Variable power supplies

[GnatGoSplat]

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.?

[HardBoot]

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.

[GnatGoSplat]

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.

[T4P]

OF course linear is, unless you do not want a massive power supply when you want some power
Well 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 years
Dave reviewed his "GW-Instek" programmble lab bench SMPS and his Manson 600W SMPS
Mike reviewed his tiny Manson lab bench SMPS
well unless you want a transformer like that ...

[GnatGoSplat]

Well 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 years

Yes, 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.

[T4P]

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 fact

Now there is just 2 considerations:
Linear camp
Live without power and have a smaller PSU
Live with power and have a massive PSU

Switching camp
Lots of power in a small footprint
If 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=17
But basically it's about what you do not need and what you need
If 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

[HardBoot]

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.

[Monkeh]

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.

It is not as simple as bringing the PS_ON# line low. ATX PSUs have regulation and loading issues.

[HardBoot]

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.

It is not as simple as bringing the PS_ON# line low. ATX PSUs have regulation and loading issues.

Good ones don't, cross loading and even no-load isn't an issue in "modern" independent designs.

[Monkeh]

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.

It is not as simple as bringing the PS_ON# line low. ATX PSUs have regulation and loading issues.

Good ones don't, cross loading and even no-load isn't an issue in "modern" independent designs.

Nobody 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.

[HardBoot]

Nobody 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.

Doubt 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.

[FenderBender]

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.

[T4P]

Using ATX PSU's as a bench supply is just as stupid as using a bench supply for a desktop!

[Monkeh]

Nobody 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.

Doubt 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.

I 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.

[GnatGoSplat]

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.

No, 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 I should be 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.

[T4P]

100 bucks? They're everywhere.
1) http://www.totobay.com/superb-minipa-msp3033-dc-power-supply_p29717.html
and also 2nd hand

[GnatGoSplat]

100 bucks? They're everywhere.
1) http://www.totobay.com/superb-minipa-msp3033-dc-power-supply_p29717.html
and also 2nd hand

That 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!

[T4P]

100 bucks? They're everywhere.
1) http://www.totobay.com/superb-minipa-msp3033-dc-power-supply_p29717.html
and also 2nd hand

That 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!

Yes, but it's a 3 output PSU at the very least
If you want to buy a programmable something just posted a Atten 3 output programmable PSU
OR wait and see korad's new ones

[GnatGoSplat]

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.

[HardBoot]

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.

Even 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.

[GnatGoSplat]

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.

[M0BSW]

 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

[GnatGoSplat]

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

Yes, 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.

[M0BSW]

 Thank you , I'll go take a look.
Paul

[T4P]

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'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