TELVM wrote:

^ What would be your system specs apart from one PIII 600 and one Voodoo 5 5500?

Oh, currently it only has Pentium III 600, Voodoo5 5500, and Sound Blaster AWE32, with Intel 440BX motherboard (DTK PRM-080000I). But I always want to make it into a comprehensive 440BX system, as follows:

Intel 440BX
Pentium III 600
3dfx Voodoo5 5500 AGP
3dfx Voodoo Graphics PCI
Diamond MonsterSound MX300 PCI
Sound Blaster AWE64 Gold ISA
Yamaha SW60XG ISA
Thrustmaster ACM Game Card ISA

So it's one AGP, two PCIs, and three ISAs. On the other hand, I already have a Thermaltake TR2 700. I wonder if it's enough to power the system. Just like modern PSUs, its 12V+ amperage is pretty high, and its 3.3V+ and 5V+ amperage is pretty low. Here's the PSU's complete specs.

Max output current:
12V+: 50A 😀
3.3V+: 20A 🙁
5V+: 17A 😵
The combined power of +5V and +3.3V is only 120W max, despite the PSU's total power is 700W. IIRC a Pentium III processor (Katmai-generation) draws about 35W, so it's only 85W left for the entire system.

I do hope the Voodoo5 draws its power mostly from 12V+ rail. After all, Voodoo Volts (the external power supply for Voodoo5 6000) is 12 volts, right?

^ That's a lot of cards, I'm not sure if 17A on +5V would be enough to feed so many mouths.

TELVM wrote:

^ That's a lot of cards, I'm not sure if 17A on +5V would be enough to feed so many mouths.

I see.. So I better stick with old PSU, do I not? One with a lot of amperage from its 5V+ and 3.3V+.

The irony of this thing is Thermaltake TR2 700 is no slouch per se. Alas, most of its power is concentrated on its 12V+ rails (just like many modern PSUs).

As a matter of fact once you lift her skirt the Thermaltake TR2 700 happens to have 2x 30A rectifiers on the +5V rail, that's plenty of rectifiers and you may get away with overloading the +5V rail moderately. But there is some danger:

- If the transformer saturates, BANG! (possibly damaging PC components).

- Under very heavy +5V load and light +12V load, the +12V rail may drop voltage way below 12V (that's how modern PSUs work). This might be explored by monitoring with a multimeter, and mitigated by adding load to +12V (like extra fans, or load resistors, or 12V car light bulbs).

If the above sounds too hardcore or hairy, for peace of mind better get a PSU with higher +5V rating, like a Seasonic SS-500ET or a S12II-520 Bronze (24A rated +5V rail).

Kreshna Aryaguna Nurzaman wrote:

So, the Voodoo5 6000 draws its power from 12V+ rails, I hope Voodoo5 5500 would be the same.

False conclusion.

Kreshna Aryaguna Nurzaman wrote:

I hope Voodoo5 5500 draws most of its power from 12V+.

False conclusion.

You are looking for an "Easy Button" and there isn't one.

Video card AUX connectors only provide power to supplement what the card pulls from the slot.
( That also applies to PCI-E video cards. )
AGP slots provide up to 2 amps of +5v directly.
The up to 6 amps of 3.3v AGP slots provide is generally powered by +5v or +12v through a step-down regulator on the motherboard near the slot.
The 1.5v is provided the same way. A regulator at the slot.
So only +12v in the AUX connector does -NOT- mean it is only using +12v.
Not quite 50 watts of power can be coming through the AGP slot and depending on the motherboard most of it can be on the +5v or +12v rails.
So: You need to look at the card AND the motherboard to really figure out what you need in the PSU.

My best guess is a BX board would use mostly +5v for AGP (through regulators) but that is just a guess.

Your Voodoo5 5500 photo earlier clearly shows the AUX is providing 5v and maybe 12v as well. The 12v is maybe.
The section I've marked as unknown could be powered from the 5v pin by way of passing through the other side of the board.
Someone will have to whip out their DMM and do some circuit tracing to fully figure out what is actually going on there.

That guy that makes water coolers for these is insanely stupid - and funny.
Makes me think of a 72 Pinto with a stock 4-banger and a 2 foot high airfoil on the back.
That is like using water cooling on a 60MHz Pentium 1. (Approximately 15 watts.)
VSA-100 chips are given in several places to be 15 watts max. Same as a 60MHz Pentium 1.
Other video cards using chips with similar watts are often fan-less so even using fans is more about show than dire need.
My guess is the real reason for fans is to allow smaller heatsinks and a less bulky assembly.

So:
15 watts x 4 chips = 60 watts.
Guessing + 10 more watts for RAM and misc chips. -- 70 watts at the card. (And the slot can provide 48 up to watts of it.)
If it passes through so-so regulators to get to the card possibly up to 95 watts total at the PSU for all voltages combined.

Kreshna Aryaguna Nurzaman wrote:

Anyway, how about Pentium III CPU? Where does it draw its power from? I hope it's 12V+.

Most motherboards use the +5v rail for P3 power.
P3 have a TDP less than 35w so even with an inefficient VRM you are looking at a max of about 50w at the PSU.
.

PCBONEZ wrote:

... That guy that makes water coolers for these is insanely stupid - and funny.
Makes me think of a 72 Pinto with a stock 4-banger and a 2 foot high airfoil on the back ...

^ That made me chuckle 🤣 🤣 🤣

This is my guess (repeat, guess, as PCBONEZ says we can't be sure until someone knowing how to wield a multimeter traces it):

It may draw juice in similar proportions, ~15W from each rail (3A from +5V and 1.25A from +12V).

So, how much is the minimum combined power required from 3.3V+ and 5.5V+, to power such following system?

Intel 440BX motherboard
Pentium III 600 Katmai
3dfx Voodoo5 5500 AGP
3dfx Voodoo Graphics PCI
Diamond MonsterSound MX300 PCI
Sound Blaster AWE 64 Gold ISA
Yamaha SW60XG ISA
Thrustmaster ACM Game Card ISA

Yes, it's plenty of peripherals; one AGP, two PCIs, and three ISAs. However, not all of them is being used at the same time:

(1) 3dfx Voodoo Graphics is only used when playing those "Voodoo1-only" games. When it's being used, the Voodoo5 isn't being used, due to the nature of Voodoo Graphics to take over the work from existing VGA card (including Voodoo5). Naturally, when the Voodoo5 is being used, the Voodoo Graphics isn't being used at all.

(2) Diamond MonsterSound MX300 is only used when playing A3D games or early EAX games. When the MonsterSound is being used, the AWE64 Gold isn't being used at all. Conversely, when the AWE64 Gold is being used, the Diamond MonsterSound is not being used at all.

(3) Yamaha SW60XG is only used for games that support MIDI.

(4) Thrustmaster ACM Game Card is only used for flight sims (or anything that requires HOTAS).

Worst case scenario is F-22 Total Air War, because (on the said system) it will use Yamaha SW60XG for MIDI, Thrustmaster ACM Game Card for HOTAS, Sound Blaster AWE64 for sound, and Voodoo5 5500 AGP for GLide acceleration. Still, it will not use Voodoo Graphics (or, if it's set to use Voodoo Graphics, the Voodoo5 won't be used), and it will not use Diamond MonsterSound MX300 either (or, if it's set to use the MX300 using Windows default sound device, the AWE64 Gold won't be used).

So how much the minimum combined power required from the 3.3V+ and 5.5V+?

Beware that just because you are not using a card's features it does not mean they are not drawing power - they are idle, not turned off. They should consume less power, but not a nil amount. Also, HDDs, floppy drives and optical drives also draw power (but not all of it) from the 5V rails. All HDDs I've seen specify how much current they draw from each rail, and I'm pretty sure that optical drives also do so.

Anyway, a rough estimate:
P3 through an inneficient regulator: 50W / 10A
Your 5 ISA/PCI cards: I'll overshoot and say each one draws 10W, thus 50W / 10A
Voodoo 5: I'll assume it saturates the power from the slot, and that 3.3V is derived from 5V on the motherboard: 36W (slot) + 25W (Aux - just a guess, hopefully overestimating it) = 61W / ~12A
1 HDD: 0.5A
1 ODD: 1.5A

Necessary current so far: 34A

Throw in another 1A for the floppy and a few for the motherboard and you are nearing a 40A requirement for your PSU. I'm probably overestimating it a bit, and not taking into account that some of those devices will be idle (thus drawing less power), but I would not dare use a PSU with less than 35A on the 5V rails.

alexanrs wrote:

Beware that just because you are not using a card's features it does not mean they are not drawing power - they are idle, not tu […]
Show full quote

Beware that just because you are not using a card's features it does not mean they are not drawing power - they are idle, not turned off. They should consume less power, but not a nil amount. Also, HDDs, floppy drives and optical drives also draw power (but not all of it) from the 5V rails. All HDDs I've seen specify how much current they draw from each rail, and I'm pretty sure that optical drives also do so.

Anyway, a rough estimate:
P3 through an inneficient regulator: 50W / 10A
Your 5 ISA/PCI cards: I'll overshoot and say each one draws 10W, thus 50W / 10A
Voodoo 5: I'll assume it saturates the power from the slot, and that 3.3V is derived from 5V on the motherboard: 36W (slot) + 25W (Aux - just a guess, hopefully overestimating it) = 61W / ~12A
1 HDD: 0.5A
1 ODD: 1.5A

Necessary current so far: 34A

Throw in another 1A for the floppy and a few for the motherboard and you are nearing a 40A requirement for your PSU. I'm probably overestimating it a bit, and not taking into account that some of those devices will be idle (thus drawing less power), but I would not dare use a PSU with less than 35A on the 5V rails.

I see. Not even a 1200W Corsair PSU meets the 5V+ amperage requirements. My old A Power 500W PSU, on the other hand, easily has 38A on its 5V+ rail.

Is there any way to modify modern PSU, to "invert" its amperage, so the 5V+ rail has bigger amperage than its 12V+ rail?

I agree with what alexanrs said.

Are you familiar with the proverb, "give a man a fish and you feed him for a day; teach a man to fish and you feed him for a lifetime".
The OP is looking for a teaching thread but right now you just want dinner.
- That's okay. I get it. You'd rather be building than doing math. But next time you will have to ask again.

For what you are putting together would look for something with 30 amps on both the 3.3v and 5v rails.
Because all your parts are not running at max at the same time that will -probably- work out, but without spec'ing everything I'm not making a promise.

I'm going to give some other PSU considerations here.
-
[1] There are two common power ratings for PSUs. Peak and Continuous.
Most consumer/retail brands give the Peak whereas OEMs like Delta and NPS usually give the Continuous power rating (or both).
The difference between continuous and peak probably ranges between 15% and 25%. Assume 20%. (The image below shows a Delta where it's ~15%.)
The manufacturers aren't -actually- lying when they use Peak but it does give a false impression of how stout the PSU actually is.
(That has nothing to do with the gutless wonder idea. Gutless wonder builders just flat out lie.)
-
[2] It is not good to perpetually run a PSU at 100% of it's Continuous rating.
The ideal range is probably 33%-75% (efficiency). Practical 10%-85%. And don't exceed 90% if at all possible.
-
[3] Rails loaded too lightly can cause regulation problems which is one reason to avoid multiple 12v rails on systems that won't have at least something on all of them.
-
[4] Using the ideas given in [1](20%) and [2](10%) above it's probably best to keep the systems actual continuous load at 70% or less of the Peak rating.
Plain and simple, the PSU will last longer. - And this is the valid reason to 'overkill' PSU ratings.
-

.

If you have a PSU that has independent regulation for each rail you mgiht be able to. But to do so you'd have to understand PSU design and analyse the circuit. For all I know it could be as simple as changing the regulators and capacitors (if you can find regulators beefy enough - perhaps you'd need a few in parallel?), but I do not really understand PSU design, I have no idea of how resonant designs work and, honestly, it would probably be safer to recap/fix older PSUs.

One thing that might be interesting to do is to get a VERY good retro-power supply and draw its schematics and PCB layout in something like Eagle or KiCad. That way if the supply of good Athon/P3 PSUs dry out anyone with the means and knowledge could just create their own PSU PCB and adapt it to the casing of a newer one. PSU circuitry doesn't look like it would be hard to analyse - all PSUs I've opened have single-sided PCBs - but I do lack a beefy 40+A specimen.

Kreshna Aryaguna Nurzaman wrote:

I see. Not even a 1200W Corsair PSU meets the 5V+ amperage requirements. My old A Power 500W PSU, on the other hand, easily has 38A on its 5V+ rail.

You will be hard put to find a modern PSU with more than 30 amps on +5v. (Without getting into server parts anyway.)
30 amps is -probably- just enough in most cases for 5v heavy retro systems only because not all the loads peak at the same time.
(Calculations are stuck using peak or max theoretical values because manufacturers for add-in cards don't publish actual load information.)
This is one reason why learning to refurbish older spec PSUs would benefit anyone into retro computers.

"A Power" is one of those 'gutless wonder' brands. If you're lucky the +5v rail is good for 20-25 amps.
I was "blessed with" some A-Power 480w and 550w a few years ago.
To me they looked like old Deer knock-offs and I wasn't confident they would hold up over 350w.

Kreshna Aryaguna Nurzaman wrote:

Is there any way to modify modern PSU, to "invert" its amperage, so the 5V+ rail has bigger amperage than its 12V+ rail?

Yes.
There are DC-DC step down converters that can do 12v to 5v for sale in droves on eBay.
The problem is I don't know of any that have been tested to make sure the ripple is low enough for PC use.
An O'Scope is required to do that.
I plan to test a few but I have to get past my shop remodeling project so it will be months probably.
Life keeps getting in the way.
.

PCBONEZ wrote:

You will be hard put to find a modern PSU with more than 30 amps on +5v. (Without getting into server parts anyway.) 30 amps is […]
Show full quote

Kreshna Aryaguna Nurzaman wrote:

I see. Not even a 1200W Corsair PSU meets the 5V+ amperage requirements. My old A Power 500W PSU, on the other hand, easily has 38A on its 5V+ rail.

You will be hard put to find a modern PSU with more than 30 amps on +5v. (Without getting into server parts anyway.)
30 amps is -probably- just enough in most cases for 5v heavy retro systems only because not all the loads peak at the same time.
(Calculations are stuck using peak or max theoretical values because manufacturers for add-in cards don't publish actual load information.)
This is one reason why learning to refurbish older spec PSUs would benefit anyone into retro computers.

"A Power" is one of those 'gutless wonder' brands. If you're lucky the +5v rail is good for 20-25 amps.
I was "blessed with" some A-Power 480w and 550w a few years ago.
To me they looked like old Deer knock-offs and I wasn't confident they would hold up over 350w.

I see. Since new PSUs have very high 12V+ power output, I guess inverting modern PSU's power distribution is a viable alternative too.

PCBONEZ wrote:

Yes. There are DC-DC step down converters that can do 12v to 5v for sale in droves on eBay. The problem is I don't know of any […]
Show full quote

Kreshna Aryaguna Nurzaman wrote:

Is there any way to modify modern PSU, to "invert" its amperage, so the 5V+ rail has bigger amperage than its 12V+ rail?

Yes.
There are DC-DC step down converters that can do 12v to 5v for sale in droves on eBay.
The problem is I don't know of any that have been tested to make sure the ripple is low enough for PC use.
An O'Scope is required to do that.
I plan to test a few but I have to get past my shop remodeling project so it will be months probably.
Life keeps getting in the way.
.

This DC/DC converter has 5V or 12VDC input, and 0 to 2000VDC ouput. It is said to have low ripple of 2mVpp. Is 2mVpp low enough for Pc use?

EDIT: Wait, found this.

The ATX specification sets these limits on computer PSU ripple levels:

+12V - 120mV
+5V - 50mV
+3.3V - 50mV
+5VSB - 120mV
-12 - 120mV

My personal preference is to see numbers in or under this range:

+12V - 80mV
+5V - 30mV
+3.3V - 30mV
+5VSB - 50mV
-12V - 80mV

So, 2mVpp should be good, no?

/\ 2mVpp should be fine. 1W output, on the other hand, is not.

alexanrs wrote:

/\ 2mVpp should be fine. 1W output, on the other hand, is not.

So, it's not that easy. Let say we found DC/DC buck converter with sufficient power output, but unacceptable ripple. Could replacing its capacitors (with better capacitors) reduce the ripple?

.
I was talking about the likes of these.
(ebay) DC 12V 5v converter buck -car -charger -usb
The open frame versions with several caps and heatsinks are the ones I mean.
Those packaged ones -might- be okay but are really for automotive use and I dunno if there is any OP filtering.
3a to 5a at 5v output is pretty common.
Some of them -claim- to have ripple within ATX specs. Others don't say.
If the ripple is too high simply adding an appropriate cap at the output (or upgrading the existing OP caps) would probably take care of it.
It needs tested by someone with an O'Scope to be sure.
.
The ones with adjustment pots would be a good idea. Can adjust the OP voltage.
If the 12v rail supplying it is off a little the 5v output will be off too, so having an adjustment capability could be important especially if moving from one PSU to another now and then.
I don't think the packaged ones are adjustable.
.
Those with low outputs are intended to replace USB chargers. Not suitable for this.
.

alexanrs wrote:

... you are nearing a 40A requirement for your PSU ... ... I would not dare use a PSU with less than 35A on the 5V rails.

IMHO Kreshna's system (single PIII 440BX) will never draw as much as 175~200W from +5V.

My guess is that it will not draw more than 100~125W from +5V, and probably less. A PSU rated 20~24A on +5V and 130~150W or so combined should suffice for his system.

/\ The Voodoo5 is the issue. We do not have official figures for how much power it draws from each rail, so I overestimated it to draw, by itself, 60W on the 5V rails. If the card's power draw is well balanced between 5V and 12V and its VRMs are somewhat efficient it could very well draw less than 40W (specially when idle), still a considerable amount but I would not be as uncomfortable running it with a 30A PSU.

My own exaggerated math, without the Voodoo, would indicate the system needs a PSU with a bit over 25A, so I'd be confortable running it with a PSU rated 20-24A even when addind something like a GeForce4 MX, as those are not known to consume a lot of power.

Moved forward to here: Re: PSU - bust the myth

alexanrs wrote:

/\ The Voodoo5 is the issue. We do not have official figures for how much power it draws from each rail, so I overestimated it to draw, by itself, 60W on the 5V rails. If the card's power draw is well balanced between 5V and 12V and its VRMs are somewhat efficient it could very well draw less than 40W (specially when idle), still a considerable amount but I would not be as uncomfortable running it with a 30A PSU.

My own exaggerated math, without the Voodoo, would indicate the system needs a PSU with a bit over 25A, so I'd be confortable running it with a PSU rated 20-24A even when addind something like a GeForce4 MX, as those are not known to consume a lot of power.

40w max is likely about right seeing they really don't put out much heat and the rest of the card is often stone cold, typical or average load is likely 25 or 30w.