Buying power supply - Page 1
Forum section: electronics / testgear

author: NemoVanHelden
author_rank: Contributor
timestamp: December 03, 2012, 08:04:30 pm
content: Hi,I want to buy a good all-round power supply, but it will be used mainly for audio and small signal analog stuff ( at least to begin with). I read in a thread here that a switching supply is not suitable for this purpose.What kind of power supply would i be looking for?

author: ptricks
author_rank: Frequent Contributor
timestamp: December 03, 2012, 09:27:26 pm
content: Switching can be used for analog but you will have to spend more money to get optimal results. Linear supplies are what most recommend for analog work. Linear supplies are basically a transformer to convert the mains voltage to a lower voltage, followed by a rectifier and capacitor, then some sort of regulator. Really pretty basic stuff which is why a lot of people just build their own.The LM317 is a common part and circuits are everywhere on how to use it, it is also cheap.If you want to spend the money though look on places like ebay for Linear power supply.

author: NemoVanHelden
author_rank: Contributor
timestamp: December 04, 2012, 10:57:37 am
content: Ok, sounds like i should get a linear supply for my lab then.The only con is that the weigh a lot more, and I'd like it to be little lighter as i will probably be moving it a bit around. If i wanted a switching supply that can be used for the purpose mentioned in the first post - what price range am I looking at? If you have one or two specific models to suggest I'd be very grateful.

author: ptricks
author_rank: Frequent Contributor
timestamp: December 04, 2012, 12:55:46 pm
content: Quote from: NemoVanHelden on December 04, 2012, 10:57:37 amIt really is going to depend on what analog circuits you are working with , how much current, and how sensitive the circuits will be to noise. For example, working with some analog circuits like an opamp with high gain, a lamp on the desk with a CFL bulb can inject noise into the circuit.If you just need low current linear you should be able to use something like this and the weight shouldn't be that much because the transformer required is going to be small.http://www.ebay.com/itm/15V-1A-Digital-DC-Power-Supply-Regulated-Precision-Variable-Test-Equipment-Phone-/370630154870?pt=LH_DefaultDomain_0&hash=item564b475a76

author: Yaksaredabomb
author_rank: Regular Contributor
timestamp: December 04, 2012, 01:47:39 pm
content: Quote from: ptricks on December 04, 2012, 12:55:46 pmFor 35 USD shipped that actually sounds fairly reasonable. Granted it's not very fancy and not terribly capable but it looks like most of the basic things are there (current and voltage meters, switched output with test point, reasonably sturdy enclosure, test leads). I was planning to build my own (eventually) but I'm not sure I could for near the same price and have it be (or at least look) anywhere near as robust.Has anyone actually bought one of these or better yet, taken one apart? I searched the forum for "PS1501S" and came up blank. I'm sure a person would be much better served spending $100-$150 on something better known with more outputs and greater power (or building their own), but if all you've got is $35 or your requirements truly are this low maybe this is a good pick.

author: ptricks
author_rank: Frequent Contributor
timestamp: December 04, 2012, 02:00:19 pm
content: Quote from: jneumann on December 04, 2012, 01:47:39 pmWhat I did to build my own was to find a cheap power supply that had the look I wanted then gutted the inside. Enclosures for the size of a power supply are way overpriced and for about $25 I got an old Elenco xp-580 model with a good transformer.Looking at the pic of the ebay listing it is using a pass transistor, 2n3055, which usually means LM317 or LM723 inside.

author: AlphZeta
author_rank: Regular Contributor
timestamp: December 04, 2012, 07:30:16 pm
content: QuoteWell, the type of applications you have in mind can actually be quite demanding. I would look for a quality dual power supply that does at least +-18V because a lot of audio circuits are using dual rails... And if you are doing power amps, I'd recommend a power supply that can handle at least +-30V 3A.Audio and signal circuits are sensitive to noise as well, and you probably want to stay away from those dirt cheap ones...

author: NemoVanHelden
author_rank: Contributor
timestamp: December 04, 2012, 09:11:11 pm
content: What price range would i be looking at for that kind of power supply? Do you have any specific ones to suggest? I would like to stay below $200, but I`d rather get a quality supply rather than have to change it because it doesn`t fit my needs.

author: AlphZeta
author_rank: Regular Contributor
timestamp: December 05, 2012, 01:11:31 am
content: For $200, you have many choices. A lot of people on this forum seem to like Mastech power supplies and brand new ones typically cost less than $200 (for example, dual 30V 3A). Or you could buy a quality used power supplies, but you really need to know what you are getting....

author: NemoVanHelden
author_rank: Contributor
timestamp: December 05, 2012, 06:58:23 pm
content: Allmost all dual PS i find are listed as 0-20V, 0-30V etc. Very few are listed as +-30V. How do I know they will provide negative voltage?Also, what kind of safety features should i be looking for in a linear power supply? Safety is my top priority.

author: robrenz
author_rank: Super Contributor
timestamp: December 05, 2012, 07:23:33 pm
content: The power supply outputs should be floating (not connected to ground unless you want to) so you jumper the positive of one supply to the negative of the other supply and that is your common. Then the unattached positive will be your +voltage and the unattached negative will be your -voltage

author: NemoVanHelden
author_rank: Contributor
timestamp: December 05, 2012, 07:58:38 pm
content: Thanks. I found this PS -https://www.distrelec.ch/laboratory-power-supply-de-ch/-/ps23023dl/925403/enwhich, if I interpret the user manual correctly, is capable of such operation. Can someone confirm this?I could not find any reviews on it. Anyone know if this is a good PS?

author: robrenz
author_rank: Super Contributor
timestamp: December 05, 2012, 08:10:58 pm
content: I have had thisthis power supplyfo about 3 years and it works very well. At $170.00 it is a bargain.It has the very important 10 turn pots on the voltage controls.

author: Bored@Work
author_rank: Super Contributor
timestamp: December 06, 2012, 07:31:20 am
content: Quote from: NemoVanHelden on December 05, 2012, 07:58:38 pmThis is hard to say for this kind of PSU. This kind is mass-produced in China by several companies. And then maybe hundred companies rebrand them, giving them their own brand and type number. From the outside they all look very similar, and you can't tell what is inside.Typically this kind of PSUs works OK and you get your money's worse. Occasionally you see some of these which are not OK (unsafe, not meeting their specs, or not working at all). If you buy from a reputable company the risk of getting a bad one is typically low. If you buy on eBay, your risk is a bit higher, but not extreme.Wherever you buy one from, before you plug it in first time open it and inspect it. Is it safe? If not, send it back. Has it acceptable build quality (don't expect first class build quality). If not, send it back. After you plug it in measure if it overshoots. If it does more than a bit, send it back. Then check the specs, if it doesn't meet the specs ...Regarding Distrelec, I do remember them as a distributor with high prices, and good quality stuff, but their service didn't match their high prices. But I think that was before they got borged or they borged others into some larger distributor holding company. Things might have changed.

author: NemoVanHelden
author_rank: Contributor
timestamp: December 06, 2012, 10:19:59 am
content: After considering what you said I`ve decided I`ll spend a little more and know what i get, rather than risk having to return some random quality power supply. From what i read in this forum TTi seem like a good choice (please correct me if I`m wrong).I think i will get the TTi EL302RT. Is this a good power supply?The product brochure says:"The EL302RD has two independent and isolated outputs each with a 0 to 30V, 0 to 2A capability and its own on-off switch. The outputs can be wired in either series or parallel to provide voltages up to 60 volts or current up to 4 amps". I interpret this as that it can be used the way robrenz suggested in order to get negative voltage. Can anyone confirm this before i order?

author: cybergibbons
author_rank: Frequent Contributor
timestamp: December 06, 2012, 10:39:11 am
content: Yes, you can use it for +/-30V operation.

author: Yaksaredabomb
author_rank: Regular Contributor
timestamp: December 06, 2012, 12:35:34 pm
content: Quote from: ptricks on December 04, 2012, 02:00:19 pmThanks for the idea! A cheap unit could be a great place to start, especially depending on how much could be salvaged. Even just the enclosure would be helpful.

author: Yaksaredabomb
author_rank: Regular Contributor
timestamp: December 06, 2012, 12:50:01 pm
content: Quote from: NemoVanHelden on December 05, 2012, 07:58:38 pmI noticed on its "Technical data" section the power is rates as 90W. That could be something to watch out for. In parallel mode, 6A@30V would be 180W. That's the same power as 3A@60V.Realistically it can be configured for 6A@15V max / 3A@30V max (parallel) or 3A@30V max / 1.5A@60V max (series). It's still a useful feature to get that 6A even if only up to 15V, or to run at 60V even if only at up to 1.5A, but it might not be what someone would think at first glance.Am I reading that right? Maybe the 90W is "per output", so with 2 outputs it can do 180W and the full range of 6A@30V/3A@60V. I wouldn't want to assume that though.Quote from: robrenz on December 05, 2012, 08:10:58 pmThis looks like a nice supply for the price and I'd even be tempted to get it versus build my own. But then, if I don't have the time to build one do I have the time to use one? Anyways, I looked at its listed "Features & Specifications" and it doesn't seem to have a power rating. Can we assume it may be subject to the same issue as the other supply (above)?Or maybe I'm just being paranoid and someone will set me straight. Thanks!

author: Yaksaredabomb
author_rank: Regular Contributor
timestamp: December 06, 2012, 01:55:59 pm
content: Quote from: jneumann on December 06, 2012, 12:50:01 pmI might've set myself straight, at least on the "VOLTEQ VARIABLE POWER SUPPLY GPC-3030D TRIPLE OUTPUTS 30 V 3A" linked above. I found a GPC-3030D with the Instek brand here, rated as 195W (even includes power for the 3A@5V source):http://www.testequipmentdepot.com/instek/powersupplies/gpc-3030d.htmIt's selling for $460, though (vs $170). The Instek name probably adds something but I doubt it's really worth an extra $300 (2.7 times the cost?!). So either the Volteq is indeed a real steal or there's something going on here. Maybe the Volteq is a real steal AND there is something going on here, haha.Anyhow, just wanted to say it looked like the GPC-3030D might indeed be rated for the full 195W output (if it's rated the same as the Instek).

author: robrenz
author_rank: Super Contributor
timestamp: December 06, 2012, 02:34:45 pm
content: I think I paid around $250.00 for it from that same site. so the $170.00 is still quite a sale. I have used mine at full load on both channels for significant lengths of time with no problems.

author: T4P
author_rank: Super Contributor
timestamp: December 06, 2012, 07:47:25 pm
content: the extra 210$ is for GW Instek's EXCELLENT quality & build.It's like a alternative to a TTi but with nonetheless great quality & NO SAMWHA CAPS! Won't find them there ... GW Instek don't do such sneaky business unlike TTi ...

author: mickpah
author_rank: Regular Contributor
timestamp: December 06, 2012, 10:40:26 pm
content: I bought one of these MANSON SMPS a couple of days agohttp://www.manson.com.hk/en/dcpowersupplies_detail.php?m=3&id=32looks like the OEM for Extechhttp://www.extech.com/instruments/product.asp?catid=39&prodid=207which sells here for twice as muchgot it hereebay :http://tinyurl.com/avokebfI stripped it down for a safety check and looks good , very solid, clean unit. Haven't done any performance check yet - no time , but so far so good.All going well I will probably get one of their linear supplies laterDave also did a tear down of one of their 40A supplies EEVblog #272

author: jwrtiger
author_rank: Contributor
timestamp: December 06, 2012, 10:56:45 pm
content: NemoVanHelden,Looks like a nice supply but I am not familiar with that company. You should be able to use it as a split power supply as robrenz suggested. Some supplies have an internal relay that connects them in series mode. I run most of my supplies in series mode for opamp circuits and that way I can get +/- 15 volts if needed. I like the power output on-off switch and the remote sensing on the one you are looking at. I have a remote switch box because mine doesn't have output on-off switching but a nice feature of my box is one switch turns off both the positive and negative voltages to the breadboard at the same time.