Lab Power supply - is it needed? - Page 1
Forum section: electronics / beginners

author: jimjam
author_rank: Regular Contributor
timestamp: June 12, 2014, 05:25:41 am
content: I am almost going to get the Rigol DP832 (or DP832A - just because it has a pretty colour display - but I guess I could use the difference in price to get a second DMM) but I'm not sure that I need a lab power supply. I have lots of wall wart adapters - some are 12V 1A,2A, 7.5V, 5V, etc and I figured I could just use them. What would be the reason to get a lab power supply?Perhaps there are some use cases that I haven't thought of, that would be encountered during practice?I found an older thread discussing this question:https://www.eevblog.com/forum/chat/does-a-hobbyist-need-a-bench-power-supply/

author: Bored@Work
author_rank: Super Contributor
timestamp: June 12, 2014, 05:33:41 am
content: Constant Current / Constant Voltage.Over-voltage protection.Over-current protection.Stability.Safety.Reliability.Calibration.Versatility.Remote control.However, I don't think the DP832 (or the A) is really worth its money. It is one of those things where half of the forum did rush out to buy one, just because Dave sad he liked it.

author: theatrus
author_rank: Frequent Contributor
timestamp: June 12, 2014, 05:36:17 am
content: In my opinion, the number one need is for adjustable current limiting / constant current mode. It saves circuits and parts from the inevitable goofs.

author: jimjam
author_rank: Regular Contributor
timestamp: June 12, 2014, 05:36:29 am
content: What would you recommend instead of DP832(A)?Quote from: Bored@Work on June 12, 2014, 05:33:41 amI hope Dave gets lots of commissions or at least freebies from Rigol!

author: jimjam
author_rank: Regular Contributor
timestamp: June 12, 2014, 05:37:38 am
content: Quote from: theatrus on June 12, 2014, 05:36:17 amGood point.... I always feel nervous whenever I connect my circuit to the wall wart adapter

author: Dave
author_rank: Super Contributor
timestamp: June 12, 2014, 05:40:42 am
content: Yes, it is needed.First of all, proper adjustable current limiting, so you don't destroy stuff when you are poking around and do something you shouldn't.You have a circuit that is designed to accept x to y volts input. You will have no problem testing that with a proper bench power supply. Good luck doing that with a wall wart.Most importantly, it's a reliable source. You can't rely on a wall wart.Having a GPIB/RS-232/USB/ethernet port on the back can also be very useful when you want to automatize circuit testing.

author: zapta
author_rank: Super Contributor
timestamp: June 12, 2014, 05:49:45 am
content: Quote from: jimjam on June 12, 2014, 05:25:41 amYou can do a lot with standard wall warts, especially the 5V ones. A lab power supply is sometimes useful though, for example to power new circuits you just assembled. You adjust the voltage, set the current limit as low as your circuit will accept and then power the board. If there are shorts and other problems the current limit will kick in and in many cases will prevent damage.The Rigol DP832 may be an overkill for a typical hobbyist (despite the beautiful display). Any good quality lab supply should be just fine. For example, check eBay for a used HP E3610A.

author: jimjam
author_rank: Regular Contributor
timestamp: June 12, 2014, 05:55:08 am
content: I wonder if I can just build a current limiting device and hook it up like this: wall wart -> current limiter -> DUT, but I guess we get convenience, neatness, and coolness out of a bench power supply.

author: VK5RC
author_rank: Unknown
timestamp: June 12, 2014, 05:58:22 am
content: I would put a lab power supply as the number 2 piece of equipment after a DMM, Almost every time I am in my 'lab' I will use one. Current limiting has saved lots of cursing! :-)

author: Dave
author_rank: Super Contributor
timestamp: June 12, 2014, 06:02:57 am
content: Quote from: Bored@Work on June 12, 2014, 05:33:41 amI feel the same way.If you ask me, it has a terrible interface (looks downright nasty and toy-like), the non-isolated CH2 and 3 are appalling and those spikes on power switching would immediately throw me off. "It's really great, just remember to disconnect your circuit before flicking the power switch," just isn't good enough in my opinion. Imagine there is a power outage just when you are testing a super sensitive $100 chip. Doesn't even have to be a power outage, maybe you accidentally bump the switch on your power strip.That's a nice big bowl of nope, Rigol.

author: EEVblog
author_rank: Unknown
timestamp: June 12, 2014, 06:05:28 am
content: Yes, you need a proper bench supply if you are at all serious about electronics.The DP832 is aprecisionbench supply. That is a different price/performance level from your basic bench supply that will do the same job for less.As long as you have adjustable current limiting, that is what makes a usable bench power supply, but you don'tneeda precision supply for most jobs, just one with adjustable current limiting.

author: EEVblog
author_rank: Unknown
timestamp: June 12, 2014, 06:07:09 am
content: Quote from: jimjam on June 12, 2014, 05:36:29 amNope. I even bought my DP832.Rigol have given me other stuff for free though.

author: EEVblog
author_rank: Unknown
timestamp: June 12, 2014, 06:11:36 am
content: Quote from: Dave on June 12, 2014, 06:02:57 amFair enough. But do you know of a better precision supply for the same money?I tried an Atten that was similar, but it was truly awful.

author: Dave
author_rank: Super Contributor
timestamp: June 12, 2014, 06:23:45 am
content: Quote from: EEVblog on June 12, 2014, 06:11:36 amWell, you can get a used HP E3631A for that price. I don't know if it quite qualifies as a precision power supply (10mV resolution on 25V channels and 1mV on 6V channel), but if you don't have sense leads and you draw anything more than a couple milliamps, the voltage drop is going to exceed that anyway.

author: zapta
author_rank: Super Contributor
timestamp: June 12, 2014, 06:24:12 am
content: Quote from: jimjam on June 12, 2014, 05:55:08 amYou are correct on all counts except for one.It doesn't matter how cool your lab equipment is, it's matters how cool your projects are. ;-)

author: Rick Law
author_rank: Super Contributor
timestamp: June 12, 2014, 06:31:01 am
content: I am not a pro but just amateur poking around. Initially, I thought all I needed was just an adjustable voltage source. I use a cheapo CC/CV "adjustable battery charger" boost-buck board as my main power source. Now I have come to rely on the CC/CV for exactly the protection already mentioned in early comments.A cleaner power source would be good too - cleaner for me means less ripple. More power would be nice (20W is plenty for me. My cheapo can't deliver that). Stability is a given (who wants a board that wonders from 5 to 7V if you set it at 5); and a nice display of CC/CV setting and current output Current and Volt wont hurt.Even with my limited requirement,CC/CV is #1on the "must have" list even just for poking around. Next is goodlineand loadregulation. My cheapo board has very good line-regulation and temperature drift (<2% combined), but very poor load regulation. I've come to realize I really want something better. (By the definition of amateur, it cannot be a need as none of my project is a must have).Next is lower ripple.Mine can at times get kick into an oscillation with up to 50mV ripple (well, it is just a $10 "charger" board), it is way too high. So more stability would be nice. 25Volt tops for me is enough. Oh, and a big large display on current (as NOW) Voltage, Current, and selected limits (on both CC and CV). That would avoid more mistakes for me.So even just as a mere amateur, Lab grade needs? Probably not. But certainly some lab-grade level features would be nice for me (as listed above.)

author: AndyC_772
author_rank: Super Contributor
timestamp: June 12, 2014, 06:56:20 am
content: Quote from: EEVblog on June 12, 2014, 06:11:36 amI have threeHP 6632Bsupplies, which set me back about £450 between them, same as the 832A. They take up a bit of space on the bench and need the electrical connections bringing round to the front, but on the plus side they're superbly accurate, electrically very quiet, built to go on forever, and output on/off control is exemplary.They also work as electronic loads, so you get that function effectively for free, and having it built into the PSU itself is fantastic if you ever need to simulate a rechargeable battery.They're quite a different proposition from a conventional bench PSU and are disproportionately expensive new, but they're readily available on the used market and well worth a look. If you have the bench space to make them a permanent fixture, then you won't find a better quality PSU anywhere IMHO.

author: Stephen Durr
author_rank: Contributor
timestamp: June 12, 2014, 07:25:03 am
content: I just received my new DP832 a few days ago and having played around with it a bit I am happy with it so far. The latest units have most of the bugs worked out including the improved top board with the big silver heat sink on the voltage regulator and the various firmware fixes that you can read about in other threads. I ordered the hi-res option too, which I think will be very useful. Now, I am also a newbie and still building out my little bench/lab but I am serious about learning electronics so I felt this was a wise investment. Even if it is overkill right now for my first small learning projects, I'm sure I will grow into it over time and I probably won't ever exceed its capabilities so it will probably be my bench supply for years to come. My main hobby is building race cars and over the years I have spent lots of money on automotive tools and equipment for my garage/shop. I compare having a good power supply for an electronics bench/lab to be like having a good air compressor for my shop. It is a piece of equipment of such high utility and frequent use that you can be assured of getting the value out of your investment over time and you probably will not regret having spent a bit more money for a more capable unit (whether that be a new Rigol, used HP, or other).

author: Dagon
author_rank: Regular Contributor
timestamp: June 12, 2014, 02:24:48 pm
content: QuoteJust curious, did you actually bring the connections to the front on yours? Was eyeing these up on ebay a while back but the size and inconvenience put me off.

author: xquercus
author_rank: Contributor
timestamp: June 12, 2014, 03:28:49 pm
content: I'm going to buck the trend here and say that you don't, strictly speaking,needa bench supply. Many people use a wall wart (linear) with a 250mA fuse to supply an on board regulator. I'm saying this mostly to make it clear that lack of a bench supply is not a reason to not build.With that said, an actual bench supply is so convenient and pretty high up there in terms of importance. The key feature isadjustable current limiting. Unless you have an immediate reason to do otherwise, look at 15V / 3A supplies which can be had for less than $100 used. You'll probably always have a reason to hang on to a supply with these specs and you can add more specialized supplies if and when you need them.

author: senso
author_rank: Frequent Contributor
timestamp: June 12, 2014, 03:36:35 pm
content: Quote from: Dagon on June 12, 2014, 02:24:48 pmI have one 6632B(wish I money for a couple more), and its extremely easy, take four screws and the top cover slides out, near the output terminals there is a 4 way header, sort of a .1" header but a little bigger, with 4 more screws you pop the front cover off, and the holes for the bananas are already there, just run a x-acto/scalpel to cut the vinil cover, and to give some structural rigidity I used a piece of veroboard, put my bananas, and its done, I also had some plugable terminal blocks that fit nicelly in the header, the two center pins are the GND/V+, the two outer ones are the sense lines, for the sense I just put two 10 ohm resistors in the back, no ideal, but for now its been sufficient.The fact that the power supply also measures down to 0.01mA(or is it 0.001mA) is great for see how low power is your low power thingy.And its a thing of beauty to open it up and see the gigantic transformer, money well spent.

author: G0HZU
author_rank: Super Contributor
timestamp: June 12, 2014, 03:47:52 pm
content: Quote from: Dave on June 12, 2014, 06:02:57 amAgreed. The DP832 is a badly designed mess IMO but will (possibly) redeem itself if ever needed as a cheap ATE PSU.When I started out I bought (at various electronics fairs) four old bench PSUs costing between £5 and £15 each. I still have all of them and they all still work. They all have adjustable voltage and adjustable current limit and they were made by Philips, Weir (2) and Coutant. They all have analogue dials which will probably scare off a few people but they seem to be bulletproof. I've had them for 15-20yrs and none of them have ever needed a repair.The total outlay was about £40 and this gave me in total:0-20V 1A0-20V 1A0-7V 5A0-15V 4A0-30V 1A0-65V 0.6AI've since acquired quite a few TTI PSUs over the years that have the convenience of a digital display but the PSUs above gave me many years' reliable service for very little outlay

author: jpb
author_rank: Super Contributor
timestamp: June 12, 2014, 04:03:12 pm
content: As a lot of people have already said, having current limiting is very useful.It is also good having a stable and smooth linear supply from the electrical noise point of view. It eliminates the need to worry about the supply side when looking at circuits.What I've found incredibly useful is having Voltmeters and Ammeters on the supply itself - I know that you could hook up external meters but it is much more convenient to have four of them built in.Other things a lab supply does are things like tracking so if you're looking at say op amp circuits and want to vary supplies but have them match you can do it - not that I've used this facility so far.Good supplies are generally built to last so should be available at a reasonable price second hand.The one down side is the space they take up.

author: retrolefty
author_rank: Super Contributor
timestamp: June 12, 2014, 04:07:01 pm
content: Quote from: jimjam on June 12, 2014, 05:55:08 amCertainly one could build such a thing. Take the below linked example. Drive this with a 30 volt or less wall wart and you have an adjustable voltage output with an adjustable current limit or adjust it into a constant current mode. Would be more convenient to replace the voltage and current trim pots with remote pots and put it in the case, but at it's price point it could be a very affordable and useful projects.http://www.ebay.com/itm/5A-Adjustable-Power-CC-CV-Step-down-Charge-Module-LED-Driver-Voltmeter-Ammeter-/360761944080?pt=LH_DefaultDomain_0&hash=item53ff166810

author: zapta
author_rank: Super Contributor
timestamp: June 12, 2014, 04:18:56 pm
content: Quote from: xquercus on June 12, 2014, 03:28:49 pmVery well said.I would also suggest not to fall to bell and whistle power supply, even inexpensive ones like Korad. A simple power supply with two displays (I prefer digital) and two potentiometers and from a good house like HP should do just fine, even if bought used.

author: jimjam
author_rank: Regular Contributor
timestamp: June 12, 2014, 04:22:44 pm
content: AFAIK, the spike in DP832 only occurred during power on, not power off.

author: Dagon
author_rank: Regular Contributor
timestamp: June 12, 2014, 05:13:29 pm
content: QuoteGood to know, thanks.

author: AndyC_772
author_rank: Super Contributor
timestamp: June 12, 2014, 09:00:21 pm
content: Quote from: Dagon on June 12, 2014, 02:24:48 pmI just ran a set of wires round to the front and mounted some banana terminals in a small box. Simple, convenient, and no need to actually modify the PSU. The box just contains a couple of 10R resistors between the main terminals and the sense terminals, so I can use them in either 2 wire or 4 wire mode easily.

author: Andy Watson
author_rank: Super Contributor
timestamp: June 12, 2014, 09:18:05 pm
content: Quote from: AndyC_772 on June 12, 2014, 09:00:21 pmDitto, except I left the box floating so that I could move it where the work is. I also terminated the sense wires at the remote box terminals.Alternatively, the front panel already has provision for two terminals. It is only necessary to cut through the plastic overlay and install the terminals - might need a small board to add some stiffness to the structure. Rapidhttp://www.rapidonline.comsell 4mm terminal that look very similar to the HP/Agilent terminals - part nos 17-3270 and 17-3271

author: pinchip
author_rank: Contributor
timestamp: June 12, 2014, 09:21:53 pm
content: I used to use batteries to power-up my projects. Not very convenient but it worked quite well.I builded then power supply myself. I used old laptop charger and aluminium wlan box from dumpster, cost 0 euro. I added voltage regulator, potetiometer and 4 banana terminals, cost few euros. It can give 1V - 18V 4A output. I might add later current regulation, but I am quite happy with it already now.

author: VK5RC
author_rank: Unknown
timestamp: June 13, 2014, 12:22:08 am
content: I use Anderson powerpoles as my dc standard connector also as the power output from my hp psus (6632, 6644), as I am not doing high accuracy stuff I use the shorting bar at the rear for the sense lead, I have a collection of powerpole to various clips, solderable ended leads for connecting to DUT.