Seeking guidance on used power supplies - Page 1
Forum section: electronics / beginners

author: Penwrecker
author_rank: Newbie
timestamp: March 26, 2021, 07:08:58 pm
content: Hey guys. I bought this "Rockseed" power supply on Amazon, but I'm not into it. Nice features, but frustrating, laggy controls & a cumbersome UI.I going to return it & look for a second-hand unit with analog meters & controls that do the thing it says on the labels next to them.Not sure if linear vs switching is a huge concern at my level, but based on my research, linear seems more suitable.My budget is around $100. Ok, maybe $120. Yeah, that's pretty tight I'm aware. Just gotta do my best.Checking eBay, I found certain models with multiple listings. Apparently, they were popular. Thirty-to-forty-year-old gear is obviously a gamble, but if you have to do it, I figure look for a workhorse.There are severalLeader LPS-152listings I could afford. I found a PDF of the manual online. It includes circuit diagrams. Searching these boards, sounds it's built from basic types of components that are still available. So I could repair it, in theory. This one seems promising.Another one I like is theTektronix CPS250.I found a vid showing how to use it. Seems intuitive. And apparently it was intended for students, so good fit there.And there are tons of listings for theBK Precision 1711.I guess that one was popular.Anyway those are the ones that stand out for me at this point. Any thoughts pro or con? Any other models I should consider?I realize I could get a new digital one with more features & a warranty for less money. But I just think I'll enjoy this other type more. In my experience, that can make all the difference.Any help would be very much appreciated. Thanks, guys.

author: wizard69
author_rank: Super Contributor
timestamp: March 27, 2021, 12:51:10 am
content: You didn't mention your intended usage nor your level of experience. If you are just starting out in electronics I don't recommend buying a lab supply at all. Instead use your need for a voltage source to learn. That is build your own power supplies.If you start out with simple three terminal type power supply chips you can implement a simple fixed voltage supply fairly cheap and without a lot of drama. However there is enough to be learned that it makes it worthwhile. A fixed voltage supply is not a long term solution for a well supplied bench but that really isn't the point here it is rather the opportunity to learn. More importantly power supplies are a common failure point and poorly implemented ones can have a real negative impact on your circuitry, so even if your interests are digital systems you really need to understand power supplies.A DIY supply isn't a waste of time either, build it well and put it in a proper enclosure and it will be useful on your bench for years as it is pretty common to need more than one supply. Over the long term you could end up with a half dozen supplies on your bench.The other option is to use batteries or regulated plug packs that can be found all over the place. All of these options are much cheaper than buying even a used supply.Starting out you should really focus on getting a good DMM followed up by any sort of O'Scope. If you are not starting out much of this message can be dismissed.There are some avenues to used equipment that are very good if you have the time to invest in the effort of getting the hardware. What I'm talking about is look at organizations that do factor close outs, liquidations and the like. One example being DoveBid >https://www.go-dove.com/.The problem here is that you need to waiting until a factory is closed down that has what you want up for auction.Quote from: Penwrecker on March 26, 2021, 07:08:58 pmNot familiar with that company at all. There are a lot of companies in China making electronics, some very good and some very bad. You need to find out who delivers the quality goods before considering purchase. That isn't always easy, but you may get comments from actually users in the various forums. Either that or stick with brand names your trust and models from those brands that are known to be good.QuoteMany of the older models are easier to repair. The problem is the high likelyhood of a repair being needed.QuoteI'm not sure why you would enjoy old tech more. In a lab supply for example I really see digital displays as important for anything I would purchase these days. I do have an old supply with analog displays and I'm seriously considering an "upgrade to digital". Beyond that digital controls often bring other advantages to a supply. If money isn't a problem I'd certainly consider modern tech over the old stuff.Quote

author: james_s
author_rank: Super Contributor
timestamp: March 27, 2021, 12:56:18 am
content: I have a digital bench supply and an old analog one. Honestly I much prefer the analog interface, knobs for voltage and current and analog meters are much nicer for that application. The only reason I end up using the digital supply more is that it's so much more powerful in terms of voltage and current it can supply. I see no advantage to digital displays on something like a bench supply, in most cases I just don't need that much precision and a good analog meter provides a better relative display. For input it's far easier to turn a knob than it is to type in a voltage or navigate through some cumbersome UI.

author: rstofer
author_rank: Super Contributor
timestamp: March 27, 2021, 04:44:51 pm
content: Wall warts can be handy as can battery packs. You can go a long way with simple 1A power supplies based on 7805 (+5V), 7905 (-5V), 7812 (+12V) and 7912 (-12V). For +-15V for older op amp circuits, you can build the Jameco +-15V supply:https://www.jameco.com/z/PD-2515-MEAN-WELL-Power-Supply-Dual-Output-Open-Frame-15V-1A-Negative-15V-1A-24W_2100857.htmlEverybody wants to build a 0-30V 3A 3 channel power supply, few succeed. Figure out what you need and build dedicated supplies. If you come up with a Jetson Nano uC where you need 5V 4A, your bench supply is likely to be too small anyway. Turns out there is a nice brick supply built for the purpose.A 3.3V regulator:https://www.adafruit.com/product/2165Figure out what you expect to need and start with wall warts. Do you really care if the output is 4.9 or 5.1V? Probably not. Don't try to impart precision into a circuit with 10% (or 20%) components.Search eBay for 'HP Power Supplies', they're all over the place. Watch some w2aew videos, particularly the transistor episodes, and see what he is using. Very old HP analog supplies.Watch his videos anyway, they're very good. I like Dave's Fundamentals Fridays episodes as well.The regulator datasheets often have complete schematics. You can start there.Look at all the circuits in this datasheet:https://www.mouser.com/datasheet/2/149/LM7805-1010961.pdf

author: Martian Tech
author_rank: Regular Contributor
timestamp: March 28, 2021, 02:55:28 am
content: Yeah, HP. Looks like you want something to handle digital (+5V) and analog (+/-12 or 15V)Triple output: 6235A or 6236B (0-6V@2.5A, 0-+/-20V@.5A)-or- What I have:6281A (0-7.5V@5A)6205B (Dual 0-20V@.6A or 0-40V@.3A)

author: wizard69
author_rank: Super Contributor
timestamp: March 28, 2021, 03:45:37 am
content: I forgot to mention simply using batteries to get started, thanks for mentioning that rstofer.Another possibility to get a solid power supply is to look at salvage from printers, computers and such. You need to have the confidence needed to salvage line voltage hardware and properly encase it (if needed). The reality is a lot of perfectly good supplies end up in the trash.As for three terminal regulators it is the perfect place to start to learn the various aspects of electronics. A newbie can learn basic design, documentation reading, bread board building, PCB design and construction, soldering, debug and chassis building. All of this can be done with low cost components. This is why I often suggest in answer to these sorts of questions - build your own. Simple supplies are just great way to start and you need the knowledge anyways.As for the newbie, that is no longer a newbie, he will have the knowledge to make a buying decision himself in a year or two. I don't want to dismiss the value of a lab supply but it is real easy to buy the wrong supply before ones interest firm up. On the other hand it can be pretty hard to go wrong buying a DMM as you will end up needing more that one anyways.

author: Penwrecker
author_rank: Newbie
timestamp: March 28, 2021, 07:00:54 am
content: Thanks a lot for the advice, all. Ok sure I'll build a power supply as an initial step. That makes sense.I searched eBay for the models you mentioned rstofer. Found some listings. Based on photos & the manual 6235B looks perfect. I found a few listed in my range. I'll keep it in mind for later.

author: MikeK
author_rank: Super Contributor
timestamp: March 28, 2021, 01:51:29 pm
content: Old HP supplies are nice - I lucked out and got one cheap - but they're selling on eBay for too much money in my opinion. Get a Korad KA3005D (or 'P').

author: james_s
author_rank: Super Contributor
timestamp: March 28, 2021, 11:54:01 pm
content: It's only opinion but I don't like power supplies like that Korad that have a single multifunction knob. It's much more convenient to have separate knobs for voltage and current for each channel.

author: MikeK
author_rank: Super Contributor
timestamp: March 29, 2021, 12:15:48 am
content: Build your own to suit your taste? Not hard to do. It makes repair/mods easier when you designed it.

author: bdunham7
author_rank: Super Contributor
timestamp: March 29, 2021, 12:36:41 am
content: Do you have specifics like voltage/power/number of channels in mind? Have a look and see what is available in Power Designs stuff. Sometimes you can find deals on ones that aren't too rough.https://www.ebay.com/itm/Power-Designs-4005R-Transistorized-Power-Supply-0-40VDC-0-500mA/231477264705?hash=item35e51ec141:g:9hEAAOSwzL9d3Y93Otherwise, the old BK Precision, Tektronix (not made by them AFAIK), etc are pretty decent mid-grade stuff that has some real advantages over many modern PSUs, like not going up in flames if you backfeed them. The old HP stuff is also excellent if you can find them for a reasonable price in non-trashed condition. However, with HP you need to know exactly what you are buying--they made a lot of different stuff, not just classroom grade general purpose supplies.

author: perdrix
author_rank: Frequent Contributor
timestamp: March 29, 2021, 01:44:47 am
content: Be warned that the HP bench supplies are highly intolerant of "back-emf" - they have a bad habit of releasing the magic smoke if the output terminal voltage rises above the voltage to which the supply is set.David

author: Penwrecker
author_rank: Newbie
timestamp: March 29, 2021, 05:51:23 am
content: It's strictly personal preference, but I really dislike multifunction controls. I bought this "Rockseed" PSU, which I plan to return...The main issue is one knob does everything, and its function at any moment is determined by a jumble of presses, long presses, & double presses of a bunch of buttons.To be fair I'm not using it as intended. You're supposed to program settings into memory slots and access them with a single button press. It's a decent product. Just not right for me. I'm kind of fussy about tools I guess.About the digital vs analog thing, again personal preference, but analog gauges are more intuitive for me. I find them easier to read. (If I do need more precision for something I think I can probably connect my DMM, right?)In any case, I'm going to follow the advice that several people posted and make my own to start with. I found a lot of videos, tutorials, etc.I actually happen to have anLM317IC that came with an assortment I got on Amazon, so that's great. Data sheet says 37V & 1.5A. 15v & 1A would be plenty.Anyway, thanks a lot for all the info, guys. I appreciate the help!

author: daqq
author_rank: Super Contributor
timestamp: March 29, 2021, 07:50:34 am
content: Agilent 6632B. It's somewhat large, but has great parameters, can be found cheap on ebay, can be remote controlled and the best thing is that it's a two quadrant device - it can sink AND source, which means you can abuse it as a load as well.

author: Berni
author_rank: Super Contributor
timestamp: March 31, 2021, 10:56:20 am
content: Yeah some digital power supplies have incredibly bad UIBut that doesn't make digital PSUs bad. Something like the Rigol DP832 is a pretty nice fully featured digital PSU. You get 3 channels for those +/- supply needs plus a digital supply. Most importantly the digital supply channel is like any other channel so its fully adjustable weith an adjustable current limit. Not like most of these digital 'channels' that are basically just fixed 5V or 3V3 outputs at max current. Sure the circular number pad on that Rigol PSU looks a bit silly but it works well.If i want 4V at 230mA on Ch2 i would go for the following sequence of buttons:Ch2 5 Volts 2 3 0 MiliampsHaving just one knob is a bit annoying at times because you have to make sure you have the right thing selected but i found myself rarely using it. Its more conveniant to type in numbers since often you need a certain voltage like 12V 5V 3.3V etc. The knob only really gets used when you want to sweep some parameter. Like you are testing to how low of a voltage your product works, so you select the knob and slowly turn it down until il the DUT stops working.But i still keep some old analog Agilent PSUs around that just have the classical voltage and current pots. Those are nice for simple tasks where you just need a voltage from it and that's it. You don't care about fine tweaking the current limit or often setting the voltage. I like these for example when im writing firmware for a board and i just need a quick source of power in the background that runs all day. The next day i just flick a switch on the PSU and it instantly provides power again.One good merge of old and new styles is the Tenma 72-2690. It looks like a classic analog single channel job, but the two knobs are actually encoders. So you set it by simply turning them, but they go in steps so its easy to hit spot on 5.00 V. You also get 1mA current resolution and the ability to preview the set current while turning the knob. No fancy buttons or menus, it also remembers the setting when you turn it off just like an analog PSU.