Is building a power supply feasible for a beginner? - Page 1
Forum section: electronics / beginners

author: mgysgthath
author_rank: Newbie
timestamp: September 25, 2016, 01:49:46 am
content: In one of Dave's videos he recommended building one rather than buying one.. however at my limited skill level I wouldn't have the first clue where to begin with that. Are there kits that are worth while? Or should I be able to answer the question of "how" myself, before even attempting to build something like this?

author: Voodoo 6
author_rank: Regular Contributor
timestamp: September 25, 2016, 02:37:03 am
content: Don't see why you couldn't build your own, probably better to find a cheapo PS and practice disassembly and assembly first though. Tear it down to the board and practice identifying parts and getting the soldering down. You learn a lot by doing that, like I need flux, I need a better soldering station, lead-free solder suck, and awee crap I wish I homeowner insurance to cover the apartment complex I just burnt down. Hope this helps! Cheers!

author: tautech
author_rank: Super Contributor
timestamp: September 25, 2016, 03:46:20 am
content: Quote from: mgysgthath on September 25, 2016, 01:49:46 amIt's a pretty straight forward project if your needs are basic. Eventually you'll want a better PSU than one you can build but don't let that discourage you from having a go.Set some parameters of what you'll likely need and go from there.For most common needs a LM317 is the easiest to use and knock together without even a PCB with point to point wiring. It need be heatsinked though.Just Google "317 diy psu" and you'll get a few hits, download the datasheet and use a "typical" application exactly as listed.Come back to us with any questions and somebody's sure to guide you.

author: edpalmer42
author_rank: Super Contributor
timestamp: September 25, 2016, 04:41:30 am
content: Check out sites like instructables.com. Find a power supply that would be useful to you and that you think you could build. If you run into problems, you could ask questions there or here.I don't recommend the ones that modify a computer power supply or similar. They have mains voltage inside and things can go very wrong. Stick to the ones that include a big transformer (i.e. linear supply) or one that uses an existing power supply as a block and adds your bits onto the output.Ed

author: Johnny10
author_rank: Frequent Contributor
timestamp: September 25, 2016, 05:07:21 am
content: As a beginner I started with building a power supply for a sensor using two 9 volt batteries in series and a voltage regulation circuit to create an adjustable power supply.Then later moved to a negative 40volt switch mode power supply using a laptop charger.I have found that the motivation to build a power supply or any type circuit depends on your needs.My very first project started with the need to build a shutter tester for vintage camera lenses.This led to using phototransistors, resistors, diodes, voltage regulators, capacitors, oscilloscopes, DMM's, and on and on.Look online for some simple circuits and start building!

author: ebclr
author_rank: Super Contributor
timestamp: September 25, 2016, 05:14:26 am
content: The only value is for educational / training purpose.http://www.instructables.com/id/Make-a-simple-12-volt-power-supply/

author: nowlan
author_rank: Frequent Contributor
timestamp: September 25, 2016, 05:29:13 am
content: Plug pack & lm371 are a good start for learning purposes.Ultimately you would want something that has current limiting to avoid oopsies.The kit in Daves video would cost more than Chinese lab psu.

author: jonovid
author_rank: Super Contributor
timestamp: September 25, 2016, 07:06:30 am
content: made this recently. moded a 1.5amp Chinese Power Supply Module, put it in a box with a 240v/ 25v transformer from an old Radio/CD player, add a Auto 15w 24v Auto bolb in series on the 1 amp side for a overload 3 pin AC IEC socket

author: DTJ
author_rank: Super Contributor
timestamp: September 25, 2016, 07:54:54 am
content: If you are concerned about working with mains (which can & will kill) look at making a power supply that runs from a wall wart or surplus printer or laptop power supply.Maybe check out eBay and see what the offerings are.

author: Kappes Buur
author_rank: Regular Contributor
timestamp: September 25, 2016, 08:46:49 am
content: Quote from: mgysgthath on September 25, 2016, 01:49:46 amThis looks more complicated than it really is.If you do not fancy to build the whole thing, it is simple enough to just extract one of them.

author: ebclr
author_rank: Super Contributor
timestamp: September 25, 2016, 09:36:40 am
content: If you know how to solder and want to start on electronic, It's easy, and it's a nice step to learn, Try I still remember my 1st circuit from 40 years ago.It's a small step by is a step

author: R005T3r
author_rank: Frequent Contributor
timestamp: September 25, 2016, 06:30:14 pm
content: I've built my PSU long time ago, but given the importance of the tool for other projects I've switched to an Agilent one. Actually, it was the first instrument I've ever bought! Anyway, yes, it's very appropriate as first project, because you will see with your eyes what are the limitations and the problems that will help you decide to buy a decent one.

author: eventhorizon
author_rank: Contributor
timestamp: September 25, 2016, 07:24:34 pm
content: I am a beginner and I am working on one that uses a 12v wall wart that may be changed out to a laptop charger when all said and done. The plan is to use 2 lm317s (one for current and one for voltage) and pots for the adjust. If you want I can share what I have and the weird things im seeing and we can work it out together and try to learn something and when all else fails come here for advice.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 25, 2016, 08:14:14 pm
content: Starting with something like an old laptop supply or similar is a good idea. As a beginner one should be careful with mains, unless you know well about this (e.g. as a trained electrician but new to electronics).A supply is a reasonable good project as a beginner, though it can get quite involved if you want a good one and really understand it. It can start easy, like a LM317 (for a adjustable voltage). One can learn quite a lot, but should usually start small for the beginning. Much less magic smoke in an 1 A supply than in a 10 A version. Nothing is wrong to have an additional version with limited capabilities (e.g. fixed current limit or limited voltage range).Using two lm317 to get voltage and current control is a bad idea however. Better go for an old LM723 and a power transistor.

author: eventhorizon
author_rank: Contributor
timestamp: September 25, 2016, 08:38:23 pm
content: Quote from: Kleinstein on September 25, 2016, 08:14:14 pmCan you explain what you mean by bad idea? Are we talking efficiency because I know about that and I understand that I would be creating a space heater if I do a 12 or 18v to 5v 1a. Or is this ability to control that you are talking about?

author: joeqsmith
author_rank: Super Contributor
timestamp: September 26, 2016, 01:43:55 am
content: QuoteI don't see why not assuming you have the skills to do it. You don't need to design anything. Maybe just a text book example. I made several cobbled up supplies when I was starting out. I built this linear supply in the early 80s and still use it. It's the first thing I ever built using a microcontroller. It's based on the old Motorola MC1566. Programmable from RS-232 and even has a separate voltage input so you can read back current, voltage and one other voltage probe. Keypad was from an old girl friend's telephone. The plastic face came from a friend of mine who worked at a molding company. This thing can output up to 10A. The transformer came from a Sperry UNIVAC terminal I had scrapped out!So sure, if a person has the knack for it, why not.

author: perieanuo
author_rank: Frequent Contributor
timestamp: September 26, 2016, 01:08:25 pm
content: Quote from: eventhorizon on September 25, 2016, 08:38:23 pmLm723 rules.you can't fry it eve if you want.317 dies sometime for a little glitch.go with 723 I built several they works for years.just put 2 transistors and capacitors 0.1 on vcc vdd vout and you're on.Regards,ovidiuEnvoyé de mon iPad en utilisant Tapatalk

author: setq
author_rank: Frequent Contributor
timestamp: September 26, 2016, 01:34:37 pm
content: Please don't build an LM317 based solution. Go for the LM723 and pass transistors suggested elsewhere in this thread.An illustration why including a power supply design effort:1. I want a 1.2-20v DC power supply with an LM317 that can shift an amp. Perfect spec.2. Build an unregulated DC supply that shifts out the dropout voltage plus the max voltage plus a couple of volts to deal with capacitor ripple of 20+3+2 volts = 25v dc. An 18v AC transformer will do the job!3. Whop the LM317 on the front end.4. Think "hey i'll set this to 3.3v for an arduino project and I need 1A out - full whack"Quite reasonable yes?Well no it isn't.The transformer isn't an 18v one. It's higher than that. More like 20v so it remains in spec when under load. So that's 28v DC.The LM317 has to drop about 24v at half an amp. P=IE, so it has to shift 24W of power. The LM317 can shift, when well heatsunk with a bastard heatsink from hell just under half that. Bye bye regulator. They do explode as well. I've done it a couple of times.The same story with a 2n3055 pass transistor is dissipation of 115W.Hence LM723+2n3055 if you're going to do this. LM317 is only suitable for light loads. Not bench supplies, even your first one.I haven't included mains transients here either which increase dissipation, dead short conditions etc. The LM723 has a programmable current limit so you can protect the rest of the circuit or the power supply in an overload condition.Lots of design information here to explain this:http://artofelectronics.net/wp-content/uploads/2016/02/AoE3_chapter9.pdfBut yes, DO build your own power supply. Just don't copy it from some idiots on the Internet. Learn about it then understand it, then build your own design confidently.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 26, 2016, 06:32:29 pm
content: The LM317 is OK for a simple supply without adjustable current limit. It just is really hard to add an adjustable current limit. The idea you sometimes find with a second 317 is just not really working. Cross over is really poor. In addition the LM317 has really limited power dissipation, so its not good if more than a 10 V difference is needed. The LM317 is made for an internal supply with fixed load, not for something like a lab supply.The LM723 is not perfect, but good enough for a supply with adjustable current limiting. Also keep in mind that the maximum power dissipation for transistors is for a kind of perfect heat sink on a cold day (e.g. 25 C case) - so something like half that value is realistic. Some de-rating also applies to the 317.

author: george.b
author_rank: Frequent Contributor
timestamp: September 27, 2016, 06:36:02 am
content: Meh, using an LM317 for your first "bench" power supply is fine. That's what my first adjustable power supply was based off, anyways. Downsides, as already mentioned, are a lack of current limit adjustment (unless you kludge two of them together, not really an elegant solution) and power dissipation (although there are TO3 parts).It does have thermal protection, though. I don't remember ever getting one to explode - except that one time when I got counterfeit ones, watch out for that.Just don't expect much from it. Use it for light loads, just having an adjustable voltage source to begin with is already something, better than nothing. It's crappy, but it's something.The "how" part is, at least partially, answered in the datasheet.After you build it and it works and you get proud of yourself for it, then you could design another, better one, maybe even cannibalize the first one for parts.That's my opinion anyways.

author: Gyro
author_rank: Super Contributor
timestamp: September 27, 2016, 09:03:26 am
content: Another vote for the 723 approach. You'll learn more and there are lots of app circuits in the datasheet (and elsewhere). Most importantly you can implementPropercurrent limiting, a most valuable feature for beginners, and used by most sensible people, for bringing up prototypes. You'll probably recoup any cost difference quite quickly in non-fried components.For a beginner, using a chunky TO3 package pass transtor (not necessarily a 2N3055, there are darlingtons too) makes it a lot easier to dump heat into the heatsink, due to the much larger interface area, It's also very easy to share the load between a couple of transistors. Optimally thermal mounting of a TO220 package at high dissipation is full of gotchas.

author: setq
author_rank: Frequent Contributor
timestamp: September 27, 2016, 09:39:16 am
content: Learning is the important bit. Agreed.I fixed the stickman above who dropped more than 12W off his LM317

author: Voodoo 6
author_rank: Regular Contributor
timestamp: September 27, 2016, 09:45:32 am
content: Not quite sure why folks are trying to peddle wares in threads. Op grab a random discarded electronic item and go to town. Tear it down and learn before you build something. You will learn as you go. If the art is for you you can progress further, and separate the chaff from the wheat.

author: just5554
author_rank: Contributor
timestamp: September 27, 2016, 11:39:08 am
content: I'm also now building my 3rd power supply, but now I want it to be more efficient, so instead of linear I want to use switching power supply and buck converter, but can I use f.e. this power supply with buck converter?https://www.aliexpress.com/item/Universal-24V-5A-120W-Regulated-Switching-Power-Supply-Transformer-100-240V-AC-to-DC-For-LED/32606322171.html?spm=2114.13010308.0.87.T9KbHB

author: Cliff Matthews
author_rank: Unknown
timestamp: September 27, 2016, 01:19:56 pm
content: Quote from: Voodoo 6 on September 27, 2016, 09:45:32 amPeddler's gain by peddling - I fail to see it aplenty on this forum..Do you refer to links offered as help suggestion's?

author: albert22
author_rank: Regular Contributor
timestamp: September 27, 2016, 02:51:09 pm
content: Building a power supply is a good starting project. And it can go as complicated as you want. It depends on your requirements, that is, what you intend to do with it. My advice is to start with a linear supply with a small transformer and aim for a 0-20V 1Amp or less. Dont be too afraid of connecting to mains, just wire the primary of the transformer thru a double pole switch and a fuse in series. ISOLATE everything so there is no possibility of any accidental contact, short or leak into the low voltage side. Double check everything BEFORE connecting to mains. And just work on the secondary side of the transformer.Start with a simple linear regulator that you are able to understand and start experimenting.

author: eventhorizon
author_rank: Contributor
timestamp: September 27, 2016, 03:22:53 pm
content: I think we lost OP on this and never meant to hijack someones thread but hey I got some good information here. I did notice that when adjusting the load the voltage out of the 317 would change and thought it was something in my wiring but it makes since on what Kleinstein said. I am looking at the information on the lm723 and looks a little complicated at first but thats what makes it fun so I need to do a bit more reading to see how the voltage limit and the current limit works and get a better understanding.

author: setq
author_rank: Frequent Contributor
timestamp: September 27, 2016, 03:34:09 pm
content: LM317 drops out way early if you start to load it, if it gets hot, if it's Tuesday, if the planets are aligned in a certain way.Voltage limit is a simple feedback loop i.e. it compares the output to a resistive divider attached to the built in voltage reference.The current limit is set by Ilimit = 0.6 / Rs. So 100mA = 6 ohms.If you need MORE POWAH then whack a 2n3055 on the output. It'll get rid of the additional voltage drop error automatically.And that's it. All much more elegantly described in the datasheet.LM723 is a power supply construction kit rather than a regulator IC. I use one to check meters against a reference as well, although I'll probably be shot for it.However if you let all hell loose through it, it'll blow up. But it's cheaper than an LM317 so meh.

author: mgysgthath
author_rank: Newbie
timestamp: September 27, 2016, 05:08:31 pm
content: Quote from: eventhorizon on September 27, 2016, 03:22:53 pmOh I'm still here. I just run a small computer store as a one man operation and I don't have much free time often. As far as losing me, the advice is a bit daunting, feel pulled in ten directions. However the general consensus seems to be yes I should try to build one or more, and to avoid 317s. Fair enough.Some further info and questions.. I don't have a particular use in mind for my power supply yet, but I know that I should have one and will find uses for it. Personally I'd like more headroom than 1A, but as a first project I can find uses for =<1A. I could use it for anything from a few milliwatt laser diode up to a larger device, say a 72W led light strip, or high powered LEDs or something. I don't have a project in mind, I just don't want to limit myself. I've seen some chinese up to 30V dc variable bench supplies under a hundred bucks. And while I wouldn't ever think of it as a permanent solution or perhaps even a good one, I'd like to make something maybe along the lines of that if it's viable.I have access to a great deal of PC switching power supplies, ranging in quality from junk to 88+ efficient or sometimes better. Obviously these things can handle a great deal more amperage than 1A @ 12v, but sometimes you might want 24V or 30V etc, and from what people have said these are pretty 'dirty' power. I also have a lot of laptop supplies around, but these are of course 18.5-19.5V generally, i even have a few bigger ones able to output say 6-8Amps. But Really where to go from there I'm not sure.I thank you all for the advice, it's given me a lot to read about. I'll hopefully have some more informed questions before too long.

author: tautech
author_rank: Super Contributor
timestamp: September 27, 2016, 07:08:59 pm
content: Many of us can chuck together a 317 supply in minutes and despite comments to the negative for simple needs it's perfectly fine. Everything else is just more complex. Period.But yes there are things you need be aware of, primarily dissipation.If you need more current and still want to keep it simple the LM338 is another alternative. My first decent PSU uses one of these for a 5A supply. Again the datasheet tells you pretty much all you need to know.Or you could go for something like these:https://www.eevblog.com/forum/testgear/cheap-variable-switching-power-supply/I've sold quite a few of these and they've been pretty good. Sure they are a SMPS and there'll always be some switching noise but appropriate local bulk capacitance can easily manage it.Whatever you decide there'll be a day you wish for better and multiple outlets......

author: boffin
author_rank: Unknown
timestamp: September 27, 2016, 07:31:07 pm
content: If you have a look at this post, you can see a little module I built into an old unregulated 12v supply I picked up for next to nothing at a ham swap meet.https://www.eevblog.com/forum/chat/what-did-you-buy-today-post-your-latest-purchase!/msg980251/#msg980251Fuse/Switch -> Transformer -> Rectifier -> 1000uF cap -> ModuleThe transformer was only 12v, so it only goes up to 12v on the output, but it created a nice small, simple finished product. If I ever put significant current through it I might add an old computer fan (handily also 12v)

author: Kleinstein
author_rank: Super Contributor
timestamp: September 27, 2016, 08:05:20 pm
content: A laptop supply could be a reasonable starting point. With a 18-19 V input you might get something like 15 to 17 V out after linear regulation. At this voltage a single power transistor could handle 2-3 amps. That laptop supplies are not that clean either and those without a PE connection might give capacitive leakage, that might be a problem in some applications.The cheap Chinese supplies are generally not that bad in design, though a few are really bad and maybe even unsafe. But generally a 3 A supply is good only up to about 2 A. They just squeeze out too much from the circuits to make them cheap or better looking. So loaded to the max / worst case they tend to overheat and may break down early.

author: eventhorizon
author_rank: Contributor
timestamp: September 27, 2016, 08:18:04 pm
content: So I remember seeing a video where Dave shows that his laptop when connected to the power supply was mains earth grounded so im not sure if I want that in a power supply and being that various wall warts are cheap with different power options I could always go with say a 24v and check it for isolation. My only thing is that until I am sure with myself and abilities I am not touching anything I make directly to the wall. And im sure explaining why I am across the room with my beard on fire and the lights out to the wife (if I was still alive) would not be an easy task.

author: Gyro
author_rank: Super Contributor
timestamp: September 28, 2016, 09:00:55 am
content: You'll probably find this thread helpful. Particularly the link in reply #5.https://www.eevblog.com/forum/projects/lm723-based-linear-power-supply/

author: george.b
author_rank: Frequent Contributor
timestamp: September 29, 2016, 03:25:02 am
content: Quote from: setq on September 27, 2016, 09:39:16 amHahaha, that made me chuckle. Cheers!