supply-power-on-spike/msg3509200/#msg3509200https://www.eevblog.com/forum/testgear/new-bench-power-supply-chinese/msg3773030/#msg3773030

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: November 24, 2021, 03:02:22 pm
content: I am sorry if I gave the impression that a triple PS is the only way to go. I most often use an old linear single PS because it is small and I can fit it on the bench. (maybe I need a bigger bench?)However if you have only one PS, with the multitude of devices that require even both Plus and Minus supply voltages these days, a triple PS is more versatile.My disappointment with switching PS is that they have spurious emissions. not necessarily ripple.It is nice to see some people sharing pics of bad switching PS output, informative.I do use a TenTec fixed switching PS for powering radios. I have not found any bad emissions with this unit but it is not a "variable" PS and it is expensive.I have found that some PS with digital readouts are not entirely accurate. Usually close but not right on. This may or may not be a significant problem to a particular user. Probably no big deal. Remedy is a good multimeter mostly.Switching PS that are intended for use with specific devices frequently have emissions that do not trouble the devices that they power. If you are experimenting with stuff you may find that these PS are troublesome.It is nice to have "clean power" so you do not confuse yourself and your measuring equipment (scopes etc)I have purchased nice "bench" PS for only a few dollars, used of course. It may be difficult for a newcomer to judge what he or she is buying however. I was a fairly ignorant buyer at times and mostly "got lucky" with most purchases. (now I am still ignorant but hopefully less so).

author: TheBay
author_rank: Unknown
timestamp: November 24, 2021, 03:11:50 pm
content: Quote from: Fungus on November 24, 2021, 02:03:49 pmThe KDSeries is a really stupid design, not only with that issue but what an annoyance not having an output switch, what were Korad thinkingThe KAseries are pretty good for the price and can be bought not far off the price of other cheap linear PSU's.

author: nctnico
author_rank: Super Contributor
timestamp: November 24, 2021, 05:27:16 pm
content: Quote from: Fungus on November 24, 2021, 02:03:49 pmThos aren't power-on spikes. Look at the time scale; what you see is the bounching of the mains switch.@TheBay: having an output on / off switch is a good feature to have!

author: Fungus
author_rank: Super Contributor
timestamp: November 24, 2021, 05:39:08 pm
content: Quote from: nctnico on November 24, 2021, 05:27:16 pmDoesn't matter where it comes from. Powering the thing on (or off) shouldn't fry your PCB.

author: nctnico
author_rank: Super Contributor
timestamp: November 24, 2021, 06:03:55 pm
content: Quote from: Fungus on November 24, 2021, 05:39:08 pmNo, it is a typical case of measurement error.

author: masterx81
author_rank: Frequent Contributor
timestamp: November 24, 2021, 10:41:38 pm
content: I have the ka3305p and do quite well it's job. No nasty spikes, output enable switch, dual channel + fixed 5v 3ch, not too noisy, cheap. The only thing to remember is to always use the on/off output switch as there is (as in most psu) some capacitance at the output that can "zap" anything before the current limiting kicks in. The things that i not like are the ui (for example it give you too little time for "edit" current and voltage values), and that if you remove the supply it remember that the outpus were powered on, and keep them on when you turn it back on.Before using it i've tested it's poweron (via the output enable button) in several conditions and never noticed anything bad

author: Brumby
author_rank: Unknown
timestamp: November 24, 2021, 11:19:00 pm
content: Quote from: Fungus on November 22, 2021, 07:38:15 amNah. It's all good.