Outgrowing my cheap bench supplies, whats next? - Page 1
Forum section: electronics / testgear

author: rx8pilot
author_rank: Super Contributor
timestamp: November 15, 2014, 07:11:39 pm
content: A while back, I purchased some low cost random brand switching bench supplies. 0-30v @10A with V and I displays. they have been reasonable little guys considering the super low cost.http://www.circuitspecialists.com/csi3010sw.htmlThe problems I have start with the voltage adjust pots are now dirty or worn out. This of course causes the supply to spit out a mess of voltage range when I am trying to make subtle changes. The next problem is I would really like better low current limiting, these little guys are adjustable, but only to a point. I am not complaining about a <$100 supply that has lasted 2 years - but it is time to step up.The question is, how much should I budget for (2) bench supplies that can deliver 0-20v (or higher) @ 10A continuous (or higher) that can deal with continuous adjustments on a daily basis. Digital pots are ok, as long as the steps are reasonably fine (.01v or so). I would also hope for current limiting at lower loads like <50ma. The cheap supplies let .25A blast through before limiting, and by then some damage has been done.Bonuses would be programmable since they are used to test battery operated equipment and it would be nice to program a discharge curve. My biggest criteria is reliability with constant fiddling and good displays so that I don't have to have external meters.I am assuming that I am >$1000 USD each but I am not sure what is out there. There are some that are extremely expensive with amazing specs, but they are likely overkill - exotic ripple specs will not be needed. (In fact, I need to 'simulate' bad power supplies to make sure my circuits can tolerate a mess) In the end, I need the proper supplies, but don't want to over do it. New gear is very much preferred since I will have a known starting point. I don't want to inherit the odd personality of a used supply even if it seems like a great deal on eBay.If anyone has practical experience or advice on some of the higher-end bench supplies, I would love to hear about it. Good brands, bad brands. I was looking at the Rigol supply for a second until I heard from someone that the display updates are very slow thus requiring external meters. I don't want a surprise like that.

author: Fsck
author_rank: Super Contributor
timestamp: November 15, 2014, 07:31:39 pm
content: would used really kill you?http://www.ebay.ca/itm/Hewlett-Packard-Agilent-6542A-DC-Power-Supply-/141247365731?pt=LH_DefaultDomain_0&hash=item20e2ffc263old "system" supplies tend to be rock solid.

author: janengelbrecht
author_rank: Regular Contributor
timestamp: November 15, 2014, 07:35:02 pm
content: Quote from: Fsck on November 15, 2014, 07:31:39 pmBut ? Only 20V ?

author: bingo600
author_rank: Super Contributor
timestamp: November 15, 2014, 07:41:25 pm
content: Get a HP 66xx from here or *Bayhttps://www.eevblog.com/forum/buysellwanted/fsft-hp-power-supplies-fluke-multimeters-(chicagoland-area)/msg548234/#msg548234/Bingo

author: Fsck
author_rank: Super Contributor
timestamp: November 15, 2014, 07:42:24 pm
content: Quote from: janengelbrecht on November 15, 2014, 07:35:02 pmhis post says 0-20V, 10A at minimum which that model meets. one could just go through the hp/agilent/keysight/whateverwillbenext catalog and flick through the list of system supplies. hp/agilent supplies in the (exact) same formfactor tend to have similar behaviour.

author: nctnico
author_rank: Super Contributor
timestamp: November 15, 2014, 07:48:02 pm
content: HP has several switching power supplies like the HP6024 or HP6038 which can deliver 200W (max 60V 10A) which are lightweight but also a bit noisy. For sensitive stuff I usually use a linear power supply from Voltcraft (I replaced the normal pots with 10 turn pots).Edit: noisy= the fan

author: rx8pilot
author_rank: Super Contributor
timestamp: November 15, 2014, 07:52:54 pm
content: Used will not kill me, but I am concerned that going that route could create a side project that I don't have the time to tend to. I would hope to take it out of the box and put it into use with little concern that the previous owner/users did bad things to it that could cause issues that are not easy to fix. 0-20v is workable BTW over 20v is a rare need for me and I could use one of my existing supplies for that.New is good for me. I don't mind spending the proper amount of money either. Like I said, I dont want to over do it, but dont want anything to blame on my bench either. At the moment, my random bench gear is among my biggest limitations to grow. I am looking at high-end scopes, 6.5 digit DMM, power supplies, and some automated test gear so that I can focus on the circuit problems instead of bench problems. I also need 2 matching supplies so getting two of the exact same on eBay is a little harder than getting two brand new ones.HP, Agilent, Keysight seem to be good brands. Who else are the good players at that level? The low-end of the high-end seems to be where I should be looking.

author: janengelbrecht
author_rank: Regular Contributor
timestamp: November 15, 2014, 07:54:23 pm
content: Quote from: nctnico on November 15, 2014, 07:48:02 pmThx - This replacement i will do too

author: Fsck
author_rank: Super Contributor
timestamp: November 15, 2014, 08:19:22 pm
content: the thing is, those used system supplies are (subjectively) very reliable and can be had for <10% MSRP which tends to make them excellent values.if it has to be new, an hp/agilent/keysight E3633A comes to mind. (you can guess my brand inclination for power supplies).my other choices would be Chroma, Keithley, TDK Lambda, etc, basically big names in ATE. obviously, I'm thinking linear here; I've never used a programmable smps.<50ma limit for a 10A range sort of cuts out a huge swath of supplies.

author: Yago
author_rank: Frequent Contributor
timestamp: November 15, 2014, 09:03:53 pm
content: Quote from: rx8pilot on November 15, 2014, 07:11:39 pmI am far from knowledgeable in this, hopefully someone can shed light on this thought...Seem to recall reading that the HP6632B was designed primarily as a constant voltage device, and so the capacitance at the output is high. It can dump energy above the CC setting.Also remember something about this being quite common in some other PSU that aim for smooth voltage output.Disclaimer of my 80's addled brain, need the boffins to chip in and confirm or refute!Edit: I think the above is the case, and HP advise shorting the output of the powersupply when turning the output on to start it in CC mode.

author: edavid
author_rank: Super Contributor
timestamp: November 15, 2014, 09:44:56 pm
content: Quote from: rx8pilot on November 15, 2014, 07:11:39 pmThese requirements are somewhat contradictory. I think that you should keep and repair your existing 10A supplies (I would try to get Circuit Specialists to send replacement pots), and get a separate dual or triple linear power supply for your lower current needs (used HP or new Korad?).

author: rx8pilot
author_rank: Super Contributor
timestamp: November 15, 2014, 10:25:55 pm
content: I may try to use an outboard protection scheme so that I don't have to depend too much about the supply limiting current. Most of my boards are power management and routing. I already have some excellent sensing circuits that are MCU programmed and monitored. I could use one of those to be programmed to allow a current profile allowing for some inrush but expecting the circuit to settle or turn it off. This will really loosen the requirements of the bench supply in the current limiting. Most of the delicate work has to be figured out at very low currents so the idea of having a separate supply for the delicate work and the high-current full load tests may be wise.If that works, the hp/agilent/keysight E3633A seems like a solid choice as I would not have to worry as much about damaging a prototype PCB that took me 4 hours to assemble.Repairing the Circuit Specialist PSU's seems a little silly - they were literally under $100! The pots have seen a LOT of turns. Maybe I will clean the pots and put them on emergency backup duty.

author: edavid
author_rank: Super Contributor
timestamp: November 15, 2014, 10:40:48 pm
content: Quote from: rx8pilot on November 15, 2014, 10:25:55 pmWell, if you feel that way, send them to me... I'd be happy to pay shipping.

author: nixfu
author_rank: Unknown
timestamp: November 15, 2014, 11:08:43 pm
content: Too many good HP 66xx programmable power supplies on the surplus market cheap these days not to take advantage of that vs buying a new poor quality one from China.I really like my $80 HP 6632A.

author: rx8pilot
author_rank: Super Contributor
timestamp: November 15, 2014, 11:15:30 pm
content: $80? Maybe I should try. I could buy 4-5 of them and always have spares. I see a bunch of them from $200-$300.Do you know which models can do better than 10A?

author: Mark Hennessy
author_rank: Frequent Contributor
timestamp: November 15, 2014, 11:23:25 pm
content: No-one has mentioned Thurlby Thandar yet - definitely worth a look. They have a large range using different technologies, so there's bound to be at least one that meets the requirement. The TSX series might be a good starting point:http://www.tti-test.com/products-tti/psu/tsx-series.htmFrom personal experience, their products are well designed and well built, and their support is superb. I have lots of their older gear at home and at work.

author: edavid
author_rank: Super Contributor
timestamp: November 15, 2014, 11:35:08 pm
content: Quote from: Mark Hennessy on November 15, 2014, 11:23:25 pmVery hard to get a good deal on them in the US...

author: nixfu
author_rank: Unknown
timestamp: November 16, 2014, 02:18:17 am
content: Quote from: rx8pilot on November 15, 2014, 11:15:30 pmI got mine as "make offer". You would suprised sometimes you can get a good deal on ebay that way from people selling surplus and often they would rather just get rid of it and take the money if they have a stack to get rid of.But if you need more amps, look for the HP 664x models, not the 663x models.

author: kxenos
author_rank: Frequent Contributor
timestamp: November 16, 2014, 03:16:05 am
content: Quote from: Mark Hennessy on November 15, 2014, 11:23:25 pmI have a CPX200 for 16 years. 2 channel, 35V 10A each. It's used everyday for 2 to 10 hours, never had any issues. I recently tested it with a calibrated keithley 2000, it was something like 3mV out per 10V output after 16 years without a single calibration. I've used it many times to test leds at 10mA without a resistor and also had it supply 24V 10A for 2 days continuously. No overshoot no hiccups, no noise, no problem. I wish I could find one for my home lab. I also use a ql355. It's perfect too. TTi is top of the line but I'm afraid out of OP's budget

author: SharpEars
author_rank: Unknown
timestamp: November 16, 2014, 03:43:31 am
content: As someone who owns more power supplies than any reasonable person should have, I can vouch for used HP/Agilent supplies being the cream of the crop. Basically, you have to consider at least the following four dimensions when buying a new (lab grade) power supply:1) Voltage/Current (e.g., will it do 20V@5, 35V@15 or 60@9 amps) (For a reasonable price, used HP/Agilent is king in this category, by a mile or ten).2) Programmability (e.g., GPIB or on a new supply USB) (For a reasonable price, used HP/Agilent is king here.)3) Accuracy and programming precision/accuracy (The higher the power of the supply, the lower the accuracy of both its metering and setting) (Rigol is king here for new supplies.)4) Ripple and other noise factors (Ripple tends to increase with power) (Very old Power Designs Precision supplies are king here, unless you're spending $5k+, but you will take a major hit on Item #1 with them, V/C)As you make demands in any of these four dimensions, the price goes up. In fact it starts to go up exponentially rather quickly. This is why I love used 10+ year old HP/Agilent supplies - they do very well in all four dimensions, in particular the first two, for a very reasonable price.Sure, you can go the $50-$100 Chinese 30@5, 30@10 or 60@5 route, but hey odds are these supplies can't handle their full load for more than 15 minutes, are noisier than a drunk neighbor having a barbecue (both fan loudness and ripple wise) and as you've noticed the parts and worksmanship are crap (and that's putting it mildly). I own one of these 30 V / 5 A jobs and when I compare it to my 20 V / 5 A HP 6632A units, it's no contest - the HP is engineered like a real power supply should be. The Chinese job looks like just a hair over something I would build on a breadboard with a 7805 (well OK, an LM318 if you must be picky and point out that we are talking about variable voltage supplies (In fact there is such a thing for sale right now on e-bay for less than $9.50, transformer not included. You may find it amusing from that ad that that Hong Kong seller won't ship to Hong Kong!)).If you absolutely must get a brand new supply (e.g., you want the ability to set at 1/10 millivolt accuracy or you like the cool new displays), the order I would consider them in is Instek followed by Rigol, for supplies under $1000. If you need more current and don't mind a loss of accuracy and the increase in ripple that accompanies a switching supply, BK Precision isn't too bad of a choice either. BK also make great precision low noise linear supplies, but those tend to be a lot more expensive (i.e., at least compared to Instek and Rigol).Whatever you decide, do your research. There are very many choices out there and it can be difficult to sort through them. Think hard about what it is specifically that you want out of your new supply and intersect those criteria with the advice all of us are sending your way in this thread.

author: mzzj
author_rank: Super Contributor
timestamp: November 16, 2014, 10:32:23 am
content: Quote from: Yago on November 15, 2014, 09:03:53 pmI am not sure how nicely other power supplies behave in short-circuit current limiting situation but 6632B I am pretty familiar with.Output capacitance has hardly anything to do with it, problem is the current limiting loop that is acting with finite speed.Output stage hard limit is something like 6 to 8 Amps and it will react without delays.I am just curious. Does anyone have measurement data on other power supplies how fast the current limit reacts?IE set current limit to 0.1A, voltage to 20volts and connect output wires to 1 ohm resistor. And measure the voltage peak over the resistor with scope?

author: rstoer
author_rank: Regular Contributor
timestamp: November 16, 2014, 12:15:07 pm
content: Quote from: Mark Hennessy on November 15, 2014, 11:23:25 pmI have two of their programmable QL series and I have nothing but good things to say about them. Very nice supplies. As someone else said, they're hard to find in the US but they surface occasionally.

author: Yago
author_rank: Frequent Contributor
timestamp: November 16, 2014, 12:38:13 pm
content: Quote from: mzzj on November 16, 2014, 10:32:23 amFound the doc.The output cap is outside of the current control loop and can dump energy into the load.http://www.keysight.com/main/editorial.jspx?cc=GB&lc=eng&ckey=1000003714:epsg:faq&nid=-536902296.384349&id=1000003714:epsg:faq

author: Marco
author_rank: Super Contributor
timestamp: November 16, 2014, 12:59:25 pm
content: Looking at the schematics in fast mode there is about 2 uF of combined output capacitance with most of that having 1 Ohm series resistance ... but it's stability with capacitive loading is close to unusable. Normally it has about 100 uF with most of it having 0.5 Ohm series resistance.

author: G0HZU
author_rank: Super Contributor
timestamp: November 16, 2014, 01:15:42 pm
content: Quote from: Mark Hennessy on November 15, 2014, 11:23:25 pmyes I would also endorse TTI PSUs if you can get them.At my place of work we have literally hundreds of lab PSUs and nearly all of them are the TTI 32 2A type or the TTI CPX200 (2x10A) or CPX400 (2x20A)We also have some Xantrex PSUs for higher power stuff.TTI supplies are very good because the display is usually big and simple and bright and easy to read. I can read a TTI CPX200 from across a large worklab at a casual glance. The UI is simple and the footprint of the PSU is very small.You can also buy then used on ebay reasonably cheaply. The newer models offer remote control but these are going to be very expensive.I won't touch a HP6632 PSU because the human factors aspect of that PSU is awful. It's an ATE PSU with a tiny display, poor UI and it is the wrong shape. i.e. it would eat into my work space and also the fan is very noisy and the power output connections are at the rear panel. If we had these at work few people would use them because they are too big to put on our typical bench shelves and for the reasons I listed above. Also, I think at least some of them don't recall previous settings when power cycled.My advice is to consider the human factors of your PSU choice. Buy something that is good to use and doesn't take up much space or cause a lot of noise. Don't just buy something (eg an ATE PSU) that looks good on a spec sheet

author: TheBay
author_rank: Unknown
timestamp: November 16, 2014, 01:27:44 pm
content: Quote from: Mark Hennessy on November 15, 2014, 11:23:25 pmTTI are awesome, I have TSX3510

author: electronic_eel
author_rank: Regular Contributor
timestamp: November 16, 2014, 03:33:06 pm
content: Just to chime in: I've got a TTi QPX1200 for the cases where I need a little bit more power than my regular bench supply can deliver:http://www.tti-test.com/products-tti/psu/qpx-series.htmYou can dial in voltage in 1mV steps and current in 10mA steps. Either with the jog wheel (digit selectable with cursor keys) or with a numeric keypad. Very conveniant.OCP and OVP are also integrated.This supply is built very robust and has never caused me any problems.About availibility: I'm from Europe so I don't know about availibility in the US, but their website says they are distributed by element 14 and a few others:http://www.tti-test.com/products-tti/howtobuy-tti-notuk.htmBut I guess used gear from them isn't that common in the US than e.g. from HP.

author: rx8pilot
author_rank: Super Contributor
timestamp: November 16, 2014, 06:11:14 pm
content: I really appreciate the collective wisdom all have offered and have totally reconsidered the option of used PSU. The availability of HP/Agilents is very good in the US and they seem to be able to deliver everything that I would need. After really looking at the nitty gritty, I finally realized that I can get 2 power supplies plus a spare for significantly less than the cost of one new one. As I said earilier, the goal was not to get the best deal possible, but rather get the very reliable and high performance power supplies that I need without spending more than I need to. I also did not want a "project" supply. Not surprising, most of the used supplies on the market have been in a stationary rack for 10 years not being used all that much. The most desireable one to me are the ones that have been in an automated environment, so the buttons and knobs rarely get used.Anyway, I am going to try an HP/Agilent 6653A that is available about 10 miles from my house. 0-35v, 15A so I will not soon outgrow it. There are a number of others available if I like it enough to get 2 more. These should be good at the full load testing and give me the option of automating the tests. The downside I can see right away is that it is a monster - huge.From what others have said, it seems I should consider a smaller supply for the more delicate jobs that don't need nearly the current, but they do need delicate control and tighter regulation. This would be used in design and testing of the control sections of the designs which are delicate digital and analog circuits. Does that make sense?Quote from: SharpEars on November 16, 2014, 03:43:31 amThis was a great addition to this thread. Thank you, the "Four Dimensions" was a great presentation of what needs to be considered in a professional lab supply. Hopefully, I will be lucky to get some clean used supplies. Thanks all for chiming in so I could look in the right direction. The original rigid requirement of buying only new, now seems silly.

author: G0HZU
author_rank: Super Contributor
timestamp: November 16, 2014, 08:36:14 pm
content: That's some step up in performance...Not sure it meets your initial requirement of having a decent display though. Purpose built ATE gear is well known for having a crappy human interface and HP seem to be masters at producing murky looking LCD displays and bland and poorly planned keypads on stuff like this. Make sure you are happy with the UI before you purchaseOne thing to watch out for is that PSUs like this can be fragile if you connect them to an active load. As you seem to be working with battery powered equipment rated at highish current then I'd recommend you don't connect it directly to any kind of active load like a battery.

author: rx8pilot
author_rank: Super Contributor
timestamp: November 16, 2014, 09:11:06 pm
content: There is no doubt that the display is seriously boring. I am hoping that it updates as quick as a normal DMM would at least. This purchase is an experiment so far, the seller has a 14 day return policy and they are only 15min from where I live. I am looking around for utilities that allow me to remote control it on my PC. Not even sure if that is possible.Shifting my wish list seemed to be inevitable based on the feedback. The high-end brands have not updated ergonomics or presentation since the mid-80's, the low-end brands seem to be putting lipstick on a pig with color displays. I had to get the priorities dialed in a little better.When looking at the latest Rigol programmable PSU, I thought it had an awesome color graphics display. I had heard through reviews that it updates slowly (1hz-ish) which would drive me nuts. On top of that, I purchased a Rigol scope after I lost my Tek in a company split-up. Now I am dying to get back to a "real" scope. The Rigols give you more than what you pay for, but less than I need.These HP/Agilent supplies should never see a battery, they will be used to simulate a battery. They do have to go from 0-full load with the switch of a FET, so I guess I will find out how well they do with sharp inrush (capacitive) loads.

author: rx8pilot
author_rank: Super Contributor
timestamp: November 18, 2014, 09:46:27 pm
content: Well, experiment #1 showed up today. Agilent 6653A 0-35v @ 15A power supply for $400. List was $3800.So far the unit does what it was designed to do. Extremely clean (noise/ripple seem to be below what I can measure on my bench which is 2mv). Displays are dead on from what I tested so far. Programability is quite awesome for sure. I have a GPIB to USB on the way. My super cheap supply was at about 45mV of ripple plus it had dirty analog scratchy pots so the voltage would jump all over creation while adjusting - not good.Check out the difference. The 6653A is a tank. Old supply sitting on top.It is safe to say that getting the used supply was wise. I am already looking at getting a second one (I need two full time)

author: Fsck
author_rank: Super Contributor
timestamp: November 18, 2014, 10:08:24 pm
content: I think you're a bit too generous on describing the display. the UI is absolutely miserable (I seriously have no clue what they were thinking, even if it is a system supply) for something that's 3U tall. it's the primary trade off to get amazing bang for your buck.I also think you paid a bit more than I would have but having it local-ish is probably worth it over the risk of shipping something so bulky and heavy.

author: rx8pilot
author_rank: Super Contributor
timestamp: November 18, 2014, 10:38:06 pm
content: Well, I was only referring to the accuracy of the display, not the digital wrist watch from 1981 look. It is ugly for sure. They are, however, accurate and fast reacting which is great. When it came time for compromise, I thought the display was better to downgrade if it allows me to have what appears to be a really solid power supply that I will see many long days of service. Really wish is had front outputs, but it's not really a bench supply.And yes, I could have found one slightly cheaper but this one was low-risk and returnable if I found anything that was not right.

author: G0HZU
author_rank: Super Contributor
timestamp: November 18, 2014, 10:50:39 pm
content: Quote from: Fsck on November 18, 2014, 10:08:24 pmI think HP must relegate all their worst performing and most clueless engineers to the task of producing ATE front panel user interfaces and murky displays on products like this.