Variable power supplies - Page 1
Forum section: electronics / beginners

author: GnatGoSplat
author_rank: Regular Contributor
timestamp: July 30, 2012, 06:03:41 pm
content: When a regulated variable power supply is rated for example, 0-30V 5A, does that mean 5A is the max available current whether the output is set to 5V, 15V, or 30V? Or does that mean the power supply is limited to 5A at 30V (150W) and could supply 30A at 5V, 10A at 15V, etc.?

author: HardBoot
author_rank: Regular Contributor
timestamp: July 30, 2012, 06:15:16 pm
content: A lot of them lie about their specs and have a lower power than their peak amp*volt combined.150w 30v 5a; you can get that from a $10 switch mode power supply, but a quality psu no noise, variable voltage and current limiting, costs a lot more, especially if it's a linear.

author: GnatGoSplat
author_rank: Regular Contributor
timestamp: July 30, 2012, 06:23:49 pm
content: So generally, because a variable PSU says 0-30V at 5A, that does NOT mean it's limited to 5A at lower voltages?Is linear better for a variable power supply? I've always read that SMPS are more efficient, smaller, and lighter, but those are all fixed voltage supplies.

author: T4P
author_rank: Super Contributor
timestamp: July 30, 2012, 07:09:52 pm
content: OF course linear is, unless you do not want a massive power supply when you want some powerWell i think you are quite virgin to the PSU scene ... no really, i've seen many adjustable SMPS PSU's everywhere already and they have been there for many yearsDave reviewed his "GW-Instek" programmble lab bench SMPS and his Manson 600W SMPSMike reviewed his tiny Manson lab bench SMPSwell unless you want a transformer like that ...

author: GnatGoSplat
author_rank: Regular Contributor
timestamp: July 30, 2012, 07:31:49 pm
content: Quote from: T4P on July 30, 2012, 07:09:52 pmYes, I would definitely agree that I'm a virgin to the PSU scene.I have been using the same unregulated linear PSU that I got for free 20-years or so ago when I was a kid, but now I think I would like a modern regulated one.I think I mis-worded what I meant to say though. I know there are many variable SMPS PSUs available, but what I mean is when I see a comparison between SMPS and linear PSUs, there are always many more pros than cons for choosing SMPS. So it sounds like for a variable PSU, there are more pros than cons to choose linear instead.

author: T4P
author_rank: Super Contributor
timestamp: July 30, 2012, 07:38:30 pm
content: Newer designs nowadays do not have half as much noise as in the past and the GW Instek Programmable SMPS is actually quite good in factNow there is just 2 considerations:Linear campLive without power and have a smaller PSULive with power and have a massive PSUSwitching campLots of power in a small footprintIf you need to frequently move you PSU about, the good one is the one Mike reviewed, it's not very heavy and really small! ( I saw it in a store and i will take a photo of the size difference )http://www.manson.com.hk/en/dcpowersupplies_detail.php?m=3&id=17But basically it's about what you do not need and what you needIf you do not need the power and want lower ripples, linear of course if you are looking for a small footprint PSU, not something like mine (I didn't mind because ... it's only 100 bucks)PS: The GW Instek i'm talking about is actually a Manson again also

author: HardBoot
author_rank: Regular Contributor
timestamp: July 30, 2012, 09:04:12 pm
content: Do you even need 30v?A quality computer power supply can provide a lot of power and has lots of 12v amperage, quite a bit of 5v, some 3.3v and a tiny -12v.Using one is as simple as shorting the green wire to ground, there's also a 5v standby and "power good"(grey) wire.You can use a cheap linear dc-dc converter to get any odd in-between values.My computer PSU only gives 10mv ripple, plenty good for most uses, and if you wanted better... well you'd have to pay a lot.

author: Monkeh
author_rank: Super Contributor
timestamp: July 30, 2012, 09:24:58 pm
content: Quote from: HardBoot on July 30, 2012, 09:04:12 pmIt is not as simple as bringing the PS_ON# line low. ATX PSUs have regulation and loading issues.

author: HardBoot
author_rank: Regular Contributor
timestamp: July 30, 2012, 10:19:31 pm
content: Quote from: Monkeh on July 30, 2012, 09:24:58 pmGood ones don't, cross loading and even no-load isn't an issue in "modern" independent designs.

author: Monkeh
author_rank: Super Contributor
timestamp: July 30, 2012, 10:25:43 pm
content: Quote from: HardBoot on July 30, 2012, 10:19:31 pmNobody in their right mind is buying a modern, high end ATX PSU to butcher into a 'lab' PSU of extremely limited capability. For the price of an ATX PSU worth paying money for, you can buy or build a more suitable linear supply.

author: HardBoot
author_rank: Regular Contributor
timestamp: July 30, 2012, 11:15:19 pm
content: Quote from: Monkeh on July 30, 2012, 10:25:43 pmDoubt you could get a linear anywhere near the price, but a switched mode, ya.I use a single rail PSU(12v server) and have linear regulators stuck on... works really well.

author: FenderBender
author_rank: Super Contributor
timestamp: July 31, 2012, 04:19:31 am
content: Everything aside, you don't really want to bother with ATX. ATX supplies are good at what they are meant to do, but for toying around in the lab, you might find yourself wanting to play with certain voltages in a circuit. set voltages doesn't help with that...and then if you add a variable supply to the ATX supplies..yuck, it just gets ugly.You'd be better off just making a simple LM317 supply without any fancy features at that point.

author: T4P
author_rank: Super Contributor
timestamp: July 31, 2012, 05:30:04 am
content: Using ATX PSU's as a bench supply is just as stupid as using a bench supply for a desktop!

author: Monkeh
author_rank: Super Contributor
timestamp: July 31, 2012, 01:39:13 pm
content: Quote from: HardBoot on July 30, 2012, 11:15:19 pmI can build a linear supply for rather less than the cost of a worthwhile ATX PSU. I spend a lot more on PSUs than most people, because the cheap ones are crap.

author: GnatGoSplat
author_rank: Regular Contributor
timestamp: July 31, 2012, 02:15:36 pm
content: Quote from: HardBoot on July 30, 2012, 09:04:12 pmNo, I seldom need more than 12V and have used computer power supplies in the past when I needed more current than my old EICO 1064 unregulated linear supply can deliver. However, most of the time, even if Ishouldbe using a regulated source, I'll still just use the old EICO because it's way more convenient. It's got banana jacks vs jamming wires into Molex connectors, I can turn its knob to get in-between voltages rather than wiring up a DC-DC converter, and I also like the handy built-in ammeter. Every now and then, I do occasionally use 14-15V to test how well old 12V lead acid batteries charge. I'm just thinking I'd like something with the convenience of my EICO, but regulated so things don't get fried when voltage fluctuates with load.Ideally, I would like to spend ~$100 for something with the features of that Korad that Dave reviewed except without the tendency to fry like his did.

author: T4P
author_rank: Super Contributor
timestamp: August 01, 2012, 01:56:26 am
content: 100 bucks? They're everywhere.1)http://www.totobay.com/superb-minipa-msp3033-dc-power-supply_p29717.htmland also 2nd hand

author: GnatGoSplat
author_rank: Regular Contributor
timestamp: August 01, 2012, 04:29:00 am
content: Quote from: T4P on August 01, 2012, 01:56:26 amThat one is showing up as $160+90 shipping for me.I ended up buying a broken BK 1665 on eBay for $37 in the hopes I can fix it. If not, then I have a pricey paperweight!

author: T4P
author_rank: Super Contributor
timestamp: August 01, 2012, 11:33:05 am
content: Quote from: GnatGoSplat on August 01, 2012, 04:29:00 amYes, but it's a 3 output PSU at the very leastIf you want to buy a programmable something just posted a Atten 3 output programmable PSUOR wait and see korad's new ones

author: GnatGoSplat
author_rank: Regular Contributor
timestamp: August 01, 2012, 12:54:51 pm
content: 3 output would be nice, but I don't feel like I can justify $250 for something I won't be using every day.I also could use a bit more current at 12V because sometimes I will use it for bench-testing car audio equipment.Yeah, if I can't fix the BK then I will take a serious look at the new Korads, if it doesn't die under Dave's testing.

author: HardBoot
author_rank: Regular Contributor
timestamp: August 01, 2012, 01:10:52 pm
content: Quote from: GnatGoSplat on August 01, 2012, 12:54:51 pmEven if you can't fix that, it'll have a lot of great salvage parts for the foundation of a crude(or advanced) DIY supply.

author: GnatGoSplat
author_rank: Regular Contributor
timestamp: September 17, 2012, 06:26:58 pm
content: I was able to repair the broken BK 1665 PSU I bought from eBay. It needed 2-MOSFETs and 2-zener diodes. It's an SMPS with APFC. What I find odd, is it seems to be using 10-11W at all times even with no load. That made me wonder if something is still not quite right, but I didn't notice anything getting unusually warm inside. Heatsinks all stay pretty cool, and regulation seems spot-on when testing the voltage display against my multimeter. I've only been able to dig up a 10W load so far, but it seemed to work perfectly with that load. I guess this is normal?I was expecting an SMPS with APFC to be way more efficient. My ancient 1960s EICO linear variable PSU only uses around 7-8W with no load.Someone on another forum said the reason is because it's cheap Chinese crap and sold for a premium with the BK name. Oh well, it'll do the job and I have less than $40 total into it.

author: M0BSW
author_rank: Frequent Contributor
timestamp: September 17, 2012, 06:56:36 pm
content: I have a Watson 15 V/30 amp variable power supply which has two meters one for volts another for amp is it possible to put digital read out for V/A as a add on or replacement

author: GnatGoSplat
author_rank: Regular Contributor
timestamp: September 17, 2012, 07:07:10 pm
content: Quote from: M0BSW on September 17, 2012, 06:56:36 pmYes, my old EICO had a literally smashed analog voltmeter, so I replaced it with a digital panel meter. I had to add a small 5V regulated supply for the panel meter, but that's easy enough to do. You can get digital LED meters really cheap from eBay, and low-current 5V regulated supplies are pretty cheap these days too.

author: M0BSW
author_rank: Frequent Contributor
timestamp: September 17, 2012, 07:10:09 pm
content: Thank you , I'll go take a look.Paul

author: T4P
author_rank: Super Contributor
timestamp: September 17, 2012, 07:52:17 pm
content: Quote from: GnatGoSplat on September 17, 2012, 06:26:58 pmI'm not surprised ... The agilent DSOX series draws 6W during "sleep"But hey, linear transformers draw constant power just to keep them magnetized and resistive losses alone just overtakes SMPS idle draw