How many PSU's needed for electronic design - Page 1
Forum section: electronics / beginners

author: Rob Sims
author_rank: Regular Contributor
timestamp: September 05, 2016, 08:44:57 pm
content: Hi,How many PSU's do you generally need to have in your electronics lab for electronic design. I think in tems of designing and testing circuits with transistors, opamps etc. In my opinion one triple output PSU or three single output PSU's are enough, but I could be wrong.regards,Rob

author: pelule
author_rank: Frequent Contributor
timestamp: September 05, 2016, 09:00:04 pm
content: As there is a unlimited number of design, there is no simples answer existing to your question.Let us speak in numbers of voltages, instead of number of PSUs - there are PSUs out there, which not have just one voltage.First question you need to answer is - what designs are you targetting?I you don't know yet, take the usuall 3 voltages, which should sufficiant for the most designs:0V...+5V/0..3A (for digital functions)0V...+15V/0A...1A and 0V...-15V/0A...1A (for analog functions).

author: setq
author_rank: Frequent Contributor
timestamp: September 05, 2016, 09:11:41 pm
content: Depends on convenience and cash really. A friend of mine gets on quite fine with a deep cycle lead acid battery and a car battery charger as a power supply. I'm happy with a cranky old Heath IP-2718 triple (0-20, 0-20, 5 fixed) supply.You need to consider that if you build a device you can't ship a lab supply inside it so you need to build a power supply into the device (switcher etc) or pick components that work at a reasonable source voltage (RRIO amps). I could get by with a 12v wall wart if I needed to. I prefer to design my stuff around the semi ubiquitous 12v AC (not DC!) wall wart as you can derive various voltages with one of them without having to deal with a switching supply.

author: uncle_bob
author_rank: Unknown
timestamp: September 05, 2016, 09:35:49 pm
content: HiI would guess that I have a couple hundred power supplies of various sorts running around here that *could* be used in design work.Roughly 2/3 of them are of the wall transformer variety. I never throw them away. The gear they came with goes into the trash, but the power supply goes into a big bucket. They have a wide range of power ratings and voltage levels. Some are regulated. Some are simple bulk supplies. I also have an inventory of them that I bought over the years on places like eBay. I usually look for auctions that are selling a bunch of "new in box" supplies cheap. Sometimes I win the bid. Mostly I loose.I have a number of high power supplies running up into the "several KW" range. They don't get used much. They are so heavy that they are hard to sell. Most of what I have was "free if you pick it up". If you are doing a high power amp, having a 0 to 50V, 100A variable supply is pretty important. Finding one when you need it is tough. If you are powering up surplus gear, a lot of it runs on 24 to 32 V. Having a number of 35A variables around to fire up the various boxes in a system lets you sort things out much quicker.Analog meter based bench supplies for some reason unknown to me went out of fashion ten or twenty years ago. They started showing up for ridiculous prices. As a result I have a few dozen of each of several models. This was the same sort of deal. Bid on auction lots of a dozen or two and win a few auctions. They work fine with analog meters. They are 0-15 or 0-30V units in the 50 to 100W output range. They are very useful for powering up just about anything you can imagine. It also is amazing how many of them you sometimes need when getting a circuit running.On top of all that I have a handful (< 20) fancy multi-outpt supplies. They are nice in terms of bench space. They also are good for bringing up all the supplies to a circuit at one time. Having everything adjustable and tracking comes in handy sometimes.====None of that is very helpful is it? It simply demonstrates that over a 50 year period you can accumulate a lot of junk. Accept that if you stick with this, you also will accumulate a lot of junk. The big take away - don't spend a lot of money on power supplies. They will come along cheap over the years. I am quite sure that none of my supplies cost over $50. People claim that you "can't find that stuff here". I have lived *many* places over the years. Each place has been a "there isn't any around here" location. I have always found gear available. The difference is that you need to put effort into finding it. When it shows up, you have to go get it right now. There is no waiting and deciding. There is no picking and choosing. You grab the whole lot and haul it away. They let it go because *they* didn't want to bother hauling it all away ....Still not really helpful ..Out of the empire of gear, the most useful stuff are the wall transformers. They are also the easiest to find for free. They are not very exciting or cool. Pretty much every circuit you design will have an on-board regulator (or several of them). That's the way things are done these days. A wall transformer will feed a 78L05 or 78L12 just fine. If you pay more than 10 cents for the regulator, you need to spend more time shopping ...I would suggest that a pair of 0-30V variable supplies with meters would get you going on anything that the wall transformers will not handle. Past that, grab what comes along.Bob

author: Rob Sims
author_rank: Regular Contributor
timestamp: September 05, 2016, 09:43:21 pm
content: Okay so 3 voltages like the Heath IP-2718 are enough. I'm talking serious business here, not amateuristic acid batteries and a car charger. Target are businesses. That means 1 PSU with triple output. But if the system fails, all three output fails. So I say three single output PSU's (not the most expensive and not the cheapest) is the way to go. Am I correct???

author: Rob Sims
author_rank: Regular Contributor
timestamp: September 05, 2016, 09:47:37 pm
content: Thanks Uncle Bob, the message is clear.

author: setq
author_rank: Frequent Contributor
timestamp: September 05, 2016, 10:01:23 pm
content: YMMV but buying two used triple rail supplies may do you better over time both for capex and redundancy. If you buy three new crappy Chinese ones, then you're down 2.5x the cost. If you buy three new Agilent ones then you're down 9x the cost. Either way you'll end up waiting on warranty if any break and if the supplier will honor it and that may be a bad business trade off.As for the car battery dude, apparently they make pretty good ripple free supplies that can shift some serious current. He sells commercial MSF receivers for remote sites that were developed with this as a power supply.I'm a big fan of making do. If you're caught short, you already know how to get out of a hole.

author: Rob Sims
author_rank: Regular Contributor
timestamp: September 05, 2016, 11:01:44 pm
content: Thanks setq. Yes you're right too. Ok a bit confusing if you're new, but i'm learning. I'll think it over and then decide what's best.

author: VEGETA
author_rank: Super Contributor
timestamp: September 06, 2016, 12:02:48 am
content: my advice is get one that is variable and work with it until you feel you must get another. one is enough in most cases especially in electronics without high voltage and high amp stuff.

author: Rob Sims
author_rank: Regular Contributor
timestamp: September 06, 2016, 12:46:27 am
content: You're welcome Vegeta. No I have two already. One with adjustable Coarse/Fine single turn pots and one with a digital rotary encoder. I like the one with the adjustable Coarse/Fine pots more, but anyway there is no need for a third one. I think my good friend got it all wrong when he told me in general designing you need at least 3 power supplies. Yeah but it all depends on different situations of course.

author: Rob Sims
author_rank: Regular Contributor
timestamp: September 06, 2016, 12:59:18 am
content: Forgot to ask too, What do electronic designers love most or let me say when do you need a programmable power supply and when do you need one with the analog Coarse/Fine pots??

author: uncle_bob
author_rank: Unknown
timestamp: September 06, 2016, 01:16:24 am
content: Quote from: Rob Sims on September 06, 2016, 12:59:18 amHiYou need a programable power supply when you are going to set up to test a few thousand units at a variety of voltages over a few months time. Fiddling pots every 10 minutes for six months on 20 supplies is *not* fun.For normal bench stuff ... why bother.Bob

author: Rob Sims
author_rank: Regular Contributor
timestamp: September 06, 2016, 01:42:49 am
content: Thanks Bob. So then I think I am already fully equipped to start. One bench power supply 0-30 volts, 5 amps with coarse/fine potentiometer adjustment knobs. One programmable bench power supply 0-30 volt, 5 amp with rotary push switch encoder knobs. A 70 MHz dual channel oscilloscope and two digital multimeters. Only thing I need now is a good soldering station, a desolder pump and some tools like pliers. I think i'm going for a Hakko soldering station. Saw some good reviews on Amazon. Oh and I forgot, I have to collect a huge amount of spare parts from old televisions, radio's etc. Hope I can receive some feedback from you guys if this is all the gear I need.

author: bitseeker
author_rank: Super Contributor
timestamp: September 06, 2016, 01:55:39 am
content: Quote from: Rob Sims on September 06, 2016, 01:42:49 amWhen you actually start working on circuits, you'll know if and when you need more. Then, you get what you need. You already have more than many people do when they first start out. So, worry less, build more.

author: uncle_bob
author_rank: Unknown
timestamp: September 06, 2016, 02:00:32 am
content: HiI would be careful about the TV parts process. I certainly stocked up that way when I started. That was a different era. Parts all had readable labels on them. TV's were made with the same "stuff" as just about everything else. About 10 years later that all had changed. The tubes (yes tubes) in a typical TV no longer crossed over to the tubes (yes there is that word again) in other gear. Today the IC's in a TV are the issue. Most of them are so highly custom that they are worthless for other stuff. SMD caps and resistors are no longer marked in a way you can read the values. I could pull parts with a pair of wire cutters. Today you need to get way more careful. The other issue is that I still have some piles of those parts sitting here ... unused.The good news is that eBay will supply you with all sorts of parts for nearly noting. They also may be *worth* nothing, but they don't cost much. As long as you check what you get, you can do pretty well.Bob

author: Rob Sims
author_rank: Regular Contributor
timestamp: September 06, 2016, 02:03:49 am
content: Thanks again Bitseeker. You're right, my next post will be about something I build or to give someone advice. Thank you.

author: Rob Sims
author_rank: Regular Contributor
timestamp: September 06, 2016, 02:08:58 am
content: Many thanks for the advice uncle Bob. Glad that there are honest people out there to give some good advice.

author: Brumby
author_rank: Unknown
timestamp: September 06, 2016, 02:49:05 am
content: Quote from: bitseeker on September 06, 2016, 01:55:39 amThis ^ ^ ^ ^ ^... and asuncle_bobsays ... be careful about pulling parts from old gear. You could end up with boxes and boxes of stuff you will never use. There are exceptions to this, but from what I have seen, it is usually by people who target specific equipment.

author: Ian.M
author_rank: Super Contributor
timestamp: September 06, 2016, 03:06:15 am
content: If you are doing any digital stuff, I'd add a fixed voltage 5V 3A and 3.3V 3A PSU with adjustable current limits. Its not unusual if you get into any sort of automation or robotics to need somewhere between +/-9V and +/-18V for analog circuits, sensors and actuators, which would tie up both of your 0-30V 5A bench supplies, so its worth having a separate supply for the digital stuff. If you are into Arduinos or similar it may also be worth having a fixed 9V or 12V output on it as well. As its primarily for digital circuits, you can use switching regulators (or even EBAY buck modules) as a little hash on the rails usually doesn't matter.The other PSU related thing that is often useful is a heavy duty four pole relay, mounted in a case with binder posts so that you can switch all the supplies to a circuit simultaneously, to avoid power sequencing issues.

author: Rob Sims
author_rank: Regular Contributor
timestamp: September 06, 2016, 05:52:05 am
content: Thanks Ian.M. Purpose of all this is to get into automation. I'm a mechanical engineer and automation is my focus and indeed i'm thinking about sensors, relays, actuators, input/output signals, pulse generators, chopper circuits, that sort of stuff.

author: tautech
author_rank: Super Contributor
timestamp: September 06, 2016, 07:19:44 am
content: Quote from: Rob Sims on September 06, 2016, 01:42:49 amFor PSU's you're good to go for normal sorts of stuff.Missing from your list and IMO you will need these at some point not too far in the future:Bench DMM for more precise measurements and logging.Some sort of function/waveform gen.

author: forrestc
author_rank: Unknown
timestamp: September 06, 2016, 07:39:38 am
content: Quote from: Rob Sims on September 05, 2016, 08:44:57 pmOn my bench, I have a triple-output variable power supply. A Rigol DP832A to be exact. This is sufficient for almost all of my work. In fact, it would be sufficient if it went to 60V instead of just 30V. So, to supplement it, I have a sorenson XHR60-10 which can do 10A @ 60V. With those two I'm pretty well set - I don't remember the last time I needed more than this.... other than:I do occasionally do some work on a breadboard. I've found that the USB powered breadboard power supply modules which plug into the bus connections on the breadboard tend to be very convenient. I'm not sure if you'd call a plug in USB power supply wired to a breadboard to be a 'power supply'....

author: tautech
author_rank: Super Contributor
timestamp: September 06, 2016, 07:43:51 am
content: Quote from: forrestc on September 06, 2016, 07:39:38 amCan't you put it in series mode for 60V ?

author: forrestc
author_rank: Unknown
timestamp: September 06, 2016, 07:51:57 am
content: Quote from: tautech on September 06, 2016, 07:43:51 amI could, but I typically need 48V and 24V at the same time. And need them isolated.If it did 0-60V on at least one of the channels, everything would be golden.I've also found having a 10A supply to be useful at times....

author: johnwa
author_rank: Frequent Contributor
timestamp: September 06, 2016, 08:06:24 am
content: Quote from: setq on September 05, 2016, 10:01:23 pmYes, lead acid batteries can make quite good supplies, especially if you don't have anything else suitable. Butmake sure they are appropriately fused!To this day, I still have a burn mark on my breadboard from not following this advice...

author: tautech
author_rank: Super Contributor
timestamp: September 06, 2016, 08:29:45 am
content: Quote from: forrestc on September 06, 2016, 07:51:57 amThen you need another PSU.QuoteAnd another to parallel the outputs for more current.

author: CJay
author_rank: Super Contributor
timestamp: September 06, 2016, 08:31:56 am
content: I can only repeat what others have said about lead acids, they're very dangerous if not used *and charged* correctly.For my needs, I've got a 0-30V, 10 amp supply, a TOPS3D 3 output dual tracking and 4-7V variable supply (tortuous description but...) and a Farnell L30BT which is dual 0-30V 1 amp.I find I use the 10 amp supply most often as I repair transceivers, the TOPS3D is useful for audio work and the L30BT, it's not really used that much now, I could probably sell it and not miss it.For higher power radio gear I use a couple of 17AH SLA batteries, fused at 50 amps and charged with a caravan battery charger which has an SLA mode.

author: forrestc
author_rank: Unknown
timestamp: September 06, 2016, 08:46:15 am
content: Quote from: tautech on September 06, 2016, 08:29:45 amYep.... or just a second one which does 60V at 10A, which is what I seem to have on my bench in addition to the three-output DP832A......

author: setq
author_rank: Frequent Contributor
timestamp: September 06, 2016, 08:55:53 am
content: Quote from: johnwa on September 06, 2016, 08:06:24 amA 10 ohm resistor in series with your circuit makes a cheap 1.2A slow-blow fuse with visual and olfactory indication

author: ZeTeX
author_rank: Frequent Contributor
timestamp: September 06, 2016, 11:01:17 am
content: allall of themyou can't have too many PSU's, the more the better.

author: uncle_bob
author_rank: Unknown
timestamp: September 06, 2016, 11:39:10 am
content: Quote from: ZeTeX on September 06, 2016, 11:01:17 amHiThat's pretty much been my approach to test gear in general....Bob

author: Rob Sims
author_rank: Regular Contributor
timestamp: September 06, 2016, 12:11:42 pm
content: Thanks guys for the advice. It's all clear now.

author: System Error Message
author_rank: Frequent Contributor
timestamp: September 06, 2016, 12:39:25 pm
content: as many as you can get your hands on. If you end up with thousands of PSUs than you have many spares, lots of spare components and lots of things you can work on at the same time (or seperately provide different voltage power rails).

author: dannyf
author_rank: Super Contributor
timestamp: September 06, 2016, 12:56:36 pm
content: "How many PSU's do you generally need to "I don't do much high powered high current stuff anymore. So I primarily use a laptop power supply (20v 6amp) down to 12v, 5v, 3.3v.Otherwise, I use phone chargers regularly or battery banks as power sources regularly. Most of the time I don't need more 500ma and 100ma is good enough.Having a whimpy power supply is a blessing and a safety feature.